Measurement of the radiative neutron capture cross section of 206 Pb and its astrophysical implications

PHYSICAL REVIEW C 76, 045805 (2007) Measu emen o he adia i e neu on cap u e c oss sec ion o 206Pb and i s as ophysical implica ions C. Domingo-Pa do,1,2,*U. Abbondanno,3G. Ae s,4H. ´ Al a ez,5F. Al a ez-Vela de,6S. And iamonje,4J. And zejewski,7 P. Assimakopoulos,8L. Audouin,1G. Badu ek,9P. Baumann,10 F. Beˇ c ´ aˇ ,11 E. Be houmieux,4S. Bis e zo,12,1F. Cal i ˜ no,13 M. Cal iani,14 D. Cano-O ,6R. Capo e,15,16 C. Ca apic¸o,17 P. Cennini,18 V. Chepel,19 E. Chia e i,18 N. Colonna,20 G. Co es,13 A. Cou u e,21 J. Cox,21 M. Dahl o s,18 S. Da id,10 I. Dillman,1R. Dol ini,22 W. D idi,4I. Du an,5 C. Ele he iadis,23 M. Embid-Segu a,6L. Fe an ,24 A. Fe a i,18 R. Fe ei a-Ma ques,19 L. Fi zpa ick,18 H. F ais-Koelbl,25 K. Fujii,3W. Fu man,26 R. Gallino,12 I. Goncal es,17 E. Gonzalez-Rome o,6A. Go e do ski,27 F. G amegna,14 E. G iesmaye ,25 C. Gue e o,6F. Gunsing,4B. Haas,28 R. Haigh ,29 M. Heil,1A. He e a-Ma inez,18 M. Igashi a,30 M. Isae ,24 E. Je icha,9F. K¨ appele ,1Y. Kadi,18 D. Ka adimos,8D. Ka amanis,8M. Ke eno,10 V. Ke le o ,27,18 P. Koehle ,31 V. Kono alo ,26,18 E. Kossionides,32 M. K iˇ cka,11 C. Lamboudis,23 H. Leeb,9A. Lindo e,19 I. Lopes,19 M. Lozano,16 S. Lukic,10 J. Ma ganiec,7S. Ma one,20 C. Massimi,33 P. Mas inu,14 A. Mengoni,34,18 P. M. Milazzo,3C. Mo eau,3 M. Mosconi,1F. Ne es,19 H. Obe humme ,9M. Oshima,35 S. O’B ien,21 J. Pancin,4C. Papach is odoulou,8C. Papadopoulos,36 C. Pa adela,5N. Pa onis,8A. Pa lik,37 P. Pa lopoulos,38 L. Pe o ,4R. Plag,1A. Plompen,39 A. Plukis,4A. Poch,13 C. P e el,13 J. Quesada,16 T. Rausche ,40 R. Rei a h,29 M. Rose i,41 C. Rubbia,22 G. Rudol ,10 P. Rullhusen,39 J. Salgado,17 L. Sa chiapone,18 I. Sa idis,23 C. S ephan,24 G. Taglien e,20 J. L. Tain,2L. Tassan-Go ,24 L. Ta o a,17 R. Te lizzi,20 G. Vannini,33 P. Vaz,17 A. Ven u a,41 D. Villama in,6M. C. Vincen e,6V. Vlachoudis,18 R. Vlas ou,36 F. Voss,1S. Wal e ,1 H. Wendle ,18 M. Wiesche ,21 and K. Wisshak1 (n TOF Collabo a ion) 1Fo schungszen um Ka ls uhe GmbH (FZK), Ins i u ¨ u Ke nphysik, Ge many 2Ins i u o de F´ ısica Co puscula , CSIC-Uni e sidad de Valencia, Spain 3Is i u o Nazionale di Fisica Nuclea e (INFN), T ies e, I aly 4CEA/Saclay - DSM/DAPNIA, Gi -su -Y e e, F ance 5Uni e sidade de San iago de Compos ela, San iago de Compos ela, Spain 6Cen o de In es igaciones Ene ge icas Medioambien ales y Technologicas, Mad id, Spain 7Uni e si y o Lodz, Lodz, Poland 8Uni e si y o Ioannina, Ioannina, G eece 9A omins i u de ¨ Os e eichischen Uni e si ¨ a en, Technische Uni e si ¨ a Wien, 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 12Dipa imen o di Fisica Gene ale, Uni e si ` a di To ino, To ino, I aly 13Uni e si a Poli ecnica de Ca alunya, Ba celona, Spain 14Is i u o Nazionale di Fisica Nuclea e (INFN), Labo a o i Nazionali di Legna o, Legna o, I aly 15In e na ional A omic Ene gy Agency, NAPC/Nuclea Da a Sec ion, Vienna, Aus ia 16Uni e sidad de Se illa, 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, Coimb a, Po ugal 20Is i u o Nazionale di Fisica Nuclea e (INFN), Ba i, I aly 21Uni e si y o No e Dame, No e Dame, Indiana, USA 22Uni e si ` a degli S udi di Pa ia, Pa ia, I aly 23A is o le Uni e si y o Thessaloniki, Thessaloniki, G eece 24Cen e Na ional de la Reche che Scien i ique/IN2P3 - IPN, O say, F ance 25Fachhochschule Wiene Neus ad , Wiene Neus ad , Aus ia 26Join Ins i u e o Nuclea Resea ch, F ank Labo a o y o Neu on Physics, Dubna, Russia 27Ins i u e o Physics and Powe Enginee ing, Kaluga egion, Obninsk, Russia 28Cen e Na ional de la Reche che Scien i ique/IN2P3 - CENBG, Bo deaux, F ance 29Los Alamos Na ional Labo a o y, Los Alamos, New Mexico, USA 30Tokyo Ins i u e o Technology, Tokyo, Japan 31Oak Ridge Na ional Labo a o y, Physics Di ision, Oak Ridge, Tennessee, USA 32NCSR, A hens, G eece 33Dipa imen o di Fisica, Uni e si ` a di Bologna, and Sezione INFN di Bologna, Bologna, I aly 34In e na ional A omic Ene gy Agency (IAEA), NAPC/Nuclea Da a Sec ion, Vienna, Aus ia 35Japan A omic Ene gy Resea ch Ins i u e, Tokai-mu a, Japan 36Na ional Technical Uni e si y o A hens, A hens, G eece 37Ins i u ¨ u Iso open o schung und Ke nphysik, Uni e si ¨ a Wien, Wien, Aus ia 38Pˆ ole Uni e si ai e L´ eona d de Vinci, Pa is La D´ e ense, F ance 0556-2813/2007/76(4)/045805(10) 045805-1 ©2007 The Ame ican Physical Socie y C. DOMINGO-PARDO e al. PHYSICAL REVIEW C 76, 045805 (2007) 39CEC-JRC-IRMM, Geel, Belgium 40Depa men o Physics and As onomy - Uni e si y o Basel, Basel, Swi ze land 41ENEA, Bologna, I aly (Recei ed 25 July 2007; published 31 Oc obe 2007) The (n, γ ) c oss sec ion o 206Pb has been measu ed a he CERN n TOF acili y wi h high esolu ion in he ene gy ange om 1 eV o 620 keV by using wo op imized C6D6de ec o s. In he in es iga ed ene gy in e al abou 130 esonances could be obse ed, om which 61 had enough s a is ics o be eliably analyzed ia he R-ma ix analysis code SAMMY. Expe imen al unce ain ies we e minimized, in pa icula wi h espec o (i) angula dis ibu ion e ec s o he p omp cap u e γ- ays, and o (ii) he TOF-dependen backg ound due o sample-sca e ed neu ons. O he backg ound componen s we e add essed by backg ound measu emen s wi h an en iched 208Pb sample. The e ec o he lowe ene gy cu o in he pulse heigh spec a o he C6D6de ec o s was ca e ully co ec ed ia Mon e Ca lo simula ions. Compa ed o p e ious 206Pb alues, he Maxwellian a e aged cap u e c oss sec ions de i ed om hese da a a e abou 20% and 9% lowe a he mal ene gies o 5 keV and 30 keV, espec i ely. These new esul s ha e a di ec impac on he s-p ocess abundance o 206Pb, which ep esen s an impo an es o he in e p e a ion o he cosmic clock based on he decay o 238U. DOI: 10.1103/PhysRe C.76.045805 PACS numbe (s): 25.40.Lw, 27.80.