PoS(Baldin ISHEPP XXII)054

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1 Study of cross-sections of yttrium (n,xn) threshold rections P. Chudob, V. Wgner, J. Vrzlov, O. Svobod, M. Suchopr, M. Mjerle, M. Stefnik, A. Kugler Nucler Physics Institute of the ASCR, v. v. i. Rez 130, Rez, Czech Republic E-mil: S. Kilim, M. Bielewicz, E. Struglsk-Gol, M. Szut Ntionl Centre for Nucler Reserch Otwock-Swierk , Polnd E-mil: Currently the development of the nucler systems is heding to systems with fst neutrons insted of therml ones. Such systems re minly fst rectors of genertion IV fmily nd ccelertor driven systems. Unfortuntely the possibilities of monitoring fst neutrons re limited. One of the possible principles is to use ctivtion detectors. It hs shown up tht yttrium is very good cndidte to ct s the ctivtion detector of the fst neutrons. The dvntges of yttrium re nmely its (n,xn) threshold rections nd the fct tht its only one nturlly occurring isotope. To be possible to use yttrium s the ctivtion detector it is necessry to know the cross-sections of the (n,xn) rections sufficiently good. This condition is fulfilled only in cse of the 89 Y(n,2n) 88 Y rection. For higher orders of rections there re lmost no experimentl dt. For this reson series of experiment were mde using qusi mono-energetic neutron source bsed on the rection of protons with 7 Li trget t Nucler Physics Institute of ASCR in Rez. Specil ttention ws pid to the 89 Y(n,3n) 87 Y rection. In this cse the nuclei re produced both in the ground stte nd in the isomeric stte. The hlf-lives re 79.8 hours for the ground stte nd hours for the isomeric stte. The isomeric stte decys minly through the gmm trnsition to the ground stte. The bet decy of the isomeric stte is within our ccurcy negligible. The cross-sections of both cses of products were nlyzed nd compred with existing experimentl dt, clculted models nd evluted vlues. XXII Interntionl Bldin Seminr on High Energy Physics Problems, September 2014 JINR, Dubn, Russi PoS(Bldin ISHEPP XXII)054 Speker. c Copyright owned by the uthor(s) under the terms of the Cretive Commons Attribution-NonCommercil-ShreAlike Licence.

2 Study of cross-sections of yttrium (n,xn) threshold rections P. Chudob 1. Introduction nd motivtion Monitoring of neutron fields is n importnt tsk for dvnced nucler systems. These systems re minly Genertion IV rectors, ccelertor driven systems (ADS) nd possibly fusion rectors. Good cndidtes for such monitoring of the neutron fields re ctivtion detectors. The principle is utiliztion of (n,xn) rections. In cse of fst rectors of Genertion IV nd fusion rectors the (n,2n) rection is suitble nd the cross-sections re in mny cses well-known. Different sitution is in cse of the ADS the neutron energy cn be in order of hundreds MeV. Therefore it is necessry to know the cross-sections of higher orders of the (n,xn) rections. Unfortuntely the knowledge of the cross-sections of higher orders of the rections is insufficient. Yttrium is good cndidte for the ctivtion detector of fst neutrons. It hs been strted to be used within the collbortion Energy&Trnsmuttion of Rdioctive Wste. An experimentl setup of the ADS is used within the frmework of this collbortion. This setup is clled QUINTA. Yttrium is widely used to monitor neutron flux in the vrious plces inside the QUINTA setup. Unfortuntely the knowledge of the cross-section of yttrium (n,xn) rections re sufficiently known only for the (n,2n) rection. For the (n,3n) rection only three points of the cross-section were published in EXFOR. Therefore in coopertion with Polish group we hve decided to mesure the cross-sections of (n,2n) nd (n,3n) rections with neutron energies 17.4, 24.5, 24.8, 27.9, 28.7, 30.0, 32.5 nd 33.5 MeV. Preliminry cross-sections re shown in this rticle. 2. Irrdition nd mesurements The irrdition hs tken plce t the Nucler Physics Institute of the ASCR in Řez. The yttrium smples were irrdited using qusi-monoenergetic neutron (QM) source [1] mounted on cyclotron U-120M. The QM neutron source works on principle of production of the QM neutrons trough rection 7 Li(p,n) 7 Be nd the neutron flux is in order of 10 8 cm 2 s 1. The neutron spectrum is chrcteristic with its QM pek nd the low energy continuum. Ech prt of the spectrum contins pproximtely 50% of the produced neutrons. The spectrum is determined by mens of n MCNPX [2] simultion. Two smples of yttrium were irrdited during ech irrdition. Ech yttrium smple ws irrdited together with the gold smple in the sme geometry. We hve evluted dt from both mterils nd compred the cross-section dt from gold smples with dt from the EXFOR dtbse. Gold hs well mesured rection 197 Au(n,2n) 196 Au nd for this reson it hs been used to ct s neutron monitor. After the irrdition the smples were mesured in γ-spectroscopic lbortory. The mesurements were conducted on spectrometer bsed on HPGe detector. Following formul [4] ws used for determintion of the yields from the peks res. N yield = S p C bs (E) I γ ε p (E) COI C re t rel t live 1 m f oil e λ t0 1 e λ t rel λ t irr 1 e λ t irr, (2.1) where S p the pek re, C bs self-bsorption correction, I γ γ-line intensity, ε p (E) detector efficiency, COI true coincidences correction, C re squre-emitter correction, t rel t live ded time correction, m f oil mss of the smple. The lst two frctions represents corrections for decy during cooling nd mesurement nd decy during irrdition respectively. Uncertinty cused PoS(Bldin ISHEPP XXII)054 2

