Method and apparatus for processing count output

Abstract

A method of processing a count output associated with a counting device, comprising: (i) calculating a first time-count average value from time-count values obtained for a number of events "n" between events x1 and xn; (ii) measuring a time-count value associated with the event xn + 1; and (iii) calculating a second time-count average value from time-count values obtained for a number of events "n" between events x2 and xn + 1.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for processing count outputs associated with a counting device. In particular, but not limited thereto, the present invention relates to a method and apparatus for processing count outputs associated with a radiation detection device, such as a Geiger-Mueller tube. Background Art

[0002] A radiation detection device (such as a radiation dosimeter) is an electronic device that measures the exposure level (dose) from an external source of ionizing radiation. Therefore, radiation dosimeters are often used to monitor and / or record radiation doses and / or dose rates in a specific environment. This can be used for continuous monitoring at a specific location. Alternatively, it can also be used to monitor ionizing radiation to which an individual may be exposed, in which case the dosimeter is usually worn by the monitored person. Such devices are often called electronic personal dosimeters. Electronic personal dosimeters usually provide continuous readings of the cumulative dose and / or instantaneous dose rate, and are usually equipped with a warning element that can provide a signal to the user (for example, an audible sound or a visual display) when a preset cumulative dose or dose rate is exceeded.

[0003] Electronic personal dosimeters are battery powered and typically use a small Geiger-Müller (GM) tube or semiconductor (Si chip) inside which the ionizing radiation releases an electrical charge that generates a measurable current. Examples of such devices include the Tracerco TM Personal electronic dosimeter.

[0004] In a Geiger-Muller tube, the GM tube consists of a chamber filled with an inert gas or halogen and a quenching gas or vapor such as a hydrocarbon. Two electrodes are mounted in the chamber, which apply a potential difference of several hundred volts across the chamber. When ionizing radiation hits the tube, the gas in the chamber is ionized by the incident radiation, thereby generating charged particles within the chamber. The electric field generated by the voltage between the electrodes causes the generated charges to move within the chamber, and the generated electrical pulses are measured by the electronics within the instrument.

[0005] The problem with radiation detectors using GM tubes is that with a continuous voltage applied, after each ionization event, the tube requires a certain amount of time to charge between pulses in order to be ready to count subsequent events (since it is essentially a capacitor being charged through a large value resistor). This is commonly referred to as "dead time". The actual dead time depends on several factors (including the active volume and shape of the detector), so it is difficult to correct for. This dead time can cause the GM tube to saturate, which can lead to an underestimation of event rates, especially in high radiation environments.

[0006] Some studies (see TJ Lewis, GEIGER-COUNTER OPERATION WITHOUT DEAD-TIME, Appl. sci. Res., 1955, Part B, Vol. 5, Queen Mary College, London) have proposed that it is theoretically possible to switch Geiger-Muller (GM) tubes to eliminate the effects of dead time and improve count rate measurements. This "time-to-count" method is independent of dead time and limits the number of discharges in high radiation fields by introducing a fixed waiting time between discharges (i.e., operating the counter by a pulse voltage). The waiting time is selected to be longer than the recovery time of the tube. However, to date, no practical technical means have been disclosed to implement this theoretical principle in an effective and reliable manner.

[0007] As mentioned above, in a Geiger-Muller tube, the GM tube comprises a chamber filled with halogen gas and a quenching medium, in which two electrodes (anode and cathode) are mounted, which apply a potential difference of several hundred volts in the chamber. Typically, in order to "charge" the tube, the voltage at the anode is increased to its target value (e.g., 550-600V). The voltage at the cathode is usually at a potential of 0V. The anode voltage is usually generated by a current passing through a high-resistance resistor on the anode to prevent or limit the risk of arcing between the electrodes during ionization. However, this traditional arrangement has some disadvantages. First, there is a "dead time" after the ionization event (discharge caused by incident radiation) occurs, which is caused by two effects: (i) the time required for multiple electron avalanches to terminate; and (ii) due to the large current limiting resistor on the anode, the tube takes a certain amount of time to charge back to full voltage, during which time the probability of the GM tube detecting radiation is reduced. Further, before the ionization event is detected, the voltage is usually continuously applied to the tube while it is charging, which is very power-consuming at high count rates.

[0008] The generation of ionizing radiation and its detection are assumed to be generated according to a statistically independent random process, characterized by a constant probability of occurrence per unit time, also known as a Poisson random process. The Poisson probability is given by the formula:

[0009] P(k events in time t) = (rt) k e -rt / k!

[0010] Where P is the Poisson probability, k is the number of events, t is the time, and r is the average occurrence rate.

[0011] A distribution function can be derived to describe the time interval between adjacent random events. The differential probability dp of an event occurring within a differential time interval dt is r.dt, where r is the average occurrence rate. Then for a finite time interval T, the average number of times an event occurs is rT.