+w, 97.10.C I. INTRODUCTION Simila o he majo i y o he s able iso opes beyond i on, 206–208Pb and 209Bi a e syn hesized by he apid ( -) and slow (s-) neu on cap u e p ocesses. Howe e , his mass egion is pa icula ly in e es ing because he -p ocess abundances a e domina ed by he decay o he sho li ed α-uns able ansbismu h iso opes [1]. This ea u e p o ides an impo an consis ency check o he -p ocess abundance calcula ions in he ac inide egion, since he in eg a ed esiduals a e cons ained by he di e ence be ween he sola abundance alues and he espec i e s-p ocess componen s. Reliable -p ocess calcula ions a e equi ed o he in e p e a ion o he obse ed Th and U abundances in he ul a me al-poo (UMP) s a s o he Galac ic halo. Since hese s a s a e conside ed o be as old as he Galaxy, he obse ed Th and U abundances can be used as cosmo-ch onome e s, p o ided he o iginal Th and U abundances a e in e ed om -p ocess models. This da ing mechanism has he ad an age o being independen o he ye unce ain -p ocess si e [1–3]. Apa om i s ele ance o es ablishing he basic con- s ain s o he -p ocess ch onome y in gene al, 206Pb con ains also da ing in o ma ion in i sel . The 206Pb/238U cosmoch onome e was i s in oduced by Clay on in 1964 [4]. The 238U p oduced by he p ocess decays wi h a hal -li e o 1/2=4.5×109y o e a chain o αand βdecays ending a 206Pb. The e o e, i s adiogenic abundance componen , N206 c, can be used o cons ain he age o he pa en iso ope 238U, and hence he age ( )o he -p ocess. Unlike he mo e di ec -p ocess abundance p edic ions de i ed om he Th and U abundances in UMP s a s, his p ocedu e equi es a Galac ic e olu ion model, which desc ibes he supe no a a e o he equency o he -p ocess e en s [5]. The d awback o his clock a ises om he di icul y o isola e he cosmo adiogenic componen o 206Pb accu a ely enough om he addi ional abundance componen s. *Co esponding au ho : cesa [email p o ec ed] Apa om hese as ophysical aspec s, he neu on cap u e c oss sec ion o 206Pb is also o impo ance o he design o as eac o sys ems based on a Pb/Bi spalla ion sou ce. Because 24.1% o na u al lead consis s o 206Pb, i s (n, γ ) c oss sec ion in luences he neu on balance o he eac o [6]. The e ha e been se e al measu emen s o he 206Pb(n, γ ) c oss sec ion, which show disc epancies ha a e di icul o unde s and (see Sec. IV A). The aim o his wo k is o pe o m a new independen measu emen wi h highe accu acy and in his way o de e mine he s-p ocess con ibu ion o he 206Pb abundance, N206 s, mo e eliably. In ac , he s-p ocess abundance o his iso ope is almos comple ely de e mined by he s ella (n, γ ) c oss sec ion, nea ly independen o he s ella model used [7]. The e o e, he unce ain y o N206 sa ises mos ly om he c oss sec ion unce ain y. Po en ial sou ces o sys ema ic e o ha e been subs an ially educed in he p esen measu emen , which was pe o med a he CERN n TOF ins alla ion. The new se up, and in pa icula he de ec o s hemsel es, we e op imized o e y low neu on sensi i i y. Fu he mo e, he de ec o s we e moun ed a ∼125◦ wi h espec o he inciden neu on beam in o de o minimize he co ec ion o angula dis ibu ion e ec s. The expe imen- al de ails a e p esen ed in Sec. II, ollowed by he adop ed da a analysis p ocedu es and an e alua ion o he a ious sys ema ic unce ain ies in Sec. III. The deduced esonance pa ame e s and he co esponding Maxwellian a e aged cap u e c oss sec ions in he s ella empe a u e egime a e p esen ed in Sec. IV. Based on hese new da a, i s as ophysical impli- ca ions o he s-p ocess abundance o 206Pb a e discussed in Sec. V. II. MEASUREMENT The ime-o - ligh (TOF) measu emen was pe o med a he CERN n TOF ins alla ion [8] using a se o wo C6D6 de ec o s. Neu ons we e p oduced by a 20 GeV p o on beam on a lead spalla ion a ge . The spalla ion sou ce was 045805-2 MEASUREMENT OF THE RADIATIVE NEUTRON CAPTURE . . . PHYSICAL REVIEW C 76, 045805 (2007) su ounded by a 6 cm hick wa e laye , which se ed as a coolan and as a mode a o o he ini ially as neu on spec um. The beam was cha ac e ized by in ense bunches o (3 o 7)×1012 p o ons, a wid h o 6 ns ( ms), and a epe i ion a e o only 0.4 Hz. This ex emely low du y-cycle allows one o pe o m (n, γ ) measu emen s o e a b oad neu on ene gy in e al om 1 eV up o 1 MeV and o achie e a o able backg ound condi ions. Da a we e eco ded by means o an ad anced acquisi ion sys em wi h ze o dead ime, based on 8-bi lash-analog- o-digi al con e e s (FADC), wi h 500 MHz sampling a e and 8 MB bu e memo y [9]. The