Radiation detection device with stable photomultiplier

Abstract

Devices and methods as described herein may be used to help stabilize the gain of semiconductor-based photomultipliers. In an embodiment, a device may include a semiconductor-based photomultiplier. The device may be configured to maintain a constant voltage output between + / -0.002% and + / -15% of the breakdown voltage. A method for stabilizing a radiation detection device may include determining a breakdown voltage of a light source. The light source may be optically coupled to a silicon photomultiplier. The method may also include measuring a plurality of light outputs of the light source provided over a temperature range of 70 degrees, and generating a personalized lookup table for the light source based on the plurality of light outputs measured over the temperature range.

Description

Technical Field

[0001] This disclosure relates to a radiation detection device having a silicon photomultiplier (SiPM) within a housing.

[0002] A radiation detection device that can be used to detect radiation such as X-rays, gamma rays, alpha, and beta radiation may include a sealed housing containing components. The radiation detection device may include a scintillator and a SiPM (SiStructured Image Processor), wherein the scintillator responds to the detection of a type of radiation by emitting photons, and the photons may be directed to and detected by the SiPM.

[0003] A SiPM is a semiconductor-based device (typically silicon) that can transmit an electronic signal with a total charge proportional to the number of photons absorbed. It consists of a large number of avalanche photodiodes (APDs) operating in Geiger mode. These Geiger-mode avalanche photodiodes (G-APDs), also known as single-photon avalanche photodiodes, are connected in parallel via individual quench resistors. The APD converts incoming photons into an electrical signal and amplifies that signal through avalanche multiplication. An APD requires a voltage to be applied across its terminals to operate. When this applied reverse voltage (or “bias voltage”) is greater than the breakdown voltage, the APD operates in so-called Geiger mode. A SiPM operating in Geiger mode can measure light intensity by counting photons. The number of photons a SiPM can count per unit time depends on the number of G-APDs included in the SiPM and the rate at which each individual G-APD discharges and recharges upon detecting a photon.

[0004] However, the gain of a SiPM decreases with increasing temperature, negatively impacting its accuracy and performance. In practice, it may be necessary to adjust the gain of a SiPM, especially when its temperature varies. Therefore, further improvements to devices using SiPMs are needed. Attached Figure Description

[0005] This disclosure will be better understood by referring to the accompanying drawings, and its many features and advantages will become apparent to those skilled in the art. The embodiments are illustrated by way of example and are not limited to the drawings.

[0006] Figure 1 This includes a depiction of a device according to an embodiment.

[0007] Figure 2 Including can be Figure 1 A description of the control module used in the device.

[0008] Figure 3 Includes optimization Figure 1 Methods for increasing the gain of the device.

[0009] Figure 4 The illustration includes a cross-sectional view of a radiation detection device including a SiPM according to an embodiment.

[0010] Figure 5 Including according to one embodiment Figure 1 A perspective view of the circuit board, SiPM, and interface printed circuit board of the device.

[0011] Those skilled in the art will understand that the elements in the figures are shown for simplicity and clarity only, and are not necessarily drawn to scale. For example, the dimensions of some elements in the figures may be enlarged relative to other elements to aid in understanding embodiments of the invention. Detailed Implementation

[0012] The following description, in conjunction with the figures, is provided to aid in understanding the teachings disclosed herein. The following discussion will focus on specific implementations and embodiments of the teachings. This focus is provided to aid in describing the teachings and should not be construed as limiting the scope or applicability of the teachings. In one embodiment, the device may include a semiconductor-based photomultiplier. The device may be configured to maintain a constant voltage output between + / - 1% and + / - 15% of the breakdown voltage. A method for stabilizing a radiation detection device may include determining the breakdown voltage of a light source. The light source may be optically coupled to a silicon photomultiplier. The method may further include measuring multiple light outputs provided by the light source over a temperature range of 70 degrees Celsius, and generating a personalized lookup table for the light source based on the multiple light outputs measured within the temperature range. The above method advantageously provides a means for stabilizing gain within 1 degree Celsius of the breakdown voltage at any given temperature. However, other embodiments may be used based on the teachings disclosed in this application.

[0013] The foregoing has already outlined the features and technical advantages of the invention in a fairly broad, non-limiting manner to facilitate a better understanding of the following detailed description. Further features and advantages of the invention will be described below. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily used as the basis for modifications or the design of other structures for achieving the same objectives of the invention. Those skilled in the art will also recognize that such equivalent constructions do not depart from the scope of the invention as set forth in the appended claims.

[0014] As used herein, the term "compound semiconductor" is intended to refer to semiconductor materials comprising at least two different elements. Examples include SiC; SiGe; GaN; InP; Al. x Ga (1-x)N, where 0 ≤ x < 1; CdTe, etc. Group III-V semiconductor materials are defined as semiconductor materials comprising at least one trivalent metal element and at least one group 15 element. Group III-N semiconductor materials are defined as semiconductor materials comprising at least one trivalent metal element and nitrogen. Group 13-15 semiconductor materials are defined as semiconductor materials comprising at least one group 13 element and at least one group 15 element. Group II-VI semiconductor materials are defined as semiconductor materials comprising at least one divalent metal element and at least one group 16 element.

[0015] The term "avalanche photodiode" refers to a light-receiving area of ​​at least 1 mm². 2 A single photodiode, and operates in scale mode.

[0016] The term "SiPM" is intended to refer to a photomultiplier comprising multiple photodiodes, wherein the unit size of each photodiode is less than 1 mm. 2 Furthermore, the photodiode operates in Geiger mode. The semiconductor material of the diode in a SiPM can include silicon, compound semiconductor, or another semiconductor material.

