Dead Time Correction Method and System

Abstract

The present application proposes a dead time correction method, including: using a timer to count the real time, where the real time is the time actually measured by the nuclear instrument; using three timers to respectively count the dead time of the fast channel, the dead time of the tail pile-up type pile-up rejection, and the dead time of the peak pile-up type pile-up rejection. The dead time of the fast channel is the time when the fast channel cannot detect the input pulse. The dead time of the tail pile-up type pile-up rejection is the dead time corresponding to the count loss caused by implementing the tail pile-up type pile-up rejection. The dead time of the peak pile-up type pile-up rejection is the dead time corresponding to the count loss caused by implementing the peak pile-up type pile-up rejection; calculating a count correction factor based on the statistically obtained real time, dead time of the fast channel, dead time of the tail pile-up type pile-up rejection, and dead time of the peak pile-up type pile-up rejection, and using the count factor for dead time correction. The present application can accurately compensate for the count loss in the multi-channel, improve the accuracy of count correction, and is widely applied to the current nuclear measurement system.

Description

Technical Field

[0001] This application relates to the field of nuclear radiation detection technology, and particularly to a dead time correction method and system. Background Art

[0002] Instruments for nuclear radiation measurement, abbreviated as nuclear instruments, all inevitably have the problem of counting loss. Nuclear instruments are generally connected after a detector. After radioactive particles enter the detector, the detector converts the energy deposited by the radioactive particles in the detector into weak current pulse signals, and these signals carry radiation information. The current pulse signals generated by radiation particles will be subjected to special operations such as conditioning amplification, digitization, filtering, and information extraction by the nuclear instrument. Common information of radiation particles includes the energy, number, and the time of entering the detector of the radiation particles, etc.

[0003] The number of radiation particles counted by the nuclear instrument is also called the count of the nuclear instrument. The nuclear instrument takes a certain amount of time to process a pulse, and during this time, the nuclear instrument cannot process other incoming pulses, thus resulting in counting loss.

[0004] The fundamental reason for counting loss is that the nuclear instrument takes a certain amount of time to process a pulse, which is specifically called "dead time" in the nuclear field. The number of radiation particles emitted by a radionuclide within a certain period of time is random, and the number of radiation particles follows a Poisson distribution. The randomness of nuclear events inevitably leads to the possibility that radiation particles enter the detector during the dead time of the nuclear instrument, and the pulses generated by these particle events cannot be processed by the instrument, thereby resulting in counting loss.

[0005] Some common factors causing dead time include: the conversion time of the ADC in an analog multi-channel, the recovery time of the pulse feedback preamplifier, the width of the pulse, and the input saturation time caused by high-energy pulses.

[0006] Generally, a nuclear instrument will filter the digitized signals separately using a fast channel and a slow channel and then perform information acquisition and processing. The fast channel filters using a smaller time constant for discriminating and timing the input pulses; the slow channel filters using a larger time constant for rejecting pulse pile-ups and is responsible for extracting the amplitude information of the input pulses.

[0007] The width of the pulse will cause the fast channel to be unable to distinguish two pulses that are very close in time, so the time resolution ability of the fast channel is limited. At the same time, the width of the pulse will also cause distortion of the amplitude information of two relatively close pulses in the slow channel, so the slow channel needs to reject pulse pile-ups to avoid extracting the amplitude information of distorted pulses.

[0008] The limited time resolution ability of the fast channel and the pile-up rejection of the slow channel will both result in count loss. Therefore, it is necessary to perform count correction to eliminate the deviation of the measurement result. Count correction refers to correcting the counts obtained by the instrument and compensating for the count loss to accurately obtain the input counts. For applications that require accurately obtaining the input count rate at high count rates, such as radioactive source activity calibration measurements, the results obtained without correction will have a large deviation. How to accurately compensate for the count loss is a key issue in instrument design.

[0009] In the field of nuclear instruments, count correction is also specifically referred to as "dead time correction". Dead time correction gives the dead time during the measurement process of the nuclear instrument, subtracts the dead time from the real time, so as to obtain the truly effective measurement time - live time during the measurement process of the nuclear instrument, and uses the ratio of the count to the live time as an estimate of the true input count.

[0010] However, due to the theoretical complexity of simultaneously considering the influence of the time resolution ability of the fast channel and the pile-up rejection of the slow channel, the current dead time correction methods often only consider the count loss caused by the slow channel, and intentionally or unintentionally ignore the influence of the fast channel on the system count loss, thus bringing errors to the dead time correction. Summary of the Invention

[0011] This application aims to solve at least one of the technical problems in the related art to some extent.

[0012] To this end, the first object of this application is to propose a dead time correction method, which solves the technical problem that the existing methods only consider the count loss caused by the slow channel and ignore the count loss caused by the fast channel. It comprehensively considers the time resolution ability of the fast channel and the count loss caused by the pile-up rejection of the slow channel, improves the accuracy of count correction, can accurately compensate for the count loss caused by the limited time resolution ability of the fast channel and the pulse pile-up of the slow channel, and can be widely applied to the current nuclear measurement system.

[0013] The second object of this application is to propose a dead time correction system.

