Measurement of the 90,91,92,93,94,96-Zr(n,gamma) and 139-La(n,gamma) cross sections at n TOF

In e na ional Con e ence on Nuclea Da a o Science and Technology 2007 DOI: 10.1051/nda a:07732 Measu emen o he 90,91,92,93,94,96Z (n,γ)and139La(n,γ) c oss sec ions a n TOF G. Taglien e1,a, U. Abbondanno2,G.Ae s 3,H. ´ Al a ez4,F. ´ Al a ez-Vela de5, S. And iamonje3, J. And zejewski6, P. Assimakopoulos†7, L. Audouin8, G. Badu ek9, P. Baumann10,F.Be ˇ c ´ aˇ 11, E. Be houmieux3, F. Cal i˜ no12, M. Cal iani13,14, D. Cano-O 5, R. Capo e15,16, C. Ca apic¸o17,3, P. Cennini18, V. Chepel19,E.Chia e i 18, N. Colonna1, G. Co es20, A. Cou u e21,J.Cox 21,M.Dahl o s 18,S.Da id 8, I. Dillmann22, C. Domingo-Pa do23,22,W.D idi 3, I. Du an4, C. Ele he iadis24,M.Embid-Segu a 5, L. Fe an †8, A. Fe a i18, R. Fe ei a-Ma ques19,K.Fujii 2,W.Fu man 25, I. Goncal es19, E. Gonz´ alez-Rome o5, F. G amegna13,C.Gue e o 5, F. Gunsing3,B.Haas 26, R. Haigh 27,M.Heil 22, A. He e a-Ma inez18,M.Igashi a 28, E. Je icha9,F.K ¨ appele 22,Y.Kadi 18, D. Ka adimos7, D. Ka amanis7, M. Ke eno10, P. Koehle 29, E. Kossionides30,M.K i ˇ cka11, C. Lampoudis24,3,H.Leeb 9, A. Lindo e19, I. Lopes19, M. Lozano16, S. Lukic10, J. Ma ganiec6, S. Ma one1,T.Ma ´ ınez5, C. Massimi31, P. Mas inu13, A. Mengoni15,18, P.M. Milazzo2, C. Mo eau2, M. Mosconi22,F.Ne es 19, H. Obe humme 9,S.O’B ien 21, J. Pancin3, C. Papach is odoulou7, C. Papadopoulos32, C. Pa adela4, N. Pa onis7, A. Pa lik33, P. Pa lopoulos34, L. Pe o 3,M.T.Pigni 9,R.Plag 22, A. Plompen35, A. Plukis3, A. Poch20, J. P aena13,C.P e el 20, J. Quesada16, T. Rausche 36,R.Rei a h 27, C. Rubbia37, G. Rudol 10, P. Rullhusen35, J. Salgado17, C. San os17, L. Sa chiapone18, I. Sa idis24, C. S ephan8,J.L.Tain 23, L. Tassan-Go 8, L. Ta o a17, R. Te lizzi1, G. Vannini31,P.Vaz 17, A. Ven u a38, D. Villama in5, M.C. Vincen e5, V. Vlachoudis18,R.Vlas ou 32,F.Voss 22, S. Wal e 22, M. Wiesche 21, and K. Wisshak22 The n TOF Collabo a ion (www.ce n.ch/n o ) 1Is i u o Nazionale di Fisica Nuclea e, Ba i, I aly – 2Is i u o Nazionale di Fisica Nuclea e, T ies e, I aly – 3CEA/Saclay-DSM/DAPNIA, Gi -su -Y e e, F ance – 4Uni e sidade de San iago de Compos ela, Spain – 5Cen o de In es igaciones Ene ge icas Medioambien ales y Tecnologicas, Mad id, Spain – 6Uni e si y o Lodz, Lodz, Poland – 7Uni e si y o Ioannina, G eece – 8Cen e Na ional de la Reche che Scien i ique/IN2P3-IPN, O say, F ance – 9A omins i u de ¨ Os e eichischen Uni e si ¨ a en, Technische Uni e si ¨ a Wien, Aus ia – 10Cen e Na ional de la Reche che Scien i ique/IN2P3-IReS, S asbou g, F ance – 11Cha les Uni e si y, P ague, Czech Republic – 12Uni e sidad Poli ecnica de Mad id, Spain – 13Is i u o Nazionale di Fisica Nuclea e, Labo a o i Nazionali di Legna o, I aly – 14Dipa imen o di Fisica, Uni e si ` a di Pado a, I aly – 15In e na ional A omic Ene gy Agency (IAEA), Nuclea Da a Sec ion, Vienna, Aus ia – 16Uni e sidad de Se illa, Spain – 17Ins i u o Tecnol´ ogico e Nuclea (ITN), Lisbon, Po ugal – 18CERN, Gene a, Swi ze land – 19LIP-Coimb a & Depa amen o de Fisica da Uni e