[0012] To derive the distribution function describing the time interval between consecutive random events, assume that the event has occurred at time t = 0. To determine the differential probability that the next event will occur within the differential time dt after a time interval of length t, two independent processes must exist: (i) no event can occur during the time interval from 0 to t; and (ii) an event must occur within the next differential time increment dt. Therefore, the total probability will be given by the product of the probabilities characterizing these two processes:

[0013] p (after a delay of t, the next event occurs within dt)

[0014] = P (0 events from time 0 to time t) × P (events within dt)

[0015] p(t)=P(0)×rdt

[0016] p(t)=(rt) 0 e -rt / 0! ×rdt

[0017] p(t)=e -rt ×rdt

[0018] dp(t) / dt=re -rt

[0019] where p(t) is a function that describes the distribution of time intervals between consecutive random events.

[0020] The average time-count length is calculated as:

[0021]

[0022] As with all measurements, there are statistical uncertainties in average time-count measurements. Due to the stochastic nature of a Poisson random process (such as radiation), the confidence that any single measurement accurately represents the true average event rate is low. Therefore, in order to meet the requirements specified in dosimeter standards, multiple measurements must be made and averaged. While it may be relatively easy to accurately estimate the event rate in radiation fields with a high event rate, this is significantly more challenging when the event rate is low because the time-count values ​​will be larger and therefore a longer period of time will be required to collect the appropriate number of events to average.

[0023] For example, referring to the radiation dose rate incident on the radiation measuring device, which results in 104 The count rate of the radiation field is 10 4 Counts / second ("counts per second" or "cps"). Placing a shield between the radiation source and the device can reduce the exposure, for example to 1 cps. Typically, the count rate is taken as the average (mean) of a fixed number of time-count values, in this case 30. Thus, when the irradiation field changes from 10 4 After the cps changes to 1 cps, it takes about 30 seconds to register 30 counts in the new radiation field. Therefore, if the fixed number of time-count values ​​used to calculate the average is 30, the device will take about 30 seconds to register a count rate change from 10 4 The change from cps to 1cps is because it takes about 30s to register 30 counts in the new radiation field. This does not meet the specified standards.

[0024] It is an object of the present invention to solve or alleviate one or more problems associated with the prior art. Summary of the invention

[0025] The present inventors have developed systems and methods configured to process the counting output associated with a counting device (e.g., a Geiger-Mueller tube). This new method allows the user to measure event rates over a wider range with faster response times. This allows compliance with the requirements specified in dosimeter standards even when the count rate is very low (e.g., the count rate approaches zero) and / or when the count rate changes rapidly from high to low.

[0026] According to a first aspect of the present specification, there is provided a method for processing a counting output associated with a counting device, the method comprising:

[0027] According to the events x1 and x n Calculate a first time-to-count average value of time-to-count values ​​obtained between a certain number of events "n";

[0028] Measurement and Event x n+1 the associated time-count value; and

[0029] According to the events x2 and x n+1 The time-count values ​​obtained between the certain number of events "n" calculate a second time-count average value.

[0030] Thus, the second time-count average, and any subsequent time-count averages calculated for a certain number "n" of events (including any subsequent time-count values), can be viewed as "rolling" averages based on the most recent certain number "n" of events.

[0031] The average count rate (e.g., the first average count rate and / or the second average count rate) may be calculated based on the associated time-count average (e.g., the first time-count average or the second time-count average). However, as described above, if the time-count value (e.g., compared to the time-count average) increases significantly, then the time required to detect the increase in the time-count average over the time of interest (e.g., over the past "n" events) may be long. The method addresses this issue by introducing a "pseudo-count" at the preset time interval "j" if no event is registered after the preset time interval "j". Therefore, if no event is registered after the preset time interval "j", the method may include introducing a pseudo-count associated with event x. n+1 Therefore, in the present method, the term "event" can be understood as both a "real" event associated with a measured time-count value and a "pseudo" event associated with a "pseudo" time-count value, such as a "pseudo" time-count value equal to "j".

[0032] The method may include introducing a "pseudo" time-count value equal to "j" associated with each subsequent event until a count or "real" event is measured or registered. In this case, when no real count is measured, the time value "j" is added to the "buffered" time-count. When an event x is m (m>n and x m >j) When a count or "real" event is measured or registered, the method may include providing a time-count value corresponding to the event x m The measured time-count value associated with event x m The time-count values ​​associated with the measured time-count values ​​may represent or define the expected time-count values.

[0033] Subsequently, if no event is registered after the preset time interval "j", the method may include introducing a "pseudo" time-count value equal to the expected time-count value (e.g., equal to the expected time-count value corresponding to event x). m The method may comprise repeating this step until:

[0034] - a new count or "real" event is measured or registered; in this case, the method may comprise providing a time-count value corresponding to the measured time-count value associated with the new count or "real" event; or

[0035] - the expected time-count value has elapsed without measuring or registering a new count, in which case,

[0036] The method may include introducing a "pseudo" time-count value equal to "j".

[0037] The method may include repeating the above steps in sequence. Typically, the "pseudo" time-count value "j" may be about 1 ms-500 ms, such as about 10 ms-200 ms, such as about 50 ms to 150 ms, such as about 100 ms.

