Electron multiplier having self-adjusting gain function

Abstract

To provide a method for determining performance parameters of an electron multiplier having a series of electron emission surfaces forming an electron multiplication chain.SOLUTION: The method includes the step of: comparing a first electron beam of a first electron emission surface of the electron multiplication chain with a second electron beam of a second electron emission surface of the electron multiplication chain or with a second electron beam of an electron collector of the electron multiplier.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates generally to components of scientific analytical equipment. More particularly, the present invention relates to electron multipliers of the type used to amplify ion signals in mass spectrometers or to amplify light in photomultipliers. The present invention provides an electron multiplier and method of operation that allows for continuous, automatic adjustment of gain to account for performance degradation due to multiplier aging. [Background technology]

[0002] In a mass spectrometer, analytes are ionized to form a range of charged particles (ions). The resulting ions are then separated according to their mass-to-charge ratio, typically by acceleration and exposure to electric or magnetic fields. The separated signal ions are directed to an electron multiplier for amplification.

[0003] Electron multipliers generally operate by secondary electron emission, whereby the impact of a single or multiple particles on the electron-emitting surface of a first multiplier causes the emission of multiple secondary electrons, which associate with atoms at the impact surface. The emitted electrons travel to the second electron-emitting surface of the multiplier, each triggering the emission of multiple secondary electrons. Secondary electrons from the second electron-emitting surface travel to the third electron-emitting surface, and so on. This arrangement establishes an amplification chain, with each stage of the chain providing a geometric increase in the number of electrons. Toward the end of the amplification chain, an avalanche of electrons occurs, forming a highly amplified signal. These electrons are collected by an anode, and the current so generated is measured and recorded by computer-assisted means. The results are displayed as a spectrum of the relative abundance of the detected ions as a function of mass-to-charge ratio.

[0004] In other applications, the particles being detected may not be ions, but may be neutral atoms, neutral molecules, electrons, or photons. In either case, an electron multiplier is used to amplify the particle signal.

[0005] One type of electron multiplier is known as a discrete dynode electron multiplier. Such a multiplier contains a series of surfaces called dynodes, each set to an increasingly positive voltage. A voltage divider is typically implemented to distribute the voltage among the dynodes. Each dynode can emit more than one electron, thereby forming a multiplication chain.

[0006] Another type of electron multiplier operates using a single continuous dynode. In these versions, the resistive material of the continuous dynode itself is used as a voltage divider to distribute the voltage along the length of the emitting surface. The continuous dynode may be a single or multiple channel device. Multichannel devices can be constructed directly or by combining single-channel continuous dynodes, for example, by twisting a bundle of single-channel dynodes around a common axis to create a single detector.

[0007] Detectors may include microchannel plate detectors, which are planar components used to detect single particles (electrons, ions, and neutrons). This is closely related to electron multipliers; both enhance single particles by multiplying electrons via secondary emission. However, microchannel plate detectors may offer additional spatial resolution because they have many separate channels.

[0008] The degradation of the performance of electron emission-based detectors over time is a problem in the art. It is believed that secondary electron emission decreases over time, reducing the gain of the electron multiplier. To compensate for this process, the operating voltage applied to the multiplier must be periodically increased to maintain the required multiplier gain. However, eventually, the multiplier will need to be replaced.

[0009] It is also a problem in the art that the performance of electron emission-based detectors can deteriorate more rapidly in gain during the early stages of their useful life. This initial loss of gain is sometimes referred to as "burn-in." Prior art engineers have addressed this problem by using an initial period of intense operation to quickly overcome the "burn-in" period before the device is used for actual analytical work. While effective, this approach is time-consuming and labor-intensive, delaying the implementation of new detectors.

[0010] In either case, the detector user bears the burden of having to periodically manually adjust the detector gain to achieve some minimum target value. Several strategies are currently implemented to extend the time between calibrations.

[0011] One strategy involves setting the operating gain higher than the minimum target value. Using a "higher-than-necessary" operating gain relies on a continuous reduction in detector gain with use. Setting a sufficiently high initial operating gain ensures that the detector output will still exceed the required signal level at the end of the experiment.

[0012] Another strategy is to design detectors for as long a service life as possible. The goal is to slow the detector's aging rate, thereby increasing the time between gain adjustments. Detector life is predicted by the machine's service cycle, which is on the order of one year for machine maintenance and seven years for machine refurbishment. Therefore, detector life needs to be approximately 15 months or more than seven years to accommodate service contracts and refurbishment periods with a reasonable buffer. Some users require a service life longer than seven years, driven by the need to achieve a specific extended workflow between calibrations. Clinical applications often require extended detector life because the FDA and other regulatory agencies mandate acceptable gain reductions with use, calibration cycles, etc.

[0013] Even with detectors with extended service lives, gain instability remains a problem for all detectors, which necessitates the user to periodically monitor and adjust the operating gain.

[0014] Gain instability can exist as a chronic or acute problem. Chronic gain instability manifests as a slow, consistent decrease in electron multiplier gain over weeks, months, or years of sustained use. Acute gain instability is a rapid change in gain over minutes, hours, or days. For context, a 10-fold decrease in gain during the first 90 minutes of detector operation is not uncommon.

[0015] Gain instability drives two behaviors in the end user: First, the user periodically adjusts the detector gain. Second, as mentioned above, the user sets the gain higher than necessary. Both of these behaviors have negative consequences.

[0016] Periodic adjustment of detector gain requires consumables, operator time, and reduces system uptime, all of which increase the system's "cost per test." They also affect the system's total throughput over large time scales.

[0017] Furthermore, setting the gain higher than required to achieve the minimum target gain reduces the detector's useful life due to the larger electron flux impinging on the electron emitting surface. Further negative consequences of setting the gain unnecessarily high result in loss of detector linearity, ion feedback, and noise.

[0018] One aspect of the present invention is to overcome or ameliorate the problems of the prior art by providing an electron multiplier that eliminates or reduces the need for manual gain adjustment when used in the context of a particle detector. The present invention may also provide an electron multiplier with extended service life or improved gain instability, response linearity, ion feedback, or noise. A further aspect is to provide a useful alternative to the prior art.

[0019] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. No suggestion or representation is made that any or all of these matters formed part of the prior art or were common general knowledge in the art relevant to this invention by virtue of existing before the priority date of each claim of this application. Summary of the Invention

[0020] In a first aspect, not necessarily in its broadest aspect, the present invention provides a method for determining a performance parameter of an electron multiplier having a series of electron emitting surfaces forming an electron multiplication chain, the method comprising the step of comparing a first electron flux of a first electron emitting surface of the electron multiplication chain to a second electron flux of a second electron emitting surface of the electron multiplication chain or to a second electron flux of an electron collector of the electron multiplier.

[0021] In an embodiment of the first aspect, the first and second electron emitting surfaces are each discrete electron emitting surfaces.

[0022] In an embodiment of the first aspect, each of the discrete electron emitting surfaces is a dynode of a discrete dynode electron multiplier.

[0023] In one embodiment of the first aspect, the first and second electron emitting surfaces are provided by a single electron emitting surface.

[0024] In an embodiment of the first aspect, the single electron emission surface is a channel of a channel electron multiplier or a plate of a microchannel plate electron multiplier.

[0025] In an embodiment of the first aspect, the first electron emitting surface precedes the second electron emitting surface in the electron multiplication chain.

[0026] In an embodiment of the first aspect, the first electron emitting surface is less susceptible to electron flux-mediated gain degradation than the second electron emitting surface.

[0027] In an embodiment of the first aspect, the first electron emitting surface carries a lower electron flux than the second electron emitting surface.

[0028] In an embodiment of the first aspect, the first electron emitting surface is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 1000, 000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 200000, 300000, 400000, 500000, 60000, 700000, 800000, 900000, or 1,000,000 less electron flux.

[0029] In an embodiment of the first aspect, a second electron flux is determined at the electron collector, the first electron emitting surface carrying less electron flux than a terminal electron emitting surface of the electron multiplication chain.

