Transcript NEUTRON SPECTROMETER BASED ON PROPORTIONAL …

Abstract
NEUTRON SPECTROMETER BASED ON PROPORTIONAL RECOIL PROTONS COUNTER WITH
POSSIBILITY OF γ-BACKGROUND DISCRIMINATION
Y. I. Vinogradov, A.M. Shvetsov, O. P. Vikhlyantsev, A.V. Kuryakin
Russian Federal Nuclear Center, All-Russian Research Institute of Experimental Physics, Sarov, Russia, Email: [email protected]
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The neutron spectrometer with proportional recoil protons counter was developed in VNIIEF and used
for a number of years [1, 2]. The bottom range of measurements of the spectrometer in mixed n-γ fields
has been limited by energy 0.5 MeV
The carried out researches [3] have shown possibility of discrimination of impulses of the counter from
neutrons and γ -quanta by their shape and expansions of a range of measurement of neutron spectra in
the field of low energies to tens keV.
Then it has been developed hardware and the spectrometer software, allowing to register amplitude of an
impulse of the proportional counter and a maximum growth rate of an impulse on forward front and to
write down them in ListMode (a mode of consecutive record of parametres of impulses). The program
part includes a number of the service possibilities allowing to adjust registration equipment during
measurements (in on-line mode), to estimate visually the quality of discrimination of impulses from
neutrons and γ-quanta and to receive hardware spectra.
The complex of the programs is used for off-line mode analysis of the received data, which provides
processing of the list of the received data with discrimination of impulses, caused by neutrons and
γ-quanta, construction of corresponding hardware spectra, calculation of response matrix of the
proportional gas counter and reconstruction of spectra.
Research of possibilities of the spectrometer with n-g discrimination, spent on 252Cf source, has shown
that the bottom range of measurements of neutron spectra decreases till 60-80 keV.
Reference list:
1.
2.
3.
Kuvshinov M. I., Shvetsov A. M., Egorov V. P. et al. Measurement of neutron spectra for spherical critical assemblies of 235U(90 %), 235U(36 %), and 239Pu(98 %) //
Proceedings International Conference on the Physics of Reactors PHYSOR96, Mito, Ibaraki, Japan, September 16–20, 1996 / Japan Atomic Energy Research Institute
Inc., Japan. 1996. Vol. 2. P.338-346.
Shvetsov A. M., Egorov V. P., Fomushkin E. F. et al. Measurements of leakage neutrons spectra for spherical assemblies of 235U(90 %), 235U(36 %), and 239Pu(98 %) //
Proceedings International Conference on Nuclear Data for Science and Technology, Trieste, Italy, May 18–23, 1997 / Italian Phis. Soc. Inc., Bologna, Italy. 1997. Part
2. P.1359–1361.
A. M. Shvetsov, Yu. I. Vinogradov, O. P. Vikhlyantsev, A. V. Kuryakin. Investigation of the possibility of γ-background discrimination in a neutron spectrometer with a
proportional counter of recoil protons. // Bulletin of the Russian Academy of Sciences: Physics, 2007, т.71, № 12, с.1748-1753.
02.07.2010
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
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Neutron detector
Designed and used in VNIIEF for number of years
Proportional gas counter, ~14% efficiency , ΔE/E~3.7%
Range: 0.5÷8 MeV without, or 0.05÷8 MeV with n-γ discrimination
~ 3 kV voltage, 3 bar methane (CH4 + some 3He uses for calibration)
CAMAC based data acquisition, n spectra reconstruction software
02.07.2010
Construction of
proportional counter:
1 – glass isolation;
2 - cathode, Ø 75 mm
× 1 m;
3 – anode, Ø40 µm;
4 – guard pipes;
5 – spring for anode;
6 - flanges,
7 – fluoroplastic gaskets;
8 – details from kovar
(Fe+Co+Ni alloy)
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
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Principle of energy calibration
• Gas counter contains some 3He for calibration
• Use 3He(n,p)T reaction with peak E=0.764 MeV
15000
N, отсчет./канал
N,Counts
Thermal
Тепловойpeak
пик
10000
=3,66%
5000
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E(k ) 
0,764
(k  k )
k0  k
E=0,764 МэВ
0
0
0,0
20
k0
0,1
40
0,2
0,3
60
0,4
Δk
0,5
80
0,6
100
0,7
120
0,8
0,9
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
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Канал k
Channel,
1,0
1,1
E, МэВ
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Why need n-γ discrimination
γ influent to low range spectra (E < 0.5 MeV)
γ influence is difficult to calculate theoretically
Low energy range limited to 0.5 MeV due to n+γ
Some kind of n-γ discrimination required for E < 0.5 MeV
4
10
n+γ
3
10
N, отсч.