sidade de Coimb a, Po ugal – 20Uni e si a Poli ecnica de Ca alunya, Ba celona, Spain – 21Uni e si y o No e Dame, No e Dame, USA – 22Fo schungszen um Ka ls uhe GmbH (FZK), Ins i u ¨ u Ke nphysik, Ge many – 23Ins i u o de F´ ısica Co puscula , CSIC-Uni e sidad de Valencia, Spain – 24A is o le Uni e si y o Thessaloniki, G eece – 25Join Ins i u e o Nuclea Resea ch, F ank Labo a o y o Neu on Physics, Dubna, Russia – 26Cen e Na ional de la Reche che Scien i ique/IN2P3-CENBG, Bo deaux, F ance – 27Los Alamos Na ional Labo a o y, New Mexico, USA – 28Tokyo Ins i u e o Technology, Tokyo, Japan – 29Oak Ridge Na ional Labo a o y, Physics Di ision, Oak Ridge, USA – 30NCSR, A hens, G eece – 31Dipa imen o di Fisica, Uni e si ` a di Bologna, and Sezione INFN di Bologna, I aly –32Na ional Technical Uni e si y o A hens, G eece – 33Ins i u ¨ u Iso open o schung und Ke nphysik, Uni e si ¨ a Wien, Aus ia – 34Pˆ ole Uni e si ai e L´ eona d de Vinci, Pa is-La D´ e ense, F ance – 35CEC-JRC-IRMM, Geel, Belgium – 36Depa men o Physics - Uni e si y o Basel, Swi ze land – 37Uni e si ` a degli S udi Pa ia, Pa ia, I aly – 38ENEA, Bologna, I aly Abs ac . Neu on cap u e c oss sec ions o Z and La iso opes ha e impo an implica ions in he ield o nuclea as ophysics as well as in he nuclea echnology. In pa icula he Z iso opes play a key ole o he de e mina ion o he neu on densi y in he He bu ning zone o he Red Gian s a , while he 139La is impo an o moni o he s-p ocess abundances om Ba up o Pb. Z is also la gely used as s uc u al ma e ials o adi ional and ad anced nuclea eac o s. The nuclea esonance pa ame e s and he c oss sec ion o 90,91,92,93,94,96Z and 139La ha e been measu ed a he n TOF acili y a CERN. Based on hese da a he cap u e esonance s eng h and he Maxwellian-a e aged c oss sec ion we e calcula ed. 1 In oduc ion The neu on cap u e c oss sec ions o 90,91,92,93,94,96Z and 139La has been measu ed wi h high esolu ion a he n TOF acili y a CERN. The neu on cap u e measu emen o hese iso opes has a pa icula ele ance in he nuclea as ophysics, since he Z belongs o he i s s-p ocess peak in he sola abundance dis- ibu ion a N =50 while he La belongs o he second s-p o- aP esen ing au ho , e-mail: [email p o ec ed] cess peak a N =82. The 90Z and he 139La a e neu on magic and a e cha ac e ized, like he 91,92,93,94Z , by a low neu on cap u e c oss sec ion and a e p edomina ely o s-p ocess o igin. The mos neu on each Z s able iso ope, 96Z , is adi ionally conside ed o be an -only iso ope wi h a small s-p ocess admix u e e s. [1,2]. I s abundance is conside ed o be a s ong indica o in he efficiency o he 22Ne neu on sou ce du ing he He shell bu ning episodes o he mally pulsing AGB s a s. The lan hanum ac s as bo leneck be ween he abundan ligh n-cap u e elemen o he i s s-p ocess peak and he ©2008 CEA, published by EDP Sciences A icle a ailable a h p://nd2007.edpsciences.o g o h p://dx.doi.o g/10.1051/nda a:07732 1304 In e na ional Con e ence on Nuclea Da a o Science and Technology 2007 hea y elemen s om Sm up o Pb and Bi, i is e y im- po an o in e p e ing he elemen abundance pa e ns in e y old, me al poo s a s. Since he La abundance is com- ple ely ep esen ed by 139La i can be used o dis inguish he s-p ocess componen s om he p oduc s o explosi e - p ocess nucleosyn hesis, he s/ a io is o u mos impo ance o he gala ical chemical e olu ion. The majo mo i a ion o he p esen measu emen was o educe he unce ain ies o a ew pe cen , as equi ed o imp o e he s ella s-p ocess model. 