[0017] As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof are intended to cover non-exclusive inclusion. For example, a method, article, or apparatus that includes a list of features is not necessarily limited to those features, but may include other features not expressly listed or inherent to the method, article, or apparatus. Furthermore, unless expressly stated to the contrary, “or” means inclusive or not exclusive. For example, any of the following satisfies condition A or B: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); and both A and B are true (or exist).

[0018] Furthermore, the use of “a” or “an” is used to describe the elements and components described herein. This is done solely for convenience and to give a general meaning to the scope of the invention. Unless its meaning is clearly stated otherwise, this description should be understood to include one, at least one, or a singular, as well as a plural, or vice versa. For example, when a single article is described herein, more than one article may be used instead of a single article. Similarly, in cases where more than one article is described herein, a single article may be used instead of more than one article.

[0019] The use of the terms "about," "approximately," or "basically" is intended to indicate that the value of a parameter is close to a specified value or position. However, small differences may prevent the value or position from being exactly as described above. Therefore, a difference of up to ten percent (10%) in the value (or up to twenty percent (20%) for semiconductor doping concentration) is a reasonable difference from the ideal target described precisely.

[0020] The group number of the corresponding column in the periodic table based on the IUPAC periodic table (November 28, 2016 version).

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Materials, methods, and examples are merely illustrative and not intended to be limiting. To the extent not described herein, many details regarding specific materials and processing behaviors are conventional and can be found in textbooks and other sources in the fields of scintillation, radiation detection, and ranging.

[0022] The apparatus and methods described herein can be used to help stabilize the gain of a semiconductor-based photomultiplier. With the gain stabilized, electronic pulses or corresponding digital signals from the semiconductor-based photomultiplier are personalized to adjust for specific scintillation crystals as temperature changes occur during device operation. Furthermore, the method for stabilizing the gain can be performed as a background function (invisible to the user) while the apparatus is used for one or more of its primary functions, such as radiation detection, imaging, ranging, etc.

[0023] The technique incorporates very fast organic and heavy inorganic scintillator detectors to access the lifetimes of nuclear excited states or radioactive isotopes, respectively, within picoseconds by utilizing the first moment of the centroid, i.e., the delay time distribution D(t) without any background contribution.

[0024] Centroid offset is derived directly from the average lifetime of the centroid in rapid timing experiments to determine the electron drift that varies with time, temperature, and source location. To ensure linearity and symmetry with the cue curve, this disclosure utilizes personalized and device-specific calculations to adjust for drift. Specifically, shortly after fabrication, personalized calculations determine the peak values ​​for each individual device, comprising a scintillation crystal and a package of electronics, over a defined temperature range. As the device is used, these calculations are then used as active feedback to compensate for voltage bias and stabilize the gain, thereby eliminating drift. Thus, each device will have a personalized reference to compensate for variations in crystal light output over a given temperature range, thereby adjusting gain stability and ensuring linearity and symmetry of the centroid measured across the full energy peak range from 0 keV to 1400 keV.

[0025] In one embodiment, the device may include a semiconductor-based photomultiplier. The device may be configured to inject a first input pulse into the semiconductor-based photomultiplier; determine a corrected bias voltage of the semiconductor-based photomultiplier based at least in part on a first output pulse corresponding to the first input pulse and a second output pulse from the semiconductor-based photomultiplier obtained at another time compared to the first output pulse; and adjust the bias voltage of the semiconductor-based photomultiplier to the corrected bias voltage. The bias voltage adjustment can be performed to bring the gain of the semiconductor-based photomultiplier closer to a predetermined value compared to not adjusting the bias voltage.

[0026] Embodiments using the gain stabilization concept described herein can be applied to a variety of devices using semiconductor-based photomultipliers. Such devices may include radiation detection devices, ranging devices, and other suitable devices. Radiation detection devices may include nuclear physics tools, medical imaging tools, logging or drilling tools, etc. Ranging tools may include light detection and ranging (“LiDAR”) tools, three-dimensional (“3D”) imaging tools, etc. The semiconductor-based photomultiplier is coupled to a light source, which may be located within or outside the device. The light source may include a scintillator, a laser, a light-emitting diode (“LED”) (inorganic or organic), or another suitable light source. In the following description, the device will be described with respect to a radiation detection device to provide exemplary embodiments. After reading this specification, those skilled in the art will understand that many other devices can be used without departing from the concepts described herein.

[0027] Figure 1 An embodiment of a radiation detection device 100 is illustrated. The radiation detection device 100 can be a medical imaging device, well logging device, security inspection device, etc., used for military applications. The radiation detection device 100 may include a light source 120, a semiconductor-based photomultiplier 152, and an optical coupler 140, the optical coupler optically coupling the light source 120 or another light-emitting material to the semiconductor-based photomultiplier 152. The semiconductor-based photomultiplier 152 is electrically coupled to a control module 170, a pulse injector circuit 130, and a bias voltage supply circuit 124. The control module 170 is coupled to the pulse injector circuit 130 and the bias voltage supply circuit 124. The control module 170 may also be coupled to another component or device (not shown) within the device (such as a computer, persistent memory, display, keyboard, etc.).