[0014] To achieve the above object, an embodiment of the first aspect of the present application proposes a dead time correction method, including: using a timer to count the real time, where the real time is the time actually measured by the nuclear instrument; using three timers to count the fast channel dead time, the tail pile-up type pile-up rejection dead time, and the peak pile-up type pile-up rejection dead time respectively, where the fast channel dead time is the time when the fast channel cannot detect an input pulse, the tail pile-up type pile-up rejection dead time is the dead time corresponding to the count loss caused by implementing the tail pile-up type pile-up rejection, and the peak pile-up type pile-up rejection dead time is the dead time corresponding to the count loss caused by implementing the peak pile-up type pile-up rejection; calculating a count correction factor based on the statistically obtained real time, fast channel dead time, tail pile-up type pile-up rejection dead time, and peak pile-up type pile-up rejection dead time, and using the count factor to perform dead time correction.

[0015] Optionally, in an embodiment of the present application, the timer has two states:

[0016] The timing state, in which the timer counts according to the system clock frequency;

[0017] The non-timing state, in which the value of the timer remains unchanged.

[0018] Optionally, in an embodiment of the present application, the timer counts the real time as follows:

[0019] Maintain the timing state throughout the measurement process.

[0020] Optionally, in an embodiment of the present application, the timer counts the fast channel dead time as follows:

[0021] Whenever the fast channel detects a pulse, the timer will maintain the timing state within the dead time of the fast channel pulse. The dead time of the fast channel pulse can be replaced by another period of time, and the time used for replacement follows the same probability distribution as the dead time of the fast channel pulse.

[0022] Optionally, in an embodiment of the present application, the timer counts the tail pile-up type pile-up rejection dead time as follows:

[0023] Whenever the fast channel detects a pulse, first reset the timer for measuring the tail pile-up type pile-up rejection dead time to the stop timing state, and at the same time, make the timer maintain the timing state within the tail pile-up type pile-up rejection dead time corresponding to the detected pulse again.

[0024] Optionally, in an embodiment of the present application, the tail pile-up type pile-up rejection dead time of a pulse is determined by the dead time of the fast channel pulse corresponding to the pulse and the tail pile-up protection time.

[0025] If the dead time of the fast-channel pulse corresponding to this pulse is less than or equal to the tail pile-up protection time, the dead time for rejecting pile-up of the tail pile-up type for this pulse is equal to the difference between the tail pile-up protection time and the dead time of the fast-channel pulse corresponding to this pulse;

[0026] If the dead time of the fast-channel pulse corresponding to this pulse is greater than the tail pile-up protection time, the dead time for rejecting pile-up of the tail pile-up type for this pulse is equal to 0;

[0027] The dead time for rejecting pile-up of the tail pile-up type for a pulse can be replaced by another period of time, and the time used for replacement follows the same probability distribution as the calculated dead time for rejecting pile-up of the tail pile-up type for the pulse.

[0028] Optionally, in an embodiment of the present application, the timer's statistical process for the dead time for rejecting pile-up of the peak pile-up type is as follows:

[0029] Whenever the fast channel detects a pulse, first reset the timer for measuring the dead time for rejecting pile-up of the peak pile-up type to the stopped timing state, and at the same time, make the timer keep timing within the dead time for rejecting pile-up of the peak pile-up type corresponding to the detected pulse again.

[0030] Optionally, in an embodiment of the present application, the dead time for rejecting pile-up of the peak pile-up type for an input pulse is determined by the dead time of the fast-channel pulse corresponding to this pulse and the peak pile-up protection time.

[0031] If the dead time of the fast-channel pulse corresponding to this pulse is less than or equal to the peak pile-up protection time, the dead time for rejecting pile-up of the peak pile-up type for this pulse is equal to the difference between the peak pile-up protection time and the dead time of the fast-channel pulse corresponding to this pulse;

[0032] If the dead time of the fast-channel pulse corresponding to this pulse is greater than the peak pile-up protection time, the dead time for rejecting pile-up of the peak pile-up type for this pulse is equal to 0;

[0033] The dead time for rejecting pile-up of the peak pile-up type for a pulse can be replaced by another period of time, and the time used for replacement follows the same probability distribution as the calculated dead time for rejecting pile-up of the peak pile-up type for the pulse.

[0034] Optionally, in an embodiment of the present application, the count correction factor is expressed as:

[0035]

[0036] where k represents the count correction factor, RT represents the real time obtained by statistics, DT1 represents the fast-channel dead time obtained by statistics, DT 2A represents the dead time for rejecting pile-up of the tail pile-up type obtained by statistics, DT 2B represents the dead time for rejecting pile-up of the peak pile-up type obtained by statistics.

[0037] To achieve the above object, an embodiment of the second aspect of the present application provides a dead time correction system, including: a timer, a control module, a data processing module, and a correction module. Among them,

[0038] The timer is used to respectively count the real time, the fast channel dead time, the tail pile-up type pile-up rejection dead time, and the peak pile-up type pile-up rejection dead time. Among them, the real time is the time actually measured by the nuclear instrument, the fast channel dead time is the time when the fast channel cannot detect the input pulse, the tail pile-up type pile-up rejection dead time is the dead time corresponding to the count loss caused by implementing the tail pile-up type pile-up rejection, and the peak pile-up type pile-up rejection dead time is the dead time corresponding to the count loss caused by implementing the peak pile-up type pile-up rejection;

[0039] The control module is used to control the state of the timer to ensure accurate timing of the timer;

[0040] The data processing module is used to calculate the count correction factor according to the measured real time, fast channel dead time, tail pile-up type pile-up rejection dead time, and peak pile-up type pile-up rejection dead time;

[0041] The correction module is used to perform dead time correction using the count factor.

