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P oduc ion o a 15C adioac i e ion beam based on 18O(n, α)
© The Au ho (s) 2019.
Published e sion
Malkiewicz, T.; Lhe sonneau, G.; Fadil, M.; Jacobsson, U.; Jones, P.; Hela iu a, K.;
Ka onen, P.; Khlebniko , S.; T zaska, W. H.
Malkiewicz, T., Lhe sonneau, G., Fadil, M., Jacobsson, U., Jones, P., Hela iu a, K., Ka onen, P.,
Khlebniko , S., & T zaska, W. H. (2019). P oduc ion o a 15C adioac i e ion beam based on
18O(n, α). Eu opean Physical Jou nal A, 55(6), A icle 88. h ps://doi.o g/10.1140/epja/i2019-
12761-y
2019
DOI 10.1140/epja/i2019-12761-y
Regula A icle – Expe imen al Physics
Eu . Phys. J. A (2019) 55:88 THE EUROPEAN
PHYSICAL JOURNAL A
P oduc ion o a 15C adioac i e ion beam based on 18O(n,α)
T. Malkiewicz1,a, G. Lhe sonneau2, M. Fadil3,U.Jacobsson
4, P. Jones5, K. Hela iu a4, P. Ka onen6, S. Khlebniko 7,
and W.H. T zaska8,b
1CSC-IT Cen e o Science L d., P.O.Box 405, Keila an a 14, 02101 Espoo, Finland
2189 All´ee Jules Ve ne, 075000 Guilhe and-G anges, F ance
3GANIL, Bld Hen i Becque el, B.P. 55027, 14076 Caen Cedex 05, F ance
4Depa men o Chemis y, Uni e si y o Helsinki, P.O.Box 55, 00014 Helsinki, Finland
5iThemba Labo a o y o Accele a o Based Science, P.O.Box 722, Some se Wes 7129, Wes e n Cape, Sou h A ica
6Powe Di ision, Fo um Co po a ion, P.O.Box 100, Keilaniemen ie 1, 02101 Espoo, Finland
7Khlopin Radium Ins i u e, 2 Mu insky A . 28, Sain Pe e sbu g, Russia
8Depa men o Physics, Uni e si y o Jy askyla, P.O.Box 35, 40351 Jy askyla, Finland
Recei ed: 22 Janua y 2019 / Re ised: 10 Ap il 2019
Published online: 7 June 2019
c
The Au ho (s) 2019. This a icle is published wi h open access a Sp inge link.com
Communica ed by P. Woods
Abs ac . In he con ex o he SPIRAL2 adioac i e beam acili y he p oduc ion a e o he neu on- ich
15C nucleus by 18O(n,α) has been in es iga ed. In a wa e a ge o 20 cm3, en iched in 18O and placed
behind he neu on con e e , a a e o a ew 1010 nuclei pe second can be eached wi h 1 mA o 40 MeV
deu e ons. A 18O(n,α) c oss-sec ion based on he ac i a ion me hod is p oposed. I is in e media e be ween
he highes and lowes e alua ions a ailable o da e.
In oduc ion
The SPIRAL2 p ojec a GANIL, Caen, F ance, is de-
signed o ex end he ange o nuclea physics expe imen s,
especially o neu on- ich and e y hea y nuclei [1,2]. The
fi s s age o SPIRAL2 is a high-in ensi y linea d i e able
o p oduce, among o he applica ions, beams o ene ge ic
neu ons by s opping deu e on beams in he so-called con-
e e a ge . The Neu ons- o -Science (NFS) p og am
o neu on expe imen s [3] is s a ing.
The mos ambi ious p ojec is ce ainly he p oduc-
ion o beams o neu on- ich fission p oduc s, based on
fission o na u al u anium wi h as neu ons. As a com-
plemen , p oduc ion schemes o nuclei ligh e han fission
p oduc s ha e been e alua ed. Tha s udy has been ca -
ied ou in he ame o he FP7 p og am o he Eu opean
Commission and esul ed in a PhD [4]. One o he nuclei
in es iga ed as a candida e o a pos -accele a ed beam
has been 15C. The only sui able eac ion seemed o be
18O(n,α)15C. Neu on p oduc ion wi h a deu e on beam
o 40 MeV has been measu ed [5]. The flux o neu ons
abo e 4 MeV is abou 0.7% pe deu e on in a a ge close
enough o in e cep neu ons emi ed up o 30 deg ees
om he beam axis. This con e s o 4.3·1013 neu ons/s
ae-mail: [email p o ec ed]
be-mail: [email p o ec ed] (co esponding au-
ho )
o a 1 mA deu e on cu en . Howe e , echnical aspec s
o he en isaged ISOL-based concep we e no encou ag-
ing. The na u al abundance o 18O o only 0.2% equi es a
high deg ee o en ichmen . The cos is ha dly compa ible
wi h a high- empe a u e solid oxyde a ge which neces-
sa ily de e io a es and needs o be eplaced. In addi ion,
efficien elease o 15C( 1/2=2.45 s) om such a a ge
is a p io i p oblema ic. These conside a ions le he 15C
beam p ojec o be, a leas , pos poned.