[0028] Optional temperature sensor 160 may be located near the interface between light source 120 and semiconductor-based photomultiplier 152. In a particular embodiment, temperature sensor 160 may be located on the light source, on the semiconductor-based photomultiplier 152, or within the semiconductor-based photomultiplier 152 (e.g., as a thermistor in an integrated circuit or circuit board). In another particular embodiment, temperature sensor 160 may be located at a distance of at most 9 cm, at most 2 cm, or at most 0.9 cm from light source 120, semiconductor-based photomultiplier 152, or both. In another embodiment, temperature sensor 160 may be located within an integrated circuit within control module 170. Additionally, temperature sensor 160 may be used for other purposes, such as considering the light output from light source 120 when the temperature of light source 120 changes.

[0029] exist Figure 1 In the diagram, arrows indicate the primary direction of signal flow. In another embodiment, one or more electrical couplers may be bidirectional. Light source 120 may be a light-emitting material (such as a scintillator) and includes halides, oxides, or another suitable material that can emit ultraviolet or visible light in response to the absorption of target radiation (such as gamma rays, neutrons, ionizing radiation, etc.). Optical coupler 140 may include a window, silicone or acrylic material, or another transparent material. If necessary or required, a wavelength shifter may be used to change the wavelength of light emitted from light source 120 to a different wavelength, allowing for higher quantum efficiency of the semiconductor-based photomultiplier 152. In another device (such as a ranging or other device), the light source may be a laser, LED, etc. In such applications, light may be emitted from the light source and reflected by an object outside the device, and received by the semiconductor-based photomultiplier 152. In another application, the light source may be external to device 100, and light from the light source may be received by the semiconductor-based photomultiplier 152. In such applications, optical coupler 140 may not be used.

[0030] The apparatus and method are well-suited for use with silicon photomultipliers (SiPMs) when the semiconductor-based photomultiplier is a silicon photomultiplier. Furthermore, the apparatus and method described herein can be used with another type of semiconductor-based photomultiplier, such as an avalanche photodiode. The gain of a SiPM can vary with temperature. The apparatus and process described in more detail below can be used to help stabilize the gain of semiconductor-based photomultipliers (such as SiPMs).

[0031] The control module 170 can provide one or more different functions. When the device is a radiation detection device, the control module 170 can receive electron pulses from the semiconductor-based photomultiplier 152 and perform one or more functions. For example, the control module 170 can be configured to count radiation events, identify radiation sources, etc. When used for ranging applications, the control module 170 can determine the distance between the semiconductor-based photomultiplier 152 and the radiation source 120, a light source, or an object reflecting light received by the semiconductor-based photomultiplier 152.

[0032] The control module 170 can also be configured to help stabilize the gain of the semiconductor-based photomultiplier 152. In a particular embodiment, the control module 170 can be coupled to a pulse injector circuit 130, and the control module 170 can send control signals to the pulse injector circuit 130, which in turn can send pulses to the semiconductor-based photomultiplier 152. The control module 170 can also be coupled to a bias voltage circuit 124, which can then set a bias voltage for the semiconductor-based photomultiplier 152. The bias voltage circuit 124 can be supplied with a DC voltage. A capacitor can be used to prevent voltage interference from the bias voltage circuit 124 from affecting the operation of the pulse injector circuit 130. Such a capacitor can be part of the pulse injector circuit 130, or it can be located between the pulse injector circuit 130 and the input signal line to which the pulse injector circuit 130 is connected to the semiconductor-based photomultiplier 152. The gain stabilization function will be described later in this specification in conjunction with flowcharts.

[0033] Figure 2 The illustration includes components within control module 170. A semiconductor-based photomultiplier 152 is coupled to amplifier 202 within control module 170. In one embodiment, amplifier 202 may be a high-fidelity amplifier. Amplifier 202 can amplify electrical pulses, and the amplified electrical pulses can be converted into digital signals that can be received by processor 222 at analog-to-digital converter (“ADC”) 204. Processor 222 may be coupled to a programmable / reprogrammable processing module (“PRPM”) such as field-programmable gate array (“FPGA”) 224 or application-specific integrated circuit (“ASIC”), memory 226 and input / output (“I / O”) module 242, pulse injector circuitry 130, and bias voltage circuitry 124. The coupling may be unidirectional or bidirectional. In another embodiment, more, fewer, or different components may be used in control module 170. For example, the functionality provided by FPGA 224 may be performed by processor 222, and therefore, FPGA 224 may not be required. FPGA 224 may process information faster than processor 222.

[0034] During operation, electronic pulses from the semiconductor-based photomultiplier 152 can be received at the control module 170. The processor 222 can analyze the signal to determine whether it corresponds to a user's use of the device for functions such as radiation detection, ranging, or gain stabilization. For example, for radiation detection, the processor 222 can analyze the digital signal from the ADC 204 and determine whether the digital signal corresponds to a radiation event that reaches a peak and then decays exponentially, or whether the digital signal corresponds to a pulse injected from the pulse injector circuit 130 into the semiconductor-based photomultiplier 152. Pulses injected from the pulse injector circuit 130 will not have exponential decay, as would be seen in the case of a radiation event.

[0035] Some or all of the functions described regarding FPGA 224 can be performed by processor 222, and therefore, FPGA 224 is not required in all embodiments. Furthermore, FPGA 224, memory 226, I / O module 242, or any combination thereof can reside within the same integrated circuit (such as processor 222). In another embodiment, control module 170 does not necessarily need to be housed within device 100. Even further, as... Figure 4 As shown, at least one component of the control module 170 may be located within the device 100, and at least one other component may be located outside the device 100. The control module 170 located within the device 100 allows for rapid operation without data transmission delays.