[0038] Advantageously, the present method may facilitate a quicker response to low count rates (e.g., to a sharp drop or decrease in count rate, e.g., from a high dose rate to a low dose rate). It will be appreciated that, when used with radiation measurement equipment, the use of "pseudo-counts" will only affect the calculation of the instantaneous (average) count rate, but will not affect the total cumulative dose measured by the equipment, nor will the "pseudo" counts be taken into account when calculating the cumulative dose. While the introduction of "pseudo-counts" will introduce a degree of noise into the calculation (e.g., into the calculated "time-count" average), it will be appreciated that the degree of error introduced is acceptable in the case of low count rates (in compliance with standard requirements), and the benefit of a quicker response to a decrease in count rate will offset this error.

[0039] Typically, the counting device in this specification may be a radiation detection device. The counting device may include a Geiger-Mueller tube. Further, the method may typically be a computer-implemented method. The method may include processing the counting output using a smoothing algorithm. The method may include using a nonlinear exponential smoothing ("NLES") algorithm.

[0040] As described above, the method comprises:

[0041] According to the events x1 and x n Calculate a first time-count average value between the time-count values ​​obtained for a certain number of events "n";

[0042] Measurement and Event x n+1 the associated time-count value; and

[0043] According to the events x2 and x n+1 The time-count values ​​obtained between the certain number of events "n" calculate a second time-count average value.

[0044] The method may include calculating an average count rate (eg, a first average count rate and / or a second average count rate) from the associated time-count averages (eg, the first time-count average or the second time-count average). The method may include filtering the values ​​of the average count rates.

[0045] The method may comprise applying an algorithm according to formula (I):

[0046] S n =(1 / t n -S n-1 )×α(|Δ n |)+S n-1 (I)

[0047] Where S n is the value of the smoothed count rate calculated by the algorithm;

[0048] t n is the current time-count average (e.g. calculated according to the method of the first aspect),

[0049] S n-1 is the value of the previous smoothed count rate calculated by the algorithm;

[0050] Δ n =|log 10 S n-1 -log 10 1 / x n |;

[0051] and

[0052]

[0053] When |Δ n | When α0 is less than or equal to a first threshold Δ0, α0 is the first filter applied; and

[0054] When |Δ n When α1 is equal to or greater than the second threshold Δ1, α1 is the second filter applied.

[0055] Therefore, a currently calculated value (eg, a time-count value or a count rate value) should be smoothed using said value, which may be a function of the difference between said current value and said previously smoothed value.

[0056] Multiple sets of filters may be provided. Two or more sets of filters may be provided, for example a first set of filters α0 and α1 and a second set of filters α′0 and α′1. Under a first condition, for example when a calculated count rate (e.g., an average count rate derived from a related time-count average (e.g., from the first time-count average or the second time-count average)) is equal to or greater than a first threshold, the algorithm may apply or may use the first set of filters α0 and α1. Under a second condition, for example, when a calculated count rate (e.g., an average count rate derived from a related time-count average (e.g., from the first time-count average or the second time-count average)) is less than the first threshold, the algorithm may apply or may use the second set of filters α′0 and α′1. Advantageously, this allows for smooth readings in high count fields and faster responses to smaller magnitude changes in low count fields. The count rate threshold may be about 1-10 cps, for example, about 2 cps.

[0057] The method may include displaying a signal representing the counting output, typically a count rate. The method may include displaying the value of the smoothed count rate. The method may include refreshing the display at a preset time interval. The preset time interval may be greater than the expected time-count value and / or the "pseudo" time-count value "j". Advantageously, this may reduce the degree of fluctuation of the displayed signal seen by a user. The preset time interval may be 0.1-5s, such as 0.5-2s, such as about 1s.

[0058] According to a second aspect of the present specification, there is provided a method for processing a counting output associated with a counting device, the method comprising:

[0059] According to the event x1n and event x n Calculate a first time-count average value between the time-count values ​​obtained for a certain number of events "n";

[0060] Measurement and Event x n+1 The associated time-count value;

[0061] According to the events x2 and x n+1 calculating a second time-count average value from the time-count values ​​obtained between the certain number of events n; and

[0062] Apply the algorithm according to formula (I) to calculate the smoothed count rate S n :

[0063] S n =(1 / t n -S n-1 )×α(|Δ n |)+Sn-1 (I)

[0064] Where S n is the value of the smoothed count rate calculated by the algorithm;

[0065] t n is the second time-count average,

[0066] S n-1 is the value of the previous smoothed count rate calculated by the algorithm;

[0067] Δ n =|log 10 s n-1 -log 10 1 / x n |;

[0068] and

[0069]

[0070] When |Δ n | When α0 is less than or equal to a first threshold Δ0, α0 is the first filter applied; and

[0071] When |Δ n When α1 is equal to or greater than the second threshold Δ1, α1 is the second filter applied.

[0072] Therefore, a currently calculated value (eg, a time-count value or a count rate value) should be smoothed using said value, which may be a function of the difference between said current value and said previously smoothed value.