[0030] In an embodiment of the first aspect, the second electron flux is determined at the electron collector, and the first electron emitting surface is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1000, 2000, 3000, 4000, 5000, 6000, 70 00, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 200000, 300000, 400000, 500000, 60000, 700000, 800000, 900000, or 1,000,000 less electron flux.

[0031] In an embodiment of the first aspect, the first electron emission surface is within the first 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, or 25% of the electron multiplication chain.

[0032] In an embodiment of the first aspect, the first electron emission surface is not within the first 5%, 10%, 15%, 20%, or 25% of the electron multiplication chain.

[0033] In an embodiment of the first aspect, the electron multiplier comprises discrete electron emitting surfaces, and the first electron emitting surface is the third, fourth, fifth, sixth, or seventh electron emitting surface of the electron multiplication chain.

[0034] In an embodiment of the first aspect, the electron multiplier comprises individual electron emitting surfaces, the first electron emitting surface being the fourth, fifth or sixth electron emitting surface of the electron multiplication chain.

[0035] In an embodiment of the first aspect, the electron multiplier comprises discrete electron emitting surfaces, the first electron emitting surface being a fifth electron emitting surface of the electron multiplication chain.

[0036] In an embodiment of the first aspect, the electron multiplier comprises individual electron emission surfaces, and the first electron emission surface and the second electron emission surface, or the first electron emission surface and the electron collector, are separated by at least two, three, four, or five intervening electron emission surfaces.

[0037] In one embodiment of the first aspect, the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and a first electron emission surface is the third, fourth, fifth, sixth, or seventh electron emission site of the electron multiplication chain.

[0038] In one embodiment of the first aspect, the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and a first electron emission surface is the fourth, fifth, or sixth electron emission site of the electron multiplication chain.

[0039] In one embodiment of the first aspect, the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, the first electron emission surface being a fifth electron emission site of the electron multiplication chain.

[0040] In one embodiment of the first aspect, the electron multiplier comprises a single electron emitting surface having a series of electron emitting sites that together form an electron multiplication chain, wherein a first electron emitting site and a second electron emitting site, or a first electron emitting site and an electron collector, are separated by at least two, three, or four intervening electron emitting sites.

[0041] In one embodiment of the first aspect, the first and second electron fluxes are compared by (i) a current measurement circuit and then comparing the determined currents, or (ii) a current comparison circuit.

[0042] In one embodiment of the first aspect, the first and second electron fluxes are each determined at the same time or within a period of time.

[0043] In one embodiment of the first aspect, the first and second electron fluxes are determined intermittently over the period of electron multiplier operation.

[0044] In one embodiment of the first aspect, the period of electron multiplier operation is about 1 second, 5 seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 1 hour or more.

[0045] In an embodiment of the first aspect, the first and second electron fluxes are determined according to a sampling rate.

[0046] In an embodiment of the first aspect, the sampling rate is equal to or less than about 1 Hz, 0.1 Hz, or 0.01 Hz.

[0047] In an embodiment of the first aspect, the sampling rate is greater than or equal to about 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz, 0.5 Hz, 0.6 Hz, 0.7 Hz, 0.8 Hz, 0.9 Hz, or 1 Hz.

[0048] In one embodiment of the first aspect, the sampling rate is between about 0.3 Hz and 0.01 Hz.

[0049] In an embodiment of the first aspect, the performance parameter is indicative of a gain of the electron multiplier.

[0050] In one embodiment of the first aspect, the comparing step includes a mathematical operation utilizing the determined first and second electron fluxes.

[0051] In an embodiment of the first aspect, the mathematical operation includes producing a ratio, a multiple, a quotient, or a difference.

[0052] In a second aspect, the present invention provides a method of operating an electron multiplier, the method comprising determining a performance parameter of the electron multiplier according to the method of any embodiment of the first aspect, comparing the determined performance parameter with a predetermined value or a predetermined range of the performance parameter, and if the determined performance parameter is not the predetermined value or outside the predetermined range of the performance parameter, modifying an operating parameter of the electron multiplier such that the determined performance parameter is at the predetermined value or within the predetermined range of the performance parameter.

[0053] In an embodiment of the second aspect, the operating parameter is a voltage bias applied to the electron multiplier.

[0054] In one embodiment of the second aspect, the method is implemented to continuously monitor the performance parameters and modify operating parameters of the electron multiplier as needed, and the determining, comparing, and modifying steps are performed sequentially multiple times over a period of time.

[0055] In an embodiment of the second aspect, the performance parameter is electron multiplier gain, and the gain of the electron multiplier is maintained at a predetermined gain or within a predetermined gain range over a period of time.

[0056] In a third aspect, the present invention provides an electron multiplier or electron multiplication system having a series of electron emitting surfaces forming an electron multiplication chain, the electron multiplier method including circuitry and optionally processor-executable program instructions configured to compare a first electron flux of a first electron emitting surface of the electron multiplication chain with a second electron flux of a second electron emitting surface of the electron multiplication chain or an electron collector of the electron multiplier.

[0057] In an embodiment of the third aspect, the first and second electron emitting surfaces are each individual electron emitting surfaces.

[0058] In an embodiment of the third aspect, each of the discrete electron emitting surfaces is a dynode of a discrete dynode electron multiplier.

[0059] In one embodiment of the third aspect, the first and second electron emitting surfaces are provided by a single electron emitting surface.

[0060] In an embodiment of the third aspect, the single electron emission surface is a channel of a channel electron multiplier or a plate of a microchannel plate electron multiplier.

[0061] In an embodiment of the third aspect, the first electron emitting surface precedes the second electron emitting surface in the electron multiplication chain.

[0062] In an embodiment of the third aspect, the first electron emitting surface is less susceptible to electron flux-mediated gain degradation than the second electron emitting surface.

[0063] In an embodiment of the third aspect, the first electron emitting surface carries a lower electron flux than the second electron emitting surface.

[0064] In an embodiment of the third aspect, the first electron emitting surface is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 1000, 000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 200000, 300000, 400000, 500000, 60000, 700000, 800000, 900000, or 1,000,000 less electron flux.

[0065] In an embodiment of the third aspect, a second electron flux is determined at the electron collector, the first electron emitting surface carrying less electron flux than a terminal electron emitting surface of the electron multiplication chain.

[0066] In an embodiment of the third aspect, the second electron flux is determined at the electron collector, and the first electron emitting surface is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1000, 2000, 3000, 4000, 5000, 6000, 70 00, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 200000, 300000, 400000, 500000, 60000, 700000, 800000, 900000, or 1,000,000 less electron flux.

[0067] In an embodiment of the third aspect, the first electron emission surface is within the first 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, or 25% of the electron multiplication chain.

[0068] In an embodiment of the third aspect, the first electron emission surface is not within the first 5%, 10%, 15%, 20%, or 25% of the electron multiplication chain.

[0069] In an embodiment of the third aspect, the electron multiplier comprises discrete electron emitting surfaces, and the first electron emitting surface is the third, fourth, fifth, sixth, or seventh electron emitting surface of the electron multiplication chain.

[0070] In an embodiment of the third aspect, the electron multiplier comprises discrete electron emitting surfaces, and the first electron emitting surface is the fourth, fifth or sixth electron emitting surface of the electron multiplication chain.

[0071] In an embodiment of the third aspect, the electron multiplier comprises discrete electron emitting surfaces, and the first electron emitting surface is a fifth electron emitting surface of the electron multiplication chain.

[0072] In an embodiment of the third aspect, the electron multiplier comprises discrete electron emitting surfaces, wherein the first electron emitting surface and the second electron emitting surface, or the first electron emitting surface and the electron collector, are separated by at least two, three, four, or five intervening electron emitting surfaces.

[0073] In one embodiment of the third aspect, the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and a first electron emission surface is the third, fourth, fifth, sixth, or seventh electron emission site of the electron multiplication chain.

[0074] In one embodiment of the third aspect, the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and a first electron emission surface is the fourth, fifth, or sixth electron emission site of the electron multiplication chain.

[0075] In one embodiment of the third aspect, the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, the first electron emission surface being a fifth electron emission site of the electron multiplication chain.