[0036] In one embodiment, before starting the method, a bias voltage can be set to a value that achieves the desired gain of the semiconductor-based photomultiplier 152. The processor 222 can send instructions to the bias voltage circuit 124. The bias voltage control circuit 124 can provide a bias voltage to the semiconductor-based photomultiplier 152 to set the gain of the semiconductor-based photomultiplier 152. When the semiconductor-based photomultiplier 152 is a SiPM, the bias voltage can be within a few volts of the average breakdown voltage of the diode in the SiPM. The bias voltage can be higher or lower than the average breakdown voltage. The breakdown voltage can depend on the semiconductor material of the diode, the dopant concentration at the np junction, and the temperature of the semiconductor-based photomultiplier 152. In one embodiment, the bias voltage can be in the range of approximately 20 VDC to 30 VDC. The actual voltage used for the bias voltage can depend on where the device 100 operates well, for example, to provide an acceptable signal-to-noise ratio. The bias voltage can be initially set at room temperature, such as in the range of 20°C to 25°C. The initial setting of the bias voltage can be performed before the final installation of device 100. Therefore, the initial setting can be performed on a test bench, at the factory, or before field installation is completed, or during the startup sequence. In another embodiment, the bias voltage can be initially set as described below with respect to the method. During operation, the semiconductor-based photomultiplier 152 can differ from the temperature used when the bias voltage was initially set by at least 1.1°C, at least 5°C, or at least 11°C.

[0037] If necessary or required, additional tests can be performed to generate temperature and corresponding bias voltage information in order to maintain the gain of the semiconductor-based photomultiplier 152 within a predetermined range (such as up to 15%, up to 9%, up to 5%, up to 3%, or up to 1%, or at least 0.002%, at least 0.02%, or at least 0.2% of the gain at initial setup or reset). Such information can be stored in FPGA 224 or memory 226.

[0038] Gain stabilization function during operation, regarding such Figure 3 The flowchart shown and such Figure 1 and Figure 2 The device 100 shown is described in terms of its various parts. The SiPM gain, i.e., the amount of charge generated per detected photon, fluctuates with temperature; the gain decreases as the temperature increases. The optical output signal also decreases with increasing temperature. Gain stabilization is necessary to eliminate this degradation. The method determines the breakdown voltage of the light source or crystal optically coupled to the semiconductor-based photomultiplier within the measured temperature range. At block 302, an input pulse is injected into the semiconductor-based photomultiplier 152 at room temperature. (Reference) Figure 1The semiconductor-based photomultiplier 152 can be a SiPM. The processor 222 can signal the pulse injector circuit 130 to send pulses to the semiconductor-based photomultiplier 152. The pulse injection can be performed before the device leaves the manufacturing location. In a particular embodiment, the pulse amplitude can be gradually increased (applied to the bias voltage) every fraction of a second until the input voltage of the semiconductor-based photomultiplier 152 is pushed above the breakdown threshold at the current operating temperature. The fraction of a second can be in the range of 2 milliseconds to 500 milliseconds, or in the range of 5 milliseconds to 50 milliseconds, and the voltage increment can be in the range of 2 mV to 500 mV, or in the range of 5 mV to 50 mV. When the semiconductor-based photomultiplier 152 is a SiPM, the breakdown threshold can be the average breakdown threshold because the SiPM has many diodes that do not have the same breakdown voltage.

[0039] The method may include receiving an output pulse from a semiconductor-based photomultiplier at block 304. The input pulse received by the semiconductor-based photomultiplier 152 causes it to generate an output pulse in the form of an electronic pulse, which is transmitted by the photomultiplier 152 and received by the control module 170. The electronic pulse is amplified by amplifier 202, converted into a digital signal by ADC 204, and received by processor 222.

[0040] The method may further include generating derivative information at block 306, at least in part, based on the output pulse from the semiconductor-based photomultiplier 152. Processor 222 may analyze the digital signal and generate the derivative information. Such derivative information may include whether neutron or gamma radiation is absorbed by the light source 120, isotope identification, rise time, decay time, emission spectrum, pulse height resolution, etc. In one embodiment, the output pulse may be the light output of a luminescent material. When the device is an imaging or ranging tool, the derivative information may include how far the radiation source or object is from the semiconductor-based photomultiplier 152. Regarding gain stability, processor 222 may analyze the corresponding signal from the semiconductor-based photomultiplier 152 and V... BR Or breakdown voltage.

[0041] refer to Figure 3The flowchart in the diagram, after determining the breakdown voltage at each desired measurement temperature, executes a branch that sets a gain reference at 310. Therefore, after determining a first gain reference for a first temperature, at 308, the temperature is changed by at least 1°C, and the method restarts at steps 302, 304, 306, and 308 until a breakdown voltage is determined for each temperature across the entire temperature range of -20°C to 55°C. A temperature sensor can provide temperature information for the light output of a luminescent material (such as a scintillator). The temperature sensor can be located within 9 cm, 5 cm, or 0.9 cm of the light source 120. Electronic pulses can be generated by a semiconductor-based photomultiplier 152, and the corresponding digital signal corresponding to the electronic pulses can be adjusted to indicate the temperature of the luminescent material. Injecting pulses, generating derivative information (e.g., integrated charge), determining a corrected bias voltage, and adjusting the bias voltage can be performed relative to individual temperatures measured within the range of -20°C to 55°C. In one embodiment, the breakdown voltage measured at each degree of temperature over a temperature range of approximately 70 degrees can be used to fine-tune the bias voltage for each individual device. Therefore, the derivative information can be used to set a gain reference based on the integration of charge from the electron pulses from the semiconductor-based photomultiplier 152 over various temperature ranges. In a particular embodiment, the V… of the semiconductor-based photomultiplier 152… BR The range is set within 70 degrees, varying by 1 degree Celsius each time. The conversion factor for each degree is obtained by plotting the breakdown voltage data as a function of the temperature corresponding to the previously collected output pulses. Therefore, the conversion factor can be based on personalized data for a specific device.