[0042] The dead time correction method and system of the embodiments of the present application solve the technical problem that the existing methods only consider the count loss caused by the slow channel and ignore the count loss caused by the fast channel. It comprehensively considers the time resolution ability of the fast channel and the count loss caused by the pile-up rejection of the slow channel, improves the accuracy of count correction, can accurately compensate for the count loss caused by the limited time resolution ability of the fast channel and the pulse pile-up of the slow channel, and can be widely applied to the current nuclear measurement system.

[0043] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and / or additional aspects and advantages of the present application will become apparent and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0045] Figure 1 is a flowchart of a dead time correction method provided by Embodiment 1 of the present application;

[0046] Figure 2 is a block diagram of the dead time correction method of the embodiments of the present application;

[0047] Figure 3 is a schematic diagram of the pile-up rejection method for quasi-Gaussian filtering of the dead time correction method of the embodiments of the present application;

[0048] Figure 4 Schematic diagram of the pile-up rejection method for trapezoidal filtering in the dead time correction method of the embodiment of the present application;

[0049] Figure 5 Overall block diagram of the dead time correction method of the embodiment of the present application;

[0050] Figure 6 Schematic diagrams of various signals during the dead time statistics process of the dead time correction method of the embodiment of the present application;

[0051] Figure 7 Schematic structural diagram of a dead time correction system provided in the second embodiment of the present application. Detailed implementation manners

[0052] The embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and should not be construed as limiting the present application.

[0053] The dead time correction method and system of the embodiment of the present application will be described below with reference to the accompanying drawings.

[0054] Figure 1 Flowchart of a dead time correction method provided in the first embodiment of the present application.

[0055] As Figure 1 shown, the dead time correction method includes the following steps:

[0056] Step 101, use a timer to count the real time, where the real time is the time actually measured by the nuclear instrument;

[0057] Step 102, use three timers to count the fast channel dead time, the tail pile-up type pile-up rejection dead time, and the peak pile-up type pile-up rejection dead time respectively. The fast channel dead time is the time when the fast channel cannot detect the input pulse. The tail pile-up type pile-up rejection dead time is the dead time corresponding to the count loss caused by implementing the tail pile-up type pile-up rejection. The peak pile-up type pile-up rejection dead time is the dead time corresponding to the count loss caused by implementing the peak pile-up type pile-up rejection;

[0058] Step 103, calculate the count correction factor according to the statistically obtained real time, fast channel dead time, tail pile-up type pile-up rejection dead time, and peak pile-up type pile-up rejection dead time, and use the count factor for dead time correction.

[0059] The dead time correction method of the embodiment of the present application uses a timer to count the real time, where the real time is the time actually measured by the nuclear instrument; three timers are used to count the fast channel dead time, the tail pile-up type pile-up rejection dead time, and the peak pile-up type pile-up rejection dead time respectively. The fast channel dead time is the time when the fast channel cannot detect the input pulse. The tail pile-up type pile-up rejection dead time is the dead time corresponding to the counting loss caused by implementing the tail pile-up type pile-up rejection. The peak pile-up type pile-up rejection dead time is the dead time corresponding to the counting loss caused by implementing the peak pile-up type pile-up rejection. The counting correction factor is calculated based on the statistically obtained real time, fast channel dead time, tail pile-up type pile-up rejection dead time, and peak pile-up type pile-up rejection dead time, and the counting factor is used for dead time correction. Thus, the technical problem that the existing method only considers the counting loss caused by the slow channel and ignores the counting loss caused by the fast channel can be solved. By comprehensively considering the time resolution ability of the fast channel and the counting loss caused by the pile-up rejection of the slow channel, the accuracy of counting correction is improved, and the counting loss caused by the limited time resolution ability of the fast channel and the pulse pile-up of the slow channel can be accurately compensated, and it can be widely applied to the current nuclear measurement system.

[0060] Further, in the embodiment of the present application, the timer has two states:

[0061] The timing state, in which the timer counts time according to the clock frequency of the system;

[0062] The non-timing state, in which the value of the timer remains unchanged.

[0063] Further, in the embodiment of the present application, the timer counts the real time as follows:

[0064] Maintain the timing state during the entire measurement process.

[0065] The general characteristic of the fast channel is to use a smaller shaping time constant. Taking the detector signal as the input, the detector pulse is shaped into a fast channel pulse with a small pulse width, so as to accurately obtain the time information of the pulse. Each detector pulse will be filtered and shaped by the fast channel into a corresponding fast channel pulse one by one. Then the fast channel judges whether there is a pulse input through threshold triggering. The fast channel dead time refers to the time when the fast channel pulse cannot detect the input pulse due to its own pulse width. The pulse width of the fast channel pulse will cause the fast channel to be unable to recognize other input pulses within a certain time after a fast channel pulse. This time is called the dead time of the fast channel pulse.

[0066] Further, in the embodiment of the present application, the timer counts the fast channel dead time as follows:

[0067] Whenever the fast channel detects a pulse, the timer keeps timing within the dead time of the fast channel pulse. In particular, the dead time of the fast channel pulse can be replaced by another period of time, as long as the time used for replacement follows the same probability distribution as the dead time of the fast channel pulse.

