uni e se
Communica ion
Fi s Resul s o he 140Ce(n,γ)141Ce C oss-Sec ion Measu emen
a n_TOF
Simone Amaducci 1,2,* , Nicola Colonna 3, Luigi Cosen ino 1, Se gio C is allo 4,5, Paolo Finocchia o 1,
Milan K iˇcka 6, C is ian Massimi 7,8, Ma io Mas oma co 9, Annama ia Mazzone 3,10, Albe o Mengoni 11,
S anisla Valen a 6, Oli e Abe le 9, Vic o Alcayne 12, Józe And zejewski 13, Lau en Audouin 14,
Vic o Babiano-Sua ez 15, Michael Bacak 9,16,17, Massimo Ba bagallo 3,9, Samuel Benne 18, E ic Be houmieux 17,
Jon Billowes 18, Dami Bosna 19, Adam B own 20, Mau izio Busso 4,21, Manuel Caamaño 22,
Luis Caballe o-On anaya 15, F ancisco Cal iño 23, Ma co Cal iani 9, Daniel Cano-O 12, Ad ia Casano as 23,
F ancesco Ce u i 9, En ico Chia e i 9,18, Guillem Co és 23, Miguel Co és-Gi aldo 24, Lucia-Anna Damone 3,25,
Paul-John Da ies 18, Ma ia Diakaki 9,26, Mi co Die z 27, Cesa Domingo-Pa do 15, Ruga d D essle 28,
Quen in Ducasse 29, Emme ic Dupon 17, Ignacio Du án 22, Zino ia Eleme 30, Bea iz Fe nández-Domínguez 22,
Al edo Fe a i 9, Val e Fu man 31, Ka h in Göbel 32, Ruchi Ga g 27, Aleksand a Gawlik 13, Simone Gila doni 9,
Isabel Gonçal es 33, En ique González-Rome o 12, Ca los Gue e o 24, F ank Gunsing 17, Hideo Ha ada 34,
S ephan Heini z 28, Jan Heyse 35, Da id Jenkins 20, A nd Junghans 36, F anz Käppele 37, Yacine Kadi 9,
A sushi Kimu a 34, Ing id Knapo a 11, Michael Kokko is 26, Yu i Kopa ch 31, Deniz Ku ulgil 32, Ion Lada escu 15,
Claudia Lede e -Woods 27, Helmu Leeb 16, Jo ge Le endegui-Ma co 24, Sa ah-Jane Lonsdale 27, Daniela Macina 9,
Alice Manna 7,8, T ini a io Ma ínez 12, Alessand o Masi 9, Pie ancesco Mas inu 38, Emilio-And ea Mauge i 28,
Emilio Mendoza 12, Vea iki Michalopoulou 9,26, Paolo Milazzo 39, Fede ica Ming one 9, Ja ie Mo eno-So o 17,
Aga ino Musuma a 1,40, Alexand u Neg e 41, F ancisco Ogálla 42, And eea Op ea 41, Nikolas Pa onis 30,
And eas Pa lik 43, Ja osław Pe kowski 13, Luciano Pie san i 4,5, C is ina Pe one 41, Elisa Pi o ano 29,
Ignacio Po as 42, Ja ie P aena 42, José-Manuel Quesada 24, Diego Ramos-Do al 14, Thomas Rausche 44,45,
René Rei a h 32, Dimi i Rochman 28, Ca lo Rubbia 9, Ma a Saba é-Gila e 9,24, Alok Saxena 46,
Pe e Schillebeeckx 35, Do o hea Schumann 28, Adhi ya Sekha 18, Ga in Smi h 18, Nikolay Sosnin 18,
Pe e Sp ung 28, A hanasios S ama opoulos 26, Giuseppe Taglien e 3, José Tain 15, A iel Ta i eño-Saldi ia 23,
Lau en Tassan-Go 9,26,14, Benedik Thomas 32, Pablo To es-Sánchez 42, And ea Tsinganis 9, Ji i Ul ich 28,
Sebas ian U lass 9,36, Gianni Vannini 7,8, Vincenzo Va iale 3, Ped o Vaz 33, Albe o Ven u a 7, Diego Vesco i 4,5,47,
Vasilis Vlachoudis 9, Rosa Vlas ou 26, An on Wallne 48, PhilipJohn Woods 27, Tobias W igh 18, Pe a Žugec 19