[0076] In one embodiment of the third aspect, the electron multiplier comprises a single electron emitting surface having a series of electron emitting sites that together form an electron multiplication chain, wherein a first electron emitting site and a second electron emitting site, or a first electron emitting site and an electron collector, are separated by at least two, three, or four intervening electron emitting sites.

[0077] In one embodiment of the third aspect, the circuitry and optionally the program instructions compare the first and second electron fluxes at least in part by (i) a current measurement circuit and then comparing the currents measured by the program instructions, or (ii) a current comparison circuit.

[0078] In one embodiment of the third aspect, the circuitry and optionally the program instructions are configured to determine the first and second electron fluxes at the same point in time or within a period of time.

[0079] In an embodiment of the third aspect, the circuitry and optionally the program instructions are configured to determine that the first and second electron fluxes are determined intermittently over a period of electron multiplier operation.

[0080] In one embodiment of the third aspect, the period of electron multiplier operation is about 1 second, 5 seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 1 hour or more.

[0081] In an embodiment of the third aspect, the circuitry and optionally the program instructions are configured such that the first and second electron fluxes are determined according to a sampling rate.

[0082] In an embodiment of the third aspect, the sampling rate is less than or equal to about 1 Hz, 0.1 Hz, or about 0.01 Hz.

[0083] In an embodiment of the third aspect, the sampling rate is greater than or equal to about 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz, 0.5 Hz, 0.6 Hz, 0.7 Hz, 0.8 Hz, 0.9 Hz, or 1 Hz.

[0084] In one embodiment of the third aspect, the sampling rate is between about 0.3 Hz and 0.01 Hz.

[0085] In an embodiment of the third aspect, the performance parameter is indicative of a gain of the electron multiplier.

[0086] In one embodiment of the third aspect, the circuitry and optional program instructions are configured to determine a performance parameter of the electron multiplier, compare the determined performance parameter to a predetermined value or a predetermined range of the performance parameter, and if the determined performance parameter is not the predetermined value or is outside the predetermined range of the performance parameter, modify an operating parameter of the electron multiplier so that the determined performance parameter is the predetermined value or is within the predetermined range of the performance parameter.

[0087] In an embodiment of the third aspect, the operating parameter is a voltage bias applied to the electron multiplier.

[0088] In one embodiment of the third aspect, the circuitry and optionally the program instructions are configured to continuously monitor the performance parameters and modify the operating parameters of the electron multiplier as needed, and the determining, comparing, and modifying steps are performed sequentially multiple times over a period of time.

[0089] In an embodiment of the third aspect, the performance parameter is electron multiplier gain, and the gain of the electron multiplier is maintained at a predetermined gain or within a predetermined gain range over a period of time. [Brief explanation of the drawings]

[0090] [Figure 1] 1 is a schematic diagram of a discrete dynode electron multiplier of the present invention, where the currents of two dynodes (D5 and DN) are used to determine the current ratio. [Figure 2] 1 is a schematic diagram of a discrete dynode electron multiplier of the present invention. The currents in one dynode (D5) and the collector anode are used to determine the current ratio. [Figure 3] 1 is a schematic diagram of a channel electron multiplier of the present invention, in which the currents at early and late sites along the electron multiplication chain are used to determine the current ratio. [Figure 4] FIG. 10 is a flow diagram of an algorithm used in program instructions to adjust the gain of the electron multiplier as needed. DETAILED DESCRIPTION OF THE INVENTION

[0091] After considering this description, it will be apparent to those skilled in the art how the present invention may be implemented in various alternative embodiments and applications. However, while various embodiments of the present invention are described herein, it is understood that these embodiments are presented by way of example only, and not by way of limitation. Thus, this description of various alternative embodiments should not be construed as limiting the scope or breadth of the present invention. Furthermore, statements of advantages or other aspects apply to particular example embodiments and do not necessarily apply to all embodiments encompassed by the claims.

[0092] Throughout the description and claims of this specification, the word "comprise" and variations of this word such as "comprising" and "comprises" are not intended to exclude other additives, ingredients, integers or steps.

[0093] Throughout this specification, reference to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment, but may.

[0094] It will be understood that not all embodiments of the invention described herein possess all of the advantages disclosed herein: some embodiments may possess a single advantage, while other embodiments possess no advantages and are merely useful alternatives to the prior art.

[0095] The present invention is based, at least in part, on the discovery that the gain of an electron multiplier can be continuously and automatically adjusted to account for gain instability (whether chronic or acute) and maintain the multiplier at or near a target gain value. The gain can be adjusted upward or downward based on a comparison between the electron flux of a relatively early electron emitting surface in the electron multiplication chain and the electron flux of a relatively late electron emitting surface in the electron multiplication chain. In some embodiments, the electron flux of the electron emitting surface at a relatively late stage in the electron multiplication chain is replaced by the electron flux of the collector anode. The comparison can be accomplished by periodically measuring the current through the associated electron emitting surface or anode and generating a current ratio. When necessary, the gain of the electron multiplier is adjusted by adjusting the voltage bias applied to the multiplier.

[0096] Thus, in a first aspect, the present invention provides a method for determining a performance parameter of an electron multiplier having a series of electron emitting surfaces forming an electron multiplication chain, the method comprising the step of comparing a first electron flux of a first electron emitting surface of the electron multiplication chain with a second electron flux of a second electron emitting surface of the electron multiplication chain or with a second electron flux of an electron collector of the electron multiplier.

[0097] When new, the gain of the multiplier may be set to a required target value. The current ratio at that gain is measured, estimated, or assumed to be a certain value. The current ratio at the target gain may be used as a comparator current ratio to which later measured current ratios are compared. If the later measured current ratio shows a significant deviation above or below the comparator ratio, the voltage bias applied to the multiplier is adjusted to bring the ratio closer to the comparator ratio, in the process returning the multiplier to the target gain.

[0098] Without wishing to be limited by theory in any way, it is proposed that the changes in the current ratio described above reflect changes in the performance of the multiplier over time due to aging, "burn-in," or some other factor. The current ratio may therefore be monitored continuously or semi-continuously with the aim of adjusting the multiplier gain in real time to maintain the gain at or near the same level as when the multiplier was new.

[0099] It is not necessary to set the comparator current ratio when the multiplier is new. The comparator current ratio can be determined at any time after first use, as long as the determination is made when the multiplier is set to the target gain value. The present invention is nevertheless operable to maintain the gain at or near the target gain value.

[0100] The comparator current ratio may be set by a priori methods. For example, for a given model of electron multiplier, a table of current ratios and gains may be generated. The table may show the relationship between current ratio and multiplier gain after various operating times. The table may be hard copy or electronic.

[0101] In accordance with the present invention, the comparator current ratio, or later test current ratio, is generated by referencing the electron flux at two points within the electron multiplier. As will be appreciated, the electron flux (which is the flow of electrons) is reflected in the current measured at each of the two points.

[0102] The first of the two points is an electron emitting surface that is relatively early in the electron multiplication chain, and the second of the two points is relatively late in the electron chain. While not wishing to be bound by theory in any way, it is proposed that a comparison of the flux at the two points is instructive because the early electron emitting surfaces experience relatively low electron flux, which will likely age little over time. For example, if each dynode in a discrete dynode multiplier has a modest yield of 2, a particle striking the first dynode will cause the emission of two secondary electrons; those two electrons will strike the second dynode, emitting four electrons; those four electrons will strike the third dynode, emitting eight electrons; those eight electrons will strike the fourth dynode, emitting 16 electrons; and those 16 electrons will strike the fifth dynode, emitting 32 electrons. As can be seen, 32 electrons is not a significant electron flux and therefore will cause only a small amount of dynode degradation over time.

[0103] However, given the geometric increase in electrons downstream in the multiplication chain, later dynodes are exposed to significantly larger electron fluxes. High levels of flux age the dynodes relatively rapidly and thus have a significant adverse effect on the overall gain of the multiplier over time. Therefore, the earlier dynodes, which degrade relatively slowly, provide a useful benchmark against which performance effects resulting from the more rapidly degrading later dynodes can be evaluated.