2 Expe imen al se -up The measu emen s we e pe o med a he neu on ime-o - ligh (n TOF) acili y a CERN in a ange o ene gy be ween 1 eV and 1 MeV wi h a pulsed neu on beam. The neu ons we e gene a ed by spalla ion eac ions induced by a pulse o beam o 20 GeV p o ons impinging on a massi e lead a ge . The low epe i ion a e o he p o on beam d i e , he ex emely high ins an aneous neu on lux, he low back- g ound condi ions in he expe imen al a ea, oge he wi h imp o ed neu on sensi i i y o he γ- ay de ec o s make his acili y unique o neu on induced eac ion c oss sec ion measu emen s wi h high accu acy. The main cha ac e is ics o he acili y and appa a us a e epo ed in [3]. 2.1 De ec o s and da a acquisi ion The measu emen is based on he de ec ion o he γ ays emi - ed in he de-exci a ion cascade ollowing a neu on cap u e e en . Two C6D6de ec o s wi h minimized neu on sensi i i y [4], placed pe pendicula o he neu on beam a a dis ance o abou 3 cm om he beam axis, we e used o de ec he γ ays. The backg ound due o in-beam γ ays was educed by placing he de ec o s 9.2 cm ups eam o he sample posi ion. The ligh ou pu o he de ec o s was calib a ed by means o he 137Cs,60Co and Pu/Cγ- ay sou ces. The calib a ed neu on ime o ligh was used o de e mine he neu on ene gy. Measu ed ups eam o he cap u e samples wi h low mass lux moni o consis ing o a Myla oil 1.5µm in hickness wi h a laye o 200 µg/cm2o 6Li su ounded by ou silicon de ec o s ou side he neu on beam, measu ing he cha ged pa icles o he 6Li(n,α)3H eac ion [14]. The da a we e acqui ed wi h high equency lash ADC (FADC) using he s anda d n TOF da a acquisi ion sys em [5]. The aw da a we e eco ded signal by signal o a de ailed off-line analysis, which allows one o ex ac he equi ed in o ma ion on iming, cha ge, ampli ude and pa icle iden i ica ion, allowing in pa icula an efficien γ-n disc imina ion. 2.2 Samples The cha ac e is ic o he samples a e summa ized in able 1. The en iched Z samples we e p epa ed om oxide powde , an admix u e o H , Na, Mg, Al, Sn and Mo we e also p esen in he Z samples. The in luence o hose con aminan s, al hough small ( hei o al con amina ion was lowe han 1%), can no be neglec ed. Addi ional Au e e ence sample as well Table 1. Samples cha ac e is ics. The Z samples whe e in he Z O2 o m. Sample Diam. (mm) Mass (g) En ich. (%) 90Z 22 2.721 97.7 91Z 22 1.407 89.9 92Z 22 1.351 91.4 93Z 22 6.595 91.4 94Z 22 2.015 19.98 96Z 22 3.401 58.5 139Z 20 1.934 99.71 Fig. 1. Cap u e yield o he La sample and o al backg ound. Bo om: Indi idual backg ound componen s [8]. as a na u al C and 208Pb sample we e used o neu on lux no maliza ion in he measu