CN103336293A - Method for optimizing capability in discriminating neutrons from gamma rays of liquid scintillator detector - Google Patents
Method for optimizing capability in discriminating neutrons from gamma rays of liquid scintillator detector Download PDFInfo
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Abstract
The invention relates to a method for optimizing capability in discriminating neutrons from gamma rays of a liquid scintillator detector and belongs to the particle detection technology field. According to the method, a photon generation process over time of particles in a liquid scintillator is simulated firstly through a Monte Carlo method, an output signal of a single photon in a photomultiplier is acquired through a single photon experiment; output signal convolution of a randomly-selected photon sequence generated during simulation and the single photon is carried out in the photomultiplier to realize light signal actualization. Through simulating a whole process of a light pulse in the photomultiplier, capabilities in discriminating the neutrons from the gamma rays of different liquid scintillator detectors can be evaluated at a design phase of the liquid scintillator detectors; the liquid scintillator detectors can be optimized through changing parameters of the designed liquid scintillator detectors, and thereby a speed and precision for discriminating the neutrons from the gamma rays are improved.
Description
Technical field
The present invention relates to a kind of detector and screen the technology of neutron and gamma, particularly a kind of liquid scintillation bulk detector of optimizing improves the method that it screens neutron and gamma ray ability, belongs to the Particel Detection Methods field.
Background technology
1931, Britain physicist James Chadwick found through experiments the existence of neutron (n).After this between decades, the neutron detection technology has obtained extensive and deep research and application.Current, the neutron detection technology has been widely used in fields such as well logging, contraband goods detection, environmental radiation detection, medical science and military affairs.Yet, owing to the reasons such as radiative capture of the inelastic scattering in neutron and the surrounding environment, degraded neutron, exist the occasion of neutron nearly all to be accompanied by a large amount of gamma (γ) ray background.And many neutron detectors are also very sensitive to gamma ray, and therefore in order to get rid of gamma-ray interference, neutron and gamma discrimination just become a gordian technique of neutron detection.
Since the liquid scintillation bulk detector have good time response feature and neutron/gamma (n/ γ) ray screen performance, and be easy to be prepared into different shape and size, therefore be suitable for the neutron detection in neutron/gamma (n/ γ) mixing field.Neutron and gamma-ray photon all are electric neutrality, can be detected by producing secondary charged particle with the liquid scintillator effect.For the liquid scintillation bulk detector, the development of neutron and gamma discriminating method is that the development with electron device and signal processing technology adapts.
At present, in analog signal processing method prevailing period, traditional neutron and gamma discriminating method mainly adopt method pulse rise time, electric charge relative method etc. all based on analogue technique.But these are based on the method for analogue technique, have the circuit of realization complexity, defectives such as the low and poor stability of pulse percent of pass.In recent years, along with increasing substantially of digital signal processor (DSP) processing speed, the appearance of high-speed AD converter (ADC), the high speed development of field programmable gate array (FPGA), neutron and gamma discriminating method just develop towards the direction of digitized signal disposal route.For this reason, Chinese scholars has proposed the discriminating method based on Digital Signal Processing such as neural network method, pulsed gradient method (PGA), Wavelet Transform, correlation method, has improved the ability that neutron and gamma are screened thus greatly.And digitalized processing methods such as pulsed gradient method (PGA), neural network method and Wavelet Transform, utilize high-speed AD converter (ADC), digital signal processor (DSP), field programmable gate array digital signal processor spares such as (FPGA) to finish functions such as filtering moulding, baseline recovery, utmost point zero-compensation and pulse amplitude analysis.It is compared with analog signal processing method and has saved a large amount of hardware components, and can improve speed and the precision of neutron and gamma examination greatly; But can obtain satisfied result with analog signal processing method generally speaking.Based on the digitized signal disposal route then relatively targetedly, for example the wavelet transformation discriminating method has higher frequency resolution and lower time sense in low frequency part, and just in time opposite at HFS, have higher time sense and lower frequency resolution.The present invention just is being based on this point and is considering, advantage in conjunction with analog signal processing method and digitized signal disposal route, by the actualization of particle overall process in the liquid scintillation bulk detector is optimized designed liquid scintillation bulk detector, improve a kind of method that it screens neutron and gamma ray ability to reach.