[0042] Other temperature-sensitive light sources with similar adjustments can also be used. Temperature can be measured at a specific breakdown voltage. The measured temperature information can be used to determine a compensation factor for the light output from the light source. This information can then be stored in the FPGA 224 or memory 226. Therefore, for every degree of temperature change, the stored information correlates the temperature with a gain reference or breakdown voltage.

[0043] Once a gain reference is set for each degree Celsius, the method may include adjusting the bias voltage to a corrected bias voltage at block 312. For any given temperature within the temperature range, the corrected bias voltage may be a constant voltage output between + / - 1% and + / - 15% of the breakdown voltage. In one embodiment, for any given temperature within the temperature range, the constant voltage output may be between + / - 1% and + / - 10% of the breakdown voltage. In another embodiment, for any given temperature within the temperature range, the constant voltage output may be between + / - 1% and + / - 5% of the breakdown voltage. In yet another embodiment, for any given temperature within the temperature range, the constant voltage output may be between + / - 1% and + / - 2% of the breakdown voltage. In yet another embodiment, for any given temperature within the temperature range, the constant voltage output may be at most 15% of the breakdown voltage, such as at most 9%, or at most 5%, or at most 3%, or at most 1%. In another embodiment, for any given temperature within the temperature range, the constant voltage output can be at least 0.002% of the breakdown voltage, such as at least 0.02% or at least 0.2%.

[0044] Processor 222 can send a signal to bias voltage circuit 124, and bias voltage circuit 124 can adjust the bias voltage to a corrected bias voltage based on a personalized table. The corrected bias voltage allows the semiconductor-based photomultiplier 152 to operate closer to its gain, as set in block 310. It is not necessary to perform bias voltage adjustment every time an input pulse from pulse injector circuit 130 is injected into the semiconductor-based photomultiplier 152. For example, a threshold can be used to determine whether to adjust the bias voltage. In a particular embodiment, V BR Compared with a single directly measured breakdown voltage V B2 The difference can be less than 0.1%, and the bias voltage can be left unadjusted. After adjusting the bias voltage, a decision can be made whether to continue. If "yes," the method continues to block 302. Otherwise, the method can terminate.

[0045] The data obtained from the radiation detector contains information about the energy of the impacting particle, and based on this information, the radioactive isotope of the emitted radiation can typically be determined using a process known as isotope identification. For reliable operation, the gain of the SiPM 152 needs to remain constant, which in turn requires a very stable and constant operating voltage applied across the circuit. In many practical applications, including for isotope identification, the gain needs to remain constant below + / - 5% (or + / - 5% to + / - 0.5%) under all operating conditions. The numerical gain of the SiPM is defined as the charge (Q) transferred after absorbing a photon divided by the electron charge e = 1.6016e-19 C.

[0046] Gain = Q / e

[0047] The numerical gain is an approximately linear function of the applied operating voltage V. Let V... BR Let be the breakdown voltage of SiPM. The gain as a function of voltage is:

[0048] For V > V BR Gain = gk * (V - V) BR )

[0049] For V < V BR Gain = 0

[0050] The coefficient gain constant gk is typically about 1. e6 / V, but depending on the specific SiPM design, its range may be 0.1 e6 / V to 10 e6 / V. Under constant operating conditions (i.e., in steady state), a practical radiation detector needs to have the same gain when measuring low-intensity background radiation as when operating in a strong radiation field.

[0051] For example, for a cylindrical (2 inches × 2 inches) NaI(Tl) scintillator crystal with a diameter of 5.08 cm and a length of 5.08 cm, there should be only a finite change in gain when the radiation field intensity increases from near zero (i.e., < 10 μrem / hr) to 5 mR / hr. For example, for VV BR For a detector operating at 3V, a 1% gain offset corresponds to a 30 mV operating voltage change. To achieve this stability, the electronics can use a power supply with a DC output impedance of 10 ohms or less. Even for the worst-case steady-state high load current of 1 mA, the voltage drop will only be 10 mV. Since the breakdown voltage is typically 25 V to 35 V, the voltage supply needs to be extremely stable. Analog boost controllers are not usually designed to provide this level of accuracy. The operation of a boost controller can be enhanced by a C program running in an ARM microcontroller. It often utilizes a high-resolution ADC (typically 16-bit) to measure the operating voltage and corrects for the nominal operating voltage to achieve a very stable output voltage. This creates a secondary feedback loop that compares the actual operating voltage with the desired voltage.

[0052] Detectors that maintain constant gain under varying radiation intensities and perform satisfactorily under dynamic conditions of sudden changes in radiation intensity are difficult to achieve. Practical detectors must respond quickly and maintain a stable operating voltage in the face of sudden load changes. Therefore, the personalized tables generated during manufacturing for each combination of crystal and photomultiplier using the methods described above advantageously provide a means to stably maintain the gain within 1 degree of the breakdown voltage at any given temperature.

