On behalf of Sichuan University CDEX Group Haoyang Xing School of Physical Science and Technology Sichuan University Symposium of SinoGerman GDT 2013411 1 CDEX Collaboration Outline ID: 670293
Download Presentation The PPT/PDF document "PROGRESS of FAST NEUTRON FLUX MEASUREME..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
PROGRESS of FAST NEUTRON FLUX MEASUREMENT in CJPL
On behalf of Sichuan University CDEX GroupHaoyang Xing
School of Physical Science and Technology, Sichuan University
Symposium of Sino-German GDT
2013/4/11
1
CDEX CollaborationSlide2
OutlineBackground Neutron in CJPLNeutron Detector Design
Fabrication of DetectorEnergy CalibrationDetection Efficiency Calibration (Discrimination between γ and n)
Next WorkSummerySymposium of Sino-German GDT2013/4/11
2Slide3
Background Neutron in CJPL
2013/4/11Symposium of Sino-German GDT
3Slide4
Source and CharacteristicSource
μ induced neutrons Spontaneous fission of U238 (α
,n) reactions from U, Th series Low neutron flux <10-7 n/cm2/s.
Energy range from thermal to some tens of MeV.
Symposium of Sino-German GDT
2013/4/11
4Slide5
Requirement of DetectorTherefore, to measure the neutron flux and energy spectra, we need:
– A high sensitivity neutron detector. – Effective way to eliminate the gamma background since most of the neutron detectors are also sensitive to gammas.
Symposium of Sino-German GDT2013/4/115Slide6
Neutron Detector Design
2013/4/11Symposium of Sino-German GDT
6Slide7
Neutron Spectrometer Characteristics
Symposium of Sino-German GDT
2013/4/117Slide8
Liquid Scintillator Choice
Because of the low neutron flux, the liquid scintillator loaded with Gd is adopted to confirm a neutron event.Schematic diagram：
p
p
Gd
γ
γ
n
PSD could be applied
Fast and slow signal coincidence measurement
Symposium of Sino-German GDT
2013/4/11
8Slide9
Configuration of DetectorLS : EJ335
PMT:
R5912
Symposium of Sino-German GDT
2013/4/11
9Slide10
Geometrical Simulation
200,000 NeutronEnergy :10MeVLocation&Direction: Outside of detector and point to detector
Symposium of Sino-German GDT
2013/4/11
10
Red, proton recoiling; Blue, captured by Gd
Distance distributionSlide11
Fast-Slow event time simulationSymposium of Sino-German GDT
2013/4/11
11For setting Time Window of Fast-Slow Identification. Slide12
Structure and Shape of LS DetectorFast-Slow coincidence
Light collecting efficiencyEffect from optic absorption lengthTwo PMT
The considered factors of Large Volume Detector :
Symposium of Sino-German GDT2013/4/11
12Slide13
Fabrication of Detector
2013/4/11Symposium of Sino-German GDT
13Slide14
Assembling and Shielding
Quartz glass container + EJ335 + Copper shield + Two PMTsLead shield
Symposium of Sino-German GDT
2013/4/11
14Slide15
DAQ system
Voltage： left（PMT1）： -850V
right（PMT2）： -880VThreshold of discriminator： channel1（
PMT1） 10 (15mv) channel2
（PMT2） 12 (15mv)
Outgoing pulse width of discriminator： 140 ns
PMT1
PMT2
FIFO
V1721
A2818
trigger
logical And
Discriminator
FIFO
Diagram of DAQ system
Symposium of Sino-German GDT
2013/4/11
15Slide16
Energy Calibration with Gamma Source for Detector
Symposium of Sino-German GDT2013/4/11
16Slide17
Background Measurement
Background Energy Spectrum
1721 setting： PreTrigger： 130 TimeWindow： 120
（240us）
Total events：
1,000,000 Time： 6522
sAverage Rate
： 153/s
Symposium of Sino-German GDT
2013/4/11
17
Background ExperimentSlide18
Energy zero-point
Using a signal generator to get a 1KHZ square signal for the random trigger signal of FADC and collect the output from the detector.
Energy Spectrum of Random Trigger From this energy spectrum,we know that the energy zero-point is at the zero channel.