measu emen was pe o med wi h an en iched me al sample 8.123 g in mass and 20 mm in diame e . The sample was en iched o 99.76% in 206Pb wi h small impu i ies o 207Pb (0.21%) and 208Pb (0.03%). Cap u e e en s we e egis e ed wi h wo C6D6γ- ay de ec o s op imized o e y low neu on sensi i i y [10]. A ske ch o he expe imen al se up is shown in Fig. 2 o Re . [11]. The absolu e alue o he neu on luence was de e mined by egula calib a ion measu emen s wi h an 0.5 mm hick gold sample and by using he sa u a ed esonance echnique [12] o he i s gold esonance a En=4.9 eV. The ene gy di e en ial neu on lux was de e mined wi h a ela i e unce ain y o ±2% om he lux measu emen wi h a 235,238U ission chambe calib a ed by Physikalisch-Technische Bundesans al (PTB) [13]. The neu on in ensi y a he sample posi ion was also moni o ed by means o a 200-µg/cm2 hick 6Li oil in he neu on beam abou 2.5 m ups eam o he cap u e sample. The 6Li oil was su ounded by ou silicon de ec o s ou side o he beam o eco ding he 3H and αpa icles om he (n, α) eac ions. Compa ed o p e ious measu emen s [14,15], he p esen se up had he ad an age ha he de ec o s we e placed a ∼125◦wi h espec o he inciden neu on beam. In his way, he co ec ions o angula dis ibu ion e ec s o he p omp cap u e γ- ays we e s ongly educed. This con igu a ion led also o a subs an ial educ ion o he backg ound om in-beam γ- ays sca e ed in he sample [16]. III. CAPTURE DATA ANALYSIS The esponse unc ion o he C6D6de ec o s needs o be modi ied such ha he de ec ion p obabili y o cap u e cascades becomes independen o he cascade mul ipola i y. This was accomplished by applica ion o he pulse heigh weigh ing echnique (PHWT) [17]. Based on p e ious expe- ience [11,18,19], he weigh ing unc ions (WFs) o he gold and lead samples we e ob ained by means o Mon e Ca lo calcula ions. The accu acy o he WFs was e i ied wi h he me hod desc ibed in Re . [18], by which he calcula ed WFs we e applied o Mon e Ca lo simula ed cap u e γ- ay spec a. Using his p ocedu e, he unce ain y o he WFs was es ima ed o be smalle han 0.5% o he samples used in he p esen expe imen . The weigh ed coun a e Nwis hen ans o med in o an expe imen al yield, Yexp = sa Nw NnEc ,(1) whe e he yield-no maliza ion ac o sa is de e mined by calib a ion measu emen s using he sa u a ed 4.9 eV esonance in gold. Nndeno es he neu on lux and Ec he e ec i e binding ene gy. The yield in Eq. (1) is s ill subjec o se e al co ec ions. The common e ec s o he backg ound and o he low ene gy cu o in he pulse heigh spec a o he γde ec o s a e desc ibed in Secs. III A and III B, espec i ely. The measu emen on 206Pb is pa icula ly sensi i e o he angula dis ibu ion o he p omp cap u e γ- ays. The impac o his e ec is desc ibed in Sec. III C. A. Backg ounds A majo sou ce o backg ound is due o in-beam γ- ays, p edominan ly om neu on cap u es in he wa e mode a o , which a el along he neu on ligh ube and a e sca e ed in he 206Pb sample. This backg ound exhibi s a smoo h dependence on neu on ene gy, wi h a b oad maximum a ound En≈10 keV. The shape o his backg ound was de e mined om he spec um measu ed wi h an iso opically pu e 208Pb sample, which con ains p ac ically no esonances in he in es iga ed neu on ene gy ange. This spec um was p ope ly scaled and used as a poin -wise nume ical unc ion in he R-ma ix analysis o he 206Pb cap u e yield (see Sec. IV). Ano he ype o backg ound a ises in he analysis o esonances wi h a dominan neu on sca e ing channel, n γ. In such cases, he e a e abou n/ γsca e ed neu ons pe cap u e e en . These sca e ed neu ons can be cap u ed in he de ec o s o in su ounding ma e ials, hus mimicking ue cap u e e en s. This e ec was es ima ed o be negligible o all he esonances epo ed in Sec. IV. B. Digi al h eshold As men ioned in Sec. II, FADCs we e used o eco ding di ec ly he analog ou pu signals o he C6D6de ec o s. Wi hou any u he disc imina ion, 8 MB o da a would ha e been acqui ed pe p o on pulse in each de ec o . Depending on he sample, his eno mous amoun o da a could be educed by ac o s o 20 o 100 by using a ze o supp ession algo i hm (see Re . [9] o de ails). By his me hod e en s below a ce ain pulse-heigh a e disc imina ed by a cons an digi al h eshold analogous o con en ional da a acquisi ion sys ems, whe e an elec onic h eshold is used o educe backg ounds and dead ime e ec s. Due o his h eshold, he pulse heigh spec a o he C6D6 de ec o s exhibi a low ene gy cu o a a ce ain alue o he signal ampli ude (see Fig. 1). In his expe imen he h eshold was se a a γ- ay ene gy o 320 keV. I he pulse heigh spec a o he 206Pb sample and o he gold sample used o no maliza ion would ha e he same shape, he ac ion o weigh ed coun s below his h eshold would nea ly cancel ou in he exp ession o he yield Yexp ∝320 keV 0keV WPb iRPb i+Ec 320 keV WPb iRPb i 320 keV 0keV WAu iRAu i+Ec 320 keV WAu iRAu i ≈Ec 320 keV WPb iRPb i Ec 320 keV WAu iRAu i .