[0053] Other actions may occur during or after the method. For example, the user may implement a more exotic control scheme. Alternatively, the user may manually adjust the bias voltage, set a gain reference, or perform another action. Furthermore, data may be collected and stored in memory 226, such as timestamps, integrated charge, bias voltage, etc. The data may be examined to monitor or determine the health status of device 100. Device 100 may be configured to analyze a set of bias voltages to monitor or determine the health status of device 100. For example, the bias voltage may increase over time. This could be a signal that the semiconductor-based photomultiplier 152 may be approaching failure or that device 100 should soon be shut down for maintenance. For example, the previous bias voltage may have been within 1%, and the most recent or set of bias voltages may be at least 2% larger than the previous adjustment. As another example, the previous adjustment to the bias voltage may have a standard deviation of 0.7%, and the most recent adjustment to the bias voltage or a set of recent adjustments may have a standard deviation of 1.1%. Statistically significant changes in the adjustment, corresponding standard deviations, or changes and standard deviations can be used. Therefore, a proactive approach can be used to maintain equipment 100, rather than waiting for a failure to occur, which may happen at an inopportune time.

[0054] The advantage of this method is that it can help stabilize the gain in real time during normal operation of the device. Since each device has its own personalized lookup table based on data from actual breakdown voltages at different temperatures, gain stabilization can generate a constant output over a + / - 1% overvoltage range of the breakdown voltage for each device using the method described previously.

[0055] In other words, the method can be performed to calibrate each individual light source when used with an actual semiconductor-based photomultiplier 152, which is placed in each individual device during manufacturing.

[0056] The apparatus and methods described herein can be used to help stabilize the gain of semiconductor-based photomultipliers. Once the gain is stable, electronic pulses or corresponding digital signals from the semiconductor-based photomultiplier, combined with measured temperature changes, are adjusted to identify and set a separate lookup table for the specific crystal already operating with the device's semiconductor-based photomultiplier. Calibration of the light source, temperature sensor, and temperature information can be used to determine the performance of each individual light source or crystal installed in each device. Furthermore, once a separate stable gain table is generated, the method for continuous stabilization can be performed as a background function (invisible to the user) while the device is being used for one or more of its primary functions, such as radiation detection, imaging, ranging, etc.

[0057] Figure 4 This is a representative cross-sectional view of a radiation detection device 400 according to some embodiments. The radiation detection device 400 may be similar to... Figure 1 Device 100. Radiation detection device 400 includes a housing 110 containing components. The housing may be removably sealed or hermetically sealed. In a particular embodiment, housing 110 may be sealed according to an IP code rating of IP67, where the IP code is International Electrotechnical Commission Standard 60529, version 2.2 (2013). Alternatively, or otherwise, the components within housing 110 may be individually hermetically sealed prior to installation in the housing.

[0058] The housing 110 contains a scintillator 102, which may include a material that emits scintillating light in response to the absorption of radiation such as gamma rays or ionizing particles. Exemplary, non-limiting materials for the scintillator 102 include alkali metal halides, rare earth halides, aluminosilicates, rare earth-containing silicates, perovskite oxides, etc. For example, the scintillator 102 may contain any one of NaI(Tl) crystal, CsI(Tl) crystal, CsI(Na) crystal, LaBr3 crystal, CLLB crystal, LYSO crystal, LSO crystal, CdWO4 crystal, CeBr3 crystal, strontium iodide crystal, BGO crystal, CaF2(Eu) crystal, etc. NaI(Tl) crystal is a sodium iodide scintillator crystal activated with thallium. CsI(Tl) crystal is a cesium iodide scintillator crystal activated with thallium. CsI(Na) crystal is a cesium iodide scintillator crystal activated with sodium. LaBr3 crystal is a lanthanum bromide crystal. (Cs₂LiLaBr₆(Ce)) crystal is a gamma neutron scintillation crystal. LYSO crystal (Lu) 1.8 Y₂SiO₅(Ce) is a cerium-doped lutetium-based scintillation crystal. LSO crystal (Lu₂SiO₅(Ce)) is a cerium-doped lutetium silicate-based scintillation crystal. CdWO₄ crystal is a cadmium tungstate (CdWO₄) scintillation crystal. CeBr₃ crystal is a cerium bromide (CeBr₃) scintillation crystal. BGO crystal (Bi₄Ge₃O₄) 12The scintillator 102 is a bismuth germanate-based scintillation crystal. CaF2(Eu) crystal is a europium-doped calcium fluoride-based scintillation crystal. Any of these scintillation crystals can be used in the articles and radiation detectors described in this disclosure. The scintillator 102 can be positioned below and optically coupled to the optical interface 140 within the housing 110, and the impact radiation 112 can pass through the housing 110 to interact with the scintillator 102. The scintillator 102 can respond to the impact radiation 112 by generating photons 114, which can travel through the optical interface 140 and be detected by the photoelectric sensor 150. The photoelectric sensor 150 can detect the photons and transmit the data to an external signal processing unit via connector 190.

[0059] When housing 110 is sealed, materials that are hygroscopic or adversely interact with environmental conditions near housing 110 are protected. Scintillator 102 is surrounded by reflector 132. Reflector 132 may surround scintillator 102 laterally or on all sides. Reflector 132 may include a specular reflector, a diffuse reflector, or both. In one embodiment, reflector 132 may be a material selected from the group consisting of: fluoropolymers of tetrafluoroethylene, Teflon-based materials, meilex, and polyester tape.

[0060] One or more elastic members can help hold the scintillator 102 in place within the housing 110. In the illustrated embodiment, an elastic material 134 may surround the reflector 132, and a spring 136 may be positioned between the scintillator 102 and the housing 110. Although not shown, a plate may be used between the spring 136 and the scintillator 102 to distribute pressure more evenly along the surface of the scintillator 102.