An al e na i e appea ed ye du ing in o mal discus-
sions among some o he au ho s o his wo k. Wa e en-
iched in 18O is comme cially a ailable. One majo use
o i is o be bomba ded by p o ons o gene a e he
18F posi on sou ce o P o on-Elec on-Tomog aphy, e.g.
e . [6] ha is used e.g. o clinical imaging o cance and o
some neu ological diseases. A wa e a ge a oom em-
pe a u e should be sui able o ex ac ing ca bon. The
na i e 15C would combine wi h oxygen in suspension and
quickly lea e he liquid as CO2bubbles.
When a possible solu ion o wo majo echnical chal-
lenges was ound, i became in e es ing o es he p oduc-
ion o 15C expe imen ally. The e appa en ly do no exis
expe imen al c oss-sec ion da a, hough he Na ional Nu-
clea Da a Cen e [7] lis s e alua ions based on models
in he ENDF da a lib a y. The c oss-sec ions shown o
18O(n,α)15C span a wide ange in ampli ude. A single
measu emen o p oduc ion a e o 15C wi h a 40 MeV
deu e on beam was he p ima y goal o his wo k. Ye ,
Page 2 o 8 Eu . Phys. J. A (2019) 55:88
Fig. 1. Schema ic layou o he expe imen , no on scale. The
neu ons gene a ed in he con e e a ge ac i a e ei he he
oils used o measu e he neu on spec um o eac wi h 18O
in he wa e a ge o p oduce 15C. Fo a de ailed desc ip ion,
see e . [9].
he e was an oppo uni y o ob ain a ough es ima e o
he 18O(n,α)15C c oss-sec ion by measu ing he ene gy
dis ibu ion and flux o he neu ons impinging on he
a ge . In his wo k, ou combina ions o beam ene gies
and a ge s enabled a ough expe imen al c oss-sec ion o
be de e mined o he fi s ime.
Expe imen al p ocedu e
The p esen wo k consis ed o i adia ing a neu on-
con e e hick a ge wi h deu e ons om he K-130 cy-
clo on a he JYFL labo a o y o p oduce as neu ons,
and i adia e a a ge con aining wa e en iched in 18O.
The neu on spec a we e de e mined by he ac i a ion
me hod applied in ou o me pape s, see e.g. e . [8] and
e e ences he ein. The p oduc ion o 15C was ob ained
ia i s adioac i i y. A 5297.8 keV γ- ay is emi ed wi h
a p obabili y o 63.2% pe decay (all nuclea da a, un-
less quo ed, ha e been aken om he ENSDF lib a y in
NNDC). The 2.45 s hal -li e o 15C equi es a as anspo
sys em o ca y he i adia ed a ge o a well-shielded lo-
ca ion o coun ing unde lowe backg ound han in he
ca e whe e i has been i adia ed. Such a sys em had
been buil o a measu emen o p oduc ion a es o fis-
sion p oduc s in a u anium a ge [9]. A schema ic layou
o he expe imen is shown in fig. 1. He e a e desc ibed
he main cha ac e is ics o he expe imen , in so a hey
a e needed o unde s anding wi hou going back o ou
p e ious pape s, and he adap a ions made o his wo k.
Ta ge s and anspo sys em
The a ge s we e wa e en iched in 18O. The wa e used
in his wo k was supplied by Camp o Scien ific [10]. The
wa e had been i adia ed by p o ons o p oduce 18Fand
had been ecycled. I consequen ly con ained a esidual
o ace oni ile (CH3CN) sol an . The espec i e ac ions
o oxygen iso opes and sol an we e ob ained wi h a gas
ch oma og aph and weigh ing. The ac ion o 18O a oms
in he a ge s was 68(3)%.
The a ge holde a ached o he anspo chain was
o simila design as he one used in e . [9], bu was big-
ge and made o aluminum. I had a ca i y o 2.5 by
2.5 cm acing he beam and o 3 mm hickness closed wi h
a 1 mm myla oil. Se e al wa e a ge s o abou 2.3 g
weigh ha e been used in he cou se o he expe imen .
The exac amoun o wa e was ob ained by weigh ing be-
o e and a e he da a had been aken. The ca i y could
also accomoda e me al oils used o measu ing he neu-
on spec um, squa es o 2.5 cm side and 1 mm hickness.
The oils we e o aluminum, nickel, indium and bismu h.
They ha e been g ouped as a s ack o Ni, In and Bi oils
in he same aluminum holde as i was used o wa e a -
ge s, and as ano he s ack o 3 Al oils in a plas ic holde
o same geome y. A a gi en deu e on ene gy he neu-
on ene gy dis ibu ions ob ained om he analysis o he
esidual adioac i i y o he oils we e he e o e he same
as hose which i adia ed he wa e a ge s. The neu on
spec a diffe ed only o he no malisa ion due o diffe en
beam cu en s and he du a ion o i adia ions. The dis-
ance om he 0.5 mm en ance Al window o he neu on-
con e e a ge o he cen e o he 3- oil s ack o o he
wa e a ge was 3.3(1) cm.
The beam cu en was measu ed each second using he
eading o he cha ge collec ed in he neu on-con e e
a ge . I allowed nume ical in eg a ion o he g ow h and
decay equa ions o be ca ied ou .
The anspo sys em was a loop o a bicycle chain. A
single a ge , ei he a oil s ack o a wa e a ge , had been
placed in i s holde on he chain. The chain was mo ed by
a s ep mo o con olled by a specially-buil module. The
module se s TTL le els o s a and s op he mo o , o de-
flec he ion beam be o e injec ion o he cyclo on, and o
ga e he acquisi ion. In ha way, he beam was off du ing
anspo and coun ing, while coun ing was enabled only
when he a ge was a i s coun ing posi ion.