[0104] When selecting the initial electron emitting surface in the electron multiplication chain, attention must be paid to any adverse effects of intermittently sampling the electron flux (i.e., current) at that point in the multiplier. In the example above, the fifth dynode was selected on the basis that it would receive a reasonable level of flux so that the sensitivity of the detector of which the multiplier is a part would not be significantly affected.

[0105] In extreme cases, the earliest (i.e., first) dynode may be selected. However, selecting the first dynode can have a significant negative impact on sensitivity, assuming a low electron flux (i.e., two electrons in the example above). Intermittent sampling of the electron flux at the first dynode can "rob" the multiplier of valuable signal, assuming only two electrons are present. The situation improves with the third dynode, as four electrons are available for sampling. Nevertheless, sampling is expected to have a negative impact on sensitivity. Therefore, the selected dynode should be early in the electron multiplication chain, but not too early.

[0106] The above example is based on each dynode having a yield of two electrons (i.e., one impacting electron triggers the emission of an average of two secondary electrons). A higher yield dynode can dictate the selection of an earlier dynode than the fifth dynode. For example, if each dynode has a yield of 10, the second or third dynode may be selected. Conversely, if the yield is 1.5, the seventh or eighth dynode may be selected.

[0107] Another consideration in the selection of the initial dynode may be the resilience of the dynode material in question to aging. If the dynode material is relatively resistant to aging, a dynode with a higher electron flux may be selected, with the attendant benefit of reducing the negative impact on sensitivity. In the example above, where the fifth dynode was selected as the initial electron emission surface, the use of a dynode material with greater aging resilience may have made it possible to select the sixth dynode.

[0108] In some embodiments of the present invention, the initial dynode is typically about 10 1 ~10 3 The electron emitter may emit electrons.

[0109] Regarding the selection of subsequent dynodes, it is only necessary that the subsequent dynodes age more rapidly than the previous dynodes. Thus, in the above example where the fifth dynode is selected, if the subsequent dynode is subjected to a higher flux than the sixth dynode, the subsequent dynode will age more rapidly than the previous dynodes. While the sixth dynode may be somewhat operational, more reliable results would be expected from the seventh, eighth, ninth, or subsequent dynodes. The current ratio obtained from the fifth and sixth dynodes may not be significant, thus reducing the accuracy of gain adjustments to account for the effects of multiplier aging. A higher ratio is more likely to reliably reflect gain changes due to aging (or any other factor) and thus may allow for more precise adjustment of the gain to achieve the target gain. Thus, the subsequent electron emission surface may be two, three, four, five, or more dynodes down the multiplication chain, counting from the previous dynode.

[0110] The above discussion regarding the selection of early and late dynodes applies equally to continuous dynode electron multipliers, except that early and late sites in the multiplication chain take the place of early and late dynodes.

[0111] In the present invention, the latter electron emitting surface may be replaced by an electron collector that forms part of a detector incorporating an electron multiplier. As will be appreciated, the function of the collector (which is the anode) is not to emit secondary electrons, but instead to collect the secondary electrons emitted by the terminal electron emitting surface of the electron multiplier. In that function, the electron flux of the collector can be considered a proxy for or approximation of the electron flux of the terminal electron emitting surface.

[0112] As reflected in the following claims, the present invention may be embodied as a method or as an article of manufacture (such as an electron multiplier configured to operate according to the method).

[0113] Referring to Figure 1, a preferred electron multiplier embodiment of the present invention is shown. A description of the construction and operation of the electron multiplier will clarify the features of the prevention method.

[0114] Figure 1 shows a series of dynodes (D1-D N ) is shown. An input particle strikes D1. If the input particle is not an electron, D1 can be thought of as functioning as a conversion dynode in that it converts particles (such as ions) into an electronic signal. In its function as a conversion dynode, D1 can also function to amplify the input signal if the impact of a single particle results in the emission of more than one electron. D1 to D N The electron multiplication chain formed by the series of resistors (R1 to R2) has a voltage bias applied by a power supply (10). N-1 ) are inserted between the dynodes to form a voltage divider. The applied voltage divides the secondary electrons (indicated by the semicircular lines with arrows) between D1 and D2. N The collector anode is connected to the terminal dynode (D N ) and collects the secondary electrons emitted by that dynode. The electron multiplier, collector anode, and amplifier together form the particle detector. The output of the particle detector is essentially an amplified signal reflecting the impact of a particle initially at D1.

[0115] The above configuration is conventional in the art. The present invention provides additional hardware elements and additional method steps, as described below.

[0116] As shown in FIG. 1, the present invention utilizes D5 as the early electron emission surface and the terminal dynode (D N) are utilized. To measure the electron flux through these dynodes, processor-controllable multiplexing switches (15) and (20) are provided to shunt the electron flux from the electron multiplication chain to current measuring devices (25) and (30), respectively. Switches (15) and (20) are normally set so as not to divert the electron flux. Periodically, D5 and D N The electron flux for each of the is sampled by setting switches (25) and (30) to divert the current to current measuring devices (25) and (30). Instead of using any switches, a beam splitting dynode may be used to continuously sample the electron beam as it continues down the multiplier. Switching electrodes to steer the electron beam are a further possible alternative.

[0117] The measured currents are sent in analog or digital form to a digital processor (35) operatively connected to a memory module (40) containing program instructions (45) configured to receive the measured currents as inputs and mathematically generate a current ratio therefrom.

[0118] The power supply 10 is processor-controllable in that the processor 35 can modulate the output voltage (i.e., move it closer to or away from 0 volts, which is taken as ground or a reference voltage) under program instructions 45. Modulation of the output voltage increases or decreases the gain of the electron multiplier.

[0119] The memory module (40) holds previously stored comparator ratios that were determined by reference to the currents measured by the units (25) and (30) when the electron multiplier was new.

[0120] During subsequent operation of the electron multiplier, program instructions (45) direct switches (15) and (20) to intermittently open and close to sample current from D5 and DN. The sampled current is input by program instructions (45), which generate a current ratio. The resulting current ratio is compared to a comparator current ratio stored in memory module (45). A ratio lower than the stored comparator ratio indicates that the electron multiplier has aged and therefore has decreased gain. In that scenario, the bias voltage applied by power supply (10) is increased (i.e., moved further away from zero) to increase the voltage applied to the electron multiplier. Under the direction of program instructions (45), as the voltage increases, D5 and DN decrease. N The currents are continuously sampled and the current ratio generated therefrom is continuously updated. When the updated current ratio is equal to or approximately equal to the comparator current ratio, program instructions 45 command power supply 10 to stop increasing the voltage and hold the voltage at its output when the comparator current ratio is reached.

[0121] Program instruction (45) is D5 and D N Further sampling of the current is commanded, and if the current ratio deviates from the comparator current ratio, the voltage output by the power supply 10 is again modulated. This continuous monitoring of the current ratio allows the gain of the electron multiplier to be maintained above a target level.

[0122] In a simple method for determining the current ratio, the electron multiplier can be configured to fix the voltage across the first, say, ten, multiplication stages. This can be accomplished, for example, by using Zener diodes to fix the voltage across the first ten stages. As the voltage increases, the voltage difference between adjacent dynodes remains substantially the same. Therefore, assuming the gain across the first ten stages is fixed, determining the current ratio is straightforward. A current "pickoff point" is provided, for example, at the eighth stage, and the currents of the eighth and tenth stages are used to generate the ratio.

[0123] Instead of using a simple current ratio directly, a more complex method can be implemented to generate a gain curve of the output at the fifth stage (or another appropriate multiplication stage, such as the third, fourth, sixth, or seventh stage). That measurement may be performed during detector gain calibration to tell how the gain across the first five multiplication stages varies with applied voltage. That information is then used to adjust the target ratio to take that into account. This approach is applicable when dynode-dynode voltages (and gain) vary across the front end (such as when resistor strings are used rather than Zener diodes). The remainder of the architecture is identical, including the use of the same signal pickoff points.

