Eu . Phys. J. A (2022) 58:147
h ps://doi.o g/10.1140/epja/s10050-022-00779-7
Regula A icle - Expe imen al Physics
High accu acy, high esolu ion 235U(n, ) c oss sec ion om n_TOF
(CERN) om 18 meV o 10 keV
M. Mas oma co1,2, S. Amaducci3,a, N. Colonna1, P. Finocchia o3, L. Cosen ino3, M. Ba bagallo7, O. Abe le7,
J. And zejewski8, L. Audouin9, M. Bacak10,7,11,J.Balib ea
12,F.Beˇc ᡠ13, E. Be houmieux11, J. Billowes14,
D. Bosna 15,A.B own
16, M. Caamaño17, F. Cal iño18, M. Cal iani7, D. Cano-O 12, R. Ca della7, A. Casano as18,
F. Ce u i7,Y.H.Chen
9, E. Chia e i7,14,19, G. Co és18, M. A. Co és-Gi aldo19, L. A. Damone3,20, M. Diakaki11,
C. Domingo-Pa do21, D. Diacono1, R. D essle 22, E. Dupon 11, I. Du án17, B. Fe nández-Domínguez17, A. Fe a i7,
P. Fe ei a23, V. Fu man24, K. Göbel25,A.R.Ga cía
12, A. Gawlik8, S. Gila doni7, T. Gloda iu26, I. F. Gonçal es23,
E. González-Rome o12, E. G iesmaye 10, C. Gue e o19, F. Gunsing11,7, H. Ha ada27, S. Heini z22, J. Heyse28,
D. G. Jenkins16, E. Je icha10, F. Käppele 29,Y.Kadi
7, A. Kalama a30, P. Ka igin10,A.Kimu a
27,N.Ki el
22,
I. Knapo a13, M. Kokko is30,M.K iˇcka13, D. Ku ulgil25, E. Leal-Cidoncha17, C. Lede e 31, H. Leeb10,
J. Le endegui-Ma co19,S.LoMeo
4,5, S. J. Lonsdale31, D. Macina7, A. Manna5,6, J. Ma ganiec8,32, T. Ma ínez12,
A. Masi7, C. Massimi5,6, P. Mas inu33, E. A. Mauge i22, A. Mazzone3,34, E. Mendoza12, A. Mengoni4,5,
P. M. Milazzo35, F. Ming one7, A. Musuma a3,36, A. Neg e 26,R.Nol e
32, A. Op ea26, N. Pa onis37, A. Pa lik38,
J. Pe kowski8, I. Po as39, J. P aena39, J. M. Quesada19, D. Radeck32, T. Rausche 40,41, R. Rei a h25, C. Rubbia7,
J. A. Ryan14, M. Saba é-Gila e7,19, A. Saxena42, P. Schillebeeckx28, D. Schumann22, P. Sedyshe 24,A.G.Smi h
14,
N. V. Sosnin14, A. S ama opoulos30, G. Taglien e3,J.L.Tain
21, A. Ta i eño-Saldi ia18, L. Tassan-Go 9, S. Valen a13,
G. Vannini5,6, V. Va iale3,P.Vaz
23, A. Ven u a5, V. Vlachoudis7, R. Vlas ou30, A. Wallne 43, S. Wa en14,
C. Weiss10, P. J. Woods31, T. W igh 14, P. Žugec15,7
1Is i u o Nazionale di Fisica Nuclea e, Sezione di Ba i, I aly
2Dipa imen o In e a eneo di Fisica, Uni e si à degli S udi di Ba i, Ba i, I aly
3INFN Labo a o i Nazionali del Sud, Ca ania, I aly
4Agenzia Nazionale pe le Nuo e Tecnologie (ENEA), Bologna, I aly
5Is i u o Nazionale di Fisica Nuclea e, Sezione di Bologna, Bologna, I aly
6Dipa imen o di Fisica e As onomia, Uni e si à di Bologna, Bologna, I aly
7Eu opean O ganiza ion o Nuclea Resea ch (CERN), Mey in, Swi ze land
8Uni e si y o Lodz, Genè e, Poland
9Ins i u de Physique Nucléai e, CNRS-IN2P3, Uni e si y Pa is-Sud, Uni e si é Pa is-Saclay, 91406 O say Cedex, F ance
10 Technische Uni e si ä Wien, Vienna, Aus ia
11 CEA I u, Uni e si é Pa is-Saclay, 91191 Gi -su -Y e e, F ance
12 Cen o de In es igaciones Ene gé icas Medioambien ales y Tecnológicas (CIEMAT), Mad id, Spain
13 Cha les Uni e si y, P ague, Czech Republic
14 Uni e si y o Manches e , Manches e , UK
15 Depa men o Physics, Facul y o Science, Uni e si y o Zag eb, Zag eb, C oa ia
16 Uni e si y o Yo k, Hesling on, UK
17 Uni e si y o San iago de Compos ela, San iago, Spain
18 Uni e si a Poli ècnica de Ca alunya, Ba celona, Spain
19 Uni e sidad de Se illa, Se ille, Spain
20 Dipa imen o di Fisica, Uni e si à degli S udi di Ba i, Ba i, I aly
21 Ins i u o de Física Co puscula , CSIC-Uni e sidad de Valencia, Valencia, Spain
22 Paul Sche e Ins i u (PSI), Villingen, Swi ze land
23 Ins i u o Supe io Técnico, Lisbon, Po ugal
24 Join Ins i u e o Nuclea Resea ch (JINR), Dubna, Russia
25 Goe he Uni e si y, F ank u , Ge many
26 Ho ia Hulubei Na ional Ins i u e o Physics and Nuclea Enginee ing, Bucha es , Romania
27 Japan A omic Ene gy Agency (JAEA), Tokai-mu a, Japan
