Billebaud, A.

Brissot, R.

Le Brun, C.

Liatard, E.

Vollaire, J.

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Calibration and monitoring of the GENEPI neutronsource for the MUSE IV experimentJ. Vollaire, A. Billebaud, R. Brissot, C. Le Brun, E. LiatardTo cite this version:J. Vollaire, A. Billebaud, R. Brissot, C. Le Brun, E. Liatard. Calibration and monitoring ofthe GENEPI neutron source for the MUSE IV experiment. 2003, pp.1-6. <in2p3-00013998>HAL Id: in2p3-00013998http://hal.in2p3.fr/in2p3-00013998Submitted on 17 Sep 2003HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.Calibration and Monitoring of the GENEPI Neutron Sourcefor the MUSE IV ExperimentJVollaire ABillebaud RBrissot CLe Brun ELiatardLaboratoire de Physique Subatomique et de Cosmologie INPCNRSUJFINPG av des Martyrs 	 Grenoble CedexJune  In order to characterize the neutron source produced by the GENEPI accelerator with the titaniumtritium TiT target an irradiation experiment was performed in January  in the SC con	guration of MASURCA with all the rods inserted During the irradiation the LPSC acquisition systemwas used to monitor the number of pulses and the recoil particles produced by the reactions inducedby the deuteron beam Experimental SetupFive natural nickel foils were symmetrically disposed in the holes of the PSI target holder and a vanadium foil was added to the central nickel foil 	gure a The target holder was inserted as closeas possible to the tritium target of GENEPI in the axial experimental channel of the tube E 	gure b3.1 cm5.08 cm2.2 cmBeam guidetritium targetE 19 - 185.5 cmFuelGENEPI Beam guide Fuel5.5 cm5.5 cm5.5 cmφ=8.4mmNitritium target3.1 cmOz( a ) ( b )12345NorthSouthLeadVa  Ni Target holder Figure  Foil locations a ZY cut b XY cut in the median planeGENEPI was operated at a repetition rate of  kHz with the deuteron energy set to ~~ kV duringthe  hours and ~~ minutes of the run Simultaneously to the foil irradiation two solid state silicondetectors located in the rear side of the deection magnet chamber were used to monitor the particlesemitted backward and associated to the reactions induced by deuterons impinging the target Thisdetection allows an indirect monitoring of the source neutrons whose number will be impossible tomeasure when the experiments are running The location of these Si detectors allows to measure thealphaparticles created by the TdnHe reactions and emitted at in the laboratory system Thesecharged particles have an energy of  MeV Are also detected the  MeV protons coming fromthe DdpT reactions that occur because of the continuous deuteron implantation into the targetBoth kinds of particles go back against the ow of deuterons in the beam guide and because they haveroughly the same magnetic rigidity they are deected by the magnet to be 	nally detected togetherunder the same solid angle see 	gure  The discrimination between protons and alphaparticleswhich have almost the same energy is done by covering one of the two detectors with a thin Al foil m which suppresses the alphaparticles in this detectorFigure  Recoil particle detection in GENEPI magnet chamberThis detector is usually used to monitor the deuterium target With the tritium target the protondetection can be useful to estimate the importance of the DdnHe reactions which occur about asoften as the DdpT reactions and therefore allows an estimation of the  MeV parasitic neutronsource Absolute Calibration MethodThe foil activation technique was used to measure the absolute number of neutrons produced per pulseTo do so one vanadium and 	ve nickels foils were used they were  mm in diameter and  mmthickThe four reactions considered are listed in table  and their respective cross sections are shownin 	gure Foil ReactionNickelNinnpCoNickelNinpCoNickelNinnNiVanadiumVanScTable  Reactions of interest for the activation measurementThe activity of the dierent radioisotopes produced by the irradiation of the foils was measured in theLow Activity Lab of the LPSC using a low background germanium detector The number of neutronsper pulse nis deduced from the measured activity using the formulanAii f exptirradwhere Aiis the measured activity of the radioisotope i iis the number of reactions occuring in thefoil per source neutron  f is the repetition rate of the GENEPI source iis the decay constant ofradioisotope i and tirradthe irradiation timeE [eV]10 5 10 6 10 7Cross section [barn]10-410-310-210-11JEF22 at 300.0 K  n,2nσNi: 2858 JEF22 at 300.0 K  n,npσNi: 2858 JEF22 at 300.0 K  n,pσNi: 2858 JENDL3 at 300.0 K  αn,σV : 2351 Figure  Cross sections of the reactions listed in table The number of reactions in the foil per source neutron iis deduced from a MCNP calculation madewith a precise description of the geometrical con	guration based on the 	gure  and the assumed shapeof the deuteron beam ellipsoidal shape     cm and using nuclear data bases cross sections forthe dierent reactions The calculation pointed out the importance of the neutron emission locationspecially for reactions characterized by high energy thresholds when foils are very close to the tritiumtarget Figure a shows the dependence of the measured activity with respect to the foil location forsome reactions and 	gure b gives the number of neutron per pulse deduced from the relation and these measurementsThe fact that the number of neutrons per pulse does not depend on the position of the foil indicatesthat the neutron transport is well simulated by the MCNP calculation On the other hand there isan important discrepancy on the value of ndepending on the reaction considered The cross sectionof theNinnNi reaction leads to a reaction rate in the foils which seems too important and thusthe calculated value of nis lower than for the others reactions This discrepancy may come from theimportant variation of these cross section in the energy range of the source neutrons around  MeVwhose distribution depends strongly on the transport calculation