and on behal o he n_TOF Collabo a ion
Ci a ion: Amaducci, S.; Colonna, N.;
Cosen ino, L.; C is allo, S.;
Finocchia o, P.; K iˇcka, M.; Massimi,
C.; Mas oma co, M.; Mazzone, A.;
Mengoni, A.; e al. Fi s Resul s o he
140Ce(n,γ)141Ce C oss-Sec ion
Measu emen a n_TOF. Uni e se
2021,7, 200. h ps://doi.o g/
10.3390/uni e se7060200
Academic Edi o s: Se gio C is allo
and Paolo Ven u a
Recei ed: 31 Ma ch 2021
Accep ed: 17 May 2021
Published: 17 June 2021
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
1INFN Labo a o i Nazionali del Sud, 95125 Ca ania, I aly
2Dipa imen o di Fisica e As onomia, Uni e si à di Ca ania, 2, 95131 Ca ania, I aly
3Is i u o Nazionale di Fisica Nuclea e, Sezione di Ba i, 70126 Ba i, I aly
4Is i u o Nazionale di Fisica Nuclea e, Sezione di Pe ugia, 06123 Pe ugia, I aly
5Is i u o Nazionale di As o isica—Osse a o io As onomico d’Ab uzzo, 64100 Collu ania, I aly
6Cha les Uni e si y, 11000 P ague, Czech Republic
7Is i u o Nazionale di Fisica Nuclea e, Sezione di Bologna, 40127 Bologna, I aly
8Dipa imen o di Fisica e As onomia, Uni e si à di Bologna, 40129 Bologna, I aly
9Eu opean O ganiza ion o Nuclea Resea ch (CERN), 1211 Gene a, Swi ze land
10 Consiglio Nazionale delle Rice che, 7, 00185 Ba i, I aly
11 Agenzia Nazionale pe le Nuo e Tecnologie (ENEA), 40129 Bologna, I aly
12 Cen o de In es igaciones Ene gé icas Medioambien ales y Tecnológicas (CIEMAT), 28040 Mad id, Spain
13 Uni e si y o Lodz, 90-137 Łód´z, Poland
14 Ins i u de Physique Nucléai e, CNRS-IN2P3, Uni e si y Pa is-Sud, Uni e si é Pa is-Saclay, CEDEX,
F-91406 O say, F ance
15 Ins i u o de Física Co puscula , CSIC—Uni e sidad de Valencia, 46980 Pa e na, Spain
16 Technische Uni e si ä Wien, 1040 Vienna, Aus ia
17 CEA I u, Uni e si é Pa is-Saclay, F-91191 Gi -su -Y e e, F ance
18 Uni e si y o Manches e , Manches e M13 9PL, UK
19 Depa men o Physics, Facul y o Science, Uni e si y o Zag eb, 10000 Zag eb, C oa ia
20 Uni e si y o Yo k, Yo k YO10 5DD, UK
21 Dipa imen o di Fisica e Geologia, Uni e si à di Pe ugia, 06123 Pe ugia PG, I aly
22 Uni e si y o San iago de Compos ela, San iago de Compos ela, 15705 Compos ela, Spain
23 Uni e si a Poli ècnica de Ca alunya, 08034 Ba celona, Spain
24 Uni e sidad de Se illa, 41004 Se illa, Spain
Uni e se 2021,7, 200. h ps://doi.o g/10.3390/uni e se7060200 h ps://www.mdpi.com/jou nal/uni e se
Uni e se 2021,7, 200 2 o 11
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2021 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
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dis ibu ed unde he e ms and
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A ibu ion (CC BY) license (h ps://
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4.0/).