(2) 045805-3 C. DOMINGO-PARDO e al. PHYSICAL REVIEW C 76, 045805 (2007) (MeV) dep E 012345678 Coun s 1 10 2 10 3 10 4 10 5 10 0 0.05 0.1 0.15 0.2 0.25 0.3 50 100 150 200 3 10 × FIG. 1. Pulse heigh spec a o he 4.9 eV esonance in gold (g ey) and o he 3.3 keV esonance in 206Pb (black), a bi a ily scaled. The dashed lines a e he MC-calcula ed γ- ay spec a o he wo esonances. The linea scale used in he inse illus a es he la ge di e ence be ween he simula ed spec a below a h eshold o 300 keV. He e, he Wiand Ria e he co esponding weigh ing ac o s and esponse unc ions o a ce ain ime o ligh channel, espec i ely. Howe e , his app oxima ion is only alid wi hin 4 o 5%, because he pulse heigh spec a o cap u es on 206Pb and 197Au di e signi ican ly nea h eshold (Fig. 1). This e ec has been aken in o accoun in he de e mina ion o he expe imen al cap u e yield by simula ing he cap u e cascades o each iso ope as desc ibed in de ail in Re s. [11,18, 19]. Figu e 1shows ha he expe imen al spec a abo e he digi al h eshold a e well ep oduced by he simula ions. Wi h his co ec ion he expe imen al yield becomes Yexp ∝ Pb Au Ec 320 keV WPb iRPb i Ec 320 keV WAu iRAu i .(3) Fo he adop ed digi al h eshold he yield o he 4.9 eV esonance in 197Au needs o be scaled by a ac o Au = 1.071(3), whe eas he yield o he esonances in 206Pb equi ed a co ec ion o Pb =1.021(5) due o hei ha de spec um. Hence, he co ec ion ac o o he inal expe imen al yield was = Pb/ Au =0.952(4). C. Angula dis ibu ion e ec s Neu on cap u e wi h o bi al angula momen um l>0 leads o an aligned s a e in he compound nucleus, pe pendic- ula o he di ec ion o he inciden neu on. Gi en he small mul iplici y (m=1 o 2) o he cap u e cascades in 206Pb, mos o he p omp γ- ays egis e ed wi h he C6D6de ec o s s ill ca y his aniso opy, which a ec s he measu ed yield. The angula dis ibu ion is in gene al gi en by W(θ)= k AkPk(cos θ)=1+A2P2(cos θ) +A4P4(cos θ)+A6P6(cos θ),(4) (a) (b) 6738.2 0.0 897.5 569.6 2623.1 6737.9 6168.6 4114.5 5/2+ 3/2− 5/2− 1/2− 5840.8 JΠ (d) (c) FIG. 2. Le el scheme and decay pa e ns o 207Pb [14]. All ene gies a e in keV. whe e Pk(cos θ) a e he Legend e polynomials o o de kand Aka e coe icien s, which depend on he ini ial (J) and inal (J) spin alues, on he mul ipola i y (l) o he ansi ion, and on he deg ee o alignmen . The angula dis ibu ion e ec s in he cap u e yield a e minimized (al hough no a oided) by se ing he de ec o s a 125◦. Since each C6D6de ec o co e s a subs an ial solid angle, cap u e γ- ays a e egis e ed a ound 125◦±θ. Fo he ac ual se up o he p esen measu emen one inds θ ≈28◦. 1. Resonances wi h spin J =1/2 Fo esonances wi h J=1/2 i can be assumed ha hey decay di ec ly o he g ound s a e (Jπ=1/2−)o o he i s o second exci ed s a es wi h Jπ=5/2−and Jπ=3/2−, espec i ely (see also Fig. 2). In hese cases, one inds ha A2=A4=A6=0. The e o e, only esonances wi h spin J>1/2 may be a ec ed by angula dis ibu ion e ec s. 2. Resonances wi h spin J =3/2 In o de o quan i y he unce ain y due o he angula dis i- bu ion o he p omp γ- ays emi ed om exci ed s a es wi h Jπ=3/2− he de-exci a ion pa e ns epo ed in Re . [14] ha e been used (Table I). Fo he i s esonance a 3.36 keV, ai ag eemen has been ound be ween he ela i e in ensi ies o Re . [14] and he a he coa se alues deduced om he expe imen al pulse heigh spec um (Table Iand Fig. 1), which su e om unce ain ies due o backg ound sub ac ion, limi ed coun ing s a is ics and poo ene gy esolu ion o he C6D6de ec o s. The e o e, an unce ain y o abou 20% has o be asc ibed o he quo ed γ- ay in ensi ies. The es ima ed e ec o he angula dis ibu ion on he cap u e yield (σ3/2− θ) is gi en in he las column o Table I. These alues we e ob ained ia Mon e Ca lo simula ions o he expe imen al se up, using he ene gies and in ensi ies lis ed in 045805-4 MEASUREMENT OF THE RADIATIVE NEUTRON CAPTURE . . . PHYSICAL REVIEW C 76, 045805 (2007) TABLE I. Measu ed decay pa e ns om esonances wi h spin J=3/2[14]. The sys ema ic unce ain y in he yield o each esonance due o he angula dis ibu ion o he in ol ed ansi ions a e gi en in he las column. E◦(keV) In ensi y Iγ(%) Eγ(keV) σ3/2− θ 6737.9 6168.6 5840.8 4114.5 3.36 76.0(27) 2.5(8) 8.58(11) 13.0(8) ±10% 3.36a60 2.5 24.5 13 ±8% 10.86 100 ±2% 21.87 100 ±2% 42.07 100 ±10% aThis wo k. Table Iand he p esc ip ion o Re . [20]. The main unce ain y in he calcula ion o he angula dis ibu ion e ec s a ises om he unknown admix u es o di e en mul ipola i ies (M1+E2) o he ansi ions connec ing he o iginal exci ed s a e Jπ=3/2−wi h any o he h ee lowes s a es [pa hs (a), (b), and (c) in Fig. 2]. As shown in Table I, he decay pa e n and he co esponding e ec on he cap u e yield σ3/2− θ a y ab up ly om one esonance o ano he . I is he e o e di icul o assess a common sys ema ic unce ain y o he emaining 3/2− esonances. Assuming ha he ou esonances lis ed in Table Icons i u e a ep esen a i e sample, one may conside hei s anda d de ia ion o σ=4% as a ealis ic es ima e o he sys ema ic unce ain y due o angula dis ibu ion e ec s. Resonances wi h Jπ=3/2+can be assumed o decay di ec ly o he g ound s a e h ough an E1 ansi ion. In his case we ha e es ima ed an e ec o 10% in he cap u e yield wi h espec o he iso opic case. Howe e , since 3/2+ esonances appea a a ela i ely high neu on ene gy, he inal e ec in he MACS is p ac ically negligible (see below Sec. IV B). 