28 Eu opean Commission, Join Resea ch Cen e (JRC), Geel, Belgium
29 Ka ls uhe Ins i u e o Technology, Campus No h, IKP, 76021 Ka ls uhe, Ge many
30 Na ional Technical Uni e si y o A hens, A hens, G eece
31 School o Physics and As onomy, Uni e si y o Edinbu gh, Edinbu gh, UK
32 Physikalisch-Technische Bundesans al (PTB), Bundesallee 100, 38116 B unswick, Ge many
33 Is i u o Nazionale di Fisica Nuclea e, Sezione di Legna o, Legna o, I aly
34 Consiglio Nazionale Delle Rice che, Ba i, I aly
0123456789().: V,- ol 123
147 Page 2 o 13 Eu . Phys. J. A (2022) 58:147
35 Is i u o Nazionale di Fisica Nuclea e, Sezione di T ies e, T ies e, I aly
36 Dipa imen o di Fisica e As onomia, Uni e si à di Ca ania, Ca ania, I aly
37 Uni e si y o Ioannina, Ioannina, G eece
38 Facul y o Physics, Uni e si y o Vienna, Vienna, Aus ia
39 Uni e si y o G anada, G anada, Spain
40 Depa men o Physics, Uni e si y o Basel, Basel, Swi ze land
41 Cen e o As ophysics Resea ch, Uni e si y o He o dshi e, He o dshi e, UK
42 Bhabha A omic Resea ch Cen e (BARC), T ombay, India
43 Aus alian Na ional Uni e si y, Mumbai, Aus alia
Recei ed: 1 Ma ch 2022 / Accep ed: 30 June 2022
© The Au ho (s) 2022
Communica ed by Na in Alaha i.
Abs ac The 235U(n, ) c oss sec ion was measu ed in a
wide ene gy ange (18 meV–170 keV) a he n_TOF acili y
a CERN, ela i e o 6Li(n, ) and 10B(n,α) s anda d eac ions,
wi h high esolu ion and accu acy, wi h a se up based on a
s ack o six samples and six silicon de ec o s placed in he
neu on beam. In his pape we epo on he esul s in he
egion be ween 18 meV and 10 keV neu on ene gy. A es-
onance analysis has been pe o med up o 200 eV, wi h he
code SAMMY. The esul ing ission ke nels a e compa ed
wi h he ones ex ac ed on he basis o he esonance pa am-
e e s o he mos ecen majo e alua ed da a lib a ies. A com-
pa ison o he n_TOF da a wi h he e alua ed c oss sec ions is
also pe o med om he mal o 10 keV neu on ene gy o he
ene gy-a e aged c oss sec ion in ene gy g oups o sui ably
chosen wid h. A good ag eemen , wi hin 0.5%, is ound on
a e age be ween he new esul s and he la es e alua ed da a
iles ENDF/B-VIII.0 and JEFF-3.3, as well as wi h espec o
he b oad g oup a e age ission c oss sec ion es ablished in
he amewo k o he s anda d wo king g oup o IAEA ( he
so-called e e ence ile). Howe e , some disc epancies, o up
o 4%, a e s ill p esen in some speci ic ene gy egions. The
new da ase he e p esen ed, cha ac e ized by a unique combi-
na ion o high esolu ion and accu acy, low backg ound and
wide ene gy ange, can help o imp o e he e alua ions om
he Resol ed Resonance Region up o 10 keV, also educing
he unce ain ies ha a ec his egion.
1 In oduc ion
The neu on-induced ission o 235U is one o he mos impo -
an eac ions o applica ions, in pa icula ela ed o ene gy
p oduc ion. I s c oss sec ion a he mal and om 0.15 o
200 MeV neu on ene gy is an es ablished s anda d, widely
employed in a a ie y o ields, om neu on lux measu e-
men s o dose e alua ion o adia ion p o ec ion pu poses
[1]. Ou side he s anda d ange, he 235U(n, ) c oss sec ion
can also be used as e e ence, al hough he p esence o
T. Gloda iu, F. Käppele : Deceased.
ae-mail: [email p o ec ed](co esponding au ho )
esonances and esonance-like s uc u es up o ~ 10 keV
makes he use o his c oss sec ion less s aigh o wa d. While
ecen ly he c oss sec ion in eg al be ween 7.8 and 11 eV
has been adop ed as an addi ional s anda d, wi h associa ed
unce ain y o 1.2%, unce ain ies o he o de o a ew pe -
cen s ill pe sis in he Resol ed Resonance Region (RRR,
co esponding o En<2.25 keV), as well in he Un esol ed
Resonance Region (URR, ex ending up o 25 keV), wi h
some disc epancies be ween di e en e alua ed da a iles.