[0068] Tail pile-up refers to the situation where when two pulses are too close in time, the latter pulse piles up at the tail of the former pulse, resulting in distortion of the amplitude information of the latter pulse. Tail pile-up type pile-up rejection means that when the time interval between two pulses detected by the fast channel is less than the set tail pile-up protection time τ e the amplitude information of the latter pulse will be distorted and thus discarded by the system, which will lead to loss of counting and generate the dead time of tail pile-up type pile-up rejection.

[0069] Furthermore, in the embodiment of the present application, the process of the timer counting the dead time of tail pile-up type pile-up rejection is as follows:

[0070] Whenever the fast channel detects a pulse, first reset the timer for measuring the dead time of tail pile-up type pile-up rejection to the stopped timing state, and at the same time make the timer keep timing within the dead time of tail pile-up type pile-up rejection corresponding to the detected pulse again.

[0071] Furthermore, in the embodiment of the present application, the dead time of tail pile-up type pile-up rejection of a pulse is determined by the dead time of the fast channel pulse corresponding to the pulse and the tail pile-up protection time.

[0072] If the dead time of the fast channel pulse corresponding to the pulse is less than or equal to the tail pile-up protection time, the dead time of tail pile-up type pile-up rejection of the pulse is equal to the difference between the tail pile-up protection time and the dead time of the fast channel pulse corresponding to the pulse.

[0073] If the dead time of the fast channel pulse corresponding to the pulse is greater than the tail pile-up protection time, the dead time of tail pile-up type pile-up rejection of the pulse is equal to 0.

[0074] In particular, the dead time of tail pile-up type pile-up rejection of a pulse can be replaced by another period of time, as long as the time used for replacement follows the same probability distribution as the dead time of tail pile-up type pile-up rejection of the pulse obtained by the above method.

[0075] Peak pile-up refers to the situation where when two pulses are too close in time, the latter pulse arrives before the amplitude information of the former pulse is extracted completely, resulting in distortion of the amplitude information of the former pulse. Peak pile-up type pile-up rejection means that when the time interval between two pulses detected by the fast channel is less than the set peak pile-up protection time τ pu the amplitude information of the former pulse will be distorted and thus discarded by the system, which will lead to loss of counting and generate the dead time of peak pile-up type pile-up rejection.

[0076] Further, in the embodiments of the present application, the timer's statistical process for the peak pile-up type pile-up rejection dead time is as follows:

[0077] Whenever the fast channel detects a pulse, first reset the timer for measuring the peak pile-up type pile-up rejection dead time to the stopped timing state, and at the same time, make the timer keep timing within the peak pile-up type pile-up rejection dead time corresponding to the detected pulse again.

[0078] Further, in the embodiments of the present application, the peak pile-up type pile-up rejection dead time of an input pulse is determined by the fast channel pulse dead time and the peak pile-up protection time corresponding to the pulse.

[0079] If the fast channel pulse dead time corresponding to the pulse is less than or equal to the peak pile-up protection time, the peak pile-up type pile-up rejection dead time of the pulse is equal to the difference between the peak pile-up protection time and the fast channel pulse dead time corresponding to the pulse.

[0080] If the fast channel pulse dead time corresponding to the pulse is greater than the peak pile-up protection time, the peak pile-up type pile-up rejection dead time of the pulse is equal to 0.

[0081] In particular, the peak pile-up type pile-up rejection dead time of a pulse can be replaced by another period of time, as long as the time used for replacement and the peak pile-up type pile-up rejection dead time of the pulse obtained by the above method follow the same probability distribution.

[0082] The purpose of tail pile-up type pile-up rejection and peak pile-up type pile-up rejection is to avoid extracting the amplitude information of pile-up pulses during the energy spectrum acquisition process, resulting in the energy spectrum collected containing incorrect information. Different peak pile-up rejection and tail pile-up rejection protection times need to be set for different filtering methods.

[0083] Further, in the embodiments of the present application, the counting correction factor is expressed as:

[0084]

[0085] where k represents the counting correction factor, RT represents the real time statistically obtained, DT1 represents the fast channel dead time statistically obtained, DT 2A represents the tail pile-up type pile-up rejection dead time statistically obtained, DT 2B represents the peak pile-up type pile-up rejection dead time statistically obtained.

[0086] In the embodiments of the present application, the counting correction factor can also be obtained in the following way:

[0087] Use a timer to measure the real time RT, where the real time is the time actually measured by the nuclear instrument; use a timer to measure the dead time of the fast channel. The dead time of the fast channel is equal to the time when the fast channel cannot detect the input pulse. Subtract the dead time of the fast channel from the real time to obtain the live time LT1 of the fast channel; use a timer to measure the dead time of the tail pile-up type pile-up rejection. The dead time of the tail pile-up type pile-up rejection is equal to the dead time corresponding to the counting loss caused by implementing the tail pile-up type pile-up rejection. Subtract the dead time of the tail pile-up type pile-up rejection from the live time LT1 of the fast channel to obtain the live time LT of the tail pile-up type pile-up rejection. 2A Use a timer to measure the dead time of the peak pile-up type pile-up rejection. The dead time of the peak pile-up type pile-up rejection is equal to the dead time corresponding to the counting loss caused by implementing the peak pile-up type pile-up rejection. Subtract the dead time of the peak pile-up type pile-up rejection from the live time LT1 of the fast channel to obtain the live time LT of the peak pile-up type pile-up rejection. 2B ; According to the live time LT1 of the fast channel, the live time LT 2A of the tail pile-up type pile-up rejection, and the live time LT 2B of the peak pile-up type pile-up rejection obtained above, calculate the system live time. The system live time LT is:

[0088]

[0089] The ratio of the system real time RT to the system live time LT is the counting correction factor.