3. Resonances wi h spin J =5/2 Fo esonances in 207Pb wi h Jπ=5/2+ he mos p obable decay would be h ough an elec ic dipole ansi ion o he i s exci ed s a e wi h Jπ=5/2−and/o o he second exci ed s a e wi h Jπ=3/2−[pa hs (b) and (c) in Fig. 2]. Unde hese assump ions, he e ec on he cap u e yield would be −12% o pa h (b) and 9% o pa h (c). Howe e , mix u es o bo h decay pa hs would pa ly compensa e he co ec ion o angula dis ibu ion e ec s. Adop ing one s anda d de ia ion o he wo ex eme cases σ5/2+ θ≃10% would, he e o e, ep esen a a he conse a i e es ima e o he co esponding unce ain y. Ne e heless, e en such a ela i ely la ge unce ain y o he c oss sec ion o Jπ=5/2+ esonances would ha e negligible consequences o he Maxwellian a e aged c oss sec ion because hese esonances con ibu e e y li le o he o al cap u e c oss sec ion (see Sec. IV B). D. Summa y o unce ain ies Wi h he WFs calcula ed ia he Mon e Ca lo echnique, he accu acy o he PHWT has been in es iga ed in de ail by he nTOF collabo a ion [18]. I has been shown ha he cap u e yield can be de e mined om he measu ed aw da a wi h an accu acy be e han 2%. O he sou ces o sys ema ic unce ain y pe aining o his measu emen a e due o he ene gy dependence o he neu on lux (±2%) and o he backg ound due o in-beam γ- ays (±1%). In he pa icula case o he (n, γ ) c oss sec ion o 206Pb, he unce ain y in oduced by he angula dis ibu ion o he cap u e γ- ays has o be conside ed as well. This e ec has been es ima ed o con ibu e an unce ain y o ±4% o esonances wi h Jπ=3/2−and less han ±10% o esonances wi h Jπ=3/2+,5/2+. IV. RESULTS A o al o 61 cap u e le els we e analyzed in he neu on ene gy ange om 3 keV up o 570 keV using he R-ma ix code SAMMY [21]. In he analysis, he o bi al angula momen a land he esonance spins Jwe e adop ed om Re . [22]. Some o he land Jpa ame e s lis ed in Table II a e en a i e o a bi a y i missing in Re . [22]. We lis all he pa ame e s used in ou analysis so ha he inal alues can be ecalcula ed i nec- essa y. The cap u e yield Y(E◦, n, γ) was pa ame ized wi h he Reich-Moo e o malism, and a channel adius o 9.5 m was used o all pa ial wa es. This pa ame e ized yield was i ed o he co ec ed expe imen al yield by a ia ion o he cap u e wid h γand/o neu on wid h n, ×Yexp =B+Y(E◦, n, γ),(5) whe e is he global yield co ec ion ac o gi en in Sec. III B.The e mBdesc ibing he backg ound was pa ame ized as an analy ical unc ion o he neu on ene gy in he ange be ween 1 eV and 30 keV. Beyond 30 keV, Bwas bes desc ibed by means o a nume ical unc ion (poin wise) de e mined om he measu emen o he 208Pb sample (see Re . [23] o de ails). The unce ain ies quo ed o he ene gy o each esonance a e only he s a is ical e o s ob ained om he i s o he cap u e da a pe o med wi h SAMMY. A. Compa ison o p e ious wo k The adia i e neu on cap u e c oss sec ion o 206Pb has been measu ed a ORNL [14,15,24], a RPI [25], and a IRMM [26]. As ep esen a i e examples o hese measu emen s we conside in his sec ion wo measu emen s made a ORELA [14,15], a mo e comple e analysis [27] o he ORELA cap u e da a [15] made in combina ion wi h ansmission da a [28] and he ecen expe imen made a IRMM [26]. In o de o compa e hese ou da a se s wi h he p esen esul s (Table II), he a io o he cap u e ke nels a e shown in Fig. 3. The alues epo ed in Re . [15] show a ela i ely good ag eemen wi h ou esul s, excep o he i s wo esonances a 3.3 keV and 14.25 keV, which a e lowe by ∼50% (see Fig. 3). Howe e , hese wo esonances and he esonance a 16.428 keV a e impo an because o hei dominan con i- bu ion o he MACS in he ene gy ange be ween 5 keV and 20 keV. I is di icul o de e mine he sou ce o disc epancy, hus no co ela ion has been ound be ween he disc epancies 045805-5 C. DOMINGO-PARDO e al. PHYSICAL REVIEW C 76, 045805 (2007) TABLE II. Resonance pa ame e s de i ed om he R-ma ix analysis o he 206Pb(n, γ ) da a. E◦lJ γγnnK aK (eV) (meV) (%) (meV) (%) (meV) (%) 3357.93(0.04) 1 3/2 78.1 3 235 117 2 10865.0(0.4) 1 3/2 64.9 9 44.1 8 52.5 6 11296.0(0.5) (1) (1/2) 455 44.6 7 40.6 7 14220.0(0.6) 1 (1/2) 152 6 1560 139 5 16428.0(0.4) 0 1/2 2268 9 936 5 662 5 19744.0(1.3) 1 (1/2) 156 7 2581 147 6 19809.0(0.9) 1 (3/2) 295 71.6 8 115 6 21885.0(0.9) 1 3/2 121 6 875 212 5 25112.0(0.9) 1 3/2 438 9 326 8 374 6 25428(5) 1 1/2 254 7 48901 253 7 36200(6) 1 1/2 312 14 35700 309 13 37480.0(1.9) 1 (3/2) 151 15 890 258 13 39028(2) 1 (1/2) 346 93.0 36 73.3 28 40647(2) 1 (1/2) 163 23 884 138 19 42083.0(1.7) 1 (3/2) 419 21 1419 91 647 26 47534(2) (1) (1/2) 184 34 1000 155 29 59233.0(0.2) (2) (3/2) 322 16 1000 487 12 63976(3) (2) 5/2 151 17 1110 400 15 65990(10) 0 1/2 1186 9 82200 1169 9 66590(6) 1 3/2 198 19 9530 387 19 70352(7) 1 1/2 163 34 10780 161 34 80388(4) 2 3/2 1490 8 7005 2457 6 83699(6) (2) (3/2) 351 16 8000 673 15 88509(6) 2 5/2 375 13 7996 1076 12 91740(4) (1) (3/2) 298 25 1000 460 19 92620(13) 0 1/2 991 15 32000 961 15 93561(6) 2 3/2 125 37 7001 246 37 94743(7) 2 (3/2) 241 20 7000 465 20 101220(7) 2 (5/2) 119 26 8000 351 25 114380(5) 1 (3/2) 655 24 2500 1037 19 114602(6) 2 (5/2) 366 19 5600 1030 18 118100(6) 2 (5/2) 390 16 5100 1087 15 124753(47) 1 3/2 2972 9 300000 5886 9 125312(7) 2 (3/2) 2783 10 21005 4915 9 126138(38) (1) (3/2) 