Pulsing and ga ing s ongly limi s he backg ound due
o he mal neu ons ha ing passed he conc e e and pa a -
fin shielding. These neu ons (e.g. 1.8·10−10 n/cm2pe
deu e on o 40 MeV [9]) ac i a e ma e ial nea he de-
ec o . In e . [9] adia ion induced by he mal neu ons
caused a high ejec ion o ue e en s because hey ig-
ge ed he ac i e BGO shields su ounding he Ge-clo e s.
The accep ance, mo eo e , a ied wi h he ime in he cy-
cle. The acquisi ion needed se e al seconds o eco e i s
ull accep ance. He e, he BGO shields we e eplaced wi h
a passi e lead shield o mos o en, i.e. below and on he
sides o he de ec o cap, 10 cm hickness, and else o 5 cm.
The s abili y o he coun ing a e o a 137Cs sou ce e sus
ime in he coun ing pe iod showed ha he accep ance
a e o e en s did no a y. I was no any longe neces-
sa y o make he acquisi ion in lis mode o ( ime, ene gy)
e en s, bu only o eco d ene gy signals as singles.
Eu . Phys. J. A (2019) 55:88 Page 3 o 8
The ac i i y does no ully all back o ze o a e com-
ple ion o a cycle. I is he so-called build-up. The nume -
ical calcula ion de ailed in e . [9] has been used he e oo.
The absence o adioac i e filia ion ende s i e y simple.
I is in e es ing o no e ha a simple analy ic o mula
can be de i ed in case o cons an beam cu en . The ex-
p ession o he numbe o decays N1 o a single i a-
dia ion, e.g. o he coun ing o he oils o measu e he
neu on spec um, is well known
N1=p1−e−λ i
λe−λ (1 −e−λ c)
wi h p he p oduc ion a e (pe deu e on in ou con en-
ion). Indices e e o i adia ion (i), anspo o wai ing
( ) and coun ing (c) imes. We de i e he o e lap o he
k- h eac ion σkn ia di ision by he numbe o a oms
pe uni su ace na .
σkn=σk(E)n(E)dE=pk/na .
Fo iden ical cycles, imes and beam cu en , build-up is
go e ned by a unique pa ame e a=e−λ
cyc , he cycle
ime cyc being i+2 + c, while λis he adioac i e
cons an . The numbe o decays Nnccumula ed du ing nc
cycles can be exp essed as
Nnc=N1nc1
1−a1−a
nc
1−anc
1−a,
which gi es he expec ed alue o 1 o a=0and(nc+1)/2
in he limi o a→1 o he co ec ion ac o wi hin he
b aces.
Acquisi ion and da a co ec ion
The γ- ays ha e been coun ed by a Ge-de ec o monoc ys-
al belonging o he phase 1 o he JUROGAM a ay a
JYFL. The coun ing dis ance om he de ec o cap o he
cen e o he 3 mm hick s ack o a ge was 10.2 cm. Co -
ec ions o posi ion o he oils in he s ack, olume and
abso p ion o he γ- ays ha e been ca ied ou in he same
way as desc ibed in ou o me measu emen s ( e . [8] and
e e ences he ein).
The ene gy spec a ha e been eco ded as ga ed sin-
gles wi h a Canbe a Mul i-Channel-Analyse unning he
Canbe a Genie 2000 so wa e. A CAEN wo-pa ame e
sys em [11] has also been used. This sys em di ec ly anal-
yses he pulses om he p eamplifie in o his og ams. I
accep s highe inpu a es and p o ides be e ene gy es-
olu ion han he con en ional analogue acquisi ion chain.
Un o una ely, ailu e o analyse all high-ampli ude pulses
such as hose o he adioac i i y o 15C p e en ed i s use
o he quan i a i e analysis. The sys em has been ye
e y use ul. Ma ices o γ- ay ene gy e sus ime in cycle
helped g ea ly o so backg ound γ- ays on he basis o
he e olu ion o hei coun ing a e du ing he cycle.
I had been no iced du ing p e ious expe imen s ha
he dead ime gi en by he MCA is unde es ima ed. A
calib a ion was made by looking a he a e o he 40K
backg ound peak in he p esence o a 1 MBq 60Co sou ce
mo ed om 2.3 m o 10 cm. I co e ed a ange o inpu
a es up o 13 kHz, o which he MCA showed 20% while
27% had been measu ed. A quad a ic co ec ion is sui -
able in his ange. A highe a e he acquisi ion e en u-
ally shows a dec easing dead ime, whe eas i is ac ually
blocked.
Coincidence-summing co ec ions ha e been ei he cal-
cula ed in simple cases o ha e been ob ained empi ically
by eco ding efficiency cu es a a ious sou ce- o-de ec o
dis ances. A la ge dis ance, e.g. 40 cm, he small dispe -
sion o expe imen al poin s wi h espec o he fi e ifies
ha he analysis o peaks is co ec . A 10 cm he dis-
pe sion inc eases as he esul o he diffe en indi idual
diffe en p obabili ies o coincidence summing. The effec
was significa i e only o 206Bi decay. The decay scheme
is e y complex, bu wo lines a e li le affec ed by co-
incidence summing and can be used as e e ence. They
indica e he ac ual efficiency o a poin sou ce a e he
usual co ec ions o he fini e size o he oil ha e been
applied back. The 895.1 and 1018.6 keV lines a e only in
p omp coincidence wi h he 184.0 keV γ- ay which, mo e-
o e , is s ongly con e ed ( he o al in e nal con e sion
coefficien is α=1.67) and a enua ed by sel -abso p ion
in he Bi- oil and when i passes he In and Ni laye s.