emen s. The Au e e ence sample was used because he gold cap u e c oss sec ion is known wi h high accu acy, pa icula ly he sa u a ed esonance a 4.9 eV. The C and 208Pb samples we e used o de e mine he backg ound componen s ela ed o sample sca e ed neu ons and in-beam γ ays. 3 Da a analysis The main s eps o he da a analysis a e: an accu a e calib a ion o he C6D6de ec o s, ambien and sample ela ed back- g ounds de e mina ion and sub ac ion by means o he spec a measu ed wi h an emp y Al can, and wi h a Pb and C sample, he absolu e no maliza ion o he cap u e yields made wi h an accu acy o 3% ia he spec um measu ed wi h a Au sample. The efficiency co ec ion was pe o med wi h he Pulse Heigh Weigh ing Technique (PHWT) [6] applied o he C6D6cap u e da a in o de o achie e a cascade de ec ion independen o he pa icula de-exci a ion pa h. The espec i e weigh ing unc ions a e sensi i e o he expe imen al se -up, including he in es iga ed sample. These unc ions we e de i ed by de ailed Mon e Ca lo simula ions. Figu e 1 shows he cap u e yield o he 139La sample compa ed o he o al backg ound and he indi idual backg ound componen s. G. Taglien e e al.: Measu emen o he 90,91,92,93,94,96Z and 139La c oss-sec ions a n TOF 1305 Fig. 2. Ra io o he 90Z cap u e ke nels measu ed in n TOF wi h da a om Mughabghab compila ion. Finally, sys ema ic unce ain ies a e signi ican ly educed by he imp o ed n TOF se -up, which exhibi s much lowe neu on sensi i i y by he use o low-mass ca bon ib e cans o he liquid scin illa o de ec o s. In addi ion, he use o FADCs p o ides an efficien way o n/γ-disc imina ion. 4 Resul s Resonances obse ed we e analyzed in e ms o R-ma ix pa ame e s in he Reich-Moo e app oxima ion wi h he code SAMMY [8]. Due o he high ene gy esolu ion o he n TOF acili y many new esonances we e ound. The esonance pa ame e s measu ed a n TOF a e o all he Z samples in gene al 10–20% smalle han p e iously epo ed while o he La sample a e 10% lowe han ha epo ed in [9] and a ew pe cen lowe han ha epo ed in [10]. A possible expla- na ion o hese sys ema ic diffe ences can be due o a mo e eliable e alua ion o he PHWT, an accu a e ea men o he co ec ions o sel shielding, mul iple sca e ing and he effec o neu on ene gy esolu ion, and he use o he well es ed R-ma ix code SAMMY. Figu e 2 shows he compa ison o he neu on cap u e ke nels gΓγΓn/Γ o o he 90Z esonances wi h hose epo ed in he Mughabghab compila ion [11]. 4.1 Maxwellian a e aged cap u e c oss sec ion In o de o s udy he s-p ocess abundances, he Maxwellian a e aged c oss sec ions (MACS) a e equi ed o e a ange o he mal ene gies. The MACS we e calcula ed olding he cap u e c oss sec ion wi h a maxwellian dis ibu ion o he neu on luence in a wide ene gy ange (1 eV–550 keV). Since he n TOF da a co e pa o his spec um, only he pa ial con ibu ion o MACS can be accu a ely de e mined. To calcula e he MACS in he ull ene gy ange he JENDL c oss sec ion we e eno malized wi h espec o he n TOF da a. Figu e 3 shows he compa ison be ween he MACS calcula ed o he 96Z wi h n TOF da a and he JENDL 3.3 lib a y