Summary of the invention
Purpose of the present invention just is based on above-mentioned consideration, and the liquid scintillation bulk detector that proposes a kind of optimization improves the method that it screens neutron and gamma ray ability.This method is earlier by Monte Carlo method simulation particle photon production process in time in liquid scintillator; Obtain single photon in the output signal of photomultiplier by the single photon experiment then; The photon sequence of picked at random simulation generation and single photon are in the output signal convolution of photomultiplier, to realize the actualization of light signal again.By the overall process of simulated light pulse at photomultiplier, obtain a kind of liquid scintillation bulk detector and can assess the ability that different liquid dodge detector examination neutron and gamma in the design phase; Optimize designed liquid by the parameter that changes designed liquid sudden strain of a muscle detector and dodge detector, and then improve speed and precision that it screens neutron and gamma.
For achieving the above object, the present invention adopts the technical scheme be made of following technical measures to realize.
A kind of liquid scintillation bulk detector of optimizing that the present invention proposes comprises following operation steps to improve the method that it screens neutron and gamma ability:
(1) simulation Monte Carlo light signal
A) use software Geant4 model fluid scintillator detector;
B) generation of utilization software Geant4 simulated photons;
(2) single photon experiment:
A) connect and debug used instrument;
B) undesired signal of measuring and observe photomultiplier thermonoise and light leak to produce;
Not luminous at light emitting diode, and wrap under the gobo situation and gather signal, after the selection of shading treatment and threshold value, obtain undesired signal again;
C) input drive signal, the signal of measurement photomultiplier;
D) gather the single photoelectron data;
Adjust the light emitting diode luminance brightness, make its decay, when the photomultiplier amplitude output signal changes when little, gather the single photoelectron data;
E) data analysis;
The single photoelectron data of gathering are handled match obtain the single photon impulse response function;
(3) convolution of signal
A) the single photon impulse response function is got a little;
B) use software Matlab that taken point in the described step a) is carried out interpolation and obtain the single photon response function, choose with liquid scintillation bulk detector described in the step (1) in the point in identical time interval of light signal of producing in time of photon;
C) get light signal convolution in software Matlab that photon produces in time in single photon impulse response function and the model fluid scintillator detector at random, and compare with the resulting signal of true particle respectively.
In the technique scheme, step (1) a) described in the model fluid scintillator detector, its concrete practice is that designed liquid scintillator detector size, form parameter at first are set, and uses software Geant4 simulation and the designed described size of liquid scintillation bulk detector, the detector that shape is identical.
In the technique scheme, step (1) b) generation of simulated photons described in, its concrete practice is that following parameter is set:
(ⅰ) photon number, resolution, energy value, speed time parameter are set; According to used liquid scintillation volume property, " scintillator speed time parameter is than arranging " arranges resolution, energy value, the speed time parameter of required photon number, scintillator in the simulation process;
(ⅱ) border and parameter thereof between photomultiplier and photoconduction are set; The border that arranges between photomultiplier and photoconduction according to laboratory condition is the dielectric metal, and its reflectivity, efficiency parameters are set; Obtain particle and in liquid scintillator, simulate the Monte Carlo light signal, be the point of series of equivalent time interval;
In the technique scheme, step (2) a) described in the debugging used each instrument, its concrete practice is:
(ⅰ) the driving signal of the used chronotron of debugging is set frequency, the width of described driving signal;
(ⅱ) make camera bellows, optical attenuator, shielding external interference;
(ⅲ) set used high pressure, observe the signal output waveform of photomultiplier by oscillograph.
In the technique scheme, step (2) c) measure the light signal of photomultiplier described in, its concrete practice is:
(ⅰ) open the driving signal of chronotron, frequency, used high pressure are set, observe the signal output waveform of photomultiplier by oscillograph;
(ⅱ) change the luminance brightness that incides photomultiplier, the variation of photomultiplier signal output waveform in the observation oscilloscope by optical attenuation;
(ⅲ) analyze optical attenuation to the influence of signal.
In the technique scheme, the single photon impulse response function is got a little described in a) in step (3), its concrete practice is:
(ⅰ) carry out described point and record by the single photon impulse response function image that obtains in the step of software digitizer (2);
(ⅱ) described point that obtains is rejected point outside the error, that obviously do not belong to the single photon signal in software Matlab.