Symposium of Sino-German GDT
2013/4/11
18Slide19
The γ source was placed near to the centre of one side of the detector through a hole which was made in the roof of the lead shield.
The position of the γ source
Symposium of Sino-German GDT
2013/4/11
19
Gamma ExperimentSlide20
Energy spectrum measurement for γ source
137Cs
60Co
Total events： 1,000,000
Time： 416 s
Average rate： 2402 /s
Total events
： 1,000,000
Time： 900 s
Average
r
ate
：
1110 /s
60
Co
spectrum (red)
，
background (blue)
137
Cs
spectrum (red)
，
background (blue)
60
Co spectrum after subtracting background
137
Cs spectrum after subtracting background
Symposium of Sino-German GDT
2013/4/11
20
Co experimentSlide21
Energy calibration of the detector
60
Co energy deposition spectrum by simulation137Cs energy deposition spectrum by simulation
Through the simulation by Geant4, we get the energy deposition spectrum of the γ
source in the detector. We perform a broadening for this energy spectrum by using . After adjusting the parameters, which is in order to make the simulation and the experiment more coherently. We can calibrate the energy of the detector through the comparison between the simulation and the experiment.
Symposium of Sino-German GDT
2013/4/11
21Slide22
137
Cs
simulation(red) and experiment(blue) spectrum60Co simulation(red)
and experiment(blue) spectrum
When α= 0.0003 and β= 0.35 (unit 10KeV) ， the simulation and the experiment
get the most coincidence.
Correspondence
： Peak position 0 590 1430
Energy(MeV) 0 0.46 1.06
Energy calibration curve
Symposium of Sino-German GDT
2013/4/11
22Slide23
Detection Efficiency Calibration
Discrimination Between Gamma and Neutron (Neutron Identification)
Symposium of Sino-German GDT2013/4/1123Slide24
Neutron Experiment
The distance between neutron source and lead shield is1m
Total events： 200,000Average Rate： 416 /sEnergy spectrum of all events (red),
background (blue)
We use the Am-Be neutron source to test the detector
Symposium of Sino-German GDT
2013/4/11
24Slide25
n- γ
discrimination
Charge comparison method is adopted to perform the n-gamma discrimination. “Qtotal” stands for the total charge of the pulse, and the integrating range is from 40ns before the peak position to 80ns after the peak position. “Qpart” stands for the charge of the pulse rising edge, and the integrating range from
30ns after the peak position to 80ns after the peak position. We define the discriminative factor：Dis = Qpart
/Qtotal
PSD:
One point stand for 2ns
Symposium of Sino-German GDT
2013/4/11
25Slide26
Left gamma, right neutron.
Symposium of Sino-German GDT
2013/4/1126n-
γ discriminative diagram
Over1.6MeV, it is hard to discriminate neutron and gamma.Slide27
More precise standard to identify n
Background ExperimentCo60 Experiment2013/4/11
Symposium of Sino-German GDT27Analysis data from Slide28
The red part is background
Symposium of Sino-German GDT
2013/4/1128Neutron experiment + BackgroundSlide29
60
CoBackgroundAm-Be
From this diagram, we can get a clear boundary of the γ signals. γ signal should have the same characteristics whether it comes from Gd capture or the 60
Co. Symposium of Sino-German GDT
2013/4/11
29
Neutron experiment + Background + CoSlide30
The fitted boundary equation:exp(9.942-67.59*x)+1.233-4.529*x+4.188*x
2
Am-BeBackground60Co
Symposium of Sino-German GDT2013/4/11
30
A
B
c
Region A, gamma? but can be used in
fast-slow
coincidence.
(<0.145)Slide31
Total
events
Valid
events
Region
B
Mono-pulse events
above
the
red
curve
Multi-pulse
events above the red curve
Neutron Exp
200,000
186839
37409(0.2002
)
21477(0.574)
15932(0.426)
Background Exp
20,000
13331
62(0.0047
)
39(0.629)
33(0.371)
Co60 Exp
50,000
40758
116(0.0029
)
84(0.724)
32(0.276)
Region
B
, events can be identified to be Neutron with very small error.