[0090] Figure 2 It is a block diagram of the dead time correction method of this application embodiment.

[0091] As Figure 2 shown, for this dead time correction method, S1: Use 1 timing circuit RT in the system to count the real time, and use 3 timing circuits DT1, DT 2A and DT 2B in the system to count 3 types of dead times of the system. The timing circuit DT1 is controlled by the logic of the fast channel, and the timing circuits DT 2A and DT 2B are controlled by the logic of the slow channel. At the beginning, the timing circuits DT1, DT 2A and DT 2B are all in the stopped timing state. At this time, the system is in a state of waiting for the fast channel to detect the input pulse. S2: After the pulse output by the detector is detected by the fast channel, the system controls the timing circuit DT1 to keep timing within the pulse width T fw of the fast channel; S3: After the timing of the timing circuit DT1 stops, according to the length T fw of the timing of DT1 and the pile-up rejection method used by the slow channel, determine DT 2A and DT 2BThe length of timing. The pile-up rejection method can usually be divided into a symmetric pile-up rejection method and an asymmetric pile-up rejection method according to the filtering method used in the slow channel. For the symmetric pile-up rejection method, DT 2A and DT 2B maintain the timing state within t1 = τ pu -T fw . If t1 < 0, then DT 2A and DT 2B do not time. For the asymmetric pile-up rejection method, DT 2A maintains the timing state within t1 = τ pu -T fw . If t1 < 0, then DT 2A does not time; DT 2B maintains the timing state within t2 = τ e -T fw . If t2 < 0, then DT 2B does not time; if the measurement is not ended, return to step S2; if the measurement is ended, enter step S4; S4: At the end of the measurement, the system will obtain the timing results of the timing circuits RT, DT1, DT 2A and DT 2B respectively. Using the name of the timer itself to represent their timing results respectively, the count correction factor k is expressed as:

[0092]

[0093] where k represents the count correction factor, RT represents the real time obtained by statistics, DT1 represents the dead time of the fast channel obtained by statistics, DT 2A represents the dead time of the tail pile-up type pile-up rejection obtained by statistics, and DT 2B represents the dead time of the peak pile-up type pile-up rejection obtained by statistics.

[0094] Figure 3 is a schematic diagram of the pile-up rejection method for quasi-Gaussian filtering in the dead time correction method of the embodiment of the present application.

[0095] As Figure 3 shown, since the quasi-Gaussian waveform has a slowly decaying tail, the minimum pulse interval for the occurrence of quasi-Gaussian waveform tail pile-up is generally greater than the minimum pulse interval for the occurrence of peak pile-up. Therefore, the peak pile-up protection time τ pu is set to be less than the tail pile-up protection time τ e . The process of pile-up rejection is as follows: If the time interval between two pulses is less than the set peak pile-up protection time τ pu , then the previous pulse of the two pulses will be discarded due to amplitude information distortion; if the time interval between two pulses is less than the set tail pile-up protection time τ eThen the subsequent pulse is discarded due to the distortion of the amplitude information. Figure 3 In Figure 3 , the interval between the first pair of aligned Gaussian pulses is very small, less than the peak pile-up protection time, thus triggering the peak pile-up rejection, so the previous pulse is discarded; at the same time, it is also less than the tail pile-up protection time, triggering the tail pile-up rejection, so the subsequent pulse is also discarded. Figure 3 In Figure 3 , the interval between the second pair of aligned Gaussian pulses is relatively farther, greater than the peak pile-up rejection time and less than the tail pile-up rejection time. Therefore, the peak pile-up rejection is not triggered, and the previous pulse is retained. However, the subsequent pulse is superimposed on the tail of the previous pulse, so the amplitude information of the pulse is distorted and discarded by the tail pile-up rejection mechanism.

[0096] Figure 4 It is a schematic diagram of the pile-up rejection method for trapezoidal filtering in the dead time correction method of the embodiment of the present application.

[0097] As Figure 4 shown, due to the good symmetry of the trapezoidal waveform, generally the peak pile-up protection time τ pu is equal to the tail pile-up protection time τ e . Therefore, for symmetric filtering methods such as trapezoidal filtering, it is equivalent to having only one parameter, the peak pile-up protection time τ pu . Figure 4 In Figure 4 , the interval between the first pair of pulses is less than the peak pile-up protection time τ pu . Therefore, both pile-up rejection mechanisms are triggered simultaneously, resulting in both pulses being discarded. While the interval between the second pair of pulses is greater than the set peak pile-up protection time τ pu . Therefore, both pulses are determined to be normal pulses. It should be noted that the rejection method for symmetric filtering can be regarded as a special case of the pile-up rejection for asymmetric filtering when τ e =τ pu . Therefore, certain simplifications can be made when implementing the dead time correction method proposed in the present application.

[0098] Figure 5 It is the overall block diagram of the dead time correction method of the embodiment of the present application.

[0099] As Figure 5 shown, this dead time correction method includes a fast channel module, a slow channel module, a timing module, an energy spectrum module, and a counting correction module. The input signals of the fast channel module and the slow channel module are the detector signals digitized by an analog-to-digital converter.