N,counts
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2
10
1
10
neutron counter spectra
n
(clean)
0
10
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
E,
МэВ
E,MeV
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
4.5
5.0
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Principle of n-γ discrimination
0,8
0,6
U, В
• Neutrons produce recoil protons
• γ–quanta produce electrons
• Hardware p, e pulses have different shapes
(front timing)
• tfront, (dE/dt)max/Emax criteria can be used for
n-γ separation
Typical shape
of pulse front
0,4
registered with
TDS-3000, 50 MHz
0,2
Hardware pulse from counter channel
0,0
0,190
0,192
0,194
0,196
0,198
0,200
0,202
0,204
0,206
-4
0,6
Emax
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t, *10 с
0,5
(dE/dt)max
U, В
0,4
Typical
hardware
signal from
gas detector
0,3
0,2
0,1
tfront
time
0,0
0,05
0,10
0,15
0,20
0,25
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
0,30
0,35
0,40
0,45
0,50
-4
t, *10 с
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n-γ discrimination criteria
Preliminary study show that:
• tfront criteria is not good for n-γ
• (dE/dt)max/Emax criteria is good
2000
1500
Нейтроны
neutrons
N, соб.
N,counts
-кванты
γ-quantum
1000
500
0
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0.2
0.4
0.6
0.8
1.0
1.2
1.4
(dE/dt)max/E
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
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n-γ discrimination efficiency and range
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Fit [E,E+ΔE] slice spectra with 2 log-normal distributions
Find Sγ, Sn and cross (mutual overlap) ΔS areas
Criteria for n-γ low range is ΔS/Sn·100% < 5%
This range depends on Nγ/Nn
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Nγ/Nn= 2.5
[70÷80] keV
slice spectra
Nγ/Nn= 0.7
Nγ/Nn= 0.3
Nγ/Nn= 0.2
Low energy n-γ range (by 5%
level) depends on Nγ/Nn ratio.
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
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Low energy n-γ range vs Nγ/Nn
0,085
Eпор, МэВ
E
n-γ(0.05),MeV
0,080
0,075
0,070
Low energy n-γ range (by 5%
level) depends on Nγ/Nn ratio.
0,065
0,060
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0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6
N/Nn
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
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n-γ discrimination tests
• n-γ discrimination tested with mixed n-γ and clear γ sources
• Low energy range without n-γ discrimination ~ 0.5 MeV
• Low energy range with n-γ discrimination ~ 60÷80 keV (depend on Nγ/Nn)
0.50
n+γ – source (252Cf)
0.50
0.45
0.45
0.40
neutrons
Нейтроны
0.35
0.35
0.30
0.30
γ-quantum
Гамма-кванты
E,MeV
E, МэВ
E, МэВ
E,MeV
0.40
0.25
0.20
0.25
0.15
0.10
0.10
0.05
0.05
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0.5
1.0
1.5
2.0
(dE/dt)max/Emax,
2.5
µs-1
Гамма-кванты
γ-quantum
0.20
0.15
0.00
0.0
γ – source (СОСГИ-М )
0.00
0.0
0.5
1.0
1.5
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
2.0
2.5
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n-γ discrimination hardware
• CAMAC based data acquisition system designed
Counter
PA
SA
In.1
Gate1
HV
ADC
SD
Gate1
FA
ST
HV – high voltage unit (Canberra 3106D), PA – charge
sensitive 10 ns preamplifier (POLON 1105A), SA –
spectrometry 2 µs amplifier (Canberra 2025), DU –
discriminator unit (Canberra 2035A), SD – logic shaper
and delay (Canberra 2055), FA – fast amplifier
(Canberra 2111), ST – stretcher (ORTEC 242), ADC –
13 bit analog to digital converter (ORTEC AD 413A),
C1,C2 – counter (POLON 420A), OR – output register
(POLON OR350), CC – CAMAC controller (PKK4,
VNIIEF designed), PC – personal computer for data
acquisition with CRW-DAQ control software by VNIIEF.
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In.2
CAMAC bus
DU
In.1
Gate1
In.2
С1
Gate2
PC
In.1
Gate1
In.2
С2
Gate2
OR
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
CC
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Online software (data acquisition)
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CRW-DAQ package designed in VNIIEF, Sarov
Registered in Russian Federation registry 
Data acquisition in List mode, 2-parameter events
CAMAC based data acquisition, up to 60 kHz rate
02.07.2010
(dE/dX) max
n
γ
E max
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
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Offline software
• Preliminary spectrum processing
– Energy calibration by 3He(n,p)T reaction
– n-γ discrimination, background subtraction
• Response matrix calculation (SUPREMAC)
– Uses NDX, ENDF/B-VI nuclear constants database
– Uses Monte-Carlo for response matrix calculation
– Optimized for performance
• Neutron spectrum reconstruction (UFONIM)
m
– Ill-posed problem (Fredholm equations of kind)
– Uses iteration method by Tarasko
– Randomization method to calculate stat. errors
1st
 GijU j  Si
j 1
G - response matrix,
U – n-spectrum to find,
S – hardware spectrum.
U k( m1)  U k( m)  
i
Si Gik
 GijU (jm)
j
• Designed in VNIIEF
02.07.2010
Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]
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