Indeed, he analy ic app oxima ion o γ- ays no mal o
he oil planes, alid in he la ge-dis ance limi , is a ans-
mission o 0.375 o he 184 keV pho ons. In con as , he
s onges 206Bi lines used o he analysis o neu on spec-
a, namely he 343.5, 537.5, 803.1, 881.0 and 1718.7 keV,
belong o high-mul iplici y cascades. Thei appa en effi-
ciency was dep essed by abou 4%, which, acco ding o
his discussion, indica es he co ec ion.
Efficiency o he Ge de ec o a 5 MeV
De i a ion o he p oduc ion a e po a γ- ay om he
peak a ea implies he knowledge o i s decay b anching bγ
and o he de ec o efficiency ε(Eγ). Fo all lines used in
his wo k, he o me a e epo ed wi h enough accu acy
o ha e negligible impac in o he final e o . Ye , es ab-
lishing he Ge-efficiency a 5298 keV, a abo e he ene -
gies o commonly a ailable s anda ds, dese es a en ion.
The efficiency cu e up o 1408 keV was made wi h 152Eu
and 137Cs s anda ds (3% e o ). Some o he ac i a ed
oils allowed o ex a poin s i hei lines a e dis ibu ed
pa ly inside he calib a ed ange and pa ly abo e. Es-
pecially use ul is 27Al(n,α)24Mg offe ing γ- ays o 1368.6
and 2754.0 keV. A linea unc ion o log(ε) e sus log(Eγ)
was used o desc ibe he ange om 336 keV — he low-
es ene gy o in e es , associa ed wi h 115In(n,n)115Inm—
up o 2754 keV. The ela i e .m.s. de ia ion o he poin s
o 152Eu and o oils once he co ec ion o hei fini e
size had been applied was 4% wi h espec o he fi ed
cu e. All in all, his esul s in a 5% sys ema ical ela i e
e o o he efficiency o he lines used o de e mine he
neu on spec a.
Page 4 o 8 Eu . Phys. J. A (2019) 55:88
A me hod o ge beyond 2.7 MeV is o use he p omp
γ- ays in he he mal-neu on cap u e by ma e ials close
o he de ec o . Rela i e in ensi ies pe a ge nucleus a e
lis ed in he CapGam lib a y o NNDC. No only ull-
ene gy peaks, bu also escape peaks could be exploi ed.
I u ned ou ha he in ensi y a ios o escape o ull-
ene gy peaks do no ob iously depend on he di ec ion
o he incoming γ- ay. These a ios ha e been calib a ed
as a unc ion o γ- ay ene gy using he 2754 keV line, o-
ge he wi h he p omp lines in he mal-neu on cap u es
in he pa affin shielding (1H) and in o he ma e ials nea
he de ec o . Ten nA o con inuous deu e on beam du ing
ypically 4 hou s u ned ou o be sufficien o see many
s ong lines up o 8 MeV. Among he ac i i ies wi h γ- ays
o ene gies below and abo e 2.7 MeV, he mos in ense
we e due o cap u es by 56Fe (suppo s, chain), 28Si (con-
c e e) and 35Cl. The fi s wo we e by a he s onges .
This is due o a la ge numbe o a oms a he han a high
cap u e c oss-sec ion (σ=2.59 b o 56Fe, 0.17 b o 28Si).
The spa ial dis ibu ion o hese nuclei is no enough well
defined o apply co ec ions back o a poin sou ce. In
con as , 35Cl which p esumably is due o spo s o clean-
ing liquid d ied on he de ec o cap has a la ge cap u e
c oss-sec ion (43.6 b). A measu emen wi h 130 g o NaCl
placed a he a ge posi ion allowed o a sou ce wi h
con olled geome y. A e sub ac ing he backg ound,
applying he abso p ion co ec ions and a no malisa ion,
he low-ene gy da a poin s o ε(35Cl) me ged wi h he
efficiency cu e. The ex a poin s abo e 2.7 MeV, he mos
impo an one a 6111.0 keV, p o ided e e ences close o
he ene gies o in e es . The clea ly oo low efficiency ob-
ained a 7790.5 keV (56Fe) indica ed ha he MCA sys-
em missed he highes -ampli ude pulses oo, hough only
a highe ene gy and in a smalle ac ion han he CAEN
sys em. A quad a ic e m in log(ε)−log(Eγ) s a ing o
ac a 2.7 MeV has been added o he linea e m o e-
p oduce he efficiency in he high-ene gy ange. Conse-
quen ly, he ex a e o inc eases like log2(Eγ/2754). The
accu acy o he a io ε(5298)/ε(2754) is es ima ed o 12%.
The la ge e o is due o s a is ics because he added sal
did inc ease he le el o 35Cl ac i i y only by 22% o i s
le el in he backg ound.