[0073] Multiple sets of filters may be provided. Two or more sets of filters may be provided, for example a first set of filters α0 and α1 and a second set of filters α′0 and α′1. Under a first condition, for example when a calculated count rate (e.g., an average count rate derived from a related time-count average (e.g., from the first time-count average or the second time-count average)) is equal to or greater than a first threshold, the algorithm may apply or may use the first set of filters α0 and α1. Under a second condition, for example, when a calculated count rate (e.g., an average count rate derived from a related time-count average (e.g., from the first time-count average or the second time-count average)) is less than the first threshold, the algorithm may apply or may use the second set of filters α′0 and α′1. Advantageously, this allows for smooth readings in high count fields and faster responses to smaller magnitude changes in low count fields. The count rate threshold may be about 1-10 cps, for example, about 2 cps.

[0074] According to a third aspect of the specification, a data processing device is provided, which includes a device for executing the method of the first aspect or the second aspect. The data processing device may include a processor configured to execute the method of the first aspect or the second aspect.

[0075] According to a fourth aspect of the present specification, there is provided a computer program comprising instructions. When a computer executes the program, the instructions cause the computer to execute the method of the first aspect or the second aspect.

[0076] According to a fifth aspect of the present specification, a computer-readable medium comprising instructions is provided. When the instructions are executed by a computer, the instructions cause the computer to execute the method of the first aspect or the second aspect.

[0077] The features related to the method of the first aspect or the second aspect described above are also applicable to the third, fourth or fifth aspect, and are not described here for the sake of brevity. The following features are also applicable to any of the above aspects.

[0078] The counting device may include or may be a radiation detection device. The counting device may include a Geiger-Mueller tube. The radiation detection device may include a Geiger-Mueller tube, which includes a chamber equipped with two or more electrodes, wherein the chamber is configured to charge by temporarily connecting the two or more electrodes to respective activation potentials. The chamber may provide or may include a pair of electrodes, typically an anode and a cathode. The chamber may be configured to charge by temporarily connecting the anode and the cathode to respective activation potentials. The activation potential of the anode may be in the range of about 300V-700V, for example, about 440V-600V, typically about 550V. The activation potential of the cathode may be in the range of about 0V-50V, typically about 0V.

[0079] The anode may maintain a constant potential, such as the anode activation potential. The device may include a voltage supply unit configured to provide the anode activation potential. Advantageously, the anode may not include or be coupled to a resistor. The anode activation potential may not be determined or defined by a resistor. It is understood that when the voltage supply unit providing the activation potential to the anode includes a resistor, the resistor may have a sufficiently low ohmic value so that the activation potential provided by the voltage supply unit is not determined or defined by the resistor.

[0080] In a conventional Geiger-Muller tube, the anode voltage is usually generated by passing a current through a high-value resistor on the anode. This is usually done to minimize the risk of arcing between the electrodes during ionization. However, this setup usually requires that the voltage be continuously applied when activating the GM tube until an ionization event is detected, which is not only power-consuming but also still carries a certain risk of arcing. In addition, due to the large current-limiting resistor on the anode, the tube requires a non-negligible time to charge back to full voltage, thereby reducing the maximum count rate that the system can detect.

[0081] In this arrangement, the chamber is configured to be charged by temporarily connecting two or more electrodes of the chamber (e.g., an anode and a cathode) to respective activation potentials, and then disconnecting at least one electrode (typically the cathode) from its activation potential until an ionization event occurs. The inventors have discovered that by utilizing the inherent capacitive properties of the GM tube, temporary activation of the tube is sufficient to charge the tube and maintain the charged or activated state long enough until an ionization event occurs. This has a number of benefits:

[0082] - First, when the gas in the GM tube is ionized, the tube is discharged instantly because there is no potential difference actively applied at the instant of ionization. Therefore, the risk of arcing can be eliminated or at least greatly reduced. This may also result in a faster system capable of detecting higher count rates.

[0083] - Secondly, the power required to keep the tube charged can be reduced, especially at high count rates. This is because, in the present system, the tube is charged at a preset time interval (typically 1ms) after the ionization event. Therefore, at very high count rates, the number of times the tube is charged will tend to be 1000 times per second. In contrast, if the tube is powered continuously, the maximum theoretical count rate will tend to be 10 per second. 6 Second-rate.

[0084] Therefore, in this system, the current required to keep the tube charged can be reduced by up to 1000 times.

[0085] Activation of the GM tube (e.g., connection of the cathode to its activation potential) can be performed in less than 1 ms, such as less than 100 μs, such as less than 10 μs, and typically less than 5 μs. Activation of the GM tube can be performed between about 10 ns-100 μs, such as about 100 ns-10 μs, typically about 500 ns-5 μs, such as between 500 ns-2 μs. In one or more embodiments, the activation time can be about 1.2 μs. Therefore, the activation time can be shorter than a typical or expected time-count value, and / or, can be shorter than the current pulse generated by the discharge of the tube.

[0086] The anode may be maintained at a constant potential, such as its activation potential.The anode may be connected (eg permanently connected) to a voltage source (eg via a voltage supply).