3 Study of cross-sections of yttrium (n,xn) threshold rections P. Chudob by the used corrections ws estimted to be less thn 1%. Only the uncertinty coming from the efficiency clibrtion is not worst thn 3%. An upper limit of combined uncertinty cused by the neutron spectrum determintion nd the bckground subtrction procedure ws determined to be 10%. With the knowledge of the yield (2.1) we cn clculte cross-section using following eqution σ = N yield S A N n N A, (2.2) where S the foil re, A molr weight, N n number of neutrons in pek, N A Avogdro s number. 3. Low energy neutron bckground subtrction Since the neutron spectrum contins besides the QM neutron pek the lower energy til it is necessry do subtrct the contribution of the lower energy neutrons to the yield of mesured isotope. For this purpose bckground subtrction procedure [3] is used. This procedure is bsed on folding of the neutron spectr nd the excittion function ccording to formul C bgr = Pek Spectrum σ(e) N(E)dE σ(e) N(E)dE = σ i N i i Pek i Spectrum σ i N i (3.1) where σ(e)(σ i ) excittion function (binned excittion function) nd N(E)(N i ) neutron spectrum (binned neutron spectrum). The binned version of definition is used becuse the neutron spectrum from the MCNPX simultion is produced in binned form with bin width of 250 kev. The procedure hs n dvntge tht it is independent on the bsolute vlues of the excittion function. It depends only on the shpe in wy tht if the shpe is wrong, thn the results diverge from it in opposite direction. Using this knowledge it is possible to check the vlidity of the bckground subtrction. The excittion functions were tken either from EAF-2010 dtbse [5] or clculted with TALYS-1.4 [6]. From the principle of the procedure, the gold smples nd results from rection 197 Au(n,2n) 196 Au ct s vlidtion of the neutron spectr shpe. 4. Cross-section results Preliminry cross-section results re shown in this section. The cross-sections re still preliminry due to discussion bout uncertinties within our group. But ll necessry corrections were involved. Therefore there shouldn t be ny significnt chnges in the results. The cross-sections of the yttrium nd gold (n,xn) rections re shown in the figure 1 nd 2 respectively. The grphs shows dt from current experiment together with currently known dt from the EXFOR dtbse nd excittion functions from EAF-2010 nd excittion functions clculted by TALYS 1.4. PoS(Bldin ISHEPP XXII)054 3