[0124] The present invention is also applicable to electron multipliers with a single electron emission surface divided into multiple electron impact sites. An example is shown in FIG. 3, which shows a multiplier formed from a curved channel, with the curvature shaped to direct secondary electrons to opposing inner surfaces of the channel and toward the channel end. In this embodiment, switches 15 and 20 do not function as multiplexers (as in the discrete dynode embodiment) but instead assume either an open or closed state. Switches 15 and 20 are normally closed, so that electrons are not diverted from the channel to current measurement devices 25 and 30. To sample the current, switches 15 and 20 are opened, causing electrons in the respective regions of the channel to migrate toward ground or a lower reference voltage and, accordingly, pass through current measurement devices 25 and 30.

[0125] Referring also to Figure 2, a further embodiment of a preferred electron multiplier of the present invention is shown. The electron multiplier of Figure 2 is similar to the electron multiplier of Figure 1, except that it is the current at one dynode (D5) and the collector anode that is used to determine the current ratio. As shown in Figure 2, processor-controllable multiplexing switches (15) and (20) are provided to divert the electron flux from the electron chain to current measuring devices (25) and (30), respectively, and switch (20) does not divert the electron flux from the terminal dynode (D5) as in the embodiment of Figure 1. N ) is connected to the anode.

[0126] In embodiments of the present invention that rely on software program instructions, a processor is required to execute those instructions. It is contemplated that a substantially self-contained device may be provided, in which the processor is provided by a microcontroller and the program instructions are stored in the form of firmware in the microcontroller's temporary or non-transitory memory. In addition to the current detection device, the self-contained device may include any switching or other means to sample current from a selected electron emitting surface or collector anode that achieves the same result. Power to the processor may be provided by an on-board battery.

[0127] In other embodiments, a system is provided in which some elements of the present invention are provided integrally with the basic electron multiplier hardware, with the processor and program instructions located remotely. For example, the processor and program instructions may be provided by the instrument (such as a mass spectrometer) in which the electron multiplier is operable. In another example, a personal computer holds the software instructions, and the computer is in data communication with the electron multiplier. In some embodiments, the electron multiplier comprises at least any switching means or other means for achieving the same result, and current measurement means.

[0128] In one aspect, the present invention is embodied in program instructions stored in temporary or non-transitory memory. However implemented, the program instructions can be configured to execute the algorithm shown in flowchart form in FIG. 4. As described below, the algorithm executes as a loop. Although not shown in the flowchart, the loop can be interrupted as needed. The algorithm operates on the assumption that the current ratio decreases over time (which may or may not be a valid assumption depending on the application), and an increase in the voltage bias applied to the electron multiplier is required to return the ratio to the predetermined comparator ratio.

[0129] As will be appreciated, the present invention, in one aspect, provides an electron multiplier that is automatically adjusted during operation to achieve a target gain, and in that regard, relieves the user of the need to periodically manually adjust the gain, thereby saving time and consumables.

[0130] As explained in the Background section of this specification, users often set the multiplier gain unnecessarily high in order to extend the period during which gain adjustments are performed. The electron multiplier of the present invention is continuously set to a gain that is just sufficient for the application to which it is applied, thereby protecting the electron emitting surface from degradation. Therefore, the overall life of the electron multiplier can be extended.

[0131] The present invention has been described primarily with reference to particle detectors incorporating discrete dynode multipliers, channel electron multipliers, and microchannel plate multipliers. It should be understood that the present invention is not limited to any particular detector configuration and is applicable to time-of-flight (TOF) detectors and dual-mode detectors. In particular, dual-mode detectors particularly benefit from the present invention for eliminating differential drift. Detectors devised in the future are within the scope of this specification.

[0132] Similarly, while the invention is described primarily with reference to detectors of the type used in mass spectrometers, it should be understood that the invention is not so limited. In other applications, the particles being detected may not be ions, but may be neutral atoms, neutral molecules, or electrons. In any case, a detector surface is still provided upon which the particles impinge.

[0133] As will be appreciated by those skilled in the art, the present invention may be deployed, in part or in whole, via one or more processors that execute computer software, program code, and / or instructions thereon. The processor may be part of a server, client, network infrastructure, mobile computing platform, fixed computing platform, or other computing platform. The processor may be any type of computational or processing device capable of executing program instructions, code, binary instructions, etc. The processor may be or include any variant of a signal processor, digital processor, embedded processor, microprocessor, or coprocessor (such as a mathematical coprocessor, graphics coprocessor, communication coprocessor, etc.), which may directly or indirectly facilitate the execution of program code or program instructions stored thereon.

[0134] Additionally, the processor may allow for the execution of multiple programs, threads, and codes.

[0135] Threads may be executed simultaneously to improve processor performance and facilitate simultaneous operation of applications. As an example, the methods, program code, program instructions, etc. described herein may be implemented with one or more threads. Threads may spawn other threads with associated priorities, and the processor may execute these threads based on priority or any other order based on instructions provided in the program code. The processor may include memory for storing the methods, code, instructions, and programs as described herein.

[0136] Any processor or mobile device or server may access a storage medium through an interface that may store methods, codes, and instructions as described herein and elsewhere. Storage media associated with a processor for storing methods, programs, codes, program instructions, or other types of instructions that may be executed by a computing or processing device may include solid-state memory and hard disk memory.

[0137] A processor may include one or more cores, which can increase the speed and performance of a multiprocessor. In some embodiments, a processor may be a dual-core processor, a quad-core processor, other chip-level multiprocessor, etc., that combines two or more independent cores (called dies).

[0138] The methods and systems described herein may be deployed, in part or in whole, through one or more hardware components executing software on a server, client, firewall, gateway, hub, router, or other such computer and / or network hardware. Software programs may be associated with a server, which may include a file server, print server, domain server, Internet server, intranet server, and other variations such as a secondary server, host server, distributed server, etc. A server may include one or more of memory, processor, computer-readable medium, storage media, ports (physical and virtual), communication devices, and interfaces capable of accessing other servers, clients, computers, and devices via wired or wireless media. The methods, programs, or codes described herein and elsewhere may be executed by a server. Additionally, other devices necessary for the execution of the methods described herein may be considered part of the infrastructure associated with the server.

[0139] A server may provide an interface to other devices, including, but not limited to, clients, other servers, printers, database servers, print servers, file servers, communication servers, distribution servers, etc. Furthermore, this coupling and / or connection can facilitate remote execution of programs over a network. Networking some or all of these devices can facilitate parallel processing of a program or method at one or more locations without departing from the scope of the present invention. Furthermore, any of the devices connected to a server via an interface can include at least one storage medium capable of storing methods, programs, code, and / or instructions. A central repository may provide program instructions to be executed on different devices. In this embodiment, the remote repository can function as a storage medium for program code, instructions, and programs.

[0140] A software program may be associated with a client, which may include a file client, a print client, a domain client, an Internet client, an intranet client, and other variations such as a secondary client, a host client, a distributed client, etc. A client may include one or more of a memory, a processor, a computer-readable medium, a storage medium, a port (physical and virtual), a communication device, and an interface capable of accessing other clients, servers, computers, and devices via a wired or wireless medium, etc. The methods, programs, or code described herein and elsewhere may be executed by a client. Additionally, other devices necessary for the execution of the methods described in this application may be considered part of the infrastructure associated with the client.

[0141] A client may provide an interface to other devices, including, but not limited to, a server, other clients, printers, database servers, print servers, file servers, communication servers, distributed servers, etc. Furthermore, this coupling and / or connection may facilitate remote execution of a program over a network. Networking some or all of these devices may facilitate parallel processing of a program or method at one or more locations without departing from the scope of the present invention. Furthermore, any of the devices connected to a client via an interface may include at least one storage medium capable of storing methods, programs, applications, code, and / or instructions. A central repository may provide program instructions to be executed on different devices. In this embodiment, the remote repository may function as a storage medium for program code, instructions, and programs.

[0142] The methods and systems described herein may be deployed partially or entirely over a network infrastructure. The network infrastructure may include elements such as computing devices, servers, routers, hubs, firewalls, clients, personal computers, communication devices, routing devices, and other active and passive devices, modules, and / or components known in the art. Computing and / or non-computing devices associated with the network infrastructure may include storage media, apart from other components. The processes, methods, program codes, instructions described herein and elsewhere may be executed by one or more of the network infrastructure elements.