319 32 100000 635 32 140570(23) 2 3/2 1387 11 103000 2736 11 145201(6) (2) (3/2) 518 30 3100 888 26 146419(24) 0 1/2 6092 8 176000 5888 8 150880(7) (1) (1/2) 554 48 4400 492 43 151290(13) 2 5/2 457 23 19000 1340 22 191217(48) (1) (1/2) 767 28 96977 761 27 196990(37) 1 1/2 584 45 64000 579 44 198618(34) 2 3/2 2730 10 132108 5350 10 274630(22) 1 (1/2) 514 65 32000 506 64 276984(49) 2 3/2 2481 13 112000 4854 13 313400(18) 2 (3/2) 1020 32 22000 1950 31 314340(84) 2 5/2 964 24 179000 2875 24 356098(22) 2 (5/2) 676 35 31000 1985 35 357465(87) 2 3/2 1998 24 455000 3979 24 406200(55) 2 5/2 656 51 102000 1955 51 407200(41) 2 3/2 2906 24 71000 5583 23 416370(127) 2 5/2 2722 16 307000 8096 16 433340(32) 2 (5/2) 4122 17 47000 11368 16 434604(37) (2) (3/2) 4695 23 58000 8687 21 443412(13) (2) (5/2) 2375 21 14000 6092 18 TABLE II. (Con inued.) E◦lJ γγnnK aK (eV) (meV) (%) (meV) (%) (meV) (%) 466320(49) (1) (3/2) 5413 15 90000 10211 14 469080(76) 2 3/2 3222 19 161000 6317 19 471789(28) (3) (5/2) 792 36 41000 2330 35 476310(172) 0 1/2 5252 18 374000 5180 17 510690(51) (2) (3/2) 3123 18 86000 6026 18 572245(181) 2 5/2 3838 13 793194 11460 13 aCap u e ke nel K =gγn/, wi h g=J+1/2. and he spins o he esonances. The la e could p obably help o de e mine i he e is any e ec ela ed o he angula dis ibu ion o he p omp cap u e γ- ays o o he WF used in he p e ious measu emen . In he second measu emen a ORELA [14] he disc ep- ancies e sus ou p esen esul s a e smalle (see Fig. 3), bu he cap u e ke nels a e sys ema ically la ge , on a e age 20 ±5% highe . This could p obably e lec ha he WF used in Re . [14] is o e weighing he ela i ely ha d pulse heigh spec um o 207Pb. Indeed, simila disc epancies ha e been ound in he pas o 56Fe [29], whe e he pulse heigh spec um is also conside ably ha de han ha o he 197Au sample used o yield no maliza ion. The pos e io analysis [27] o he ORELA cap u e da a [15] in combina ion wi h ansmission [28] shows, on a e age, be e ag eemen wi h he cap u e a eas epo ed he e (see Fig. 3). Finally, he esul s epo ed in he measu emen a IRMM [26] show he bes ag eemen wi h he cap u e ke nels o nTOF (see Fig. 3). A En⩽40 keV bo h measu emen s ag ee ORNL’73/nTOF 0 1 2 3 ORNL’79/nTOF 0 0.5 1 1.5 2 ORNL’80/nTOF 0 0.5 1 1.5 2 4 10 5 10 IRMM/nTOF 0 0.5 1 1.5 2 (eV) n E FIG. 3. (Colo online) Ra io be ween he cap u e ke nels epo ed in Re s. [15] ( op), [14] (second), [27] ( hi d), and [26] (bo om) and he ke nels de e mined he e. 045805-6 MEASUREMENT OF THE RADIATIVE NEUTRON CAPTURE . . . PHYSICAL REVIEW C 76, 045805 (2007) (keV) n E 3.35 3.36 3.37 Yield 0.05 0.1 0.15 This Wo k IRMM, 2007 ORELA, 1979 Mughabghab 2006 This Wo k IRMM, 2007 ORELA, 1979 Mughabghab 2006 (keV) n E 15 20 25 Yield 0.01 0.02 0.03 0.04 FIG. 4. (Colo online) (le ) The bold ed line ep esen s an R-ma ix i o ou expe imen al cap u e yield s a ing om he ini ial pa ame e s (solid g een line) in Re . [22]. The dashed and do -dashed cu es co espond o he cap u e yields de e mined in Re s. [26]and[14], espec i ely. ( igh ) The i ed cap u e yield in he 10–30 keV ene gy ange ( hin ed line). wi hin a ew pe cen . A highe ene gy he luc ua ions a e la ge , bu he ag eemen is s ill good wi hin he quo ed e o ba s. As an illus a i e example, he cap u e yield measu ed a nTOF o he i s esonance a 3.3 keV is compa ed in he op panel o Fig. 4 e sus he yield calcula ed om he esonance pa ame e s epo ed in Re s. [14,22,26]. Ob iously, he IRMM and n TOF esul s show good ag eemen in bo h he cap u e a ea and he esonance ene gy. B. Maxwellian a e aged cap u e c oss sec ion The Maxwellian a e aged c oss sec ion (MACS) was de e mined using he SAMMY code in he ange o he mal ene gies ele an o s ella nucleosyn hesis, i.e., om kT = 5 keV up o kT =50 keV. As discussed in he p e ious sec ion, ou esul s ag ee bes wi h he alues epo ed in Re . [26]. The la e da a se seems also o be he mos comple e in e ms o numbe o analyzed esonances, wi h abou 283 le els. The e o e ou esul s we e complemen ed wi h esonances om Re . [26] in o de o a oid any disc epancy due o esonances missing in Table II. The con ibu ion o hese supplemen a y esonances o he MACS is <0.1% a kT = 5 keV and 6% a kT =25 keV. The ac ha his co ec ion s a s o be signi ican owa d kT > ∼25 keV is no ele an o he s udy o he nucleosyn hesis o 206Pb. Indeed, as i is discussed below in Sec. V,206Pb is mos ly syn hesized be ween he He-shell lashes o he asymp o ic gian b anch s a s. These in e als be ween pulses p o ide abou 95% o he neu on exposu e ia he 13C(α, n)16O eac ion, which ope a es a a he mal ene gy o kT =8 keV. A his s ella empe a u e less han 0.5% o he MACS is due o he supplemen ed esonances. The unce ain ies shown in Fig. 5a e only s a is ical. The sys ema ic unce ain ies o he MACS quo ed in Table III include all con ibu ions discussed in Sec. III D. Assuming sys ema ic unce ain ies o 4% and 10% o 3/2− and 5/2− esonances, espec i ely, he inal unce ain ies a e comple ely domina ed by he 4% unce ain y o he 3/2− esonances. A change o 10% in he c oss sec ion o he ewe 5/2+ esonances has a negligible in luence on he MACS a kT =5 keV, i con ibu es only 0.5% a