[0087] Advantageously, the cathode may be associated with a switch. The switch may be capable of connecting or disconnecting the cathode to its activation potential (e.g., about 0V). The switch may be disposed within a cathode interface unit configured to activate and / or deactivate the cathode, for example, configured to drive the connection and disconnection of the cathode from its activation potential. The cathode switch may include or may be a transistor, preferably an N-type MOSFET ("nFET"). Advantageously, such a switch may provide a very fast way to activate the cathode, thereby providing a very fast way to charge the GM tube. The device may include a controller, such as a microcontroller unit (MCU), configured to control an anode voltage source and / or a cathode interface unit, such as a switch. Preferably, the controller may be configured to control the anode voltage source and the cathode interface unit.

[0088] A controller may be provided for a radiation detection device, the radiation detection device comprising:

[0089] A Geiger-Muller tube comprising a chamber containing an anode and a cathode, wherein the chamber is configured to be charged by temporarily connecting the anode and the cathode to respective activation potentials;

[0090] a voltage supply unit configured to provide the anode activation potential; and

[0091] The cathode interface unit is configured to drive the cathode to be connected to and / or disconnected from its activation potential, wherein the controller is configured to control the driving of the anode voltage supply unit and the cathode interface unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] In order to better understand the invention and to show how it may be implemented, some embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0093] Figure 1 is a schematic diagram of a radiation detection device in the prior art;

[0094] Figure 2 The general principle of the "time-to-first-count" method is explained;

[0095] Figures 3 to 5 A schematic diagram showing a radiation detection device suitable for use in the method of the present invention; and

[0096] Figure 6 Instructions for use Figures 3 to 5 The device implements the principle of the "time-to-first count" method. DETAILED DESCRIPTION

[0097] As described in the Summary of the Invention, the present specification provides a system and method for controlling a Geiger-Mueller tube, which achieves an expansion of the detection range of a radiation detection device, that is, the ability to operate under very high radiation fields while maintaining sensitivity to low count rates. Some more detailed examples will be listed below to illustrate different embodiments of the present invention.

[0098] Figure 1 1 is a schematic diagram illustrating a radiation detection device in the prior art, generally designated 10. The device includes a GM tube 20, which includes a chamber filled with an inert gas and a quenching gas or vapor. Two electrodes (anode 30 and cathode 40) are mounted in the chamber, and the two electrodes apply a potential difference of hundreds of volts in the chamber. In this setting, the high voltage 34 on the anode is usually generated after the current passes through the high resistance resistor 32 on the anode 30. This is to minimize the risk of arcing between the electrodes when ionization occurs in the GM tube 20. However, this setting usually requires continuous application of voltage when activating the GM tube 20 until the ionization event is detected, which is not only power-consuming, but also still has a certain arc risk. In addition, due to the large current limiting resistor 32 on the anode, the tube requires a non-negligible time to charge back to full voltage, which results in the existence of a "dead time" during which the GM tube cannot detect radiation. Resistor 32 usually has a large value to provide the above characteristics, in this case 2MΩ.

[0099] At cathode 40, when a current pulse passes through the GM tube, a voltage is generated across resistor 42 due to the radiation, because voltage = current x resistance. A short voltage pulse across resistor 42 switches transistor 51 (or another amplifier element). This signal can then be connected to a counting device 60, such as a microcontroller. By detecting the number of counts per second, the radiation "dose rate" (Sieverts / hour) can be calculated. The relationship between count rate and dose rate is approximately proportional.

[0100] As previously mentioned, a disadvantage of this method of operating the GM tube 20 is that it takes a certain amount of time for the GM tube 20 to charge back to 550V due to the large current limiting resistor 32. In addition, the gas in the GM tube 20 must have time to "quench" any free electrons before the next radiation event is detected. This charging and quenching typically creates a "dead time" during which the GM tube 20 cannot detect radiation. This limits the maximum count rate that the detector can measure.

[0101] Figure 2The general principle of the "time-first count" method is described. Under this method, such as that proposed by TJ Lewis (1955) discussed in the background section, the sequence 110 is initiated by simultaneously opening the GM tube 120a and starting the timer 120b. Figure 2 , the steps related to the hardware are suffixed with "a" and the steps related to the firmware are suffixed with "b". An ionizing event occurs when ionizing radiation hits the GM tube 130a. This will generate a pulse signal 135a in the circuit. This simultaneously causes the tube to shut down 140a and the timer to stop 140b. The time required for the system buffer is then recorded 150b, and before the next sequence 110 can be started again, a period of time longer than the dead time associated with the tube (for example 1 ms) must pass 160b. In this example, the waiting time 160b is selected to be 1 ms, but it will be understood that the selected waiting time can allow the tube to return to a ground state, for example between about 50μs and about 700μs.

[0102] However, as mentioned above, a difficulty with the method described by TJ Lewis (1955) is that at the beginning of each cycle, when the tube is turned on, it takes a non-negligible amount of time for the tube to reach its target full potential, which may introduce timing errors. This makes the implementation of the technique difficult or impractical.