ResultFinally the chosen value for the neutron production is the average of the ones obtained with theNinpCo reactions and theVanSc reactions and is equal to   neutrons per0 1 2 3 4 5 605101520Activity ( Bq )Ni 58 (n,np) Co 57Ni 58 (n,p) Co 58Va 51 (n,α) Sc 480 1 2 3 4 5 6foil location number01e+062e+063e+064e+065e+06Ni 58 (n,np) Co 57Ni 58 (n,p) Co 58Ni 58(n,2n) Ni 57Va 51 (n,α) Sc 48foil location number(a) (b)neutrons per burst n0Figure  a Measured activitiesb Number of neutrons per pulsepulse for the present TiT target This value corresponds to the target activity on the ndof January initial activity  Ci at loading in November  under standard and optimized deuteron beamintensity  mA peak current  oscilloscope measurement Parasitic  MeV Neutron SourceThe number of protons detected during the irradiation run corresponding to reactions occuring on thedeuterium implanted into the target can give an estimation of the  MeV neutron production asthis reaction occurs about as often as the one producing neutrons If we assume that the tramsmissionof protons and alphaparticles is roughly the same we will see that this assumption holds in section we can estimate the fraction of this parasitic source to  of the total number of source neutronswhich will have no signi	cant eect on the total energy spectrum of the source Online Monitoring of the Source Source Intensity MonitoringThe intensity of the  MeV source along the MUSE IV experimental programme will be monitoredusing the detection of alphaparticles to do so the number of alphaparticles detected must be correlated to the number of neutrons produced by the source Consequently the monitoring detectors wererecorded during the foil irradiation The amplitude distribution measured by the silicon detector isshown in 	gure  Peaks corresponding to the simultaneous detection of one or several alphaparticlesor protons  leading to pileup events  are clearly seenThus the total number of alphas particles detected is easily calculated taking into account the multiplicity of each peak NTot i	ini The number of alphaparticles detected per pulse of deuteriumions is found equal to  Finally for the experimental conditions described in section  the ratioof alphaparticles counted in the silicon detector per neutron produced by the TiT target is equal toNn    This value will be used for future online monitoring of the source withoutforgetting that it depends on GENEPI tuningChannel number0 500 1000 1500 2000 2500 3000 3500 4000Counts101021031041051 alpha 2 alphas 3 alphas 4 alphasFigure  Multiplicity distribution of recoil particles Time Shape of the Neutron PulseThe time shape of the neutron pulse is obtained from the time distribution of the alpha particles inthe silicon detector Figure a shows on a logarithmic scale the spectrum for all particles impingingthe silicon detector Two main peaks are seen The small one on the left side corresponding tothe shorter time of ight of the particles corresponds to the detection of protons coming from dDparasitic reactions occuring in the magnet chamber and due to deuteron implantation in the magnetwalls The main peak at longer times of ight is due to events occuring in the target The distributionshown in 	gure b was obtained by selecting the two alphas events see 	gure  in order to avoidparasitic events A Gaussian 	t performed on this time distribution gives a value of    ns whichcorresponds to a FWHM   ns for a standard GENEPI pulseChannel number ( 100 ns per channel )0 20 40 60 80 100Counts10-410-310-210-1100.050.10.150.20.25Channel number ( 100 ns per channel )FWHM(b)(a)0 20 40 60 80 100Figure  Time spectrum of the particle emitted backward Amplitude Distribution of the Deuteron Pulse IntensityThe distribution of the integral value of the deuteron current pulse shown in 	gure  gives a reliableidea of the uctuation of the beam intensity of pulses during a 	ve hours run The small peak on theleft side corresponds to the two beam losses which occurred during the run The distribution followsa gaussian shape characterized by a relative dispersionII  which con	rms the good stability ofthe machine and the reproducibility of the pulseChannel number 0 200 400 600 800 1000Counts0.0020.0060.010.014∆IIFigure  Amplitude distribution of the integrated deuteron pulse current Neutron Production and Monitoring with the Deuterium TargetThe 	rst titanium deuterium target TiD installed in GENEPI in November   mg of deuterium was also the subject of a calibration experiment performed on the thof April  Theexperiment consisted in the irradiation of  nickel foils in a way very similar to that described aboveThe result of the absolute calibration of the source was neutrons per pulse for a  mApeak current oscilloscope measurement The source monitoring done in this case by the two detectors both of them receiving only protons gave proton detected per pulse leading toproton per source neutron We can notice that this transmission factor is rather closeto the one of alphaparticles as expected apart from the focalization conditions which are optimizedbut might have changed during the  years of operation ConclusionFrom this irradiation experiment the source characteristics were obtained with a good accuracy Theabsolute value of the neutron source was measured but also the relation between the online monitoringand the source To follow more precisely the source evolution in time another irradiation will beperformed before the target removal scheduled in June This future irradiation will be a good way tocheck that this method is relevant for the monitoring of the neutron production AcknowledgmentsThe authors are very grateful to CDestouches for his help during the running of these experimentsand would like to thank the MASURCA and GENEPI operating teams and especially MFruneauPChaussonnet and JMLaurens

Calibration and monitoring of the GENEPI neutron source for the MUSE IV experiment

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