kT =25 keV and inc eases linea ly up o 1% a kT =50 keV. An e ec o 10% in he cap u e yield o he 3/2+ esonances makes only a 1% di e ence in he MACS a kT =25 keV and i becomes also negligible owa d lowe s ella empe a u es. The 3% sys ema ic unce ain y o he expe imen al me hod i sel o igina es om he PHWT, he neu on lux shape, and he use o he sa u a ed esonance echnique. In summa y, he MACS o 206Pb can now be gi en wi h o al unce ain ies o 5% and 4% a he s ella empe a u es co esponding o 5 keV and 25 keV he mal ene gies, espec- i ely. This imp o emen wi h espec o he p e iously ec- ommended alues o Re . [30] becomes pa icula ly impo an o de e mining he s-p ocess con ibu ion o he p oduc ion o lead and bismu h in he Galaxy. V. T H E s-PROCESS ABUNDANCE OF 206Pb AS A CONSTRAINT FOR THE U/TH CLOCK The s-p ocess p oduc ion o 206Pb akes place in low mass asymp o ic gian b anch (AGB) s a s o low me allici y [31], TABLE III. Maxwellian a e aged c oss sec ion o 206Pb. The mal ene gy kT MACS σs a σsys (keV) (mba n) (%) (%) 521.31.85 820.41.83 10 19.41.93 12 18.42.03 15 17.12.13 20 15.62.23 25 14.72.33 30 14.22.34 40 13.52.24 50 12.82.14 045805-7 C. DOMINGO-PARDO e al. PHYSICAL REVIEW C 76, 045805 (2007) The mal ene gy (keV) 10 20 30 40 50 MACS (mb) 12 14 16 18 20 22 24 26 28 This wo k IRMM 2007 Mughabghab’06 Bao e al. FIG. 5. (Colo online) Maxwellian a e aged (n, γ ) c oss sec ions o 206Pb om he esonance pa ame e s o his wo k (bold ed) com- pa ed o he IRMM measu emen [26] (dashed), o he ecommended da a o Re . [30] (g ey), and o he compiled da a o Re . [22] (solid g een). whe e abou 95% o he neu on exposu e is p o ided by he 13C(α, n)16O eac ion a a he mal ene gy o kT ≈8keV. A his s ella empe a u e he p esen MACS is abou 20% lowe and wo imes mo e accu a e (see Fig. 5) han he alues om Re . [30], which ha e been commonly used so a o s ella nucleosyn hesis calcula ions. The addi ional neu on i adia ion p o ided by he 22Ne(α, n)25Mg eac ion a he highe he mal ene gy o kT =23 keV du ing he He shell lash is a he weak. Wi h he new MACS he s-p ocess abundance o 206Pb has been ede e mined mo e accu a ely. A model calcula ion was ca ied ou o he mally pulsing AGB s a s o 1.5 and 3 M and a me allici y o [Fe/H] =−0.3. The abundance o 206Pb is well desc ibed by he a e age o he wo s ella models, which ep esen he so-called main componen [32]. Since he con ibu ion o 206Pb by he s ong componen is only 2%, he main componen can be used o app oxima e he e ec i e p oduc ion o 206Pb du ing Galac ic chemical e olu ion (GCE) [31,33,34]. This app oach yields an s-p ocess abundance o 206Pb, which ep esen s 70(6)% o he sola abundance alue N206 =0.601(47)/106Si [35]. The same calcula ion made wi h he olde MACS ecommended by Bao e al. [30] yields 64%. The unce ain y on he calcula ed s-p ocess abundance is mos ly due o he unce ain y on he sola abundance o lead (7.8%) [36]. The con ibu ion om he unce ain y on he MACS a 8 keV is less han 2%. Finally, he con ibu ion om he s-p ocess model is ±3%. The la e co esponds o he mean oo squa e de ia ion be ween obse ed and calcula ed abundances o s-p ocess only iso opes [32]. This unce ain y is jus i ied o 206Pb because i s nucleosyn hesis is domina ed by he main componen and i is only ma ginally a ec ed (∼2%) by he s ong componen [31–34]. Fu he mo e, be- cause o he much lowe c oss sec ions o 208Pb and 209Bi, he syn hesis o 206Pb emains p ac ically una ec ed by he α- ecycling a e 209Bi [7]. This lends u he con idence ha he p oduc ion o 206Pb, and hence i s unce ain y, ollows he same end as he main s-p ocess componen . In o de o es ima e a cons ain o he -p ocess abundance o 206Pb one needs o ake in o accoun i s adiogenic con ibu ion, N206 c, due o he decay o 238U. As i is shown (yea s)∆ 051015 9 10× 238 /N c 206 R=N 0 0.5 1 1.5 2 2.5 3 3.5 Sudden 43% SN Ra e Uni o m ∆ FIG. 6. Es ima e o he adiogenic componen o 206Pb using he Fowle ’s model wi h di e en nucleosyn he ic assump ions (see labels in cu es) and he -p ocess age  = U−4.6 Gy ( e ical dashed line) de i ed om he age o he Uni e se U[37]. in he ollowing, his componen is ela i ely small bu canno be neglec ed. Based on he schema ic model o Fowle , which assumes an exponen ial dec ease o he -p ocess yield du ing GCE [4] supe no a a e =(0.43 )−1Gy −1] and using he cu en bes es ima es o he age o he Uni e se ( U= 13.7±0.2Gy )[37], one ob ains N206 c=0.027(2)/106Si (see Fig. 6and Table IV). This numbe , combined wi h ou esul o N206 s, yields an -p ocess esidual, N206 =N206 −N206 s−N206 c=0.153 ±0.063.