25 Dipa imen o di Fisica, Uni e si à degli S udi di Ba i, 70121 Ba i, I aly
26 Na ional Technical Uni e si y o A hens, A hens, 10682, G eece
27 School o Physics and As onomy, Uni e si y o Edinbu gh, Edinbu gh EH9 3FD, UK
28 Paul Sche e Ins i u (PSI), 5232 Villingen, Swi ze land
29 Physikalisch-Technische Bundesans al (PTB), Bundesallee 100, 38116 B aunschweig, Ge many
30 Uni e si y o Ioannina, 451 10 Ioannina, G eece
31 Join Ins i u e o Nuclea Resea ch (JINR), 141980 Dubna, Russia
32 Goe he Uni e si y F ank u , 60323 F ank u am Main, Ge many
33 Ins i u o Supe io Técnico, 1049-001 Lisbon, Po ugal
34 Japan A omic Ene gy Agency (JAEA), Tokai-mu a 319-1184, Japan
35 Eu opean Commission, Join Resea ch Cen e, Geel, Re ieseweg 111, B-2440 Geel, Belgium
36 Helmhol z-Zen um D esden-Rossendo , 01328 D esden, Ge many
37 Ka ls uhe Ins i u e o Technology, Campus No h, IKP, 76021 Ka ls uhe, Ge many
38 Is i u o Nazionale di Fisica Nuclea e, Sezione di Legna o, 35020 Legna o, I aly
39 Is i u o Nazionale di Fisica Nuclea e, Sezione di T ies e, 34149 T ies e, I aly
40 Dipa imen o di Fisica e As onomia, Uni e si à di Ca ania, 95123 Ca ania, I aly
41 Ho ia Hulubei Na ional Ins i u e o Physics and Nuclea Enginee ing, P.O. Box MG-6,
RO-76900 Bucha es , Romania
42 Uni e si y o G anada, 18010 G anada, Spain
43 Facul y o Physics, Uni e si y o Vienna, 1090 Vienna, Aus ia
44 Depa men o Physics, Uni e si y o Basel, CH-4056 Basel, Swi ze land
45 Cen e o As ophysics Resea ch, Uni e si y o He o dshi e, He s AL10 9AB, UK
46 Bhabha A omic Resea ch Cen e (BARC), Maha ash a 400094, India
47 G an Sasso Science Ins i u e, 67100 L’Aquila, I aly
48 Aus alian Na ional Uni e si y, 2600 Canbe a, Aus alia
*Co espondence: [email p o ec ed]; Tel.: +39-3387997513
Abs ac :
An accu a e measu emen o he
140
Ce(n,
γ
) ene gy-dependen c oss-sec ion was pe o med
a he n_TOF acili y a CERN. This c oss-sec ion is o g ea impo ance because i ep esen s a
bo leneck o he s-p ocess nucleosyn hesis and de e mines o a la ge ex en he ce ium abundance in
s a s. The measu emen was mo i a ed by he signi ican di e ence be ween he ce ium abundance
measu ed in globula clus e s and he alue p edic ed by heo e ical s ella models. This disc epancy
can be asc ibed o an o e es ima ion o he
140
Ce cap u e c oss-sec ion due o a lack o accu a e
nuclea da a. Fo his measu emen , we used a sample o ce ium oxide en iched in
140
Ce o 99.4%.
The expe imen al appa a us consis ed o ou deu e a ed benzene liquid scin illa o de ec o s, which
allowed us o o e come he di icul ies p esen in he p e ious measu emen s, hanks o hei e y
low neu on sensi i i y. The accu a e analysis o he p-wa e esonances and he calcula ion o hei
a e age pa ame e s a e undamen al o imp o e he e alua ion o he
140
Ce Maxwellian-a e aged
c oss-sec ion.
Keywo ds:
ce ium;
140
Ce; neu on; cap u e; c oss-sec ion; s-p ocess; n_TOF; MACS; nucleosyn hesis
1. In oduc ion
I has been well asce ained since he la e 1950s ha he as majo i y o he elemen s
abo e he i on peak a e syn hesized in s a s, ia sequences o neu on cap u es and
β
-
decays [
1
,
2
]. Depending on he ypical ime elapsing be ween wo consecu i e neu on
cap u es, and hence on he a ailable neu on densi ies, hese p ocesses a e e e ed o
as slow (s) o apid ( ). In he -p ocess, neu on densi ies as high as 10
18
–10
22
cm
−3
a e a ained, igge ing he p oduc ion o e y neu on- ich nuclei in an ex emely sho
ime, by means o neu on cap u e sequences much as e han he
β
-decays. The physical
condi ions o he -p ocess a e me in explosi e scena ios, such as neu on s a me ge s o
co e-collapse supe no ae, which ha e ypical ime scales o he o de o a ew seconds. The
s-p ocess mainly akes place in he la e e olu iona y phases o low-mass s a s, in pa icula
du ing hei he mally pulsing asymp o ic gian b anch (TP-AGB) phase. Du ing ha
e olu iona y s age, a succession o bu ning and mixing episodes leads o he p oduc ion o
neu ons h ough he eac ions
13
C(
α
,n)
16
O and
22
Ne(
α
,n)
25
Mg. While he o me eac ion
Uni e se 2021,7, 200 3 o 11
is he majo neu on sou ce in low-mass AGBs, he la e signi ican ly con ibu es o hea y-
elemen nucleosyn hesis in mo e massi e AGBs (5–6 M
sun
) (see, e.g., [
3
,
4
]). Typical neu on
densi ies in AGB s a s a e
≈
10
7
cm
−3
: he ela i ely long ime be ween wo consecu i e
cap u es allows he uns able nuclei o e en ually
β
-decay; he esul ing s-p ocess pa h hen
ollows he alley o s abili y up o he syn hesis o lead and bismu h.
