Abstract

AbstractNEUTRON SPECTROMETER BASED ON PROPORTIONAL RECOIL PROTONS COUNTER WITH POSSIBILITY OF -BACKGROUND DISCRIMINATIONY. I. Vinogradov, A.M. Shvetsov, O. P. Vikhlyantsev, A.V. KuryakinRussian Federal Nuclear Center, All-Russian Research Institute of Experimental Physics, Sarov, Russia, Email: [email protected] 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- fields has been limited by energy 0.5 MeVThe carried out researches [3] have shown possibility of discrimination of impulses of the counter from neutrons and -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 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 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:KuvshinovM.I., ShvetsovA.M., EgorovV.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 1620, 1996 / Japan Atomic Energy Research Institute Inc., Japan. 1996. Vol. 2. P.338346.ShvetsovA.M., EgorovV.P., FomushkinE.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 1823, 1997 / Italian Phis. Soc. Inc., Bologna, Italy. 1997. Part 2. P.13591361.A. M. Shvetsov, Yu. I. Vinogradov, O. P. Vikhlyantsev, A. V. Kuryakin. Investigation of the possibility of -background discrimination in a neutron spectrometer with a proportional counter of recoil protons. // Bulletin of the Russian Academy of Sciences: Physics, 2007, .71, 12, .1748-1753.

Alexey Kuryakin, RFNC-VNIIEF, Sarov, Russia, [email protected]

Neutron detectorDesigned and used in VNIIEF for number of yearsProportional gas counter, ~14% efficiency , E/E~3.7%Range: 0.58 MeV without, or 0.058 MeV with n- discrimination~ 3 kV voltage, 3 bar methane (CH4 + some 3He uses for calibration)CAMAC based data acquisition, n spectra reconstruction softwareConstruction of proportional counter:1 glass isolation; 2 - cathode, 75 mm 1 m;3 anode, 40 m; 4 guard pipes; 5 spring for anode;6 - flanges, 7 fluoroplastic gaskets; 8 details from kovar (Fe+Co+Ni alloy)


Principle of energy calibrationGas counter contains some 3He for calibrationUse 3He(n,p)T reaction with peak E=0.764 MeV


Why need n- discrimination influent to low range spectra (E < 0.5 MeV) influence is difficult to calculate theoreticallyLow energy range limited to 0.5 MeV due to n+Some kind of n- discrimination required for E < 0.5 MeV


Principle of n- discriminationNeutrons produce recoil protonsquanta produce electronsHardware p, e pulses have different shapes (front timing)tfront, (dE/dt)max/Emax criteria can be used for n- separationEmax(dE/dt)maxtimeHardware pulse from counter channeltfrontTypical shape of pulse front registered with TDS-3000, 50 MHz


n- discrimination criteriaPreliminary study show that:tfront criteria is not good for n-(dE/dt)max/Emax criteria is good-quantumneutronsN,counts


n- discrimination efficiency and rangeFit [E,E+E] slice spectra with 2 log-normal distributionsFind S, Sn and cross (mutual overlap) S areasCriteria for n- low range is S/Sn100% < 5%This range depends on N/Nn[7080] keVslice spectraLow energy n- range (by 5% level) depends on N/Nn ratio.N/Nn= 2.5N/Nn= 0.7N/Nn= 0.3N/Nn= 0.2


Low energy n- range vs N/NnLow energy n- range (by 5% level) depends on N/Nn ratio.


n- discrimination testsn- discrimination tested with mixed n- and clear sourcesLow energy range without n- discrimination ~ 0.5 MeVLow energy range with n- discrimination ~ 6080 keV (depend on N/Nn)-quantumneutrons-quantum(dE/dt)max/Emax, s-1E,MeVE,MeVn+ source (252Cf) source (- )


n- discrimination hardwareCAMAC based data acquisition system designedHV high voltage unit (Canberra 3106D), PA charge sensitive 10 ns preamplifier (POLON 1105A), SA spectrometry 2 s 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.


SA

PA

Counter

FA

DU

ADC

Gate1

Gate1

CC

PC

ST

SD

CAMAC bus

HV

1

In.2

Gate2

2

In.1

In.2

In.1

Gate1

In.1

Gate1

In.2

Gate2

OR

Online software (data acquisition)CRW-DAQ package designed in VNIIEF, SarovRegistered in Russian Federation registry Data acquisition in List mode, 2-parameter eventsCAMAC based data acquisition, up to 60 kHz raten(dE/dX) maxE max


Offline softwarePreliminary spectrum processingEnergy calibration by 3He(n,p)T reactionn- discrimination, background subtractionResponse matrix calculation (SUPREMAC)Uses NDX, ENDF/B-VI nuclear constants databaseUses Monte-Carlo for response matrix calculationOptimized for performanceNeutron spectrum reconstruction (UFONIM)Ill-posed problem (Fredholm equations of 1st kind)Uses iteration method by TaraskoRandomization method to calculate stat. errorsDesigned in VNIIEF

G - response matrix,U n-spectrum to find,S hardware spectrum.


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