In o de o y o sol e disc epancies in cu en lib a ies o
235U and o he key iso opes ele an o nuclea applica ions,
a Collabo a i e In e na ional E alua ion Lib a y O ganiza-
ion (CIELO) was es ablished in 2013, coo dina ed by he
Nuclea Ene gy Agency (NEA) o he O ganiza ion o Eco-
nomic Coope a ion and De elopmen (OECD). A de ailed
desc ip ion o his p ojec and ela ed esul s can be ound in
[2]. Despi e he achie ed p og ess wi hin his amewo k o
se e al eac ions, open ques ions and di e ences in he e al-
ua ions s ill emain, documen ed in wo di e en da ase s,
adop ed by di e en e alua ed da a lib a ies. Di e ences o
he o de o a ew pe cen s ill pe sis on some c ucial eac-
ions, including he 235U(n, ) eac ion ou side he s anda d
egion. In an a emp o educe he unce ain ies, new col-
labo a i e e o s a e being unde aken, such as he INDEN
p ojec coo dina ed by IAEA [3], ha aims a imp o ing he
e alua ion me hodology and p oducing upda ed nuclea da a
iles. In his espec , while e-analysis and combina ion o
p e ious da a can lead o some imp o emen s, a majo unce -
ain y educ ion can be achie ed by inco po a ing new, high
esolu ion and high accu acy da a, ha can help o so ou
exis ing disc epancies. In his espec , he n_TOF acili y [4]
is cu en ly one o he bes sui ed acili ies wo ldwide o
collec ing new da a on he 235U(n, ) c oss sec ions in he
Resol ed and Un esol ed Resonance Regions, hanks o he
e y con enien ea u es o he neu on beam, in pa icu-
la he high esolu ion, he wide ene gy ange and he low
backg ound. An o e iew o he acili y and o he ission
expe imen al p og am a n_TOF can be ound in [5].
Da a om n_TOF in he RRR collec ed wi h Pa allel Pla e
A alanche Coun e s (PPAC) (Re . [6], he ea e e e ed o
as Pa adela’s da a) we e al eady made a ailable in 2016, and
ha e been used in he ecen ENDF/B-VIII and JEFF-3.3
123
Eu . Phys. J. A (2022) 58:147 Page 3 o 13 147
e alua ions. On a e age hey showed a good ag eemen up
o 2 keV wi h he IAEA e e ence ile (being ~ 1% lowe ),
while a la ge di e ence was obse ed ela i e o ENDF/B-
VII (being ~ 2% highe ). A di e ence o 3% has also been
epo ed by Capo e e al. [7] be ween ENDF/B-VII and he
new IAEA CIELO e alua ed c oss sec ion be ween 100 eV
and 2.25 keV ( he la e being consis en wi h he IAEA 2017
e e ence ile, see Fig. 2 in [7]). We ecall ha he ENDF/B-
VIII.0 e alua ion, o icially eleased in 2018 [8,9], has now
adop ed he IAEA CIELO e alua ions o he conside ed
eac ion. Pa adela’s da a in he RRR [6,10] ha e also been
used in he new JEFF-3.3 e alua ion, o icially eleased in
2017 [11]12. Howe e , as will be shown in his wo k, small
di e ences be ween ENDF/B-VIII.0 and JEFF-3.3 on he
235U(n, ) c oss sec ion up o 10 keV s ill pe sis .
Pa adela’s da a men ioned abo e we e collec ed in he
long ligh -base expe imen al a ea (EAR1) o n_TOF, and
a e he e o e cha ac e ized by a high esolu ion (E/E <
10–3). Howe e , hose da a we e no he esul o a dedica ed
measu emen ela i e o a s anda d, such as he 6Li(n, ) o
10B(n,α), being he 235U sample used as e e ence o o he
ac inide samples measu ed simul aneously. Ra he , he c oss
sec ion was ex ac ed ela i e o he neu on lux ha had
p e iously been de e mined on he basis o a ious s anda ds,
including he 235U(n, ) eac ion i sel , wi h a ela i ely low
esolu ion and an unce ain y o up o 5% in he keV egion
[13]. Fu he mo e, he ene gy ange did no ex end down
o he mal ene gy, hinde ing an accu a e no maliza ion o a
well es ablished s anda d. As a consequence, he da a we e
no malized o he c oss sec ion in eg al in he egion be ween
7.8 and 11.0 eV, and he alue o 246.4 b·eV in he IAEA
2009 e e ence ile was used o ha pu pose (a ha ime no
ye adop ed as an addi ional s anda d, he cu en ly adop ed
s anda d alue being 247.5 b·eV).
Recen ly, a measu emen was pe o med a n_TOF speci -
ically dedica ed o he high- esolu ion, high-accu acy mea-
su emen o he 235U(n, ) eac ion in he whole ene gy egion
om he mal o 170 keV neu on ene gy. The main aim o
ha measu emen was o in es iga e a disc epancy ha had
p e iously been no ed in he 10–30 keV ene gy ange. De ails
on he measu emen , he expe imen al se up and he analysis
p ocedu e can be ound in Re . [14]. The main ea u es o
his new da ase a e ha he 235U(n, ) c oss sec ion is mea-
su ed di ec ly ela i e o he 6Li and 10B s anda ds, and ha
he ene gy ange encompasses he he mal poin and ex ends
up o 170 keV, i.e. in he s anda d egions, so ha a high con-
idence on he absolu e no maliza ion can be achie ed. The
p esen pape complemen s he p e ious publica ion [14],
by epo ing he poin wise da a in he ange om he mal o
10 keV, in an a emp o p o ide some o he mos accu a e and
high- esolu ion da a achie ed so a on he 235U(n, ) c oss
sec ion in he Resol ed and Un esol ed Resonance Region.