[0061] One or more semiconductor-based photomultipliers (SiPMs) 152 of the photoelectric sensor 150 can be optically coupled to the scintillator 102 via an optical interface 140. In one embodiment, the photoelectric sensor 150 can be a semiconductor-based photomultiplier, which may include a SiPM or an avalanche photodiode. In one embodiment, the semiconductor-based photomultiplier may include one or more SiPMs 152. The optical interface 140 and the scintillator 102 can be assembled into a hermetically sealed assembly before being assembled in the housing 110. The optical interface 140 and the scintillator 102 can be optically coupled together using optical coupling materials such as epoxy, grease, silicon, etc. In the illustrated embodiment, the SiPM 152 is mounted on a PCB 154. In one embodiment, the SiPM 152 may be located between the PCB 154 and the optical coupler 140. In one embodiment, the optical coupler 140 may be silicon dioxide. In another embodiment, the SiPM 152 can be coupled to the optical coupler 140 using epoxy or rubber silicone resin.

[0062] Electron pulses from the SiPM 152 can be routed to the interface board 172 via the PCB 154 and conductor 162. Conductor 162 can be a wire (as shown), solder ball, optical fiber, or other device capable of communicatively coupling the PCB 154 to the interface board 172. Impact radiation 112 can pass through the housing 110, spring 136, and reflector 132 to interact with the scintillator 102, which can emit scintillation light as photons 114. As the scintillator 102 is surrounded by reflector 132, the photons should be guided to the optical interface 140 and the SiPM 152. The reflective layer 156 surrounding the SiPM 152 can reflect the photons 115 back into the scintillator 102 for later detection and absorption by the SiPM 152.

[0063] Microcells within the SiPM can detect photons 114 (including reflected photons 115) and generate current signals output to the PCB 154. Current signals from multiple microcells can be analyzed to determine the number of photons detected, the detection rate (i.e., detections per second), and other characteristics of photon 114, and thus the characteristics of the impact radiation 112. Interface board 172 may include electronic components 174, 176, and 178 for processing and other control of device 100. Interface board 172 can couple connector 190 to photodetector 150 to transmit signals from photodetector 150 to connector 190. Photodetector 150 may include PCB assembly 154, one or more SiPMs 152, and reflector 156, wherein photodetector 150 is optically coupled to optical interface 140 (e.g., glass). Scintillator 102 may be positioned below and optically coupled to optical interface 140 within the housing, and impact radiation 112 may pass through housing 110 to interact with scintillator 102. The scintillator 102 can respond to impact radiation 112 by generating photons 114, which can travel through the optical interface 140 and be detected by the photoelectric sensor 150. The photoelectric sensor 150 can detect the photons and transmit the data to an external signal processing unit via connector 190.

[0064] Sensor data, as well as command and control information, can be transmitted between device 100 and the signal processing and control system via connector 190 and conductor 192. These conductors 192 (and conductor 162) can be any medium for transmitting energy between source and destination, such as electrical conductors, optical conductors, etc. It should also be understood that when device 100 communicates with the signal processing and control system wirelessly, the wires may not be in use.

[0065] Figure 5 Printed circuit board 154 and interface board 172, separated from each other, are shown. Four SiPMs are shown, although more or fewer SiPMs may be used in another embodiment. In one embodiment, printed circuit board 154 may include a first surface 133 facing scintillator 102. In one embodiment, SiPM 152 may be located on the first surface 133 of printed circuit board 154. Electronic components on interface board 172 are shown, but are not individually labeled with reference numerals. Interface board 172 may include connector 362 for data transmission. Radiation detection device 100 may include modular components such as SiPM 152, interface board 172, and cover on carrier board 154. Figure 2 As shown, the electronic components on the interface board 172 can be configured to act as a control module 170.

[0066] Various embodiments

[0067] Example 1. A device comprising a semiconductor-based photomultiplier, the device being configured to maintain a constant centroid offset of zero over a temperature range of 75°C.

[0068] Example 2. A device comprising a semiconductor-based photomultiplier, the device being configured to maintain a constant energy output per channel over a temperature range of 75°C.

[0069] Example 3. An apparatus comprising a semiconductor-based photomultiplier, the apparatus being configured to maintain a characteristic peak of interest (POI) as measured by a channel analyzer within a temperature range of 75°C.

[0070] Example 4. A device comprising a semiconductor-based photomultiplier, the device being configured to maintain a bias voltage such that the energy output is less than + / - 5% of the breakdown voltage.

[0071] Example 5. The device according to Example 1, wherein the constant voltage is maintained within any temperature range between -20°C and +55°C.

[0072] Example 6. The device according to Example 1, wherein the device further comprises a scintillation crystal.

[0073] Example 7. The device according to Example 1, wherein the device further includes a pulse injector circuit configured to inject a first input pulse into the semiconductor-based photomultiplier during initial operation of the device.

[0074] Example 8. The device according to Example 6, wherein the device further includes a memory containing a gain-stable personalized lookup table for a particular scintillation crystal provided.

[0075] Example 9. A method for stabilizing a radiation detection device, the method comprising:

[0076] Determine the breakdown voltage of the light source, wherein the light source is optically coupled to a silicon photomultiplier;

[0077] Measure the multiple light outputs provided by the light source within a temperature range of 75 degrees Celsius; and

[0078] A personalized lookup table for the light source is generated based on multiple light outputs measured within the stated temperature range.

