Production of a 15C radioactive ion beam based on 18O(n, α)

This is a sel -a chi ed e sion o an o iginal a icle. This e sion may di e om he o iginal in pagina ion and ypog aphic de ails. Au ho (s): Ti le: Yea : Ve sion: Copy igh : Righ s: Righ s u l: Please ci e he o iginal e sion: CC BY 4.0 h ps://c ea i ecommons.o g/licenses/by/4.0/ 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 1. M.G. Sain -Lau en , G. Lhe sonneau, J. Ays ¨o, S. B an- denbu g, A.C. Muelle , J. Ve ie , SPIRAL Phase II Eu opean RTT Final Repo , in2p3-00263539 (2001) h p://hal.in2p3. /in2p3-00263539. 2. S. Gal`es, Nucl. Phys. A 834, 717 (2010) and h p://www. ganil-spi al2.eu/. 3. X. Ledoux, M. A¨ıche, M. A igeanu, V. A igeanu, E. Balanza e al., Radia . P o . Dosim. 180, 115 (2018) and hal-01669642, h ps://hal.a chi es-ou e es. / hal-01669642. 4. A. Picha d, PhD Thesis, D´e eloppemen de aisceaux d’ions adioac i s pou le p oje SPIRAL 2,Uni e si ´ede Caen (2010) and h ps:// el.a chi es-ou e es. / el-00544206. 5. G. Lhe sonneau, T. Malkiewicz, K. Kolos, M. Fadil, H. Ke unen, M.G. Sain -Lau en , A. Picha d, W.H. T zaska, G. Tyu in, L. Cousin, Nucl. Ins um. Me hods Phys. Res. A603, 228 (2009). 6. M. Be idge, R. Kjells m, Appl. Radia . Iso . 50, 699 (1999). 7. Na ional Nuclea Da a Cen e , E alua ed (ENDF) and expe imen al (EXFOR) c oss-sec ions, eac ion Q- alues, e alua ed decay and s uc u e da a (ENSDF), and he mal- neu on cap u e γ- ays (CapGam),h ps://www.nndc. bnl.go . 8. G. Lhe sonneau, T. Malkiewicz, M. Fadil, D. Go elo , P. Jones, P.Z. Ngcobo, J. So i, W.H. T zaska, Eu . Phys. J. A52, 364 (2016). 9. G. Lhe sonneau, T. Malkiewicz, P. Jones, P. Ka onen, S. Ke elhu , O. Bajea , M. Fadil, S. Gaudu, M.G. Sain - Lau en , W.H. T zaska, Nucl. Ins um. Me hods Phys. Res. A 698, 224 (2013). 10. Camp o Scien ific GmbH, Be lin, Ge many, www.camp o. eu/. 11. Dual Digi al Mul i Channel Analyze DT5780, h ps:// www.caen.i /p oduc s/d 5780/. 12. G. Lhe sonneau, T. Malkiewicz, P. Jones, S. Ke elhu , W.H. T zaska, Eu . Phys. J. A 48, 116 (2012). 13. T. Sa o, Y. Iwamo o, S. Hashimo o, T. Ogawa, T. Fu u a, S. Abe, T. Kai, P.E. Tsai, N. Ma suda, H. Iwase, N. Shigyo, L. Sih e , K. Nii a, J. Nucl. Sci. Technol. 55, 684 (2018). 14. R.O. Nelson, M.B. Chadwick, A. Michaudon, P.G. Young, Nucl. Sci. Eng. 138, 105 (2011).