In he las ew decades, accu a e knowledge o he s-p ocess si e led o a conside able
e o in modeling he e olu ion o he AGB s a s and e alua ing he con ibu ion o all he
nuclea eac ions in ol ed in he nucleosyn hesis o hea y elemen s (see, e.g., [
5
–
8
]). These
models allowed s udying he AGB chemical e olu ion and hei ole as pollu e s o he
galac ic medium. Clea ly, high-quali y nuclea da a a e equi ed in o de o de e mine he
inal abundances o all he elemen s p oduced in s ella in e io s. This holds in pa icula
o neu on cap u e c oss-sec ions. The compa ison be ween he obse ed abundances and
he ones p edic ed by s ella models ep esen s an essen ial ool o es he obus ness o
he models, in pa icula o hose elemen s ha a e syn hesized mainly ia he s-p ocess.
Such a kind o compa ison was ca ied ou by S anie o e al. [
9
], conside ing he
globula clus e s M4 [
10
] and M22 [
11
]. Thanks o he p esence o many s a s, which
allow calcula ing he a e age dis ibu ions and he clea de e mina ion o he -p ocess
con ibu ion, hese clus e s ep esen an ideal si e o es he obus ness o s-p ocess p edic-
ions. Figu e 1shows he compa ison be ween s ella models’ p edic ions and he chemical
composi ion o M22 s a s, in he usual spec oscopic no a ion
1
. In his case, AGB s a s
in he mass ange 3–6 M
sun
con ibu e o he s-p ocess p oduc ion. In gene al, a good
ag eemen is obse ed o mos o he elemen s, bu a la ge disc epancy is p esen in he
case o Ce (Z = 58). Fo ce ium, belonging o he second s-p ocess peak (Ba-La-P -Nd), he
heo e ical expec a ion is
≈
30% lowe han he alues obse ed in he M22 clus e , while
nea by elemen s as onishingly ag ee wi h he heo y. Being a neu on-magic nucleus,
140
Ce
ep esen s a e y in e es ing iso ope, since i s e y small cap u e c oss-sec ion ac s as a
bo leneck o he s-p ocess, g ea ly enhancing i s abundance wi h espec o he nea by
non-magic iso opes. Since he majo i y o na u al ce ium is made o
140
Ce (89%), i s de-
s uc ion channel, i.e., he cap u e o a neu on, la gely de e mines he ce ium abundance
on he s ella su ace. The eac ion
140
Ce(n,
γ
) lacks accu a e expe imen al da a, while i s
p oduc ion channel, he neu on cap u e on
139
La, has al eady been in es iga ed wi h high
accu acy a n_TOF [
12
]. The e o e, a nuclea o igin o he disc epancy needed o be u he
in es iga ed, since a educ ion o he
140
Ce(n,
γ
) c oss-sec ion could jus i y he obse ed
o e es ima ion. Conside ing he po en ial con ibu ions om AGBs wi h di e en ini ial
masses, he e alua ion o a a ia ion o he neu on cap u e a e on he whole ene gy
spec um will be pe o med when he s ella neu on cap u e a e is a ailable.
The main nuclea cap u e quan i ies ha se e as he inpu o s-p ocess nucleosyn-
hesis models a e he MACS, i.e., he con olu ion o he cap u e c oss-sec ions and he
Maxwellian ene gy dis ibu ion o neu ons o a gi en empe a u e kT. The esul s p e-
sen ed in [
9
] we e ob ained by using he MACS p o ided by he da abase KADoNiS0.3 [
13
],
which is a (on-line) da abase o c oss-sec ions ele an o he s- and p-p ocesses. The
MACS epo ed in KADoNiS comes om ac i a ion measu emen [
14
] o a na u al ce ium
sample using a quasi-s ella neu on spec um o kT = 25 keV. Theo e ical models, based
on he Hause –Feshbach (HF) heo y, pe mi ed ex apola ing he expe imen al MACS o
o he alues o kT. The HF calcula ions o he 30 keV MACS epo ed in [
14
] o e es ima ed
he expe imen al MACS by 30% in he case o
140
Ce. The disag eemen is ela ed o he
unce ain y and inco ec ness o he a e age esonance pa ame e s used in he calcula ions.
