Pre-amplification circuit for NaI probe and NaI probe

Abstract

The invention discloses a pre-amplification circuit for a NaI probe and the NaI probe, and relates to the technical field of radiation detection equipment. A time-varying circuit is adopted, and signals are kept in the NaI light emitting period. And meanwhile, after NaI light emission is finished, the signal can be quickly discharged, so that the circuit output is recovered to a base line to wait for next measurement. By means of the mode, the pulse width of the whole signal is reduced to 1.35 microseconds from existing 6 microseconds, the event passing rate can reach 440 kcps, and compared with the mode that a decay time constant is not changed in the prior art, the measuring range of the detector is increased by more than four times.

Description

Technical Field

[0001] The invention relates to the technical field of radiation detection equipment, in particular to a preamplifier circuit and a NaI probe with a variable attenuation time constant. Background Art

[0002] Photomultiplier tube + NaI crystal uses the ionization and excitation of gamma rays on NaI scintillator to generate photons. After conversion and multiplication by photomultiplier tube, photons form electronic pulses. The back-end electronics measures the charge number of a single pulse, obtains the energy loss of incident rays, and obtains the energy spectrum distribution of surrounding rays after processing. Since the size of NaI crystal can be made very large, its detection efficiency is high and the total energy peak efficiency is also high, so it is the most widely used gamma spectrum probe in environmental measurement. In order to obtain sufficient sensitivity, the size of NaI detector is generally more than 3 inches, such as the commonly used size of 100mm×100mm×400mm. Due to its high sensitivity, the event rate under the background can reach 4kcps.

[0003] In the existing technology, the preamplifier adopts RC discharge design, and the luminescence decay time of NaI crystal is 230ns. In order to ensure that the RC discharge has a small attenuation on the total signal amplitude during the signal collection process, and under the condition of not affecting the resolution, its RC time constant must be above 1μs (4 times the luminescence decay time of NaI crystal), the pulse width is about 6μs, and the event pass rate is up to 100kcps. Therefore, when the ambient dose rate reaches above 2.5μSv / h, the electronics will be blocked and the energy spectrum will be deformed, and it cannot be used in severe cases. Summary of the invention

[0004] In view of the above problems, the present invention provides a preamplifier circuit and a NaI probe for overcoming the above problems or at least partially solving the above problems.

[0005] The present invention provides the following scheme:

[0006] A preamplifier circuit for a NaI probe, comprising:

[0007] A time-varying circuit consisting of an integration circuit and a trigger circuit;

[0008] The time-varying circuit is used to make the decay time constant of the preamplifier RC circuit greater than 100 μs during the luminescence of the NaI crystal; and after the luminescence of the NaI crystal ends, the decay time constant of the preamplifier RC circuit becomes 40ns, the signal is released, and the circuit output is restored to the baseline, waiting for the next measurement.

[0009] Preferably: the integration circuit includes a capacitor C1 and a photoelectric switch U1;

[0010] The charge is integrated on the capacitor C1, and the photoelectric switch U1 is disconnected, so that the decay time constant of the preamplifier RC circuit is greater than 100 μs.

[0011] Preferably: the trigger circuit includes a comparator U4 and a delay circuit U5;

[0012] The output voltage continues to increase. When the voltage output by the integration circuit exceeds the voltage threshold, the comparator U4 flips and outputs a rising edge. The rising edge triggers the delay circuit U5 to work. The delay circuit U5 outputs a square wave signal with a width of 200ns after 900 to 1100ns. The square wave signal is used to control the photoelectric switch U1 to close so that the on-resistance is 38 to 42Ω, and the decay time constant of the preamplifier RC circuit becomes 40ns. After the capacitor C1 discharges for about 190 to 210ns, the output signal of the integration circuit returns to the baseline and waits for the next signal measurement.

[0013] Preferably: the delay circuit U5 outputs a square wave signal with a width of 200ns after 1000ns.

[0014] Preferably: the square wave signal is used to control the photoelectric switch U1 to close so that the on-resistance is 40Ω.

[0015] Preferably, the output signal of the integration circuit returns to the baseline after the capacitor C1 is discharged for about 200ns.

[0016] Preferably, after the luminescence of the NaI crystal decays by more than 99%, the decay time constant of the preamplifier RC circuit becomes 40ns.