[0103] Figures 3 to 5 Schematic diagram of a radiation detection device 210 suitable for use with the method of the present invention is shown. Although obviously different, for ease of reference, Figure 3 The radiation detection device 210 and Figure 1 The radiation detection device 10 in FIG. 1 is substantially similar, and like parts are represented by like numbers but incremented from "200".

[0104] The radiation detection device 210 includes a Geiger-Mueller tube 220, which includes a chamber 222 containing an anode 230 and a cathode 240. In this embodiment, the Geiger-Mueller tube circuit is designed for explosion-proof scenarios (intrinsically safe, referred to as "IS") and non-IS applications. The anode 230 is powered by a 550V power supply unit 270 (see Figure 4 ) and is directly connected to the 550V power supply unit 270 to place and / or maintain the anode at its activation potential. Figure 1 Unlike the configuration of FIG. 1 , in this configuration, the anode 230 is not coupled to a resistor to provide the target activation potential, which can help reduce the dead time.

[0105] Cathode 240 is connected to interface circuit 280 (see Figure 5). Both the power supply unit 270 and the interface circuit 280 are connected to the microcontroller unit (MCU) 290, using a straight-through current-limited connection to meet IS requirements. In IS applications, the entire module device 210 can be potted (encapsulated), including the GM tube 220. For convenience, in the event of a GM tube failure, a portion of the device 210 (such as a housing portion or sleeve) can be discarded and replaced with a replacement GM tube encapsulated module as a whole.

[0106] Reference Figure 4 , the power supply unit 270 has a small resistor 271, which is used only to limit the ignition current when the diodes 272, 273 limit the voltage that can be fed back from the high voltage (HV) power supply. This is done for IS protection. Although the power supply unit 270 includes the resistor 271, it is understood that the ohmic value of the resistor 271 is very small (3.9Ω in this example) so that the voltage provided by the unit 270 is not determined or defined by the resistor 271 (unlike conventional systems).

[0107] A switched inductor 274 is provided which is the basis of the boost regulator. The switched inductor 274 produces a transient voltage of approximately 80V. The switching operation is controlled by a controller 275 which drives a transistor 276. The controller 275 operates at a set frequency determined by a set resistor. When the first stage charge pump reaches V>71V, a comparator 277 shuts off the supply at the MOD pin of the controller 275 to prevent further switching operation. The effect of this is that the controller 275 operates only to "top up" the HV supply. In this example, a seven stage charge pump is used to obtain 550V. Capacitor 278 maintains the voltage of the GM tube and quickly charges the tube after an ionization event.

[0108] Reference Figure 5 , the interface circuit 280 has a transistor 281 (Q4) that connects the GM tube cathode 240 to 0V. In this embodiment, the transistor 281 is an N-type MOSFET ("nFET"). Advantageously, such a transistor can provide a very fast way to activate the cathode 240, thereby providing a very fast way to charge the GM tube 220.

[0109] Transistor 281 is normally in the off state. Transistor 281 is turned on for 1.2us, but in reality it is fully turned on for only about 700ns. This period of time is sufficient to charge GM tube 220 to 550V. GM tube 220 can be modeled as a 1.8pF capacitor. Experiments have shown that once charged, the tube 220 will maintain its charge indefinitely due to the low leakage current through transistor 281, but the circuit is configured to charge the tube 220 once every 100ms to ensure that the GM tube 220 remains "primed".

[0110] When an ionization event occurs in the tube 220, the tube 220 discharges through the capacitor 282 and turns on the transistor 283 (Q3). This will produce a short (less than 100 μs) active low pulse at the output of the circuit. When the pulse is detected, the MCU 290 waits for a preset time (1 ms in this embodiment) to allow the tube 220 to quench. Then, the MCU 290 outputs a 1.2 us signal to the transistor 281 to restart the working cycle.

[0111] Figure 6 Instructions for use Figures 3 to 5 The device implements the principle of the "time-first count" method. Figure 2 As shown, hardware-related steps are suffixed with an "a", and firmware-related steps are suffixed with a "b".

[0112] In this method, as detailed above, the cathode is connected to 0V for approximately 1.2 μs via the nFET to pre-charge the GM tube—charged to 550 V. Although the "connection time" in this example is 1.2 μs, it can be understood that the specific amount of time can be selected within a very short time range, that is, less than the pulse width 360b.

[0113] In this embodiment, sequence 310 is initiated by simultaneously precharging the GM tube 320a and starting the timer 320b of the MCU 290. In other words, in this embodiment, the timer is started at the beginning of the charging pulse. However, it is understood that in other embodiments, the counter can be started at the end of the charging pulse. In other words, the timer start 320b can occur immediately at the end of the GM tube precharging 320a.

[0114] When ionizing radiation hits the GM tube 330, an ionization event occurs. This will generate a pulse signal 335a in the circuit. This simultaneously causes the tube to discharge momentarily 340a and the timer to stop 340b. The time required for the system buffer is then recorded 350b, and the next sequence 310 is started again after a preset time period (e.g., 1 ms) (160b) selected for the device 210.