Al hough he e exis es ima es based on expe imen al da a o esonance spacing (D0) and
adia ion wid h (
Γγ
) o s-wa e esonances, any es ima e o he a e age
Γγ
o p-wa e (and
highe l) esonances is missing (and is hus based only on calcula ions). Fu he mo e, since
he la ge pa o he
140
Ce cap u es ake place a kT
≈
8 keV, i s abundance esul s in being
e en mo e sensi i e o he ex apola ion o he MACS owa ds lowe ene gies, especially
because ela i ely ew esonances a e p esen in his ene gy ange.
Uni e se 2021,7, 200 4 o 11
Figu e 1.
A e age abundances obse ed in he globula clus e M22 ( ed poin s) compa ed o he
heo e ical expec a ions deduced om s ella models ( om [9]).
Ve y ew expe imen al ene gy-dependen c oss-sec ions o
140
Ce a e a ailable, and
he c oss-sec ion epo ed by he nuclea lib a ies la gely elies on ansmission expe i-
men s, usually pe o med wi h na u al ce ium samples, hence wi h la ge e ec s due o
he p esence o
142
Ce (which ac s as a con aminan ). The only cap u e measu emen wi h
an ene gy esolu ion su icien o e ec i ely esol e indi idual esonance was pe o med
by Musg o e e al. [
15
], whe e C
6
F
6
de ec o s we e employed, which a e known o be
no pa icula ly sui ed o cap u e measu emen on iso opes wi h e y high sca e ing
c oss-sec ions [16], such as 140Ce.
The lack o highly eliable expe imen al da a makes he e alua ion p ocess e y
challenging, so ha i is no su p ising ha he MACS e alua ed wi h he esonance
pa ame e s o he majo nuclea lib a ies (as ENDF, JEFF, and JENDL) led o e y di e en
esul s, as shown in Figu e 2. In pa icula , he MACS calcula ed wi h he ENDF/B-
VIII [
17
], JENDL-4.0 [
18
], and JEFF3.3 [
19
] esonance pa ame e s la gely disag ee, and all
a e sys ema ically lowe han KADoNiS0.3 and he mos ecen KADoNiS1.0 [
20
]. The
accu acy o he MACS can be signi ican ly imp o ed by adding new expe imen al da a.
In pa icula , mo e s ic cons ain s on he s a is ical model pa ame e s a e equi ed o
educe he unce ain y o he heo e ical calcula ions. In o de o cla i y he disc epancy
ha eme ged in [
9
] and o p oduce a mo e accu a e e alua ion o he MACS, a new
measu emen o he 140Ce(n,γ) c oss-sec ion was pe o med a he n_TOF acili y in 2018.
Uni e se 2021,7, 200 5 o 11
Figu e 2.
The MACS calcula ed wi h he esonance pa ame e s p o ided by majo lib a ies compa ed
wi h he alues epo ed in KADoNiS0.3 and KADoNiS1.0.
2. Expe imen al Appa a us and Da a Analysis
The n_TOF acili y ep esen s a unique si e whe e high-p ecision measu emen s o
neu on-induced c oss-sec ions can be pe o med. Since i s ope a ional s a in 2001, he
n_TOF collabo a ion [
21
] has la gely con ibu ed o he imp o emen o nuclea da a o
in e es o he nuclea as ophysics communi y, in pa icula pe o ming many accu a e
neu on cap u e c oss-sec ion measu emen s (see, e.g., he wo ecen wo ks [
22
,
23
]). The
n_TOF whi e pulsed neu on beam is p oduced by spalla ion eac ions on a cylind ical lead
a ge induced by a 20 GeV/c p o on beam accele a ed wi h he CERN P o on Synch o on
(PS). The kine ic ene gy o he neu ons eaching he wo expe imen al a eas is measu ed
wi h he ime-o - ligh echnique. The
140
Ce(n,
γ
) measu emen equi ed he high-ene gy
esolu ion o he beam p esen in Expe imen al A ea 1 (EAR1), hanks o i s long ligh
pa h o
≈
185 m. In EAR1, i is possible o each a esolu ion om 5
×
10
−4
a 1 keV o
3×10−3
a 100 keV [
24
], which is essen ial o e ec i ely esol e he esonances in he
egion o in e es .