[0100] The fast channel module is used to discriminate and time the input pulses. The fast channel is connected after the digital-to-analog converter, and its input signal is the digitized detector signal. The general characteristic of the fast channel is to use a smaller shaping time constant, which has a smaller pulse width and can accurately obtain the time information of the pulse. The fast channel determines whether there is a pulse input by judging whether the input pulse exceeds the threshold. When there is no input pulse, the output of the fast channel is near the baseline, and at this time the fast channel itself is in the non-threshold-exceeding state. When a pulse with a certain amplitude arrives, the output of the fast channel will exceed the threshold. At this time, the fast channel enters the threshold-exceeding state and will give a logic signal indicating the arrival of the pulse and the time information corresponding to the arrival time of the pulse. After a period of time, the input pulse will gradually decay, the output of the fast channel will return to near the baseline, and the fast channel re-enters the non-threshold-exceeding state.

[0101] Since the fast channel pulse has a certain width, its time resolution ability is limited, and the time resolution ability of the fast channel is related to the dead time of the fast channel. When a pulse with a certain amplitude enters the fast channel, within a period of time T fw the fast channel cannot respond to other fast channel input pulses anymore, and this period of time is the dead time T fw of the fast channel pulse. Affected by the charge collection time, noise, and pulse pile-up, the dead time T fw caused by each fast channel pulse is not the same. In this application, the threshold-crossing time of the fast channel pulse is approximately used as the dead time T fw caused by the fast channel pulse.

[0102] The slow channel module is used to discard piled-up pulses and extract the amplitude information of the input pulses. The slow channel is connected after the digital-to-analog converter, and its input signal is the digitized detector signal. The general characteristic of the slow channel is to use a larger time constant to obtain a better signal-to-noise ratio, and the slow channel uses the method of discarding piled-up pulses to accurately obtain the amplitude of the non-distorted pulses. The slow channel will judge whether the arriving pulse is affected by pile-up according to the time information provided by the fast channel.

[0103] When the fast channel detects a pulse from the detector, the slow channel will first judge whether the pulse is affected by pile-up. If the pulse is not affected by pile-up, then the amplitude information of the pulse will be extracted. In this application, the dead time correction method proposed in this application is illustrated by taking the pile-up discard for quasi-Gaussian filtering as an example. Therefore, the peak pile-up protection time τ pu is less than the tail pile-up protection time τ e .

[0104] The timing module is used to count the time quantity required during the measurement process. The timing module is connected after the fast channel module and the slow channel module, and it needs the fast channel module to provide the dead time T fwAnd the slow channel provides the parameter peak accumulation rejection protection time τ for peak accumulation rejection pu And the tail accumulation protection time τ e .

[0105] The operation of the timing module is divided into four steps in total.

[0106] S1: In the system, 1 timing circuit RT is used to count the real time RT, and 3 timing circuits DT1, DT 2A and DT 2B are used to count the dead time DT1 of the fast channel, the dead time DT 2A for peak accumulation rejection and the dead time DT 2B for tail accumulation rejection. The timing circuit DT1 is controlled by the logic of the fast channel, and the timing circuits DT 2A and DT 2B are controlled by the logic of the slow channel. At the beginning, the timing circuits DT1, DT 2A and DT 2B are all in the stopped timing state, and at this time the system is in the state of waiting for the fast channel to detect an input pulse.

[0107] S2: After the pulse output by the detector is detected by the fast channel, the system controls the timing circuit DT1 to keep timing within the pulse width T fw of the fast channel.

[0108] S3: After the timing of the timing circuit DT1 stops, according to the length T fw of the timing of DT1, the lengths of the timing of DT 2A and DT 2B are determined. DT 2A keeps timing within t1 = τ pu - T fw , and if t1 < 0, then DT 2A does not time; DT 2B keeps timing within t2 = τ e - T fw , and if t2 < 0, then DT 2B does not time.

[0109] If the measurement is not over, return to step S2; if the measurement is over, enter step S4.

[0110] S4: At the end of the measurement, the system will obtain the timing results of RT, DT1, DT 2A and DT 2B respectively, and use RT, DT1, DT 2A , DT 2B to represent them respectively.

[0111] The timer has two states: the timing state and the non-timing state, and can perform timing according to the system clock frequency.

[0112] The counting correction module is used to correct the counts in the energy spectrum. The counting correction module is connected to the timing module and utilizes the timing results RT, DT1, DT generated by the timing module 2A 、DT 2B , and calculates the counting correction factor k using the following formula

[0113]

[0114] where k represents the counting correction factor, RT represents the real time obtained by statistics, DT1 represents the fast channel dead time obtained by statistics, and DT 2A represents the tail pile-up type pile-up rejection dead time obtained by statistics, and DT 2B represents the peak pile-up type pile-up rejection dead time obtained by statistics.

[0115] The energy spectrum module is connected after the slow channel module and the counting correction module, and is used to statistically store the energy spectrum before counting correction and the energy spectrum after counting correction. Each time the slow channel completes the extraction of a pulse amplitude, the energy spectrum module is responsible for incrementing the count of the corresponding channel by 1 in the energy spectrum before correction at the channel address proportional to the pulse amplitude, and incrementing the count of the corresponding channel by the correction factor k of the correction in the energy spectrum after correction at the channel address proportional to the pulse amplitude.

[0116] Figure 6 This is a schematic diagram of each signal during the dead time statistical process of the dead time correction method according to the embodiment of the present application.