[0143] The methods, program codes, calculations, algorithms, and instructions described herein may be implemented on a cellular network having multiple cells. The cellular network may include mobile devices, cell sites, base stations, repeaters, antennas, towers, etc. The cell network may be a GSM, GPRS, 3G, 4G, 5G, EVDO, mesh, or other network type.

[0144] The methods, program codes, calculations, algorithms, and instructions described herein may be implemented on or via a mobile device. Mobile devices may include mobile phones, personal digital assistants, laptops, palmtops, netbooks, pagers, e-book readers, etc. These devices may include, among other components, storage media such as flash memory, buffers, RAM, ROM, and one or more computing devices. The computing devices associated with the mobile devices may be capable of executing program codes, methods, and instructions stored thereon.

[0145] Alternatively, the mobile device may be configured to execute instructions in cooperation with other devices. The mobile device may communicate with a base station interfaced with a server and configured to execute program code. The mobile device may communicate over a peer-to-peer network, a mesh network, or other communication network. The program code may be stored in a storage medium associated with the server and executed by a computing device embedded within the server. The base station may include a computing device and a storage medium. The storage may store program code and instructions executed by the computing device associated with the base station.

[0146] Computer software, program code, and / or instructions may be stored and / or accessed on computer-readable media, which may include computer components, devices, and recording media that hold digital data used for computations for some interval of time, storage devices known as random access memory (RAM), mass storage devices for more permanent storage, typically in the form of optical disks, magnetic storage devices like hard disks, and the like.

[0147] The methods and systems described herein can transform physical and / or intangible items from one state to another. The methods and systems described herein can also transform data representing physical and / or intangible items from one state to another.

[0148] The elements described and shown herein may imply logical boundaries between the elements. However, in accordance with software or hardware engineering practices, the shown elements and their functionality may be implemented on a computer through a computer-executable medium having a processor capable of executing program instructions stored thereon, as a monolithic software structure, as a stand-alone software module, or as a module employing external routines, code, services, etc., or any combination thereof; all such implementations may be within the scope of the present disclosure.

[0149] Additionally, the illustrated elements may be implemented on machines capable of executing program instructions. Thus, while this description describes functional aspects of the disclosed system, the specific configuration of software for implementing these functional aspects should not be inferred from these descriptions unless explicitly stated or apparent from the context. Similarly, it will be appreciated that the various steps identified and described above may be varied, and the order of steps may be adapted to particular applications of the techniques disclosed herein. All such variations and modifications are intended to fall within the scope of the present disclosure. Thus, the depiction and / or description of the order of various steps should not be understood as requiring a particular order of execution of those steps unless required by a particular application or unless explicitly stated or apparent from the context.

[0150] The above-described methods and / or processes, and steps thereof, may be implemented in hardware, software, or any combination of hardware and software suitable for a particular application. Hardware may include general-purpose computers and / or special-purpose computing devices or specific computing devices or specific aspects or components of specific computing devices. The processes may be implemented in one or more microprocessors, microcontrollers, embedded microcontrollers, programmable digital signal processors, or other programmable devices, along with internal and / or external memory. The processes may also, or instead, be embodied in application-specific integrated circuits, programmable gate arrays, programmable array logic, or any other device or combination of devices that can be configured to process electronic signals. Furthermore, it will be understood that one or more of the processes may be implemented as computer-executable code capable of being executed on a computer-readable medium.

[0151] Application software may be written using a structured programming language such as C, an object-oriented programming language such as C++, or any other high-level or low-level programming language (including assembly language, hardware description languages, and database programming languages ​​and techniques) that can be stored, compiled, or interpreted for execution on one of the above devices, as well as heterogeneous combinations of processors, processor architectures, or combinations of different hardware and software, or any other machine capable of executing program instructions.

[0152] Thus, in one aspect, each of the methods described above and combinations thereof may be embodied in computer-executable code that, when executed on one or more computing devices, performs the steps. In another aspect, the method may be embodied in a system that performs the steps, may be distributed in some manner across devices, or all of the functionality may be integrated into a dedicated standalone device or other hardware. In another aspect, the means for performing the steps associated with the processes described above may include any of the hardware and / or software described above. All such permutations and combinations are intended to fall within the scope of the present disclosure.

[0153] Any of the methods disclosed herein may be performed by application software executable on any past, present, or future operating system of a processor-enabled device, such as Windows®, Linux®, Android®, iOS®, etc. It will be understood that any software may be distributed across multiple devices or in a "software-as-a-service" or "platform-as-a-service" format, whereby participants need only some computer-based means of engaging with the software.

[0154] In describing exemplary embodiments of the invention, it will be understood that various features of the invention may be grouped together in a single embodiment, figure, or description for the purpose of streamlining the disclosure and facilitating an understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment.

[0155] Furthermore, some embodiments described herein include some features included in other embodiments but not other features, and combinations of features from different embodiments are within the scope of the present invention and are meant to form different embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0156] In the description provided herein, numerous specific details are set forth. However, it will be understood that embodiments of the present invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0157] Thus, while what are believed to be preferred embodiments of the present invention have been described, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the present invention. Functions may be added or deleted from the diagrams, and operations may be interchanged between functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

[0158] Although the present invention has been described with reference to specific examples, those skilled in the art will appreciate that the present invention may be embodied in many other forms.

[0159] term Implementations of the present disclosure are disclosed in the following sections.

[0160] Item 1: A method for determining a performance parameter of an electron multiplier having a series of electron emitting surfaces forming an electron multiplication chain, the method comprising a step of comparing a first electron flux of a first electron emitting surface of the electron multiplication chain with a second electron flux of a second electron emitting surface of the electron multiplication chain or with a second electron flux of an electron collector of the electron multiplier.

[0161] Item 2: The method of item 1, wherein the first and second electron emitting surfaces are each discrete electron emitting surfaces.

[0162] Item 3: The method of item 2, wherein each of the discrete electron emitting surfaces is a dynode of a discrete dynode electron multiplier.

[0163] Item 4: The method of item 1, wherein the first and second electron emission surfaces are provided by a single electron emission surface.

[0164] Item 5: The method of item 4, wherein the single-electron emission surface is a channel of a channel electron multiplier or a plate of a microchannel plate electron multiplier.

[0165] Clause 6: The method of any one of clauses 1 to 5, wherein the first electron emitting surface precedes the second electron emitting surface in the electron multiplication chain.

[0166] Clause 7: The method of any one of clauses 1 to 6, wherein the first electron emitting surface is less susceptible to electron flux-mediated gain degradation than the second electron emitting surface.

[0167] Clause 8: The method of any one of clauses 1 to 7, wherein the first electron emitting surface carries a lower electron flux than the second electron emitting surface.

[0168] Item 9: The first electron emitting surface is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000 8. The method of any one of paragraphs 1 to 7, wherein the cations of the cations of the present invention have a smaller electron flux than the cations of the present invention.

[0169] Clause 10: The method of any one of clauses 1 to 9, wherein a second electron flux is determined in the electron collector, the first electron emission surface carrying less electron flux than the terminal electron emission surface of the electron multiplication chain.

[0170] Item 11: A second electron flux is determined at the electron collector, and the first electron emitting surface is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 1000, 11. The method of any one of paragraphs 1 to 10, wherein the cations of the cations of the present invention have an electron flux that is 0, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 200,000, 300,000, 400,000, 500,000, 60,000, 700,000, 800,000, 900,000, or 1,000,000 less.

[0171] Item 12: The method of any one of items 1 to 11, wherein the first electron emission surface is within the first 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, or 25% of the electron multiplication chain.

[0172] Clause 13: The method of any one of clauses 1 to 12, wherein the first electron emission surface is not within the first 5%, 10%, 15%, 20%, or 25% of the electron multiplication chain.

[0173] Item 14: The method of any one of items 1, 2, 3, and 6 to 13, wherein the electron multiplier comprises discrete electron emission surfaces, and the first electron emission surface is the third, fourth, fifth, sixth, or seventh electron emission surface of the electron multiplication chain.