The sample employed was composed o 12.318 g ams o CeO
2
powde , en iched
o 99.4% o
140
Ce, wi h only 0.6% o
142
Ce as a ele an con amina ion (na u al ce ium
p esen s 11% o
142
Ce). The sample was p oduced a Paul She e Insi u (PSI) ia he
sin e ing p ocess. The CeO
2
powde was p essed and enclosed in a PEEK (polye he e he
ke one) cylind ical capsule o 1 mm in hickness and hea ed a 100
◦
C o 4 h in a glo e
box wi h a con olled O
2
and H
2
O a mosphe e (concen a ion lowe han 1 ppm). A
197
Au
sample, ha ing a diame e almos iden ical o he ce ium one, was used o no malize he
ce ium da a and o exac ly de e mine he ligh pa h leng h. The la e was ob ained om
i ing he gold cap u e esonances in he ene gy in e al om 100 eV o 2 keV. In o de o
e alua e he di e en sou ces o backg ound da a, an emp y sample was used o measu e
he componen ela ed o he beam, while a lead sample was employed o measu e he
sample- ela ed backg ound. Finally, he de ec o s we e calib a ed, acqui ing da a on a
weekly basis wi h ou γsou ces: 137Cs, 137Y, Am-Be, and Cm-C.
The neu on cap u es we e obse ed by de ec ing he
γ
- ays p oduced by he decay
o he compound nucleus
141
Ce. The expe imen al appa a us was made o ou deu e a ed
benzene (C
6
D
6
) liquid scin illa o de ec o s [
25
] encapsula ed in a cylind ical case made
o ca bon ibe , o gua an ee a e y low neu on sensi i i y. A ela i ely high neu on
sensi i i y is one o he di icul ies encoun e ed wi h C
6
F
6
de ec o s employed in he
measu emen by [
15
]. The de ec o s we e placed a
≈
10 cm om he cen e o he sample
holde a angles o 125
◦
wi h espec o he neu on beam. The adop ed con igu a ion
minimized he e ec o he aniso opic emission o
γ
- ays; mo eo e , he ups eam posi ion
Uni e se 2021,7, 200 6 o 11
wi h espec o he sample posi ion educed he backg ound due o he in-beam
γ
- ays,
which we e sca e ed by he sample. In o de o moni o he neu on lux, he Silicon
Moni o (SiMon) de ec o [
26
] was ins alled ups eam wi h espec o he cap u e appa a us.
The da a analysis employed he o al ene gy de ec ion p inciple in combina ion wi h
he pulse heigh weigh ing echnique [
27
,
28
] o elimina e he dependence o he de ec ion
e iciency om he
γ
cascade pa h ollowing he neu on cap u e. This is achie ed i he
de ec ion e iciency o an i- h
γ
ay, emi ed du ing he
γ
cascade, is p opo ional o i s
ene gy
Ei
γ
. In such a case, he de ec ion o he ull cascade becomes p opo ional o i s o al
ene gy E o
γ:
εcascade =
m
∑
i=1
εi(Ei
γ) =
m
∑
i=1
k×Ei
γ=k×E o
γ(1)
In he case o C
6
D
6
de ec o s, he p opo ionali y be ween he deposi ed ene gy and
he
γ
- ays de ec ion e iciency is achie ed h ough an o -line weigh ing unc ion applied
o he de ec o signals. These unc ions we e calcula ed by simula ing he ull expe imen al
appa a us wi h a Mon e Ca lo simula ion, pe o med wi h he Gean 4 [
29
] code. A e he
weigh ing p ocedu e, he expe imen al cap u e yield can be w i en as:
Yexp(En) = NCw(En)−Bw(En)
ε(En)φ(En)(2)
whe e
Cw
a e he weigh ed coun a es wi h he sample,
Bw
is he weigh ed backg ound,
φ
he neu on lux on he a ge , and N a no maliza ion ac o . The la e includes many
geome ical ac o s, such as he sample a ea, he beam in e cep ion ac o (BIF), and he
di e en solid angle o he lux moni o and he cap u e se up. The neu on lux measu ed
wi h SiMon was compa ed wi h he o icial n_TOF lux [
30
], e alua ed wi h di e en
de ec o s and s anda d eac ions, esul ing in an excellen ag eemen in he ene gy in e al
o in e es . The e o e, in o de o calcula e he
140
Ce cap u e yield, he o icial neu on lux
was used, which is known wi h an unce ain y be e han 1% below 3 keV and wi hin
4–5% up o 100 keV.