[0079] Example 10. The method according to Example 9 further includes maintaining a constant voltage output between + / - 0.002% and + / - 3% of the determined breakdown voltage of the light source.

[0080] Example 11. The method according to Example 9 further includes injecting an input pulse into the silicon photomultiplier.

[0081] Example 12. The method according to Example 11 further includes receiving an output pulse from the silicon photomultiplier.

[0082] Example 13. The method according to Example 12 further includes generating a gain value based at least in part on the output pulse provided by the light source in a temperature range of 70 degrees.

[0083] Example 14. The method according to Example 13, wherein the temperature range is between -20°C and +55°C.

[0084] Example 15. The method according to Example 13 further includes generating a lookup table having the gain value for each degree within the temperature range.

[0085] Example 16. The method according to Example 15 further includes maintaining a constant voltage output of + / - 1% of the determined breakdown voltage of the light source based on the generated lookup table.

[0086] Example 17. The method according to Example 9, wherein the light source is a light-emitting material optically coupled to the semiconductor-based photomultiplier.

[0087] Example 18. The method according to Example 17, wherein the device further includes a temperature sensor adjacent to the interface between the luminescent material and the semiconductor-based photomultiplier.

[0088] Example 19. A method for stabilizing a radiation detection device, the method comprising:

[0089] The first input pulse is injected into the semiconductor-based photomultiplier;

[0090] Determine the breakdown voltage of the luminescent material, wherein the luminescent material is optically coupled to the provided silicon photomultiplier.

[0091] Measured multiple optical outputs of the scintillator provided within a temperature range of 75 degrees Celsius; and

[0092] A personalized lookup table for the scintillator is generated based on multiple light outputs measured within the temperature range.

[0093] Example 20. The method according to Example 19 further includes receiving an output pulse from the silicon photomultiplier.

[0094] Example 21. The method according to Example 20 further comprises generating a gain value based at least in part on the output pulse provided by the light source within a temperature range of 70 degrees.

[0095] Example 22. The method according to Example 21, wherein the temperature range is between -20°C and +55°C.

[0096] Example 23. The method according to Example 21, wherein the lookup table contains a gain value for each degree within the temperature range.

[0097] The foregoing embodiments represent differences from existing technologies. It is worth noting that the embodiments herein include combinations of features not previously recognized in the art and contribute to performance improvements.

[0098] The foregoing subject matter is illustrative, not restrictive, and the appended claims cover all variations, modifications, and other embodiments that fall within the actual scope of the invention. Therefore, for the maximum permissible extent permitted by law, the scope of the invention shall be determined by the broadest possible interpretation of the following claims and their equivalents and shall not be limited to or restricted by the foregoing detailed description.

[0099] An abstract of the specification has been provided in accordance with patent law, and it is understood that it is not intended to interpret or limit the scope or meaning of the claims. Furthermore, in the foregoing embodiments of the drawings, various features may be grouped together or described in a single embodiment for the purpose of simplification. This disclosure should not be construed as reflecting an intention that the claimed embodiments require more features than are clearly listed in each claim. Rather, as reflected in the following claims, the subject matter of the invention may be less than all the features of any of the disclosed embodiments. Therefore, the following claims are incorporated into the illustrated detailed embodiments, and each claim, in itself, is treated as if it were a separate definition of the claimed subject matter.

Claims

1. An apparatus comprising a semiconductor-based photomultiplier that maintains a constant centroid offset of zero over a temperature range of 75°C.

2. The device according to claim 1, wherein the device maintains a constant energy output per channel within a temperature range of 75°C.

3. The device according to claim 1, wherein the device maintains the characteristic peak of interest (POI) as measured by the channel analyzer within a temperature range of 75°C.

4. The device of claim 1, wherein the device maintains a bias voltage such that the energy output is less than + / - 5% of the breakdown voltage.

5. The apparatus of claim 1, wherein the constant voltage is maintained within any temperature range between -20°C and +55°C.

6. The device of claim 1, wherein the device further comprises a scintillation crystal.

7. The device of claim 1, wherein the device further comprises a pulse injector circuit configured to inject a first input pulse into the semiconductor-based photomultiplier during initial operation of the device.

8. The device of claim 6, wherein the device further comprises a memory containing a gain-stable personalized lookup table for a particular scintillation crystal provided.

9. The device of claim 1, wherein maintaining the constant centroid offset to zero comprises maintaining a constant voltage output of + / - 1% of the determined breakdown voltage of the light source based on the generated lookup table.

10. A method for stabilizing a radiation detection device, the method comprising: Determine the breakdown voltage of the light source, wherein the light source is optically coupled to a silicon photomultiplier; Measure multiple light outputs provided by the light source within a temperature range of 75 degrees Celsius; as well as A personalized lookup table for the light source is generated based on multiple light outputs measured within the stated temperature range.

11. The method of claim 9, further comprising: Maintain a constant voltage output between + / - 0.002% and + / - 3% of the determined breakdown voltage of the light source; The input pulse is injected into the silicon photomultiplier; Receive output pulses from the silicon photomultiplier; as well as The gain value is generated at least in part based on the output pulses provided by the light source within a temperature range of 70 degrees.

12. The method of claim 11, wherein the temperature range is between -20°C and +55°C.

13. The method of claim 11, further comprising generating a lookup table having the gain value for each degree within the temperature range.

14. The method of claim 13, further comprising maintaining a constant voltage output of + / - 1% of the determined breakdown voltage of the light source based on the generated lookup table.

15. The method of claim 11, wherein the light source is a light-emitting material optically coupled to the semiconductor-based photomultiplier.

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