[0115] The present method and apparatus are capable of implementing a "time-to-first count" approach while overcoming many of the associated disadvantages or limitations of the prior art.

[0116] As previously described, the present inventors have developed systems and methods configured to process count output associated with a counting device (e.g., a Geiger-Mueller tube). This new method allows the user to measure event rates over a wider range with faster response times. This allows compliance with the requirements specified in dosimeter standards even when the count rate is very low (e.g., the count rate approaches zero) and / or when the count rate changes rapidly from high to low.

[0117] When calculating a "moving" or "rolling" average, methods include:

[0118] According to the events x1 and x n Calculate a first time-count average value between the time-count values ​​obtained for a certain number of events "n";

[0119] Measurement and Event x n+1 the associated time-count value; and

[0120] According to the events x2 and x n+1 A second time-count average is calculated from the time-count values ​​obtained between a certain number of events n.

[0121] Thus, the second time-count average, and any subsequent time-count averages calculated for a certain number of events n (including any subsequent time-count values), can be viewed as "rolling" averages based on the latest certain number "n" of events. An average count rate (e.g., the first average count rate and / or the second average count rate) can be calculated based on the associated time-count averages (e.g., the first time-count average or the second time-count average).

[0122] “Dummy” counts

[0123] If the time-count value increases significantly (e.g., compared to the time-count average), then the time required to detect the increase in the time-count average over the time of interest (e.g., over the past "n" events) may be long. The present method solves this problem by introducing a "pseudo-count" at a preset time interval "j" if no events are registered after that time interval.

[0124] In this example, we consider starting the device at time t=0 and establishing a list of stored time-count values ​​[]. Whenever a new event is registered, a new time-count value is added to the list so that it can be averaged as described above. If no event is registered after a specified period of time j, a "pseudo" time-count value is inserted into the list, which is recorded as ttc=t+j, where ttc is the time-count value. Here, t=0, so ttc=j. Therefore, the list currently becomes [j]. If a period of time j passes and no count is received, it is added to the list again, and the "pseudo" value will be ttc=j+ttcprevious=2j. Therefore, the value list will be [j, 2j]. This process continues until the count is received.

[0125] In this example, if we choose a time interval "j" of 0.1s and the first count is received at 0.95s, the list of time-to-count values ​​would be: [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95]. Once the actual ("true") time-to-count (TTC) value is measured, the device now has the "expected" TTC value, which it will insert into the list after each time period j until a new count is received, or until the expected TTC value passes without a count being registered, in which case time j will be repeatedly added until a count is detected. So, in this example, if the second count is measured at 0.5s, the list of values ​​would be: [0.1, 0.2, 0.3, 0.4, ..., 0.9, 0.95, 0.95, 0.95, 0.95, 0.95, 0.5, ...]. If the third count is measured at 0.76s, the list will be: [0.1, 0.2, 0.3, 0.4, …, 0.9, 0.95, 0.95, 0.95, 0.95, 0.95, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.6, 0.7, 0.76, …]. This process will continue until the preset number of counts required to calculate the time-count average is reached.

[0126] The advantage of this method is that it can respond more quickly to a steep drop in counts from a high radiation field to a low radiation field than an averaging method that does not use "pseudo" counts. It is understood that when used with radiation measurement equipment, the use of "pseudo" counts will only affect the calculation of the instantaneous (average) count rate, but will not affect the total cumulative dose measured by the equipment, and the "pseudo" counts will not be taken into account when calculating the cumulative dose. Although the introduction of "pseudo" counts will bring a certain degree of noise to the calculation (for example, to the calculated "time-count" average), it is understood that the degree of error introduced is acceptable when the count rate is low (in compliance with standard requirements), and the benefit of responding more quickly to the drop in count rate will offset this error.

[0127] Smoothing algorithm

[0128] The method may include processing the count output using a smoothing algorithm. For example, the method may include using a nonlinear exponential smoothing ("NLES") algorithm. The method may include applying an algorithm according to formula (I)':

[0129] y n =(1-α)·y n-1 +α·x n (I)'

[0130] where y represents the filtered value, and

[0131] x is a ratio derived from a calculated rolling average (eg, a second time-count average).

[0132] Advantageously, the value of α can be varied according to the magnitude of the error ε determined by formula (II), interpolating between two values:

[0133] ε=|log 10 y n-1 -log 10 x n | (II).