Measu emen p ocedu es
The deu e on beam ene gies used we e 22, 31.5, 40 and
45 MeV. These alues esul om he eques o a sho
b eak o change he beam ene gy. The neu on-con e e
a ge s had been planned o be g aphi e powde all, bu
D2O has been used a 22 and 40 MeV. The change o con-
e e a ge was mean o lowe he ene gy dis ibu ion
o he neu ons as a subs i u e o lowe beam ene gy. I
had been seen in e . [5] ha he a e age neu on ene gy is
lowe wi h D2Oo e enH
2O han wi h ca bon. The beam
cu en has been adjus ed be ween 10 nA o 100 nA, ac-
co ding o he beam ene gy, o keep he dead ime o he
acquisi ion below 10%.
Fo neu on measu emen s a single i adia ion o yp-
ically hal -an-hou , has been ca ied ou o each o he
Table 1. Neu on o e laps in mb o 100 deu e ons. The
heade line shows he deu e on beam ene gy in MeV and he
neu on-con e e a ge . E o s do no include a common scale
e o o 6%, see ex .
Reac ion 22, D2O31.5, C 40, D2O 45, C
In(n,n)19.0(17) 29.3(16) 59.6(21) 29.4(19)
Ni(n,p) 40.3(19) 67.5(33) 119.4(57) 86.8(45)
Al(n,p) 3.0(14) 7.2(9) 15.0(12) 10.0(8)
Al(n,α)2.1(2) 6.4(3) 14.1(8) 11.8(6)
Ni(n,2n) 0.5(1) 2.2(2) 7.5(5) 6.0(3)
Bi(n,4n) –1.0(1) 13.0(6) 12.8(5)
Ni-In-Bi and Al s acks. To accoun o he e y diffe en
hal -li es o he esidual ac i i ies, he coun ing was di-
ided in o 3 pe iods. The fi s one ollowed he i adia ion
o abou 2 hou s, and was spli in o sho coun ings o
sa e y. The second one, o 2 o 4 hou s, ook place when a
new beam ene gy was being p epa ed, i.e. abou 20 hou s
a e i adia ion. Finally, he hi d one was done du ing
a ew days a e he un o ob ain be e da a abou he
su i ing 6.24 days 206Bi and 70.9 days 58Co ac i i ies.
The numbe o cycles o measu emen s o 15Cwas
abou n= 1000. The acquisi ion was di ided in a leas
3 pa s o allow o a check o consis ency. A cycle con-
sis ed o an i adia ion o 6 s, a coun ing o 12 s, and ans-
po imes back and o h o 2 s each. These alues ha e
been chosen o a oid la ge build-up. Typical alues o he
e ms be ween b aces in he build-up o mula, we e 1.002
(15C) and 1.133 (16N). The 7.13 s 16N ac i i y is p oduced
by (n,p) on 16O emaining in he a ge .
Resul s
Neu on spec a
O e laps o c oss-sec ion and neu on spec a o eac-
ions wi h ac i a ion oils a e shown in able 1. I is e-
ma kable ha o e laps a Ed= 40 MeV wi h hea y-wa e
con e e a e la ge han hose a 45 MeV wi h g aphi e
con e e . The gain in neu on flux when using D2Oin-
s ead o ca bon is highe han he inc ease due o highe
beam ene gy, which empi ically [8] is (45/40)2.5=1.34.
This confi ms he obse a ion ha a Ed= 42 MeV [5]
he neu on flux wi h hea y-wa e was 1.5 imes highe
han wi h g aphi e. The able does no include he e -
o s due o he Ge-efficiency, no ano he 3% e o o he
calib a ion o he beam-cu en eading de ice. These e -
o s add 6% o he e o on he lis ed o e laps. Since he
e e ence c oss-sec ions a e o en gi en wi h 10% o e all
accu acy, addi ion o all e o s sugges s ha he neu on
flux is co ec wi hin 15%.
The un olded expe imen al neu on spec a a e shown
in fig. 2. The ene gy dis ibu ions o g aphi e (solid lines)
and hea y wa e (dashed lines) a e clea ly diffe en , in
ag eemen wi h measu emen s a 40 MeV [9].

Eu . Phys. J. A (2019) 55:88 Page 5 o 8
Fig. 2. The neu on spec a seen by he wa e a ge s o
a ious deu e on-beam ene gies and neu on con e e s. The
cu es a e in e pola ed be ween he do s which a e he pa am-
e e s used in he i e a i e un olding.
The neu on spec a o be expec ed ha e been ob-
ained om he in e pola ion and in eg a ion o he
double-diffe en ial dis ibu ions measu ed p e iously by
us wi h he same me hod ( e . [8] and e e ences he ein)
and o spec a in eg a ed on qui e he same angles as his
expe imen a Ed= 55 MeV [12]. A sho dis ance he
neu on sou ce canno be ega ded as a poin , bu is a
line co esponding o he ange o he deu e ons. An es i-
ma ed cen e o g a i y o neu on emission [12] has been
used o define he maximum angle o in eg a ion.
I is no ewo hy ha he in eg a ed flux is on he a e -
age 3.4 imes less han i has been expec ed. The esul o
a misalignmen o beam axis and oil has been in es iga ed
by in eg a ion o he expe imen al double-diffe en ial dis-
ibu ions a ailable om ou o me expe imen s, and also
by a Mon e-Ca lo simula ion. The calcula ion was ca ied
ou wi h he Pa icle and Hea y Ion T anspo code Sys-
ems (PHITS-3.02) de eloped a he Japan A omic En-
e gy Agency [13]. The misalignmen is exp essed by he
angle θwhich loca es he cen e o he oil wi h espec
o he nominal beam axis, when i is iewed om he
cen e o he con e e . Fo he 40 MeV deu e on beam
on he ca bon con e e a ge a dec ease by a ac o o
3 was ob ained o a misalignmen o abou 25◦(expe i-
men ) and 30◦(simula ion) deg ees. These alues a e e y
su p isingly la ge. Ye , wha e e had happened, he mea-
su emen s o ac i a ion oils and o oxygen a ge s ha e
been ca ied ou unde he same condi ions. The expe i-
men al neu on spec a mus be he ones o use o un old
he o e laps o 15C.