In the technique scheme, step (3) b) described in the liquid scintillation bulk detector photon produce the point in the identical time interval of signal in time, finished by following step:
(ⅰ) utilize software Matlab method of interpolation fitting function;
(ⅱ) point in the identical time interval of utilizing software Matlab to choose to produce in time with photon in the liquid scintillation bulk detector of signal.
The present invention has following advantage and beneficial technical effects:
1, a kind of method that the liquid scintillation bulk detector is screened neutron and gamma ray ability of optimizing of the present invention, before making the liquid scintillation bulk detector, namely can assess the ability that this detector is screened n/ γ exactly, to be convenient to do the liquid scintillation bulk detector that high ability neutron/gamma is screened.
2, method of the present invention is simple, convenient, easy to implement, the liquid scintillation bulk detector that applicability is wide, can be applied to any model.
3, owing to the inventive method just can be assessed its ability of screening neutron and gamma before making the liquid scintillation bulk detector, thereby come optimal design liquid scintillation bulk detector by changing parameters such as designed liquid scintillator detector size, shape, to improve speed and the precision that it is screened the n/ gamma-rays.
Description of drawings
The liquid scintillator panel detector structure synoptic diagram that Fig. 1 the present invention simulates with software Geant4;
The particle of Fig. 2 the present invention simulation is thrown the structural representation among Fig. 1 into;
The photon of neutron in liquid scintillator of Fig. 3 the present invention simulation; Its horizontal ordinate is the time, and unit is 20ns; Ordinate is counting, and unit is individual;
The photon of gamma in liquid scintillator of Fig. 4 the present invention simulation; Its horizontal ordinate is the time, and unit is 20ns; Ordinate is counting, and unit is individual;
The used single photon experimental circuit of Fig. 5 the present invention structured flowchart;
Fig. 6 the present invention is by the photomultiplier tube signal oscillogram of the driving signal generation of manual setting;
The undesired signal figure that Fig. 7 photomultiplier thermonoise of the present invention and light leak produce;
Fig. 8 optical attenuation of the present invention is to the influence of photomultiplier output signal;
Intercepting synoptic diagram when Fig. 9 the present invention adopts the sampling of Plot digitizer software described point;
Figure 10 single photon signal graph of the present invention; Its horizontal ordinate is number; Ordinate is counting;
Figure 11 photomultiplier single photon of the present invention spectrogram;
The contrast of Figure 12 neutron of the present invention and gamma convolution signal and actual signal, wherein (a) simulation gamma and true gamma ray comparison diagram; (b) simulation neutron and true neutron ray comparison diagram; (c) true gamma and true neutron ray comparison diagram; (d) simulation gamma and simulation neutron ray comparison diagram.
Among the figure, 1 is organic glass, and 2 is photoconduction, 3 is radioactive source, 4 particle and the scattering particles that send for simulation signal generator, and 5 is the part secondary, 6 is lead brick, and 7 are the liquid scintillation bulk detector, and 8 is chronotron, 9 is fan-in fan-out plug-in unit, and 10 is camera bellows, and 11 is light emitting diode, 12 is photomultiplier, 13 put plug-in unit before fast, 14 is quick digital-to-analog conversion plug-in unit, and 15 is oscillograph.
Embodiment
Carry out further concrete description below by the present invention of embodiment; be necessary to be pointed out that at this present embodiment only is used for invention is further specified; but should not be understood as any restriction to protection domain of the present invention, the person skilled in the art in this field can do some nonessential improvement and adjustment according to the content of the invention described above.
Figure 1 shows that model fluid scintillator detector structural representation: column part material is the thick organic glass of 4mm 1 in the middle of it, the two ends symmetric part is photoconduction 2, photoconduction 2 connects photomultiplier 12 both-ends and meets read output signal, be coupled by silicone grease between organic glass 1 and photoconduction 2 and photoconduction 2 and the photomultiplier 12, to increase the collection efficiency of light.
Figure 2 shows that simulation particle throws the synoptic diagram of liquid scintillation bulk detector into: wherein comprised radioactive source 3, the particle that simulation signal generator sends and scattering particle 4, part secondary 5, lead brick 6, liquid scintillation bulk detector 7.