[0017] Preferably: after the NaI crystal emits light for 1150ns, the attenuation time constant of the preamplifier RC circuit becomes 40ns.

[0018] A NaI probe comprises the above-mentioned preamplifier circuit for the NaI probe.

[0019] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0020] The embodiment of the present application provides a preamplifier circuit and NaI probe for NaI probe, which adopts a time-varying circuit to hold the signal during the NaI luminescence period. At the same time, when the NaI luminescence ends, the signal can be quickly released so that the circuit output returns to the baseline and waits for the next measurement. The above method reduces the pulse width of the entire signal from the existing 6μs to 1.35μs, and the event passing rate can reach 440kcps, which increases the detector range by more than 4 times compared with the prior art that adopts the method of keeping the decay time constant unchanged.

[0021] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 is a circuit schematic diagram of an integration circuit provided by an embodiment of the present invention;

[0024] Figure 2 It is a circuit schematic diagram of a trigger circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0026] See also Figure 1 , Figure 2 , is a preamplifier circuit for a NaI probe provided by an embodiment of the present invention, such as Figure 1 , Figure 2 As shown, the circuit may include:

[0027] A time-varying circuit consisting of an integration circuit and a trigger circuit;

[0028] The time-varying circuit is used to make the decay time constant of the preamplifier RC circuit greater than 100 μs during the luminescence of the NaI crystal; and after the luminescence of the NaI crystal ends, the decay time constant of the preamplifier RC circuit becomes 40ns, the signal is released to restore the circuit output to the baseline, and wait for the next measurement.

[0029] The preamplifier circuit for the NaI probe provided in the embodiment of the present application adopts a time-varying circuit. During the luminescence of the NaI crystal, the preamplifier RC decay time constant is greater than 100μs, and the signal is held. When the luminescence of the NaI crystal ends, the preamplifier RC decay time constant becomes 40ns, and the signal is quickly discharged, so that the circuit output returns to the baseline and waits for the next measurement, so that the pulse width of the entire signal is reduced from the existing 6μs to 1.35μs, and the event pass rate can reach 440kcps, which can be more than 4 times higher than the method of the prior art in which the decay time constant remains unchanged.

[0030] The preamplifier circuit for the NaI probe provided in the embodiment of the present application adopts an integration circuit and a trigger circuit to form a time-varying circuit. In a specific implementation, the embodiment of the present application can provide that the integration circuit includes a capacitor C1 and a photoelectric switch U1;

[0031] The charge is integrated on the capacitor C1, and the photoelectric switch U1 is disconnected, so that the decay time constant of the preamplifier RC circuit is greater than 100 μs.

[0032] Further, the trigger circuit includes a comparator U4 and a delay circuit U5;

[0033] The output voltage continues to increase. When the voltage output by the integration circuit exceeds the voltage threshold, the comparator U4 flips and outputs a rising edge. The rising edge triggers the delay circuit U5 to work. The delay circuit U5 outputs a square wave signal with a width of 200ns after 900 to 1100ns. The square wave signal is used to control the photoelectric switch U1 to close so that the on-resistance is 38 to 42Ω, and the decay time constant of the preamplifier RC circuit becomes 40ns. After the capacitor C1 discharges for about 190 to 210ns, the output signal of the integration circuit returns to the baseline and waits for the next signal measurement.

[0034] In order to better determine the timing when the delay circuit sends out the square wave signal, the embodiment of the present application can also provide that the delay circuit U5 outputs a square wave signal with a width of 200ns after 1000ns.

[0035] The square wave signal is used to control the photoelectric switch U1 to close so that the on-resistance is 40Ω.

[0036] After the capacitor C1 is discharged for about 200ns, the output signal of the integration circuit returns to the baseline.

[0037] In order to better determine the timing when the NaI crystal light emission ends, the embodiment of the present application can also provide that after the light emission of the NaI crystal decays by more than 99%, the decay time constant of the preamplifier RC circuit becomes 40ns.

[0038] Or, after the NaI crystal emits light for 1150ns, the attenuation time constant of the preamplifier RC circuit becomes 40ns.