The esul s he e epo ed could help o sol e exis ing disc ep-
ancies be ween di e en e alua ions, p o iding an impo an
con ibu ion o u u e upg ades o e alua ed lib a ies and/o
ongoing collabo a i e e o s, such as he INDEN p ojec o
IAEA, wi h he inal goal o imp o ing he accu acy o his
impo an c oss sec ion in his ene gy egion.
The pape is o ganized as ollows: he main ea u es o he
expe imen al se up and p ocedu e a e desc ibed in Sec . 2,
and c oss sec ion de e mina ion in Sec . 3. A esonance anal-
ysis up o 200 eV is epo ed in Sec . 4, oge he wi h a
compa ison o he esul ing ission ke nels wi h cu en e -
sions o majo lib a ies. Ene gy-a e aged c oss sec ion da a
om he mal o 10 keV neu on ene gy a e p esen ed and
discussed in Sec . 5, in compa ison wi h cu en and pas
e alua ions and p e ious expe imen al da a. Conclusions a e
d awn in Sec . 6.
2 Expe imen al se up and da a analysis
The expe imen al appa a us consis s o a s ack o six Si-
de ec o s wi h six samples, wo o each 6Li, 10B and 235U
iso ope, moun ed in be ween in a closely-packed geome y
[14]. The main ea u es o he se up we e: a la ge solid angle
co e age, he possibili y o de ec ing eac ion p oduc s bo h
in he o wa d and backwa d di ec ion, a ea u e pa icula ly
impo an o he 6Li(n, ) and 10B(n,α) eac ions, a ec ed
by angula aniso opy o he emi ed cha ged pa icle ha
s a s becoming ele an o neu on ene gy abo e a ew keV.
Finally, he se up was cha ac e ized by a good pa icle iden-
i ica ion capabili y, o impo ance o backg ound ejec ion.
The se up was hos ed in a acuum chambe placed on he
neu on beam line, wi h hin windows a he ai – acuum
in e ace. The measu emen was pe o med in he expe i-
men al a ea (EAR1) posi ioned a he end o he 183.49 (2) m
long neu on ligh pa h. In his a ea, he ene gy esolu ion o
he neu on beam goes om 3·10–4 a he mal up o 10–3 a
10 keV [4].
The 235U(n, ) c oss sec ion was de e mined di ec ly ela-
i e o he 6Li(n, ) and 10B(n,α) eac ions, whose c oss sec-
ions a e s anda ds o measu emen all he way om he mal
o 1 MeV. Ano he impo an ea u e o he measu emen was
he la ge ene gy ange co e ed, ex ending om he mal neu-
on ene gy o 170 keV. Rela i e o Pa adela’s da a men ioned
abo e, he new measu emen has he ad an age o including
bo h he he mal poin and an ene gy egion abo e 150 keV,
whe e he 235U(n, ) c oss sec ion is s anda d, hus allow-
ing o an accu a e no maliza ion o he da a in he whole
ene gy ange measu ed. In ac , he da ase he e p esen ed
is one o he mos comple e in e ms o ene gy ange co -
e ed, and accu a e in e ms o e e ence eac ions used, as
well as in no maliza ion. Combined wi h he high esolu ion
and low backg ound o he n_TOF neu on beam in EAR1,
123
147 Page 4 o 13 Eu . Phys. J. A (2022) 58:147
he wide ene gy ange and high accu acy makes he p esen
da ase a he unique in he landscape o expe imen al c oss
sec ions a ailable on he 235U(n, ) eac ion in he Resol ed
and Un esol ed Resonance Regions, and sui able o e i y-
ing cu en majo e alua ions, possibly iden i ying esidual
p oblems (i any). To his aim, we pe o m he e a ho ough
compa ison o he da a wi h h ee lib a ies: ENDF/B-VII,
ENDF/B-VIII.0 and JEFF-3.3 (e alua ed c oss sec ions in
he JENDL-5 lib a y a e simila o ENDF/B-VIII.0 and a e
he e o e no included in his compa ison).
3 C oss sec ion de e mina ion
The yield wi h coa se ene gy binning om he mal o
170 keV neu on ene gy has al eady been epo ed in Re .
[14] and uploaded on he nuclea da a eposi o y EXFOR
[15]. In his pape we epo on he analysis o he da a,
up o 10 keV, wi h he highe esolu ion equi ed o pe -
o m a esonance analysis and a mo e de ailed compa ison
wi h e alua ed da a lib a ies. These da a will hen be made
a ailable on EXFOR o dissemina ion and possible use in
u u e e alua ions o he 235U(n, ) eac ion in he Resol ed
and Un esol ed Resonance Regions.
The main ea u es o he p esen da a, in e ms o
backg ound, no maliza ion and unce ain y es ima es, ha e
mos ly been discussed in [14]. We ecall he e ha , hanks o
he cha ac e is ics o he n_TOF acili y and he low mass
o he de ec o s, he measu emen is a ec ed by a negligi-
ble backg ound. This ea u e is pa icula ly impo an in he
alleys be ween esonances, as i leads on he one hand o a
mo e eliable esonance analysis in he ails, and on he o he
hand o a mo e accu a e de e mina ion o he ene gy-a e aged
c oss sec ion, bo h a ec ed by a non-negligible con ibu ion
o he alleys. The low backg ound o he measu emen is
e iden in Fig. 1, whe e he n_TOF da a in he alleys a e
compa able o, o lowe han, he e alua ed c oss sec ions,
showing in some egions s uc u es no p esen in he e al-
ua ions, and ha could ha e been p e iously masked by a
highe backg ound. These s uc u es a e s a is ically signi -
ican , as hey canno be due o con aminan s whose con en
in he samples was ce i ied below 10–6, and in se e al cases
we e also obse ed in Pa adela’s da a [6].