Single photon experimental circuit block diagram shown in Figure 5, each instrument plug-in unit correctly connects by this experiment block diagram.Its experimentation is the driving signal of at first manual adjustments chronotron 8, it is made up of the two-way time delayed signal, one the tunnel is used for the width of regulating impulse, the width that another road is used for regulating between per two pulses is the regulating impulse frequency, and end (end) termination of every road signal is gone into beginning (start) end on another road as the triggering on another road.Just the sustainable driving signal that provides after manually beginning is realized the function of similar pulse producer, and different is can distinguish regulating impulse frequency and pulse width here, generally requires the signal period much larger than pulse width; By the observation regulating impulse frequency eaily of oscillograph 15, to provide standard NIM signal be the square-wave signal of 800mV to chronotron 8 here; Setting its frequency is 2000Hz, and width is 35ns.
Camera bellows 10 used in the experiment can be formed by airtight common cardboard carton by small one and large one two.Little carton be used for to be installed photomultiplier 12, and accepts illumination at photomultiplier 12 and penetrate the carton of one side and cut a hole, and light emitting diode 11 is fixed in the middle of the hole, is used for accepting the light that light emitting diode 11 sends.Certainly, in order to satisfy the single photoelectron experimental requirements, need decay to the light of light emitting diode 11, here use common A4 printer paper doubling 4 times, one side is sticked friction tape, another side subtend photomultiplier 12, the light emitting diode 11 selection thickness that can be clipped in the middle reaches the effect of optical attenuation.During experiment, little carton is wrapped up two-layer gobo, be placed in the big carton, again with big carton outer wrapping one deck gobo, so then can reach the effect that the shielding ambient light is disturbed, reduce to test background.
The negative high voltage of used photomultiplier 12 is provided by the NIM cabinet, is connected on photomultiplier 12 photocathodes, is chosen to be-1100V.
Below be that embodiment simulates the output signal of n/ γ under the used instrument and equipment condition in laboratory.
Used photomultiplier 12 is that R5912-02 type photomultiplier, the scintillator of the loose company in Japanese shore is the EJ335 scintillator of the loose company in Japanese shore;
Used high-voltage power supply N1470, negative high voltage power source NIM cabinet; Put plug-in unit 13 before fast and adopt N978; The time-delay plug-in unit is that chronotron 8 adopts N93B; It is oscillograph 15 that fan-in fan-out plug-in unit 9 adopts N65 (FIFO), quick analog to digital conversion plug-in unit 14 to be FADCY1721, RIGO; Light emitting diode 11 is the LED lamp, use physical process, the software Matlab that is used for convolution that existing software Geant4 simulation particle transports in material, the software Plot digitizer that is used for described point.
Embodiment
The used instrument and equipment condition of present embodiment as mentioned above, concrete operations step and implementation thereof are as follows:
(1) simulation Monte Carlo light signal
A) utilization software Geant4 model fluid scintillator detector is installed on computers
At first setting designed its diameter of liquid scintillation bulk detector is 30cm, and length is the cylindrical detector of 40cm, uses the software Geant4 simulation liquid scintillation bulk detector identical with its size and dimension;
B) generation of using software Geant4 simulated photons is installed on computers;
This time that simulation is liquid scintillator EJ331, wherein add mass ratio and be 0.5% gadolinium, to improve the ability of capturing of neutron, character according to used liquid scintillator, set parameters needed in the simulation process: the photon number that unit energy produces in the liquid scintillator is 11000./MeV, a Gaussian distribution is obeyed in the average fluctuation that produces photon, and its resolution is set to 1.0, and luminous speed, luminescence decay time constant in the liquid scintillator are set to 3.8ns and 24.9ns;
Because liquid scintillator is luminous relevant with particle types, different and make under the situation that fast slow component changes by particle types, can for the scitillation process call method of every class particle " scintillator speed time parameter is than arranging " (SetScintillationExcitationRatio), it will arrange different fast slow components for different particles is luminous, the speed time ratio of neutron is 0.752, and the speed time ratio of gamma is 0.799;
The border that photomultiplier 12 and photoconduction are 2 is set to the dielectric metal, it is 0 that its reflectivity is set, efficient is 1, the photon that then incides photoelectric surface can be absorbed fully, obtain the Monte Carlo light signal that neutron, gamma simulate and be respectively Fig. 3 and shown in Figure 4 in liquid scintillator, be the point of series of equivalent time interval.