Ve ifica ion ia he 16O(n,p)16N o e laps
Figu e 3 shows, as an example, a spec um o he adioac-
i i y o wa e a ge aken a Ed=31.5 MeV. The ac-
i i y is s ongly domina ed by he 56Fe(n,p)56Mn eac-
ion ( h eshold = 3.0 MeV) ha occu s in he i adia ion
ca e. Pa o he chain nea he a ge is ac i a ed and
Fig. 3. Gamma spec um o he wa e a ge i adia ed by
neu ons o d + C a Ed=31.5 MeV. The inse (in uni s o
104) shows he γ- ays o in e es in his wo k. The da a, aken
wi h 8 nA du ing 2 hou s, ep esen abou 1/3 o he s a is ics
ob ained a his beam ene gy.
is no enough shielded du ing coun ing. The 2.58 h hal -
li e o 56Mn is why he dead ime does no a y du ing
a cycle. Beam pulsing emo es almos all he lines due o
he mal-neu on cap u e, as shown in he inse whe e only
he peaks a 5298 keV (15C) and 6128 keV (16N) and hei
single (SE) and double (DE) escape peaks eme ge abo e
he backg ound.
The c oss-sec ion o 16O(n,p)16N is well known up o
20 MeV acco ding o he compila ion in NNDC. E alua-
ions shown in he ENDF lib a y and expe imen al alues
shown in he EXFOR lib a y ag ee. Only one e alua ion,
namely EAF-2010, and a se o expe imen al poin s [14]
lis alues abo e 30 MeV. The e alua ion seems o d op
oo quickly, whe eas he o iginal expe imen al da a poin s
do no connec well nei he wi h he expe imen al alues
om o he au ho s no wi h he e alua ions. We kep he
ene gy dependance o he expe imen al high-ene gy ail
bu connec ed hem o he alues below 30 MeV by us-
ing a mul iplica ion ac o . The unce ain y on he ail
o σ(16O(n,p)16N) has no isible impac on he o e laps
owing o he small ac ion o neu ons con ibu ing o
he σno e laps. The c oss-sec ions o 16O(n,p)16Na e
shown in fig. 4.
Table 2 shows he expe imen al o e laps and hei a-
io o hose calcula ed by olding he expe imen al neu on
spec a shown in fig. 2 wi h he c oss-sec ions discussed
abo e, fig. 4. The e o s quo ed a e due o coun ing only.
They a e mainly due o he dispe sion o he esul s o
he a ious subse s a he han o s a is ical fluc ua ions.
The unweigh ed a e age o he abula ed a ios is 1.10.
I one ecalls he 13% unce ain y on he Ge-efficiency a
6128 keV and a 10% e o on he abundance o 16Oin
he a ge , he ag eemen should appea as an acciden .
Ye , i ends o show ha no la ge sys ema ical e o was
bound wi h he analysis. We no e ha , i he expec ed
neu on flux had been used ins ead o he obse ed one,
Page 6 o 8 Eu . Phys. J. A (2019) 55:88
Fig. 4. C oss-sec ions o 16O(n,p)16N. Below 20 MeV all li-
b a ies a e in ag eemen , while abo e EAF (solid line) de-
c eases as e han he o he s. The dashed line is an ex apola-
ion ha keeps he ene gy dependence o a measu emen , bu
has been scaled upwa ds o connec o he bulk o he da a.
Table 2. Expe imen al o e laps (Expe .) in mb o 100
deu e ons o 16O(n,p)16N and hei a io o o e laps cal-
cula ed by olding he expe imen al neu on spec um wi h
a ious c oss-sec ions lis ed in NNDC; ENDF/B-VII.1, EAF-
2010, JEFF-3.2, TENDL16 and RUSFOND-2010. JEFF and
TENDL gi e he same esul and a e lis ed oge he as J,T. A
common sys ema ical expe imen al unce ain y o 17% is no
included.
Ed(MeV) Ta ge Expe . ENDF EAF J,T RUSF
22 D2O0.55(12) 0.91 0.99 0.91 0.91
31 C 1.65(12) 0.85 0.92 0.85 0.87
40 D2O3.46(43) 0.87 0.96 0.87 0.90
45 C 4.71(24) 1.36 1.48 1.36 1.40
h ee imes highe alues o expec ed o e laps had been
ob ained, in clea disc epancy wi h he expe imen al ones.
The a ios, howe e , a e no cons an . They a e sligh ly
lowe han 1.0 a Ed= 22, 31 and 40 MeV, bu he a-
io is clea ly highe a 45 MeV. The ac o 1.4 canno be
accoun ed o by a ealis ic inc ease o he high-ene gy
ail o σ. I is, consequen ly, p obable ha he e exis s
some uncon olled expe imen al ac o . While i had been
emp ing o eadjus he scale o he 16O(n,p)16N da a,
his p ocedu e is difficul o jus i y, conside ing ha he
expe imen al unce ain ies a e la ge han he co ec ion
ac o .