As al eady men ioned, an impo an ea u e o he p esen
da a is ha he c oss sec ion is ex ac ed di ec ly om he
a io o he measu ed coun - a e o he 235U sample o he
e e ence 6Li and 10B samples. This p ocedu e comple ely
emo es he e ec o s uc u es, in pa icula abso p ion dips,
ha a e ypically p esen in he neu on lux, ela ed o he
neu on sou ce i sel o o windows a he ai - acuum in e -
ace on he neu on beam line. A n_TOF, he p esence o a
hick Al window p oduces se e al la ge dips, while a 0.2%
Zn con en p oduces smalle dips ha howe e could lead o
a ew pe cen e o in he c oss sec ion de e mina ion (as will
be shown in Sec . 5).
As discussed in [14], he no maliza ion o he measu ed
c oss sec ion was pe o med ela i e o he c oss sec ion in e-
g al in he neu on ene gy ange be ween 7.8 and 11.0 eV,
ecen ly adop ed as a s anda d (247.5 ±3b·eV)[16]. The
combina ion o he sys ema ic unce ain y on he s anda d
(1.2%) wi h he s a is ical e o on he measu ed in eg al
(0.4%) esul s in an o e all unce ain y o 1.3% up o 1 keV.
Abo e his ene gy an addi ional 0.8% unce ain y on he e i-
ciency co ec ions has o be conside ed, leading o a o al
alue o 1.5% (being o he ene gy-dependen unce ain ies
negligible in he ange conside ed in his wo k). The peculia
ea u es o he n_TOF neu on beam and o he expe imen-
al se up and he adop ed p ocedu e o he no maliza ion o
he esul s makes he p esen measu emen one o he mos
accu a e e e pe o med on his eac ion. Finally, a unda-
men al ea u e o he p esen da ase (as compa ed o mos
p e ious ones), is he wide ene gy ange co e ed in a single
measu emen , ha makes possible o di ec ly compa e he
da a wi h he 235U(n, ) c oss sec ion s anda d in wo egions,
i.e. a he mal and a ound 150 keV. The e y good ag eemen
obse ed a hose ene gies (shown in Sec . 5) p o ides high
con idence on he c oss sec ion alues in he whole ene gy
egion, he e epo ed.
In he ollowing, we p esen he esul s and a compa ison
wi h e alua ed nuclea da a o majo lib a ies, by pe o m-
ing on he one hand a esonance analysis a lowe ene gy, and
on he o he hand by a e aging he measu ed c oss sec ion in
wide ene gy bins up o 10 keV. The p esen da a a e also com-
pa ed wi h some p e ious da ase s cha ac e ized by simila
esolu ion. The new, high accu acy and high esolu ion da a
on his impo an eac ion could be bene icial o checking he
eliabili y o cu en e alua ions in majo da a lib a ies, pos-
sibly iden i ying esidual sho comings o u u e upda es.
4 Resonance analysis
A esonance analysis was pe o med wi h he SAMMY code
[17], wi hin he Reich–Moo e app oxima ion, om he mal
o 200 eV. Al hough he limi o he Resol ed Resonance
Region is cu en ly assumed a 2.25 keV, and esonance s uc-
u es a e obse ed e en abo e his limi , in he p esen wo k
we ha e conside ed only esonances up o 200 eV, since a
highe ene gy he clus e ing o esonances becomes domi-
nan , and he numbe o missing le els inc eases. Fu he -
mo e, up o his ene gy he n_TOF neu on beam esolu-
ion unc ion has a negligible in luence, being he esolu ion
essen ially domina ed by Dopple b oadening. I should be
conside ed ha e en a his low ene gy, se e al esonance
s uc u es a e made o clus e s o un esol ed esonances,
due o he small a e age le el spacing, as compa ed o hei
123
Eu . Phys. J. A (2022) 58:147 Page 5 o 13 147
Fig. 1 Measu ed 235U(n, ) c oss sec ion in he 1–10 eV neu on ene gy ange, compa ed wi h e alua ed da a. The high esolu ion o he n_TOF
da a makes possible o dis inc ly obse e small s uc u es in he alleys be ween esonances, clea ly es i ying he low backg ound
na u al wid h and o he e ec o he Dopple b oadening.
Finally, abo e 200 eV a mo e s a is ically meaning ul com-
pa ison wi h lib a ies and p e ious da ase s can be pe o med
by a e aging he c oss sec ion in sui ably wide ene gy bins
as discussed in Sec . 5.