(2) single photon experiment
A) connect and debug used instrument;
Behind connection shown in Figure 5 and good each instrument of debugging, regulate time delayed signal, just can observe the signal that photomultiplier 12 sends by oscillograph 15, owing to be luminous for the LED lamp by chronotron 8 triggering light emitting diodes 11, and detect light signal by photomultiplier 12, so all certain hour time-delay appearance behind the square-wave signal that drives of light signal, choose one of them signal as shown in Figure 6 with oscillograph 15, it is said as the standard NIM signal that drives that square-wave signal is the front, and the another one signal is the signal output waveform of photomultiplier;
B) undesired signal of measuring and observe photomultiplier thermonoise and light leak to produce;
Open the NIM cabinet, when not producing the driving signal, the LED lamp is not luminous, this moment photomultiplier 12 is added-high pressure of 1100V, some that can see on oscillograph 15 do not have rule, amplitude signal not of uniform size, and these are because the undesired signal that the thermonoise of photomultiplier and light leak produce; After having added gobo, can see that the quantity of undesired signal has tangible minimizing; Fig. 7 is that the LED lamp is not luminous, and wraps the signal under adopting behind the gobo, and as can be seen, through shading treatment, interfering noise signals is when-1100V, substantially all below 100mV, as shown in Figure 6; Each little lattice width of setting oscillograph 15 herein is 20 μ s, highly be 100mV, and when the actual measurement photomultiplier tube signal, setting each little lattice width is 20ns, highly constant, can see that undesired signal relatively still seldom, is not very big to measuring by the measurement influence that drives the photomultiplier output signal that produces, namely too much spurious count can not occur;
C) input drive signal, the signal of measurement photomultiplier;
(ⅰ) open the driving signal of chronotron 8, frequency, high pressure are set, the signal of observation oscilloscope 15;
The driving signal of manual unlocking chronotron 8, the just sustainable driving signal that provides of plug-in unit N93B of after this delaying time, its frequency is 2000Hz, adds-high pressure of 1100V to photomultiplier then, observes before fast by oscillograph and puts the signal that plug-in unit 13 comes out; When not taking the optical attenuation measure, can see the signal of the superimposed pulses that a lot of amplitudes are bigger, its pulse amplitude values can be bigger;
(ⅱ) change the luminance brightness that incides photomultiplier, the variation of signal in the observation oscilloscope by optical attenuation;
When the thickness that slowly increases the used paper of decay changes the luminance brightness that incides photomultiplier, thereby change photoelectronic generation probability, can see that the output pulse amplitude value is reducing; When luminance brightness was reduced to certain value, the photomultiplier amplitude output signal changed little, and the very fast reduction of example number that is associated with the LED lamp can think that the single photoelectron example is higher relatively this moment;
(ⅲ) analyze optical attenuation to the influence of signal;
Be the pulse signal of photomultiplier output when not taking the optical attenuation measure shown in (a) figure among Fig. 8, the amplitude of its every little lattice representative is 200mV, and (b) figure among Fig. 8 is depicted as the single photoelectron example when higher, the amplitude of its every little lattice representative is 100mV, as seen along with optical attenuation, the photon that enters photomultiplier reduces, and the amplitude output signal of photomultiplier slowly reduces;
D) gather the single photoelectron data
Photomultiplier all is operated in-high pressure of 1100V under, need earlier high pressure is reduced to 0 before the image data carrying out next time, carry out to gather and go up again after preparing, in order to avoid operating process not at that time high pressure human body is damaged; Observe the output signal of photomultiplier at oscillograph after, adjust the LED lamplight brightness, after making its decay, the photomultiplier amplitude output signal changes little, if can observe b in the step (2)), c) phenomenon stated of step, illustrate that then each experimental apparatus all is operated under the normal condition, take over for use this moment to do slightly in the paper number of decay and adjust, block from 1 to 3 of the thickness of LED lamp paper, image data respectively as change; Only need during image data digital to analog converter FADC is opened, corresponding software arranges memory address and gets final product in computer;
The signal of photomultiplier output when blocking 9,8,7,6,5 paper before the LED lamp has been gathered in this experiment respectively, gathers 100,000 data at every turn;
E) data analysis
With d) data that collect are carried out analyzing and processing in the step, and the single photoelectron of every group of 100,000 data of drawing spectrum, and so just can respond the single photoelectron of photomultiplier have conclusion more intuitively; This raw data is stored as the bin form, operates in during analysis under the ROOT environment, to data programmed process draw single photoelectron spectrum and match, and draws parameters such as peak-to valley ratio and resolution according to each spectrum of gained; The output signal of single photoelectron is approximately Landau and distributes, signal output and single photon spectrum as shown in figure 10, the photomultiplier single photon spectrum that records can be by following exponential function match background:
expo(x)＝exp(p0+p11x) (1)
And by following two Gaussian function match single photoelectron peak positions;
gaus1(x)＝p2*exp(-0.5*((x-p3)/p4)∧2) (2)
gaus2(x)＝p5*exp(-0.5*((x-p6)/p7)∧2) (3)
Last matched curve:
simulation(x)＝expo(x)+gaus1(x)+gaus2(x) (4)
Wherein p0 to p7 corresponding to the fitting parameter among the figure, exponential signal expo (x) characterizes noise spectrum, gaussian signal gausl (x) characterizes the single photon spectrum, gaussian signal gaus2 (x) characterizes the multi-photon spectrum, during the sampling single photon pulses, the area integral of pulse equals the corresponding road of single photoelectron spectrum peak number.