C oss-sec ion o 18O(n,α)15C
Table 3 shows he expe imen al o e laps and hei a io
o calcula ed o e laps o 18O(n,α)15C. The common sys-
ema ical e o is 14%. The sligh dec ease wi h espec
o 16O(n,p) esul s om he smalle ela i e e o on he
abundance o 18O. The p oposed e alua ions in he ENDF
NNDC lib a y a e now qui e diffe en . Only JEFF-3.2 and
Table 3. Expe imen al o e laps (Expe .) in mb o 100
deu e ons o 18O(n,α)15C and hei a io o o e laps calcu-
la ed by olding he expe imen al neu on spec um wi h a -
ious c oss-sec ions lis ed in NNDC. The lib a ies do no ag ee
nei he wi h he expe imen , no wi h each o he , excep JEFF
and TENDL15 lis ed as J,T showing mino diffe ences. A com-
mon sys ema ical expe imen al e o o 14% is no included.
Ed(MeV) Ta ge Expe . EAF J,T RUSF
22 D2O0.75(12) 4.45 0.42 1.51
31 C 1.60(14) 3.46 0.36–0.38 1.09
40 D2O2.04(34) 2.23 0.24 0.63
45 C 1.98(18) 2.67 0.39–0.31 0.74
Fig. 5. C oss-sec ions o 18O(n,α)15C acco ding o lib a ies
e alua ed in NNDC (solid lines wi h labels) and he en a i e
c oss-sec ion ex ac ed in his wo k by un olding he o e laps
a 4 deu e on beam ene gies (line wi h do s). The dashed line
o RUSFOND is a en a i e ex apola ion needed o calcula e
he o e laps o e he whole ene gy ange. Do s do no ep esen
fi ed pa ame e s, bu a e me ely a guide o d aw he cu e by
in e pola ion, see ex o mo e.
ENDF/B-VII a e in ag eemen , bu hey s ongly o e -
es ima e he σno e laps. The o he se s EAF-2010,
he lowes one, and RUSFOND-2010 unde es ima e hem.
He e also, he high-ene gy ail o c oss-sec ions ha e been
en a i ely ex apola ed, excep o EAF-2010 o which
alues a e lis ed. The a ia ion o expe imen al/calcula ed
o e lap a ios is an o e all dec ease wi h beam ene gy.
The exis ence o a se o diffe en neu on spec a could
ha e allowed o an un olding o he σn
ko e laps in o -
de o ex ac he c oss-sec ion. The me hod had been sim-
ila o he one ca ied ou when he neu on spec a ha e
been ob ained, excep ha he ole o spec um nk(E)and
σ(E) had been exchanged. Howe e , he p esen numbe
o 4 beam ene gies is oo limi ed o a con en ional fi . The
c oss-sec ion in fig. 5 has he e o e been d awn by ial-
and-e o , mo ing he do s by s eps. Du ing he i e a ions,
he χ2o he compa ison o expe imen al and calcula ed
o e laps was kep low, while he cu e was cons ained by
he eac ion h eshold and he a emp o d aw he ising
Eu . Phys. J. A (2019) 55:88 Page 7 o 8
Table 4. In- a ge p oduc ion a es o 15C expec ed pe sec-
ond o 1 mA o 40 MeV deu e ons and o he condi ions like
in his wo k, bu wi h an expec ed h ee imes highe flux
pe deu e on, see ex . They a e he expe imen al poin s (Ex-
pe ) and poin s calcula ed om he old o neu on spec a,
fig. 2, wi h he en a i e c oss-sec ion, fig. 5 (Cu e). A global
sys ema ical e o o 14% is no included. The flux (n/s) and
median ene gy Emed o he neu ons abo e 1 MeV a e gi en
o quick e e ence.
EdTa ge Expe . Cu e n/s Emed
(MeV) 15C/s (109)(1013)(MeV)
22 D2O0.97(15) 0.84 1.9 4.7
31 C 2.06(18) 1.84 2.9 8.8
40 D2O2.63(43) 3.49 6.1 9.4
45 C 2.55(23) 2.48 3.9 12.9
edge o emind he one o he e alua ed c oss-sec ions.
The cu e p esen ed in fig. 5 is he e o e a ough and sub-
jec i e guess o σ.
P oduc ion a e o 15C
The da a allow o an es ima e o he p oduc ion a e o
15C in he a ge o RIB acili y, unde he same condi ions
as his expe imen . In able 4 he beam in ensi y has been
aised o 1 mA acco ding o he expec ed pe o mance o
he SPIRAL2 linac. The alues ha e been no malised o a
weigh o 2 g, somewha less han he a ious expe imen al
ones, o allow o easie in e pola ion e sus beam ene gy.
The abundancy o 18O in he a ge has been kep o 68%.
In addi ion, he p oduc ion a es ha e been scaled up a
ac o o 3 o he assumed missing neu on flux. The 3%
e o on he ion-beam cu en , he 13% due o efficiency
o he de ec o a 5.3 MeV and he 4% on he abundance
o 18O in he a ge , in o al a 14% sys ema ical e o ,
should be added o he lis ed e o s. Compa ison o he
p oduc ion a es in he columns “expe ” and “cu e” (cal-
cula ed by olding) indica es he quali y o he adjus men
o he p oposed σ(E) o 18O(n,α)15C.
