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].
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