(3) convolution of signal
A) the single photon impulse response function is got a little;
(ⅰ) carry out described point and record by the single photon impulse Response Function image that obtains in the step of software digitizer (2);
Select a single photon signal at random, integration utilizes the single photon signal of software Plot digitizer to get point sampling corresponding to the corresponding road of single photon spectrum peak number, and sampling is noted resulting point as shown in Figure 9;
The described point that (ⅱ) obtains is rejected fitting function with point outside the error, that obviously do not belong to the single photon signal in software Matlab;
The point that obtains is rejected point outside the error, that obviously do not belong to the single photon signal in software Matlab; Utilize the data that obtain Matlab to do fitting function at last, obtain the impulse response function h(t that the single photon Landau distributes);
B) convolution and comparing;
Respectively with the neutron of simulating in the step (1) and the gamma convolution function conv (x1 by software Matlab, x2), with single photon impulse response function h(t) the signal g (t) that produces in time with its photon in the liquid scintillation bulk detector makes convolution: it should be noted that, because the single photon signal of gathering is lattice with 20ns, is consistent so also need the time interval of single photon impulse response in convolution.
To simulate neutron and simulation gamma respectively, the comparison of after normalization, putting together of true neutron and true gamma, as shown in figure 12,----expression simulation gamma ray wherein,
Represent true gamma ray,---expression simulation neutron ray,---represent true neutron ray; Change detector shape, size etc., obtain the ability that different detectors is screened neutron and gamma, select a size liquid scintillation bulk detector, thereby optimize the examination neutron of liquid scintillation bulk detector and the detector of gamma.The result contrasts among the following Figure 12 of pulse diagram a), b) figure: with real pulsion phase relatively, the goodness of fit is relatively good; The size Selection optimum that changes the model fluid scintillator detector is optimized its examination neutron and gamma ability.In scintillator, the fast composition share of pulse that gamma ray produces is little, slow composition share is many, neutron is then opposite, and therefore shown in d figure among Figure 12, the rising edge of neutron and gamma ray almost overlaps, when simulation neutron and the negative edge of simulating gamma at first are that neutron descends comparatively fast, it is very fast to be that gamma descends then, and namely two lines have intersection point, and simulation neutron, simulation gamma ray be optimum in the time of clear and legible.
List of references:
[1]I.Fedorko,S.Tokar.Simulation of Photomultiplier Response[J].ATL-TILECAL,1999,012:2-3。
[2] Soren JETTER, Dan DWYER. photomultiplier waveform modeling at the Daya Bay experiment[J] .Chiness Physics C, 2012,36 (8): 734-735.
[3]S.Riggi,P.La Rocca.GEANT4simulation of plastic scintillator strips with embedded optical fibers for a prototype of tomographic system[J].Nuclear Instruments and Methods in Physics Research A,2010,624:585。
[4]EJ331-335GADOLINIUM LOADED LIQUID SCINTILLATORS.http://www.ggg-tech.co.jp/naker/eljen/ej331.html。
[5]GANT4USE’S GUIDE。
[6] radiation detection and measurement [M]. Sichuan University, 102.