[0174] Item 15: The method of any one of items 1, 2, 3, and 6 to 13, wherein the electron multiplier comprises discrete electron emission surfaces, and the first electron emission surface is the fourth, fifth, or sixth electron emission surface of the electron multiplication chain.

[0175] Item 16: The method of any one of items 1, 2, 3, and 6 to 13, wherein the electron multiplier comprises discrete electron emission surfaces, and the first electron emission surface is the fifth electron emission surface of the electron multiplication chain.

[0176] Item 17: The method of any one of items 1, 2, 3, and 6 to 13, wherein the electron multiplier comprises discrete electron emitting surfaces, and the first electron emitting surface and the second electron emitting surface, or the first electron emitting surface and the electron collector, are separated by at least two, three, four, or five intervening electron emitting surfaces.

[0177] Item 18: The method of any one of items 1, 4, and 5, wherein the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and a first electron emission surface is the third, fourth, fifth, sixth, or seventh electron emission site of the electron multiplication chain.

[0178] Item 19: The method of any one of items 1, 4, and 5, wherein the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and the first electron emission surface is the fourth, fifth, or sixth electron emission site of the electron multiplication chain.

[0179] Clause 20: The method of any one of clauses 1, 4, and 5, wherein the electron multiplier comprises a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and the first electron emission surface is the fifth electron emission site of the electron multiplication chain.

[0180] Item 21: The method of any one of items 1, 4, and 5, wherein the electron multiplier comprises a single electron emitting surface having a series of electron emitting sites that together form an electron multiplication chain, and wherein a first electron emitting site and a second electron emitting site, or a first electron emitting site and an electron collector, are separated by at least two, three, or four intervening electron emitting sites.

[0181] Clause 22: The method of any one of clauses 1 to 21, wherein the first and second electron fluxes are compared by (i) a current measurement circuit and then comparing the determined currents, or (ii) a current comparison circuit.

[0182] Item 23: The method of any one of items 1 to 22, wherein the first and second electron fluxes are each determined at the same time or within a period of time.

[0183] Clause 24: The method of clause 23, wherein the first and second electron fluxes are determined intermittently over a period of electron multiplier operation.

[0184] Item 25: The method of item 24, wherein the period of electron multiplier operation is about 1 second, 5 seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 1 hour or more.

[0185] Clause 26: The method of any one of clauses 1 to 25, wherein the first and second electron fluxes are determined according to a sampling rate.

[0186] Item 27: The method of item 26, wherein the sampling rate is equal to or less than about 1 Hz, 0.1 Hz, or about 0.01 Hz.

[0187] Item 28: The method of item 26 or 27, wherein the sampling rate is greater than or equal to about 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz, 0.5 Hz, 0.6 Hz, 0.7 Hz, 0.8 Hz, 0.9 Hz, or 1 Hz.

[0188] Item 29: The method of any one of items 26 to 28, wherein the sampling rate is approximately 0.3 Hz to 0.01 Hz.

[0189] Item 30: The method of any one of items 1 to 29, wherein the performance parameter indicates the gain of the electron multiplier.

[0190] Clause 31: The method of any one of clauses 1 to 30, wherein the comparing step includes a mathematical operation utilizing the determined first and second electron fluxes.

[0191] Clause 32: The method of any one of clauses 1 to 31, wherein the mathematical operation includes producing a ratio, multiple, quotient, or difference.

[0192] Item 33: A method of operating an electron multiplier, comprising: Determining performance parameters of the electron multiplier according to the method of any one of paragraphs 1 to 32; comparing the determined performance parameter with a predetermined value or range for the performance parameter; If the determined performance parameter is not a predetermined value or is outside a predetermined range of the performance parameter, modifying an operating parameter of the electron multiplier so that the determined performance parameter is a predetermined value or is within a predetermined range of the performance parameter.

[0193] Item 34: The method of item 33, wherein the operating parameter is a voltage bias applied to the electron multiplier.

[0194] Clause 35: The method of clause 33 or clause 34, wherein the method is implemented to continuously monitor the performance parameters and modify the operating parameters of the electron multiplier as needed, and the determining, comparing, and modifying steps are performed sequentially multiple times over a period of time.

[0195] Clause 36: The method of clause 35, wherein the performance parameter is electron multiplier gain, and the gain of the electron multiplier is maintained at a predetermined gain or within a predetermined gain range over a period of time.

[0196] Item 37: An electron multiplier or electron multiplier system having a series of electron emitting surfaces forming an electron multiplication chain, the electron multiplication method including circuitry and optionally processor-executable program instructions configured to compare a first electron flux of a first electron emitting surface of the electron multiplication chain with a second electron flux of a second electron emitting surface of the electron multiplication chain or an electron collector of the electron multiplier.

[0197] Item 38: An electron multiplier or electron multiplying system according to Item 37, wherein the first and second electron emitting surfaces are each discrete electron emitting surfaces.

[0198] Item 39: An electron multiplier or electron multiplying system according to Item 38, wherein each of the discrete electron emitting surfaces is a dynode of a discrete dynode electron multiplier.

[0199] Item 40: An electron multiplier or electron multiplying system according to item 37, wherein the first and second electron emitting surfaces are provided by a single electron emitting surface.

[0200] Item 41: An electron multiplier or electron multiplying system according to item 40, wherein the single electron emission surface is a channel of a channel electron multiplier or a plate of a microchannel plate electron multiplier.

[0201] Clause 42: An electron multiplier or electron multiplier system according to any one of clauses 37 to 41, wherein the first electron emitting surface precedes the second electron emitting surface in the electron multiplication chain.

[0202] Clause 43: An electron multiplier or electron multiplier system according to any one of clauses 37 to 42, wherein the first electron emitting surface is less susceptible to electron flux mediated gain degradation than the second electron emitting surface.

[0203] Clause 44: An electron multiplier or electron multiplier system according to any one of clauses 37 to 43, wherein the first electron emitting surface carries a smaller electron flux than the second electron emitting surface.

[0204] Item 45: The first electron emitting surface is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000, 40000, 50000 44. An electron multiplier or electron multiplying system according to any one of clauses 37 to 43, carrying an electron flux that is 0,000, 60,000, 70,000, 80,000, 90,000, 100,000, 200,000, 300,000, 400,000, 500,000, 60,000, 700,000, 800,000, 900,000 or 1,000,000 less.

[0205] Clause 46: An electron multiplier or electron multiplier system described in any one of clauses 37 to 45, wherein a second electron flux is determined in the electron collector, and the first electron emission surface carries less electron flux than the terminal electron emission surface of the electron multiplication chain.

[0206] Item 47: A second electron flux is determined at the electron collector, wherein the first electron emitting surface is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10 ...10000, 10000, 10000, 10000, 10000, 10000, 10000, 10000, 10000, 10000, 10000, 1000 47. An electron multiplier or electron multiplying system according to any one of paragraphs 37-46, carrying an electron flux that is 00, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 200,000, 300,000, 400,000, 500,000, 60,000, 700,000, 800,000, 900,000, or 1,000,000 less.

[0207] Item 48: An electron multiplier or electron multiplication system according to any one of items 37 to 47, wherein the first electron emission surface is within the first 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, or 25% of the electron multiplication chain.

[0208] Item 49: An electron multiplier or electron multiplication system according to any one of items 37 to 48, wherein the first electron emission surface is not within the first 5%, 10%, 15%, 20%, or 25% of the electron multiplication chain.

[0209] Item 50: An electron multiplier or electron multiplication system described in any one of items 37, 38, 39, and 42 to 49, wherein the electron multiplier comprises discrete electron emission surfaces, and the first electron emission surface is the third, fourth, fifth, sixth, or seventh electron emission surface of the electron multiplication chain.

[0210] Item 51: An electron multiplier or electron multiplying system described in any one of items 37, 38, 39, and 42 to 49, wherein the electron multiplier comprises discrete electron emission surfaces, and the first electron emission surface is the fourth, fifth, or sixth electron emission surface of the electron multiplication chain.

[0211] Item 52: An electron multiplier or electron multiplying system described in any one of items 37, 38, 39, and 42 to 49, wherein the electron multiplier has discrete electron emission surfaces, and the first electron emission surface is the fifth electron emission surface of the electron multiplication chain.