In he SAMMY i s, ini ial inpu pa ame e s o he eso-
nances we e aken om he la es e alua ed da a iles, ei he
ENDF/B-VIII.0 o JEFF-3.3. The ene gy, neu on and cap-
u e wid hs we e kep ixed, while bo h ission wid hs we e
le ee, wi h a udge ac o se a 0.1 (co esponding o he
possibili y o modi ying he alue by 10% o each i e a-
ion). The nume ical n_TOF esolu ion unc ion was used in
he i s. In o de o check he consis ency o he no maliza ion
alue o he n_TOF yields, he co esponding pa ame e was
ini ially le ee when i ing he ene gy egion om 20 meV
o 10 eV. The alues ob ained using ini ial esonance pa am-
e e s om he ENDF/B-VIII.0 and JEFF-3.3 we e 0.993 and
0.997, espec i ely, indica ing ha he no maliza ion o he
n_TOF yield was consis en wi h e alua ed c oss sec ions
wi hin a ew pe mill. Fo he i s om 10 o 200 eV neu on
ene gy, he no maliza ion pa ame e s we e kep ixed a he
alues men ioned abo e. Fo he esonance i s in he whole
neu on ene gy egion analysed, he le el o backg ound was
ini ially le ee, showing ha he esul ing alues we e in all
cases negligible. Figu e 2shows he expe imen al da a wi h
he esul s o he SAMMY i (ini ial esonance pa ame e s
om ENDF/B-VIII.0) in he whole ange om he mal o
200 eV neu on ene gy, along wi h he esiduals de ined as
he di e ence be ween i and da a di ided espec i ely by he
da a (and exp essed in pe cen ) and by he da a s anda d de i-
a ion. The quali y o he i s in selec ed ene gy egions can
also be app ecia ed in Fig. 3. The expe imen al ission yield
and he esul o he esonance analysis pe o med wi hin
his wo k a e ep esen ed by he symbols, wi h hei s a is i-
cal unce ain y, and by he ed cu e, espec i ely. They a e
compa ed wi h he ission yield calcula ed by SAMMY on he
basis o he esonance pa ame e s o he wo mos ecen e al-
ua ed da a lib a ies, ep esen ed in he igu es by he g een
cu e ( o cla i y, he compa ison wi h ENDF/B-VIII.0 and
JEFF-3.3 is shown sepa a ely). Fo mos esonances, he new
i and e alua ed ission yields a e indis inguishable, indica -
ing a e y good ag eemen be ween he n_TOF da a epo ed
he e and he e alua ed c oss sec ions. In some cases, howe e ,
he e alua ions all sho o ep oducing he obse ed eso-
nances, as can be in e ed om he di e ences be ween he
ed and he g een cu e in Fig. 3. Mos o he di e ences a e
obse ed in he neu on ene gy ange be ween 20 o 100 eV
(as con i med by he analysis o he ene gy-a e aged c oss
sec ion in Sec . 5). The anges in Fig. 3co espond o egions
whe e la ge di e ences be ween da a and e alua ions we e
ound.
A mo e quan i a i e compa ison can be pe o med by con-
side ing he ission wid hs. Howe e , al hough his is clea ly
he mos impo an pa ame e o be de e mined om he es-
onance analysis o ission da a, he alues o such wid h a e
co ela ed o he neu on and, o a lesse ex en , he cap u e
123

147 Page 6 o 13 Eu . Phys. J. A (2022) 58:147
Fig.2 Measu ed yields o he 235U(n, ) eac ion, oge he wi h he esul
o esonance analysis pe o med wi h he SAMMY code, using ini ial
pa ame e s om ENDF/B-VIII.0, be ween 18 meV and 200 eV ( op
panel). The esiduals be ween i and da a in pe cen (middle panel) and
in s anda d de ia ion uni s (bo om panel) a e also epo ed in he igu e
wid hs, which may be di e en in he wo majo lib a ies. As
a consequence, i is mo e app op ia e, when compa ing he
expe imen al da a wi h bo h lib a ies, o conside he ission
ke nel de ined as ollows,
K gn 1+ 2
n+γ+ 1+ 2
(1)
He e gis he spin ac o , nand γa e he neu on and cap-
u e wid h, espec i ely, while  1 and  2 he wo ission
wid hs. Figu e 4shows he a io o he expe imen al ission
ke nels o he ones ex ac ed using he ENDF/B-VIII.0 and
JEFF-3.3 esonance pa ame e s. The e o ba s ep esen he
unce ain y in he SAMMY i , and a e essen ially ela ed o
he s a is ical unce ain y on he n_TOF ission yield da a.
A e y good ag eemen is obse ed on a e age be ween he
p esen da a and bo h majo lib a ies. Indeed, a weigh ed
a e age o 1.0037(3) and 1.0016(2) is ound o he a io
ela i e o ENDF/B-VIII.0 and JEFF-3.3, espec i ely. How-
e e , as al eady men ioned, di e ences o se e al pe cen can
be obse ed o some esonances (o clus e o esonances),
mos ly small ones, as can be in e ed om he la ge e o
ba s. As o he la ge disc epancy a 1.3 eV, i cas s some
doub s on he exis ence o a esonance in ha egion, on he
ail o he much la ge esonance a 1.14 eV. Ne e heless,
123
Eu . Phys. J. A (2022) 58:147 Page 7 o 13 147
Fig. 3 Example o SAMMY i s o 235U(n, ) esonances om he
p esen n_TOF yield da a ( ed cu es and symbols, espec i ely) com-
pa ed wi h yields calcula ed in SAMMY om esonance pa ame e s
o he wo mos ecen lib a ies, ENDF/B-VIII.0 and JEFF-3.3 (g een
cu es). Whe e di e ences exis , he ed and g een cu e depa om
each o he . The a ow a ound 22 eV in he op le plo indica es one
o he s uc u es men ioned in he ex ha was possible o obse e in a
alley due o he low backg ound
he weigh ed oo mean squa e o he a io, ha p o ides an
indica ion o he wid h o he a io dis ibu ion, u ns ou o be
also small, being less han 1% o bo h lib a ies (0.0096 and
0.0064 o ENDF/B-VIII.0 and JEFF-3.3, espec i ely). This
u he implies ha he wo lib a ies a e essen ially equi a-
len and on a e age closely ep oduce he obse ed n_TOF
esonances up o 200 eV.