Symposium of Sino-German GDT
2013/4/11
31Slide32
fast-slow coincidence
Region B was also inspected by F-S coincidence.
Fast signal
(or recoil proton signal)
Slow signal
(or
γ
signal
)Threshold ?
Symposium of Sino-German GDT
2013/4/11
32
Region
C
, can be used to
retrieve
more neutron by F-S coincidence
.Slide33
Gamma
energy Threshold (
MeV)in Region
A
Neutron Exp
(multi-pulse
events 15932
)
Background Exp
(multi-pulse
events 33
)
Co60 Exp
(multi-pulse
events 32
)
>2.6
4778(0.299)
12(0.364)
4(0.125)
>2.4
5348(0.335)
14(0.424)
4(0.125)
>2.2
5964(0.374)
15(0.455)
5(0.156)
>2.0
6625(0.415)
16(0.485)
5(0.156)
>1.8
7216(0.452)
17(0.515)
6(0.188)
>1.6
7835(0.491)
17(0.515)
8(0.250)
>1.4
8446(0.530)
17(0.515)
9(0.281)
>1.2
9147(0.574)
18(0.545)
13(0.406)
>1.0
9899(0.621)
19(0.576)
15(0.469)
>0.8
10669(0.669)
20(0.606)
15(0.469)
>0.6
11293(0.708)
21(0.636)
15(0.469)
>0.4
11796(0.740)
22(0.667)
16(0.500)
>0.2
12247(0.768)
22(0.667)
16(0.500)
fast-slow coincidence
(Region B
)
Symposium of Sino-German GDT
2013/4/11
33Slide34
Total
events
Valid
events
Events
inside
the
red
line
Mono-pulse event
inside
the
red
curve
Multi-pulse
events inside the red curve
Neutron Exp
200,000
186839
43856(0.2347)
27772(0.633)
16084(0.367)
Background Exp
20,000
13331
747(0.0560)
712(0.953)
35(0.047)
Co60 Exp
50,000
40758
7925(0.1944)
6329(0.798)
1596(0.202)
Symposium of Sino-German GDT
2013/4/11
34
Region
C
, events probably includes amount of Neutron Slide35
Gamma
energy Threshold (
MeV)in
Region A
Neutron Exp
(16084)
Background Exp
(35)
Co60 Exp
(1596)
>2.6
3785(0.235)
8(0.229)
2(0.001)
>2.4
4252(0.264)
8(0.229)
3(0.002)
>2.2
4707(0.293)
8(0.229)
7(0.004)
>2.0
5227(0.325)
8(0.229)
20(0.013)
>1.8
5774(0.359)
9(0.257)
30(0.019)
>1.6
6253(0.389)
11(0.314)
38(0.024)
>1.4
6729(0.418)
11(0.314)
52(0.033)
>1.2
7290
(0.453)
13(0.371)
125(0.078)
>1.0
7909(0.492)
13(0.371)
278(0.174)
>0.8
8522(0.530)
16(0.457)
407(0.255)
>0.6
9064(0.564)
19(0.543)
471(0.295)
>0.4
9510(0.591)
21(0.600)
517(0.324)
>0.2
9999(0.622)
24(0.686)
563(0.353)
fast-slow coincidence
Symposium of Sino-German GDT
2013/4/11
35
Using this way,
37409 + 7290 can be get from 200000 Neuron Exp event (22%). Slide36
Neutron Identification StandardPSD over 1.6MeVFast - slow coincidence, Gamma threshold over 1.2
MeV2013/4/11
Symposium of Sino-German GDT36Slide37
Next workCalibration of detection efficiency for the detector.
Symposium of Sino-German GDT
2013/4/1137Slide38
Steps to Calibrati detection efficiency of n
Symposium of Sino-German GDT2013/4/11
38A known γ
HpGe detector
Radioactivity measurement of Gamma source
Neutron radioactivity
Calibrating neutron detector
γ
/n is known for
AmBe
Source Slide39
SummeryDesign Detector, finishedFabrication, finishedEnergy calibration, almost finished
Efficiency calibration, in workMeasure the neutron flux, in recent future2013/4/11
Symposium of Sino-German GDT39Slide40
Thank you!
Symposium of Sino-German GDT2013/4/11
40