[0212] Item 53: An electron multiplier or electron multiplying system according to any one of items 37, 38, 39 and 42 to 49, wherein the electron multiplier comprises individual electron emission surfaces, and the first electron emission surface and the second electron emission surface, or the first electron emission surface and the electron collector, are separated by at least two, three, four or five intervening electron emission surfaces.

[0213] Item 54: An electron multiplier or electron multiplying system described in any one of items 37, 40, and 41, wherein the electron multiplier includes a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and a first electron emission surface is the third, fourth, fifth, sixth, or seventh electron emission site of the electron multiplication chain.

[0214] Item 55: An electron multiplier or electron multiplying system described in any one of items 37, 40, and 41, wherein the electron multiplier includes a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and the first electron emission surface is the fourth, fifth, or sixth electron emission site of the electron multiplication chain.

[0215] Item 56: An electron multiplier or electron multiplying system described in any one of items 37, 40, and 41, wherein the electron multiplier includes a single electron emission surface having a series of electron emission sites that together form an electron multiplication chain, and the first electron emission surface is the fifth electron emission site of the electron multiplication chain.

[0216] Item 57: An electron multiplier or electron multiplying system described in any one of items 37, 40, and 41, wherein the electron multiplier includes a single electron emitting surface having a series of electron emitting sites that together form an electron multiplication chain, and the first electron emitting site and the second electron emitting site, or the first electron emitting site and the electron collector, are separated by at least two, three, or four intervening electron emitting sites.

[0217] Clause 58: An electron multiplier or electron multiplying system as described in any one of clauses 37 to 57, wherein the circuitry and optionally the program instructions compare the first and second electron fluxes, at least in part, by (i) a current measurement circuit and then comparing the current measured by the program instructions, or (ii) a current comparison circuit.

[0218] Clause 59: An electron multiplier or electron multiplying system according to any one of clauses 37 to 58, wherein the circuitry and optionally the program instructions are configured to determine the first and second electron fluxes at the same point in time or within a period of time.

[0219] Item 60: An electron multiplier or electron multiplying system as described in Item 59, wherein the circuitry and optionally program instructions are configured to determine the first and second electron fluxes, determined intermittently over a period of electron multiplier operation.

[0220] Item 61: An electron multiplier or electron multiplying system as described in Item 60, wherein the duration of electron multiplier operation is about 1 second, 5 seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 1 hour or more.

[0221] Clause 62: An electron multiplier or electron multiplying system as described in any one of clauses 37 to 61, wherein the circuitry and optionally the program instructions are configured such that the first and second electron fluxes are determined according to a sampling rate.

[0222] Item 63: An electron multiplier or electron multiplying system according to Item 62, wherein the sampling rate is equal to or less than about 1 Hz, 0.1 Hz, or about 0.01 Hz.

[0223] Item 64: An electron multiplier or electron multiplying system according to Item 62 or Item 63, wherein the sampling rate is greater than or equal to about 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz, 0.5 Hz, 0.6 Hz, 0.7 Hz, 0.8 Hz, 0.9 Hz, or 1 Hz.

[0224] Item 65: An electron multiplier or electron multiplying system according to any one of items 62 to 64, wherein the sampling rate is between approximately 0.3 Hz and 0.01 Hz.

[0225] Item 66: An electron multiplier or electron multiplying system according to any one of items 37 to 65, wherein the performance parameter indicates the gain of the electron multiplier.

[0226] Item 67: The circuit and optionally the program instructions determining performance parameters of the electron multiplier; comparing the determined performance parameter with a predetermined value or a predetermined range for the performance parameter; 67. An electron multiplier or electron multiplying system as described in any one of clauses 37 to 66, configured to, if the determined performance parameter is not a predetermined value or is outside a predetermined range of the performance parameter, modify the operating parameters of the electron multiplier so that the determined performance parameter is a predetermined value or is within a predetermined range of the performance parameter.

[0227] Item 68: An electron multiplier or electron multiplying system according to Item 67, wherein the operating parameter is a voltage bias applied to the electron multiplier.

[0228] Clause 69: An electron multiplier or electron multiplying system as described in any one of clauses 37 to 68, wherein the circuitry and optionally the program instructions are configured to continuously monitor the performance parameters and modify the operating parameters of the electron multiplier as necessary, and the determining, comparing, and modifying steps are performed sequentially multiple times over a period of time.

[0229] Item 70: An electron multiplier or electron multiplying system according to Item 69, wherein the performance parameter is electron multiplier gain, and the gain of the electron multiplier is maintained at a predetermined gain or within a predetermined gain range over a period of time.

Claims

1. 1. A method for determining a performance parameter of an electron multiplier having a series of electron emitting surfaces forming an electron multiplication chain, the method comprising the step of comparing a first electron flux of a first electron emitting surface of the electron multiplication chain to a second electron flux of a second electron emitting surface of the electron multiplication chain or to a second electron flux of an electron collector of the electron multiplier.

2. 10. The method of claim 1, wherein the first and second electron emitting surfaces each form part of a discrete dynode, continuous or microchannel plate multiplier.

3. The method of claim 1 , wherein the first electron emitting surface is earlier in the electron multiplication chain than the second electron emitting surface.

4. The method of claim 1 , wherein the first electron emitting surface is less susceptible to electron flux-mediated gain degradation than the second electron emitting surface.

5. The method of claim 1 , wherein the first electron emitting surface carries a lower electron flux than the second electron emitting surface.

6. 10. The method of claim 1, wherein the first electron emission surface is within about the first 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, or 25% of the electron multiplication chain.

7. The method of claim 1 , wherein the second electron emission surface is within about the last 5%, 10%, 15%, 20%, or 25% of the electron multiplication chain.

8. 10. The method of claim 1, wherein the first and second electron fluxes are compared by (i) a current measurement circuit and then comparing the determined currents, or (ii) a current comparison circuit.

9. The method of claim 1 , wherein the first and second electron fluxes are determined at the same time or within a period of time.

10. 10. The method of claim 9, wherein the first and second electron fluxes are determined intermittently over a period of electron multiplier operation.

11. The method of claim 1 , wherein the performance parameter is indicative of a gain of the electron multiplier.

12. 10. The method of claim 9, wherein the comparing step includes a mathematical operation utilizing the determined first and second electron fluxes.

13. The method of claim 12 , wherein the mathematical operation includes producing a ratio, a multiple, a quotient, or a difference.

14. 1. A method of operating an electron multiplier, comprising: Determining performance parameters of the electron multiplier according to a method according to any one of claims 1 to 13; comparing the determined performance parameter with a predetermined value or a predetermined range for the performance parameter; if the determined performance parameter is not the predetermined value or is outside the predetermined range of the performance parameter, modifying an operating parameter of the electron multiplier so that the determined performance parameter is the predetermined value or is within the predetermined range of the performance parameter.

15. 15. The method of claim 14, wherein the method is implemented to continuously monitor the performance parameters and modify the operating parameters of the electron multiplier as needed, and wherein the determining, comparing, and modifying steps are performed sequentially multiple times over a period of time.

16. 16. The method of claim 15, wherein the performance parameter is a gain of an electron multiplier, and the gain of the electron multiplier is maintained at a predetermined gain or within a predetermined gain range over a period of time.

17. 1. An electron multiplier or electron multiplication system having a series of electron emitting surfaces forming an electron multiplication chain, comprising: said electron multiplier or electron multiplication system comprising: a circuit having a processor; and processor-executable program instructions, When executed by the processor, the processor: determining a performance parameter of the electron multiplier by comparing a first electron flux of a first electron emitting surface of the electron multiplier chain with a second electron flux of a second electron emitting surface of the electron multiplier chain or with a second electron flux of an electron collector of the electron multiplier; comparing the determined performance parameter with a predetermined value or a predetermined range for the performance parameter; and if the determined performance parameter is not the predetermined value or is outside the predetermined range of the performance parameter, modifying an operating parameter of the electron multiplier so that the determined performance parameter is the predetermined value or is within the predetermined range of the performance parameter.

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