The gold sample backg ound was e alua ed acco ding o he me hod desc ibed in [
28
],
using he da a collec ed wi h he emp y sample and wi h he lead sample, p ope ly scaled.
As an example, Figu e 3shows he gold neu on ene gy spec um o one o he de ec o s,
compa ed wi h he backg ound and he beam-o componen . The la e co esponds o
he ambien backg ound, and i is almos negligible o E
n
> 10 eV. As expec ed, om
20 o 50 eV, he gold spec um is almos equal o he backg ound because o he e y
small
197
Au cap u e c oss-sec ion, con i ming he co ec ness o he p ocedu e adop ed o
he backg ound e alua ion. The same me hod could no be applied o ce ium, since he
componen o he backg ound depending on he sample was dominan , due o he e y high
a eal densi y o he ce ium sample (1.291×10−2a oms/ba n) and high neu on sca e ing
c oss-sec ion. A he p esen s age o analysis, he ce ium backg ound is conside ed o be
linea in he icini y o each i ed esonance. A mo e igo ous app oach, by means o a
Mon e Ca lo simula ion, is cu en ly unde s udy.
Uni e se 2021,7, 200 7 o 11
Figu e 3.
Ene gy spec um measu ed wi h he gold sample ( ed), compa ed wi h he o al e alua ed
backg ound (blue) and he ambien backg ound (g een).
The no maliza ion ac o N was calcula ed by applying he sa u a ed esonance
me hod [
31
] o he opaque gold cap u e esonance a 4.9 eV. The esul ing alue (N =
0.7127
±
0.0014) was subs an ially in ag eemen wi h he beam in e cep ion ac o epo ed
in [
24
] o he 2 cm-diame e samples. The ce ium da a we e sui ably co ec ed o ake
in o accoun he sligh ly smalle diame e o he sample (1.95 cm). The gold da a allowed
e i ying he obus ness o he analysis in he ene gy in e al whe e he
140
Ce cap u e
esonances a e loca ed. Figu e 4shows ha he expe imen al esul s on a e age ag eed
wi h he
197
Au(n,
γ
) c oss-sec ion e alua ed by he ENDF/B-VIII lib a y, in he neu on
ene gy ange om 1 keV o 100 keV.
Figu e 4.
Expe imen al
197
Au(n,
γ
) c oss-sec ion (black do s) compa ed o he e alua ion o ENDF/B-
VIII ( ed dashed line).
A p elimina y analysis o he ce ium cap u e yield was ca ied ou wi h he Bayesian
R-ma ix code SAMMY [
32
]. This code can manage he sel -shielding and mul iple in-
e ac ions o neu ons in he sample and o he expe imen al e ec s such as Dopple and
esolu ion b oadening by including he esolu ion unc ion, which is a p ope y o all
neu on ime-o - ligh acili ies, which desc ibes he dis ibu ion o he neu on ime o
ligh o a gi en kine ic ene gy. The esonance pa ame e s p o ided by he JENDL-4.0
Uni e se 2021,7, 200 8 o 11
lib a y we e ini ially adop ed as a e e ence, including he spin-pa i y assignmen , which
was almos iden ical o hose o o he lib a ies, such as ENDF/B-VIII.
3. Discussion and pe spec i es
The p elimina y
140
Ce da a allowed esol ing and pe o ming he esonance shape
analysis (RSA) o 81 o he 102 esonances epo ed by he lib a y JENDL-4.0 below 65
keV, o de e mine hei ke nel
2
and in some cases he adia ion and sca e ing wid hs (
Γγ
and
Γn
, espec i ely). Be ween 2.5 keV, whe e he i s
140
Ce esonance is loca ed, and 34
keV, he da a made i possible o i he pa ame e s o 46 esonances, while JENDL-4.0
epo ed 47 esonances. F om 34 keV o 65 keV, JENDL-4.0 indica ed he p esence o 55
esonance, while he expe imen al da a allowed i ing 35 o hem; no esonances could be
clea ly iden i ied abo e. Only one s uc u e due o he
142
Ce con amina ion was obse ed
in he expe imen al cap u e yield a 1.15 keV, a away om any
140
Ce esonance; hence,
he p esence o 142Ce did no ep esen an issue o he analysis.