5 Ene gy-a e aged ission c oss sec ions om he mal
o 10 keV neu on ene gy
While he esonance analysis shown abo e can p o ide some
indica ions on he accu acy o he e alua ions up o 200 eV,
a mo e comple e compa ison can be pe o med, all he way
om he mal o 10 keV neu on ene gy, by conside ing he
a e age c oss sec ions in wide ene gy bins. Simila compa -
isons in his sense ha e been epo ed in he li e a u e bo h
be ween da a and lib a ies (see o example Re . [6]) and
be ween e alua ed da a iles [7,11]. In pa icula , in Re s. [6,
7], i was shown ha he c oss sec ions in ENDF/B-VII we e
highe han he IAEA e e ence ile and Pa adela’s da a, by
se e al pe cen . Following he CIELO p ojec , a modi ica-
ion was in oduced in ENDF/B-VIII.0, which adop ed he
esul ing e alua ions (mos ly based o his eac ion on he
IAEA e e ence ile). Simila ly, he new e sion o JEFF-3.3
was shown o ep oduce he la es s anda d e alua ions [1],
as well as he p e ious one [18] in he neu on ene gy ange
100–2000 eV (see Table 3 in [11]).
Taking ad an age o he wide ene gy ange o he p esen
n_TOF da a, we ha e pe o med a comple e compa ison
wi h he wo cu en e alua ions, as well as wi h he p e-
ious ENDF/B-VII, wi h he aim o e i ying imp o emen s
and/o esidual di e ences. The compa ison o e he ull
ene gy ange measu ed a n_TOF is shown in Fig. 5, whe e
he epo ed R alues ep esen he ela i e di e ence (i.e.
esiduals) be ween he cu en da a and he e alua ions.
R100% ·da a
e e ence
−1(2)
Fo a mo e de ailed analysis he whole neu on ene gy
egion om he mal o 10 keV has been di ided in di e -
en panels in Fig. 6. I has o be conside ed, howe e , ha
be ween 10 and 30 keV he new e alua ions s ill show an
123
147 Page 8 o 13 Eu . Phys. J. A (2022) 58:147
Fig.4 Ra io o he n_TOF ission ke nels (de e mined om SAMMY i
o he esonances), and hose calcula ed om he esonance pa ame e s
o he wo mos ecen e alua ed da a lib a ies (ENDF/B-VIII.0 and
JEFF-3.3). See ex o de ails
impo an disc epancy ela i e o he n_TOF da a, as al eady
discussed in Re . [14], linked o he node desc ip ion used
in he s anda d e alua ion. The chosen ene gy binning is 10
bins/decade, a alue ha ul ils he bes comp omise be ween
he need o a easonable esolu ion and ha o minimizing
s a is ical luc ua ions, in pa icula in he keV ene gy egion.
The measu ed ene gy-a e aged c oss sec ion was ob ained
om he ission yield di iding by he a eal densi y o he
sample (numbe o a oms/ba n). In his espec , he sel -
abso p ion co ec ion is no aken in o accoun , as he small
hickness o he 235U samples used in he n_TOF measu e-
men esul s in a negligible e ec , o he o de o 10–4.
Fo he e alua ions, he ene gy-a e aged c oss sec ion was
de i ed om he poin wise alues, by i s in e pola ing hem
(acco ding o he lib a y p esc ip ions) a a e y ine esolu-
ion (2000 bins/decade), and hen in eg a ing he esul ing
c oss sec ion o e he same ene gy in e als o he expe i-
men al da a (i.e. 10 bins/decade). In he plo s, a gene ally
good ag eemen o he new lib a ies wi h he n_TOF da a
can be obse ed, in he whole ene gy egion om he mal o
10 keV. On he con a y, he olde ENDF/B-VII lib a y shows
a a he la ge sys ema ic disc epancy, being he n_TOF da a
conside ably highe han he e alua ions by se e al pe cen ,
om a ew hund ed meV o a ew keV. While he unde -
es ima e o he c oss sec ion in ENDF/B-VII in he ecen ly
es ablished s anda d om 7.8 o 11.0 eV had been p e iously
epo ed, as compa ed o he IAEA e e ence alue (see o
example Re . [6]), a somewha unexpec ed inding is he dis-
c epancy in he 100–300 meV neu on ene gy. In hese wo
ene gy anges, he ecen e-e alua ion wi hin he CIELO
p ojec , adop ed in he mos ecen lib a ies, has led o a sub-
s an ial imp o emen o he c oss sec ion, ela i e o p e ious
e alua ed da a, as demons a ed by he e y good ag eemen
wi h he p esen n_TOF da a. Howe e , some disc epancies
can s ill be no ed e en o he new lib a ies. A low ene gy, up
o app oxima ely 1 eV, he n_TOF c oss sec ions a e sligh ly
lowe han JEFF-3.3 e alua ions, by a ound 1%, while hey
a e in good ag eemen wi h he ENDF/B-VIII.0 e alua ions.