4 Study of cross-sections of yttrium (n,xn) threshold rections P. Chudob e t p x E y yp y p u sf s lf l F lt lo lx ls l T O X s C -] r yg p E Ep x 3 3 C -] r yg p E Ep x C -b r yy yx yt yx y y X t x y E x ymx i y 3 3 C -] r yg e F X d t p x E y p E Ep x Figure 1: Preliminry results of the 89 Y(n,2n) 88 Y nd 89 Y(n,3n) 87 Y rections. 6 s C iy] o iy] l s u X 6 sm C iym s sf u uf X u sf s lf l F 6 s C iy] l s u X lnX 1 msl 2 2 Figure 2: Preliminry results of the 197 Au(n,2n) 196 Au nd 197 Au(n,4n) 194 Au rections. In both cses the dt shows good greement with the existing experimentl dt. In cse of the 89 Y(n,3n) 87m Y rection there is possible to see differences in bsolute vlues between the experimentl, clculted nd dtbse dt, however the shpes re gin in good greement. PoS(Bldin ISHEPP XXII)054 4

5 Study of cross-sections of yttrium (n,xn) threshold rections P. Chudob 5. Conclusion We hve mesured cross-sections of the (n,2n) nd (n,3n) rections on yttrium nd (n,2n) nd (n,4n) on gold. In cse of the (n,3n) rection on yttrium nd (n,2n) rection on gold we hve seprted the cross-sections of isomeric sttes. These dt re unique in the mesured energy region. The greement of our results with currently known dt shows good pplicbility of described method nd good knowledge of the neutron spectr of the QM neutron source. It is possible to see it minly in the cses of 197 Au(n,2n) 196 Au+ 196m Au nd 89 Y(n,2n) 88 Y rections where for the highest neutron energies the yield produced by the bckground neutrons exceeds the yield produced by the QM pek. 6. Acknowledgments At this plce, we would like to thnk the personnel of fst neutron genertors t the NPI nd the NPI cyclotron stff for excellent bem qulity nd service. The reserch hs been conducted t the CANAM (Center of Accelertors nd Nucler Anlyticl Methods LM ) infrstructure with funding from the Ministry of Eduction, Youth nd Sports of the Czech Republic. Prt of the experiment ws supported by ERINDA. References [1] P. Bem et l., The NPI cyclotron-bsed fst neutron fcility, in: Interntionl Conference on Nucler Dt for Science nd Technology 2007, [2] D.B. Pelowitz (Ed.), MCNPX User s Mnul Version 2.7.0, LA-CP , LANL, [3] O. Svobod, Experimentl study of neutron production nd trnsport for dtt, Disserttion thesis, Czech Technicl University in Prgue (2011), [4] V. Wgner et l., Mesurement of neutrons in different Pb/U setups irrdited by reltivistic protons nd deuterons by mens of ctivtion smples, in: Proceedings of the XIX Interntionl School on Nucler Physics nd Applictions, Journl of Physics: Conference Series 366, Vrn, Bulgri, [5] J.-Ch. Sublet et l., The Europen Activtion File: EAF-2010 neutron-induced cross section librry, CCFE Report, 2010, CCFE-R (10) 05. [6] A. J. Koning, S. Hilire, M. C. Duijvestijn, Tlys-1.0, in: O. Bersillon, F. Gunsing, E. Buge, R. Jcqmin, S. Lery (Eds.), Proceedings of the Interntionl Conference on Nucler Dt for Science nd Technology, April 22 to April 27, 2007, Nice, Frnce, EDP Sciences, PoS(Bldin ISHEPP XXII)054 5

Available online at ScienceDirect. Physics Procedia 59 (2014 )

Available online at ScienceDirect. Physics Procedia 59 (2014 ) Available online at www.sciencedirect.com ScienceDirect Physics Procedia 59 (24 ) 4 8 GAMMA-2 Scientific Workshop on the Emission of Prompt Gamma Rays in Fission and Related Topics Measurement of cross-sections