(6) The unce ain y in his esul includes con ibu ions o 8.4% om N206 c(co esponding o he unce ain y on he sola abundance o 238U[36]), 7.8% om he o al sola abundance o 206Pb, N206 [35,36], and 8.6% om he de e mina ion o N206 sas discussed abo e. This means ha , apa om he unce ain ies ela ed wi h he simpli ied assump ions in he GCE model o Fowle , he -p ocess abundance can be eliably cons ained be ween 16% and 36% o he sola 206Pb. The -p ocess esiduals de i ed he e a e consis en wi h -p ocess model calcula ions a ailable in he li e a u e, i.e., N206 =26.6% [1]. Mo e ecen calcula ions yield N206 alues be ween 27% and 35% [3]. One can also de i e ha d limi s o he -p ocess abundance, conside ing he wo ex eme cases o sudden nucleosyn hesis (→∞) and uni o m nucleosyn hesis (→0). This yields cons ain s be ween 10% and 37% o sola 206Pb (see Table IV). The si ua ion is a he di e en o he co esponding 207Pb/235U a io, which has been in es iga ed as a po en ial clock in he pas [38]. In his case, he s-p ocess abundance TABLE IV. Radiogenic abundance o 206Pb, N206 c(Si =106), de i ed om he model o Fowle and he age o he Uni e se (see Fig. 6). -P ocess esiduals ob ained ia Eq. (6). GCE N206 c=RN238 N206 =N206 −N206 s−N206 c (Fig. 6) 106Si 106Si N206 /N206 (%) 43% SN a e 0.027(2) 0.15(6) 26(10) Sudden 0.058(5) 0.12(6) 20(10) Uni o m 0.0161(14) 0.16(6) 27(10) 045805-8 MEASUREMENT OF THE RADIATIVE NEUTRON CAPTURE . . . PHYSICAL REVIEW C 76, 045805 (2007) TABLE V. Radiogenic abundance o 207Pb, N207 c(Si =106), de i ed om he model o Fowle and he age o he Uni e se. -P ocess esiduals ob ained ia Eq. (6). GCE N207 c=RN235 N207 =N207 −N207 s−N207 c 106Si 106Si N207 /N207 (%) 43% SN a e 0.150(13) 0.003(73) 0(11) 90% SN a e 0.08(7) 0.073(72) 11(11) Uni o m 0.047(4) 0.106(72) 16(11) o 207Pb was ecen ly de e mined o be N207 s=77(8)% [19]. A simila calcula ion o ha shown in Fig. 6gi es N207 c= 0.150(13) (see Table V). The la e alue e lec s he la ge ela i e adiogenic abundance o 207Pb, N207 c/N207 =22%, due o he much sho e hal -li e o 235U. F om he o al sola abundance o 207Pb [35] and he N207 sand N207 c alues quo ed abo e, he -p ocess esidual becomes N207 =0.003 ±0.073, which means ha N207 can no be la ge han 11% o he 207Pb abundance in he sola sys em, N207 =0.665(52) [35] (Table V). This esul is in con as wi h -p ocess model calcula ions, which yield alues be ween 22.7% and 25.3%, wi h a ela i e unce ain y o 15–20% [1,3]. The s-p ocess abundances o 206,207Pb a e a he eliable and no e y sensi i e o de ails o he s ella models [7,39]. The e o e, his disc epancy indica es ha -p ocess abundances migh ha e been o e es ima ed, possibly because he odd-e en e ec is no p ope ly e- p oduced by he ETFSI-Q mass model implemen ed in he -p ocess calcula ions [1,3]. Indeed, one needs o inc ease he supe no a a e in he s anda d Fowle model om 43% up o 90% [=(0.90 )−1Gy −1] in o de o achie e ag eemen be ween hese -p ocess cons ain s and he la e -p ocess calcula ions [1,3]. Ob iously he less ealis ic uni o m scena io would also p o ide ag eemen wi h he abundances om hese -p ocess models (see Table V). Howe e he si ua ion has been imp o ed ecen ly a e mo e de ailed -p ocess model calcula ions [40] p edic ed anewN207 alue, which is 35% lowe han he p e ious one o Re . [1]. This yields N207 /N207 =16.8%, which is subs an ially close (conside ing an unce ain y o 20%) o he uppe limi o 11% de i ed he e. In his case a good ag eemen would be ound o a mo e easonable inc ease o he supe no a a e o 55% in he Fowle model. These cons ain s o he -p ocess abundances o 206,207Pb become ele an o he alida ion o -p ocess model calcu- la ions and hence, o he eliable in e p e a ion o ac inide abundances obse ed in UMP s a s and hei use as cos- moch onome e s. The s-p ocess aspec s will be mo e igo ously in es iga ed in a comp ehensi e s udy o he Pb/Bi egion [41], whe e he ole o s ella modeling and GCE will be discussed wi h a comple e se o new c oss sec ions o he in ol ed iso opes, including he p esen da a o 206Pb, and ecen esul s o 204Pb [23], 207Pb [19], and 209Bi [11]. VI. SUMMARY The neu on cap u e c oss sec ion o 206Pb as a unc ion o he neu on ene gy has been measu ed wi h high esolu ion a he CERN n TOF ins alla ion using wo C6D6de ec o s. Cap u e wid hs and/o adia i e ke nels could be de e mined o 131 esonances in he neu on ene gy in e al om 3 keV up o 620 keV. Sys ema ic unce ain ies o 3%, 5%, and < ∼10% we e ob ained o esonances wi h spin-pa i ies o 1/2±,3/2−, and 5/2+, espec i ely. The Maxwellian a e aged c oss sec ions we e ound o be signi ican ly smalle by 10% o 20% compa ed o alues epo ed ea lie [30], esul ing in a co espondingly enhanced s-p ocess p oduc ion o 206Pb. Fi s calcula ions wi h a s anda d AGB model yield an s-p ocess componen o 70(6)% o he 206Pb abundance. Combined wi h an es ima e o he adiogenic p oduc ion o 206Pb, he -p ocess abundance is cons ained be ween 16% and 36% o he sola 206Pb abundance, well in ag eemen wi h -p ocess model calcula ions epo ed in he li e a u e [1,3]. A simila analysis o 207Pb shows ag eemen only wi h mos ecen -p ocess model calcula ions [40]. [1] J. J. Cowan, B. P ei e , K.-L. K a z, F.-K. Thielemann, C. Sneden, S. Bu les, D. Ty le , and T. C. Bee s, As ophys. J. 521, 194 (1999). [2] H. Scha z, R. Toenjes, B. P ei e , T. C. Bee s, J. J. Cowan, V. Hill, and K.-L. K a z, As ophys. J. 579, 626 (2002). [3] K.-L. K a z, B. P ei e , J. J. Cowan, and C. Sneden, New As on. Re . 48, 105 (2004). [4] D. D. Clay on, As ophys. J. 139, 637 (1964). [5] W. A. Fowle and F. Hoyle, As on. J. 70, 345 (1960). [6] A. He e a e al., in Wo kshop on Nuclea Da a o he T ansmu a ion o Nuclea Was e, edi ed by A. Kelic and K. 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