and igu e 4 shows he compa ison o MACS calcula ed o he 139La wi h n TOF da a and he one calcula ed om an FZK wi h ac i a ion me hod [15] and Fig. 3. Compa ison be ween he 96Z MACS calcula ed wi h n TOF da a and he JENDL3.3 da a. Fig. 4. Compa ison among he 139La MACS calcula ed wi h n TOF da a and FZK and Musg owe da a. Table 2. MACS calcula ed wi n TOF da a compa ed wi h ecom- mended alues o he p e ious da a. Iso ope n TOF Bao e al. [13] 90Z 18.1±121±2 91Z 51.6±260±8 92Z 29.7±233±4 94Z 27.6±126±1 96Z 7.5±0.410.7±0.5 139Z 32.4±338.4±2.7 Musg owe da a. In able 2 he alues calcula ed o he MACSs a e compa ed wi h ecommended alues de i ed om p e ious da a [13]. The MACS calcula ed on he p esen expe imen al da a excep o he 94Z esul lowe han hose epo ed in li e a u e, al hough apa o he 96Z he new alues a e wi hin he e o ba s o he p e ious da a. 5 Conclusions The (n,γ) c oss sec ions o he 90,91,92,93,94,96Z and 139La ha e been measu ed o e a wide neu on ene gy ange using he inno a i e ea u es o he n TOF CERN acili y. The cap u e ke nel p esen ed in his wo k a e o all sample excep o 94Z weake han wha epo ed in he p e ious measu emen s and 1306 In e na ional Con e ence on Nuclea Da a o Science and Technology 2007 in he lib a ies e alua ed da a. This esul can be explained in e ms o he op imized pe o mance o he acili y, expe - imen al se -up, da a acquisi ion and he mo e accu a e da a analysis ools, as he PHWT and SAMMY code. The new cap u e c oss sec ion ha e led o an imp o emen o he MACS which we e calcula ed wi h mo e accu acy and he alues ound esul s lowe han he alues ecommended om he li e a u e. Fu he mo e some o he nuclea quan i ies has been calcula ed as he le el densi y, which implica ion o he 139La a e published in [8]. This wo k was suppo ed by he EC unde con ac FIKW-CT-2000- 00107 and by unding agencies o he pa icipa ing ins i u es. Re e ences 1. F. K¨ appele , P og. Nucl. Pa . Phys. 43, 419 (1999). 2. K.A. Toukan, K. Debus, F. K¨ appele , G. Reffo, Phys. Re . C 51, 1540 (1995). 3. C. Bo cea e al., Nucl. Ins um. Me h. A 513, 523 (2003). 4. R. Plag e al., Nucl. Ins um. Me h. A 496, 425 (2003). 5. U. Abbondanno e al., Nucl. Ins um. Me h. A 538, 692 (2005). 6. U. Abbondanno e al., Nucl. Ins um. Me h. A 521, 454 (2004). 7. R. Te lizzi e al., Phys. Re . C 75, 35807 (2007). 8. N.M. La son, Repo ORNL/TM-979, Oak Ridge Na ional Lab- o a o y, 2000. 9. Y. Nakajima, N. Ohnishi, Y. Kanda, M. Mizumo o, Y. Kawa asaki, Y. Fu u a, A. Asami, J. Nucl. Sci. Technol. 20, 183 (1983). 10. L. Musg o e, B.J. Allen, R.L. Macklin, Aus alian J. Phys. 30, 599 (1977). 11. S.F. Mughabghab, M. Di adeenam, N.E. Holden, Neu on C oss Sec ions, Vol. 1, and Neu on Resonance Pa ame e s and The - mal C oss Sec ions, Pa A, Z =1-60 (Academic P ess, O lando, 1981). 12. Z.Y. Bao e al., A . Da a Nucl. Da a Tables 76, 70 (2000). 13. S. Ma one e al., Nucl. Ins um. Me h. A 513, 692 (2003). 14. S. OB ien, S. Dababneh, M. Heil, F. Kppele , R. Gallino, M. Pigna a i, As ophys. J. 647, 685 (2006). 15. J.M. Smi h, Eu . Phys. J. Appl. Phys. 25, 123 (2004).