[0117] As Figure 6 shown, the tail pile-up type pile-up rejection dead time of a pulse is determined by the fast channel pulse dead time corresponding to the pulse and the tail pile-up protection time. When the fast channel pulse dead time T fw corresponding to an input pulse is less than or equal to the tail pile-up protection time τ e , the tail pile-up type pile-up rejection dead time of the pulse is equal to the difference between the tail pile-up protection time and the fast channel pulse dead time corresponding to the pulse, τ e -T fw ; when the fast channel pulse dead time corresponding to the pulse is greater than the tail pile-up protection time, the tail pile-up type pile-up rejection dead time of the pulse will be equal to 0. The peak pile-up type pile-up rejection dead time of an input pulse is determined by the fast channel pulse dead time corresponding to the pulse and the peak pile-up protection time. When the fast channel pulse dead time T fw corresponding to an input pulse is less than or equal to the peak pile-up protection time τ pu , the peak pile-up type pile-up rejection dead time of the pulse is equal to the difference between the peak pile-up protection time and the fast channel pulse dead time corresponding to the pulse, τ pu -Tfw ; when the dead time of the fast channel pulse corresponding to the pulse is greater than the peak pile-up protection time, the pile-up discard dead time of the peak pile-up type of this pulse will be equal to 0.

[0118] Figure 7 It is a schematic structural diagram of a dead time correction system provided in the second embodiment of the present application.

[0119] As Figure 7 shown, this dead time correction system includes: a timer, a control module, a data processing module, and a correction module. Among them,

[0120] The timer 10 is used to respectively count the real time, the fast channel dead time, the tail pile-up type pile-up discard dead time, and the peak pile-up type pile-up discard dead time. Among them, the real time is the time actually measured by the nuclear instrument, the fast channel dead time is the time when the fast channel cannot detect the input pulse, the tail pile-up type pile-up discard dead time is the dead time corresponding to the count loss caused by implementing the tail pile-up type pile-up discard, and the peak pile-up type pile-up discard dead time is the dead time corresponding to the count loss caused by implementing the peak pile-up type pile-up discard;

[0121] The control module 20 is used to control the state of the timer to ensure accurate timing of the timer;

[0122] The data processing module 30 is used to calculate the count correction factor according to the measured real time, fast channel dead time, tail pile-up type pile-up discard dead time, and peak pile-up type pile-up discard dead time;

[0123] The correction module 40 is used to perform dead time correction using the count factor.

[0124] The dead time correction system of the embodiment of the present application includes: a timer, a control module, a data processing module, and a correction module. Among them, the timer is used to respectively count the real time, the fast channel dead time, the tail pile-up type pile-up rejection dead time, and the peak pile-up type pile-up rejection dead time. The real time is the time actually measured by the nuclear instrument. The fast channel dead time is the time when the fast channel cannot detect the input pulse. The tail pile-up type pile-up rejection dead time is the dead time corresponding to the count loss caused by implementing the tail pile-up type pile-up rejection. The peak pile-up type pile-up rejection dead time is the dead time corresponding to the count loss caused by implementing the peak pile-up type pile-up rejection. The control module is used to control the state of the timer to ensure accurate timing of the timer. The data processing module is used to calculate the count correction factor based on the measured real time, fast channel dead time, tail pile-up type pile-up rejection dead time, and peak pile-up type pile-up rejection dead time. The correction module is used to perform dead time correction using the count factor. Thus, the technical problem that the existing method only considers the count loss caused by the slow channel and ignores the count loss caused by the fast channel can be solved. By comprehensively considering the time resolution ability of the fast channel and the count loss caused by the pile-up rejection of the slow channel, the accuracy of count correction is improved. The count loss caused by the limited time resolution ability of the fast channel and the pulse pile-up of the slow channel can be accurately compensated, and it can be widely applied to the current nuclear measurement system.

[0125] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0126] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0127] Any process or method description represented in a flowchart or otherwise described herein can be understood to represent a module, segment, or portion of code including one or more executable instructions for implementing a customized logic function or process. The scope of the preferred embodiments of the present application includes additional implementations, where functions may be executed in a substantially simultaneous manner or in a reverse order according to the functions involved, rather than in the order shown or discussed, which should be understood by those skilled in the art to which the embodiments of the present application pertain.

[0128] Logic and / or steps represented in a flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing a logical function, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device), or in conjunction with such instruction execution systems, apparatuses, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by or in conjunction with an instruction execution system, apparatus, or device. More specific examples (non-exhaustive list) of computer-readable media include the following: an electrical connection (electronic device) having one or more wirings, a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable media on which the program can be printed, as the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or otherwise processing as appropriate, and then storing it in a computer memory.

[0129] It should be understood that various parts of the present application can be implemented by hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0130] Those of ordinary skill in the art can understand that all or part of the steps carried out in the methods of the above embodiments can be completed by instructing relevant hardware through a program, and the program can be stored in a computer-readable storage medium. When the program is executed, it includes one or a combination of the steps of the method embodiments.