[0134] The value may not be extrapolated, but may stay at the minimum or maximum value. For example:

[0135] If ε min =0.5,α min =0.001,ε max =2.9,α max =0.99,

[0136] ε=1→α=0.207

[0137] ε=2→α=0.619

[0138] ε=10→α=0.99

[0139] Advantageously, multiple filters may be provided. Two filters may be provided, for example a first filter for the high count rate field and a second filter for the low count rate field. If the raw count rate x n is equal to or greater than a first threshold (e.g., equal to or greater than two counts per second), the method may include applying a first filter. n Below a first threshold (e.g., below two counts per second), the method may include applying a second filter. Advantageously, this allows for smooth readings in high count fields, and faster response to smaller magnitude changes in low count fields. Thus, in this example:

[0140] Filter coefficients for high counts:

[0141] x n >2cps→ε min =0.5,α min =0.001,ε max =2.9,α max =0.99

[0142] Filter coefficients for low counts:

[0143] x n <2cps→εmin =0.1,a min =0.2,e max =2,a max =0.99

Claims

1. A method for processing a counting output associated with a counting device, characterized in that, include: (i) According to the events x1 and x n Calculate a first time-count average value between the time-count values ​​obtained for a certain number of events "n"; (ii) Measurement and event x n+1 The associated time-count value; as well as (iii) According to the events x2 and x n+1 The time-count values ​​obtained between the certain number of events "n" calculate a second time-count average value.

2. The method according to claim 1, wherein: If no event is registered after a preset time interval "j", the method comprises: (iv) introducing a n+1 The associated "pseudo" time-count value equal to "j".

3. The method according to claim 2, comprising: (v) Introducing a "pseudo" time-count value equal to "j" associated with each subsequent event until a count or "real" event is measured or registered.

4. A method according to any preceding claim, wherein: When the event x m (m>n and x m >j) when a count or "real" event is measured or registered, the method comprises: (vi) providing a time-count value corresponding to the event x m The measured time-count value is related.

5. The method according to claim 4, wherein the m The time-count values ​​associated with the measured time-count values ​​represent or define expected time-count values.

6. The method according to claim 5, wherein: If no event is registered after the preset time interval "j", the method comprises: (vii) introducing a "pseudo" time-count value which is equal to the event x m The expected time-count value is associated.

7. The method of claim 6, wherein the method comprises repeating step (vii) until: - a new count or "real" event is measured or registered; in this case, the method may include: (viii) providing a time-count value corresponding to said measured time-count value associated with said new count or "real" event; - or, the expected time-count value has passed and no new count has been measured or registered, in which case the method may include: (ix) introducing a "pseudo" time-count value equal to "j".

8. The method according to any one of claims 2 to 7, wherein the "pseudo" time-count value "j" is approximately 1ms-500ms, optionally approximately 10ms-200ms, optionally approximately 50ms-150ms, optionally approximately 100ms.

9. A method according to any preceding claim, wherein the method comprises processing the count output using a non-linear exponential smoothing ("NLES") algorithm.

10. A method according to any preceding claim, comprising calculating an average count rate (optionally a first average count rate and / or a second average count rate) based on associated time-count averages (optionally the first time-count average or the second time-count average). The method of claim 10 , comprising filtering the value of the average count rate.

12. A method according to claim 10 or 11, comprising applying an algorithm according to formula (I): S n =(1 / t n -S n-1 )×α(|Δ n |)+S n-1 (I) Where S n is the value of the smoothed count rate calculated by the algorithm; t n is the current time-count average, S n-1 is the value of the previous smoothed count rate calculated by the algorithm; Δ n =|log 10 S n-1 -log 10 1 / x n |; and When |Δ n | When α0 is less than or equal to a first threshold Δ0, α0 is the first filter applied; and When |Δ n When α1 is equal to or greater than the second threshold Δ1, α1 is the second filter applied.

13. A method for processing a counting output associated with a counting device, characterized in that: The method comprises: According to the event x1n and event x n Calculate a first time-count average value between the time-count values ​​obtained for a certain number of events "n"; Measurement and Event x n+1 The associated time-count value; According to the events x2 and x n+1 Calculate a second time-count average value from the time-count values ​​obtained between the certain number of events n; as well as Apply the algorithm according to formula (I) to calculate the smoothed count rate S n : S n =(1 / t n -S n-1 )×α(|Δ n |)+S n-1 (I) Where S n is the value of the smoothed count rate calculated by the algorithm; t n is the second time-count average, S n-1 is the value of the previous smoothed count rate calculated by the algorithm; Δ n =|log 10 S n-1 -log 10 1 / x n |; and When |Δ n | is less than or equal to the first threshold Δ0, α0 is the first filter applied; and When |Δ n When α1 is equal to or greater than the second threshold Δ1, α1 is the second filter applied.

14. A method according to claim 12 or 13, wherein the algorithm uses a first set of filters α0 and α1 under a first condition (optionally, when the calculated count rate is equal to or greater than a first threshold), and wherein the algorithm uses a second set of filters α′0 and α′1 under a second condition (optionally, when the calculated count rate is less than the first threshold).

15. A method according to any preceding claim, comprising displaying a signal representative of the count output.

16. The method of claim 15, comprising displaying the value of the smoothed count rate.

17. A method according to any preceding claim, wherein the counting device comprises a Geiger-Muller tube.

18. A data processing device, characterized in that: Comprising apparatus for carrying out the method of any preceding claim.

19. A computer program, characterized in that The program comprises instructions, and when a computer executes the program, the instructions cause the computer to perform the method according to any one of claims 1 to 17.

20. A computer readable medium, characterized in that The method comprises instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 17.

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