Figu e 5shows he con ibu ion o he MACS o a di e en sub-se o esonances
using hei pa ame e s om he JENDL-4.0 lib a y. I is no ewo hy ha he esonances
wi h ene gies lowe han 60 keV ( ed line) made he majo con ibu ion o he MACS in
he empe a u e in e al o in e es o he s-p ocess (<30 keV). One can also obse e he
impo ance o he p-wa es’ con ibu ion, which was esponsible o app oxima ely 50%
o he MACS a 8 keV and e en mo e wi h inc easing ene gy. The n_TOF measu emen
ensu ed he accu a e measu emen s o he esonances ke nel; u he mo e, i can inc ease
he accu acy on hei a e age wid h and spacing wi h espec o he alues a ailable du ing
he e alua ion o he MACS by [14].
Figu e 5.
Maxwellian a e aged c oss-sec ion calcula ed wi h he indi idual esonance pa ame e s
as p o ided by JENDL-4.0 (o ange dashed line), compa ed wi h he con ibu ion gi en by di e en
sub-se s o esonances.
An example o he RSA in he case o a p-wa e esonance is shown in Figu e 6, whe e
he quali y o he expe imen al da a is clea ly su icien o accu a ely de e mine he ke nel
and esonance ene gy. I is in e es ing ha he n_TOF i o he cap u e yield showed la ge
disc epancies compa ed o bo h he JENDL-4.0 and ENDF/B-VIII lib a ies. As shown by
Table 1
, he alue o g
ΓγΓn/Γ
measu ed a n_TOF was a ac o o wo la ge wi h espec
o bo h lib a ies and o he alues om [
15
]. The esul s showed an excellen ene gy
esolu ion achie able a n_TOF; in ac , we we e able o de e mine he esonance ene gy
wi h a p ecision o wo o de s o magni ude be e han [15].
Uni e se 2021,7, 200 9 o 11
Figu e 6.
Example o he RSA in he case o p-wa e esonance; in his case, he n_TOF i ( ed) o he
cap u e yield shows la ge disc epancies, compa ed o bo h he JENDL-4.0 (g een) and ENDF/B-VIII
(blue) lib a ies.
Table 1.
Cap u e ke nel measu ed a n_TOF compa ed o he alues epo ed by he ENDF/B-VIII
and JENDL-4.0 lib a ies and by [15].
Sou ce Ene gy (eV) gΓγΓn/Γ(meV)
n_TOF 5636.56 ±0.05 21.6 ±1.2
JENDL-4.0 5640 11.0
ENDF/B-VIII 5640 10.5
Musg o e e al. 5640 ±5 10 ±1
The i s esul s demons a ed ha he accu a e ene gy-dependen c oss-sec ion o
140
Ce(n,
γ
) was measu ed success ully a n_TOF and he esonances pa ame e s we e de e -
mined wi h unce ain ies signi ican ly lowe han p e ious expe imen s. The combina ion
o he C
6
D
6
de ec o s, wi h hei e y low neu on sensi i i y, and he high ene gy eso-
lu ion o n_TOF we e decisi e o measu e his e y low cap u e c oss-sec ion. The da a
allowed pe o ming a eliable RSA o app oxima ely 80 esonances, a la ge ac ion o
which a e p-wa es. These a e o pa icula in e es o he s-p ocess, since hey p o ide a
la ge con ibu ion o he MACS be ween 8 keV and 30 keV. Di ec expe imen al in o ma-
ion will la gely de e mine he MACS a 8 keV and signi ican ly igh en he cons ain s o
he s a is ical model o calcula e he MACS a abou 30 keV. The new neu on cap u e a e,
once included in he nucleosyn hesis s ella models, will shed mo e ligh on he disc epancy
wi h he ce ium abundance measu ed in he M22 globula clus e .
Au ho Con ibu ions:
Concep ualiza ion, S.C., C.M. and A.M. (Albe o Mengoni); o mal analysis,
S.A. and A.M. (Annama ia Mazzone); in es iga ion, S.A., L.C., C.M. and A.M. (Albe o Mengoni);
supe ision, N.C., L.C., S.C., P.F., C.M. and A.M. (Albe o Mengoni); me hodology, M.K. and S.V.;
w i ing—o iginal d a , S.A.; w i ing— e iew and edi ing, all he au ho s; da a cu a ion, all he
au ho s. All au ho s ha e ead and ag eed o he published e sion o he manusc ip .
Funding: This esea ch ecei ed no ex e nal unding.
Acknowledgmen s:
The ce ium oxide ma e ial o his measu emen was p o ided by T. Ka abuchi
o he Tokyo Ins i u e o Technology.
Con lic s o In e es : The au ho s decla e no con lic o in e es .