[0039] See also Figure 1 , Figure 2The time-varying circuit is composed of an integration circuit and a trigger circuit. During the luminescence of the NaI crystal, the charge is integrated on the capacitor C1 of the integration circuit. At this time, the photoelectric switch U1 is in the disconnected state, and the preamplifier RC decay time constant is greater than 100μs. As the output voltage continues to increase, when the output voltage of the integration circuit exceeds the threshold TH0, the comparator U4 flips and outputs a rising edge, which triggers the delay circuit U5 to work. U5 outputs a square wave with a width of 200ns after 1000ns.

[0040] The square wave signal controls the photoelectric switch U1 to close (while the NaI light emission has ended), the photoelectric switch is closed, the on-resistance is about 40Ω, the RC decay time constant becomes 40ns, the preamplifier C1 discharges quickly, and the output signal of the integration circuit returns to the baseline after about 200ns, waiting for the next signal measurement. The single time signal pulse width is 1.35μs, and the event passing rate can reach 440kcps, which is more than 4 times higher than the existing technology.

[0041] In summary, the preamplifier circuit for NaI probe provided by the present application adopts a time-varying circuit to hold the signal during the NaI luminescence period. At the same time, when the NaI luminescence ends, the signal can be quickly released so that the circuit output returns to the baseline and waits for the next measurement. The above method reduces the pulse width of the entire signal from the existing 6μs to 1.35μs, and the event passing rate can reach 440kcps, which is more than 4 times higher than the existing technology that uses the attenuation time constant to keep constant.

[0042] The embodiment of the present application may also provide a NaI probe, including the above-mentioned preamplifier circuit for the NaI probe.

[0043] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0044] It can be known from the description of the above implementation methods that those skilled in the art can clearly understand that the present application can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present application can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in the various embodiments of the present application or certain parts of the embodiments.

[0045] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A preamplifier circuit for a NaI probe, characterized in that: A time-varying circuit including an integration circuit and a trigger circuit; The time-varying circuit is used to make the decay time constant of the preamplifier RC circuit greater than 100 μs during the luminescence of the NaI crystal; and after the luminescence of the NaI crystal ends, the decay time constant of the preamplifier RC circuit becomes 40ns, the signal is released, and the circuit output is restored to the baseline, waiting for the next measurement.

2. The preamplifier circuit for NaI probe according to claim 1, characterized in that: The integration circuit includes a capacitor C1 and a photoelectric switch U1; The charge is integrated on the capacitor C1, and the photoelectric switch U1 is disconnected, so that the decay time constant of the preamplifier RC circuit is greater than 100 μs.

3. The preamplifier circuit for NaI probe according to claim 2, characterized in that: The trigger circuit includes a comparator U4 and a delay circuit U5; The output voltage continues to increase. When the voltage output by the integration circuit exceeds the voltage threshold, the comparator U4 flips and outputs a rising edge. The rising edge triggers the delay circuit U5 to work. The delay circuit U5 outputs a square wave signal with a width of 200ns after 900 to 1100ns. The square wave signal is used to control the photoelectric switch U1 to close so that the on-resistance is 38 to 42Ω, and the decay time constant of the preamplifier RC circuit becomes 40ns. After the capacitor C1 discharges for about 190 to 210ns, the output signal of the integration circuit returns to the baseline and waits for the next signal measurement.

4. The preamplifier circuit for NaI probe according to claim 3, characterized in that: The delay circuit U5 outputs a square wave signal with a width of 200ns after 1000ns.

5. The preamplifier circuit for NaI probe according to claim 3, characterized in that: The square wave signal is used to control the photoelectric switch U1 to close so that the on-resistance is 40Ω.

6. The preamplifier circuit for NaI probe according to claim 3, characterized in that: After the capacitor C1 is discharged for about 200ns, the output signal of the integration circuit returns to the baseline.

7. The preamplifier circuit for NaI probe according to claim 1, characterized in that: After the luminescence of the NaI crystal decays by more than 99%, the decay time constant of the preamplifier RC circuit becomes 40ns.

8. The preamplifier circuit for NaI probe according to claim 1, characterized in that: After the NaI crystal emits light for 1150ns, the attenuation time constant of the preamplifier RC circuit becomes 40ns.

9. A NaI probe, characterized in that: The invention comprises the preamplifier circuit for NaI probe according to any one of claims 1 to 8.

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