On he con a y, he wo lib a ies mos ly ag ee in he ange
1–100 eV, bu he n_TOF da a a e sys ema ically highe han
bo h o hem a a ew eV and be ween 20 and 80 eV. I is
in e es ing o no e ha in ha ange he e we e only sligh
changes in he new e alua ions wi h espec o he p e ious
ones (see compa ison wi h ENDF/B-VII). I should be also
no ed ha , as shown p e iously, impo an di e ences a e
obse ed in he esonances in ha ange, he e o e calling
o a be e e alua ion o he esonance pa ame e s in u u e
lib a y eleases.
In he 100 eV o 1 keV ange, no pa icula p oblems
a e obse ed, excep o a 2% disc epancy a ound 200 eV
neu on ene gy. Finally, he compa ison in he 1 o 10 keV
ange highligh s a p oblem a ound 2 keV. This ene gy co e-
sponds app oxima ely o he limi o he Resol ed Resonance
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Eu . Phys. J. A (2022) 58:147 Page 9 o 13 147
Fig. 5 Rela i e di e ence R
be ween he 235U(n, )
ene gy-a e aged c oss sec ion
measu ed a n_TOF in he ull
neu on ene gy ange, om
he mal o 170 keV, and he
e alua ed c oss sec ion om
majo cu en da a lib a ies,
namely ENDF/B-VIII.0 and
JEFF-3.3. The disc epancy wi h
he olde ENDF/B-VII.1 lib a y
is also shown o compa ison.
The a e age was calcula ed o e
10 bins/decade
Region in he lib a ies, and a leas pa o he obse ed dis-
c epancy could be a ibu ed o he di e ence o ea men
in he e alua ion be ween he RRR and URR. A e a ca e-
ul in es iga ion, howe e , we ha e come o he conclusion
ha mos p obably his is no he eason o he di e ences
be ween he p esen n_TOF da a and e alua ions. A com-
pa ison wi h p e ious da a, in pa icula Pa adela’s ones [6],
shows a la ge di e ence be ween 2 and 3 keV (a di e ence is
also obse ed, ela i e o Wes on [19], al hough smalle ). In
his egion, he n_TOF lux exhibi s a small dip, as i can be
app ecia ed in he neu on lux de e mined in he measu e-
men he e epo ed om he 6Li(n, ) and 10B(n,α) eac ions
(seeFig.11o Re .[14]). The dip can be a ibu ed o he
2.63 keV esonance in he o al c oss sec ion o 64Zn (dom-
ina ed by elas ic sca e ing). Zinc is p esen in he neu on
sou ce a n_TOF, being a 0.2% con aminan o he Al alloy
6082, used o he window a he in e ace be ween he spal-
la ion a ge and he acuum beam line. Being he dip small
and ba ely isible in he adop ed ene gy dis ibu ion o he
neu on beam in EAR1 [13], i was no accoun ed o in he
analysis o Re . [6], in which he c oss sec ion was ex ac ed
ela i e o ha ene gy dis ibu ion. I can he e o e be con-
cluded ha he di e ence ela i e o he IAEA e e ence ile
obse ed in Re . [6] a ound 2 keV neu on ene gy is essen-
ially ela ed o he men ioned abso p ion dip, and i canno
be excluded ha a simila p oblem migh also be p esen in
o he p e ious da ase s, as al eady men ioned. As i can be
no ed in Fig. 6, in he ecen e alua ions he c oss sec ion has
been inc eased in ha ene gy bin, and ag ee be e wi h he
p esen da a. A eminiscence o he p oblem migh howe e
s ill be p esen a sligh ly lowe ene gy, being he n_TOF
da a in he bin a 2 keV highe , by 3% and 6% ela i e o
ENDF/B-VIII.0 and JEFF-3.3, espec i ely. A e-e alua ion
o he c oss sec ion in his ene gy egion migh he e o e be
needed o accoun o he new e idences he e discussed.
The o e all pe o mance o he wo mos ecen e alua ed
da a lib a ies, in ep oducing he new n_TOF da a epo ed
he e can be in e ed om Fig. 7, ha shows he weigh ed
a e age de ia ion o he e alua ed c oss sec ions om he
p esen da a, in he ull ene gy ange examined, i.e. be ween
he mal and 10 keV, and in ou sub- anges. The employed
weigh is he in e se o he squa e o he s a is ical e o . F om
he igu e, one can app ecia e he la ge imp o emen s in he
mos ecen lib a ies, ollowing he CIELO p ojec , ela i e
o he p e ious one. O e all, bo h ENDF/B-VIII.0 and JEFF-
3.3 ag ee wi h he new da a wi hin less han hal a pe cen , a
ema kable esul , in pa icula i compa ed wi h he sys em-
a ic di e ence o he p esen da a ela i e o ENDF/B-VII
by 2%. Howe e , i should be no ed ha such a good o e all
ag eemen wi h he mos ecen e alua ions is he esul o
posi i e and nega i e de ia ions in di e en ene gy egions
ha compensa e each o he . Ne e heless, in all anges he
ag eemen wi h he wo cu en e alua ed da a lib a ies is
a ound 1%, excep o he 1–100 eV ange, whe e a 2% di -
e ence is obse ed o ENDF/B-VIII.0, mos ly ela ed o
a p oblem in he 20–80 eV egion, as shown in Fig. 4by
he a io be ween he esonance ke nels and in Fig. 6by he
compa ison o he ene gy-a e aged c oss sec ions.
I is also in e es ing o compa e he p esen da a wi h a ew
p e ious expe imen al da ase s, ha ha e been conside ed in
123