Claims (7)
1. optimize the method that the liquid scintillation bulk detector is screened neutron and gamma ability for one kind, it is characterized in that comprising following operation steps:
(1) simulation Monte Carlo light signal
A) use software Geant4 model fluid scintillator detector (7);
B) generation of utilization software Geant4 simulated photons;
(2) single photon experiment
A) connect and debug used instrument;
B) undesired signal of measuring and observe photomultiplier (12) thermonoise and light leak to produce;
Not luminous at light emitting diode (11), and wrap under the gobo situation and gather signal, after the selection of shading treatment and threshold value, obtain undesired signal again;
C) input drive signal, the signal of measurement photomultiplier (12);
D) gather the single photoelectron data;
Adjust light emitting diode (11) luminance brightness, make its decay, when photomultiplier (12) amplitude output signal changes when little, gather the single photoelectron data;
E) data analysis;
The single photoelectron data of gathering are handled match obtain the single photon impulse response function;
(3) convolution of signal
A) the single photon impulse response function is got a little;
B) use software Matlab that taken point in the described step a) is carried out interpolation and obtain the single photon response function, choose with liquid scintillation bulk detector described in the step (1) in the point in identical time interval of light signal of producing in time of photon;
C) get light signal convolution in software Matlab that photon produces in time in single photon impulse response function and the model fluid scintillator detector at random, and compare with the resulting signal of true particle respectively.
2. method according to claim 1, it is characterized in that model fluid scintillator detector described in step (1) a), its concrete practice is that designed liquid scintillation bulk detector (7) size, form parameter at first are set, and uses software Geant4 simulation and the designed described size of liquid scintillation bulk detector (7), the detector that shape is identical.
3. method according to claim 1 is characterized in that step (1) b) described in the generation of simulated photons, its concrete practice is that following parameter is set:
(ⅰ) photon number, resolution, energy value, speed time parameter are set; According to used liquid scintillation volume property, " scintillator speed time parameter is than arranging " arranges resolution, energy value, the speed time parameter of required photon number, scintillator in the simulation process;
(ⅱ) border and parameter thereof between photomultiplier and photoconduction are set; The border that arranges between photomultiplier (12) and photoconduction (2) according to laboratory condition is the dielectric metal, and its reflectivity, efficiency parameters are set; Obtain particle and in liquid scintillator, simulate the Monte Carlo light signal, be the point of series of equivalent time interval.
4. method according to claim 1 is characterized in that debugging used each instrument described in step (2) is a), and its concrete practice is:
(ⅰ) the driving signal of the used chronotron of debugging is set frequency, the width of described driving signal;
(ⅱ) make camera bellows, optical attenuator, shielding external interference;
(ⅲ) set used high pressure, observe the signal output waveform of photomultiplier by oscillograph.
5. method according to claim 1 is characterized in that step (2) c) described in measure the light signal of photomultiplier, its concrete practice is:
(ⅰ) open the driving signal of chronotron, frequency, used high pressure are set, observe the signal output waveform of photomultiplier by oscillograph;
(ⅱ) change the luminance brightness that incides photomultiplier, the variation of photomultiplier signal output waveform in the observation oscilloscope by optical attenuation;
(ⅲ) analyze optical attenuation to the influence of signal.
6. method according to claim 1 is characterized in that described in step (3) is a) the single photon impulse response function being got a little, and its concrete practice is:
(ⅰ) carry out described point and record by the single photon impulse response function image that obtains in the step of software digitizer (2);
(ⅱ) described point that obtains is rejected point outside the error, that obviously do not belong to the single photon signal in software Matlab.
7. method according to claim 1 is characterized in that step (3) b) described in the liquid scintillation bulk detector photon produce the point in the identical time interval of signal in time, finished by following step:
(ⅰ) utilize software Matlab method of interpolation fitting function;
(ⅱ) point in the identical time interval of utilizing software Matlab to choose to produce in time with photon in the liquid scintillation bulk detector of signal.
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| CN104678425A (en) * | 2015-02-02 | 2015-06-03 | 中国原子能科学研究院 | Fast-neutron multiple measuring-analyzing method based on liquid scintillation detector |
| CN104898157A (en) * | 2014-03-04 | 2015-09-09 | 环境保护部核与辐射安全中心 | Device and method for measuring neutron dose equivalent |
| CN104898158A (en) * | 2014-03-04 | 2015-09-09 | 环境保护部核与辐射安全中心 | Method and device for measuring neutron dose equivalent |
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