[0131] In addition, in each of the embodiments of the present application, the functional units can be integrated into a processing module, or each unit can exist physically alone, or two or more units can be integrated into a module. The above-mentioned integrated module can be implemented in the form of hardware or in the form of a software functional module. When the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0132] The above-mentioned storage medium can be a read-only memory, a magnetic disk, an optical disc, etc. Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A dead time correction method, characterized in that, It includes the following steps: Use a timer to count the real time, where the real time is the time actually measured by the nuclear instrument; Use three timers to count the fast-channel dead time, the tail-pileup type pileup rejection dead time, and the peak-pileup type pileup rejection dead time respectively. Among them, the fast-channel dead time is the time when the fast channel cannot detect an input pulse, the tail-pileup type pileup rejection dead time is the dead time corresponding to the count loss caused by implementing the tail-pileup type pileup rejection, and the peak-pileup type pileup rejection dead time is the dead time corresponding to the count loss caused by implementing the peak-pileup type pileup rejection; Calculate the count correction factor based on the statistically obtained real time, fast-channel dead time, tail-pileup type pileup rejection dead time, and peak-pileup type pileup rejection dead time, and use the count factor to perform dead time correction. Among them, the count correction factor is expressed as: Among them, k represents the counting correction factor, RT represents the actual time obtained statistically, DT1 represents the dead time of the fast channel obtained statistically, and DT 2A represents the dead time of the tail pile-up type pile-up rejection obtained statistically, and DT 2B represents the dead time of the peak pile-up type pile-up rejection obtained statistically.

2. The method according to claim 1, wherein The timer has two states: The timing state. In the timing state, the timer counts according to the system clock frequency; The non-timing state. In the non-timing state, the value of the timer remains unchanged.

3. The method according to claim 2, wherein The timing process of the timer for the real time is as follows: Maintain the timing state throughout the measurement process.

4. The method according to claim 2, wherein The timing process of the timer for the fast-channel dead time is as follows: Whenever the fast channel detects a pulse, the timer will maintain the timing state within the pulse dead time of the fast channel; The pulse dead time of the fast channel can be replaced by another period of time, and the time used for replacement follows the same probability distribution as the pulse dead time of the fast channel.

5. The method according to claim 2, wherein The statistical process of the timer for the tail-pileup type pileup rejection dead time is as follows: Whenever the fast channel detects a pulse, first reset the timer for measuring the tail-pileup type pileup rejection dead time to the stop timing state, and at the same time, make the timer maintain the timing state within the tail-pileup type pileup rejection dead time corresponding to the detected pulse again.

6. The method according to claim 5, wherein The tail-pileup type pileup rejection dead time of a pulse is determined by the fast-channel pulse dead time corresponding to the pulse and the tail-pileup protection time. If the fast-channel pulse dead time corresponding to the pulse is less than or equal to the tail-pileup protection time, the tail-pileup type pileup rejection dead time of the pulse is equal to the difference between the tail-pileup protection time and the fast-channel pulse dead time corresponding to the pulse; If the fast-channel pulse dead time corresponding to the pulse is greater than the tail-pileup protection time, the tail-pileup type pileup rejection dead time of the pulse is equal to 0; The tail-pileup type pileup rejection dead time of a pulse can be replaced by another period of time, and the time used for replacement follows the same probability distribution as the calculated tail-pileup type pileup rejection dead time of the pulse.

7. The method according to claim 2, wherein The statistical process of the timer for the peak-pileup type pileup rejection dead time is as follows: Whenever the fast channel detects a pulse, first reset the timer for measuring the peak-pileup type pileup rejection dead time to the stop timing state, and at the same time, make the timer maintain the timing state within the peak-pileup type pileup rejection dead time corresponding to the detected pulse again.

8. The method according to claim 7, characterized in that The peak-pileup type pileup rejection dead time of an input pulse is determined by the fast-channel pulse dead time corresponding to the pulse and the peak-pileup protection time. If the dead time of the fast channel pulse corresponding to this pulse is less than or equal to the peak pile-up protection time, the pile-up rejection dead time of the peak pile-up type of this pulse is equal to the difference between the peak pile-up protection time and the dead time of the fast channel pulse corresponding to this pulse; If the dead time of the fast channel pulse corresponding to this pulse is greater than the peak pile-up protection time, the pile-up rejection dead time of the peak pile-up type of this pulse is equal to 0; The pile-up rejection dead time of the peak pile-up type of one pulse can be replaced by another period of time, and the time used for replacement and the pile-up rejection dead time of the peak pile-up type of the pulse obtained by calculation follow the same probability distribution.

9. A dead time correction system, characterized in that, Including a timer, a control module, a data processing module, and a correction module, where The timer is used to respectively count the real time, the fast channel dead time, the tail pile-up type pile-up rejection dead time, and the peak pile-up type pile-up rejection dead time. Among them, the real time is the time actually measured by the nuclear instrument, the fast channel dead time is the time when the fast channel cannot detect the input pulse, the tail pile-up type pile-up rejection dead time is the dead time corresponding to the counting loss caused by implementing the tail pile-up type pile-up rejection, and the peak pile-up type pile-up rejection dead time is the dead time corresponding to the counting loss caused by implementing the peak pile-up type pile-up rejection; The control module is used to control the state of the timer to ensure accurate timing of the timer; The data processing module is used to calculate the count correction factor according to the measured real time, fast channel dead time, tail pile-up type pile-up rejection dead time, and peak pile-up type pile-up rejection dead time. Among them, the count correction factor is expressed as: Among them, k represents the counting correction factor, RT represents the statistically obtained real time, DT1 represents the statistically obtained fast-channel dead time, and DT 2A represents the statistically obtained tail pile-up type pile-up rejection dead time, and DT 2B represents the statistically obtained peak pile-up type pile-up rejection dead time; The correction module is used to perform dead time correction using the count factor.

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