The hickness used in able 4 is s ill 3 mm. A longe
a ge , o a ew cm, should no be echnically p oblem-
a ic, bu he inc ease migh be hen less han linea wi h
hickness. The geome y a ies because o he longe a -
e age dis ance. I is a mino d awback. Ano he ac o is
neu on mode a ion in hyd ogen. I may mo e some neu-
ons below he peak o sigma and e en below he eac ion
h eshold. Ye , in a a ge o ew cm leng h, a gain ac o
o 10 may no be un ealis ic, so ha he p oduc ion a e
o 15C nuclei in he a ge could each 2 ·1010 pe second.
Summa y and ou look
Summa y o he me hod
Fas neu ons ha e been p oduced by s opping deu e on
beams in a hick a ge , he so-called con e e . The p o-
duc ion o 15C ia18O(n,α)15C, using an en iched wa e
a ge placed behind he con e e , has been s udied. In
addi ion, a se o a ge s chosen o hei known neu on-
ac i a ion c oss-sec ions, σk(E), ha e been i adia ed in
he same geome ic condi ions. The neu on spec um
n(E) was ob ained by un olding he se o expe imen al
o e laps σkn. Measu emen s ha e been epea ed a a -
ious beam ene gies in o de o ob ain diffe en neu on
spec a. A en a i e un olding, now wi h a known neu-
on spec um a each beam ene gy, allowed o a ough
es ima e o he 18O(n,α)15C c oss-sec ion. In he mea-
su emen o he p oduc ion a e all ac o s need o be
known because i is an absolu e alue. In con as , he
c oss-sec ion measu emen in ol es ac o s, e.g. ion-beam
cu en calib a ion and he scale o he neu on spec a,
which cancel. Those which do no , such as a ge en ich-
men and weigh , acquisi ion dead ime, nuclea decay
da a, con ibu ed only weakly o he e o . All oge he ,
10% accu acy on he c oss-sec ion could ha e been eas-
ily eached i he a io o Ge-efficiencies a 5 MeV and a ,
say, 1 MeV had been be e known. S a is ical e o s ha e
no been playing a big pa in he p esen measu emen
nei he , being smalle han sys ema ical e o s. Based on
he coun ing s a is ics ob ained in his measu emen , he
lowe limi o sensi i i y o such a measu emen could be
o a c oss-sec ion peaking a abou 1 mb.
The p esence o 16N lines in he γ-spec a sugges s a
compa a i e measu emen as an al e na i e, i a e e ence
σis well known. Ye , he ene gy dis ibu ion o he neu-
ons has o be es ablished a each beam ene gy. In o de
o ensu e ully iden ical condi ions, he a ge s ack should
ha e included oils o neu on spec a and a ge s o he
σo in e es o be i adia ed oge he .
Scheme o p oduc ion o 15C
The p oduc ion a e o 15C o be expec ed in he a ge
a SPIRAL2 is es ima ed om his expe imen by scaling
he da a. Wi h 1 mA o 40 MeV deu e ons on a ca bon
con e e , a wa e a ge o 6 cm2a ea and 4 cm leng h
wi h 70% en ichmen in 18O, he 15C a e is a ew 1010
pe second.
The p oposed a ge cons uc ion is a cell filled wi h
wa e en iched in 18O, wi h pe haps a supply o oxygen o
sa u a e he liquid, and a ube o ex ac CO2. The cell
can be placed behind he neu on con e e , qui e nea
and is a oom empe a u e. I is a e y sa e cons uc ion.
Release o 15C combined wi h oxygen as bubbles should
be as and efficien , in con as o he op ions wi h a
hea ed solid a ge . The loss ac o s a e he e o e hose
du ing ionisa ion, maybe op ional cha ge b eeding, and
accele a ion. They canno be a oided in he ISOL me hod
and dese e a u he independen s udy.
The au ho s acknowledge he suppo o se e al g oups a
Jy ¨askyl¨a o lending a ious equipmen s: IGISOL (now Ex-
o ic Nuclei and Beams) o he Mul i-Channel Analyse , RITU-
GAMMA (now Nuclea Spec oscopy) o he Ge-de ec o and
he CAEN acquisi ion module, and he RADEF g oup o he
Page 8 o 8 Eu . Phys. J. A (2019) 55:88
beam cu en moni o ing module. They a e also indeb ed in
M .J.Hy ¨onen who kindly accep ed o change he beam en-
e gy ou side o his egula schedule. One au ho (GL) wishes
o hank bo h he GANIL and JYFL labo a o ies o g an ing
e-mail and compu e access.
Da a A ailabili y S a emen This manusc ip has no associ-
a ed da a o he da a will no be deposi ed. [Au ho s’ com-
men : All ele an da a a e in he ables.]
Publishe ’s No e The EPJ Publishe s emain neu al wi h
ega d o ju isdic ional claims in published maps and ins i u-
ional affilia ions.
Open Access This is an open access a icle dis ibu ed
unde he e ms o he C ea i e Commons A ibu ion
License (h p://c ea i ecommons.o g/licenses/by/4.0), which
pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any
medium, p o ided he o iginal wo k is p ope ly ci ed.
Re e ences
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denbu g, A.C. Muelle , J. Ve ie , SPIRAL Phase II
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neu on cap u e γ- ays (CapGam),h ps://www.nndc.
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