Production and Monitoring of Neutron Flux by Activation Detectors

Abs ac —The neu on gene a ion echnique was es ed on he mic o on M-10 wi h an ou pu elec on beam o 8.7 MeV. Gi en he low ene gy ha he mic o on can p o ide o elec ons, he b emss ahlung induced pho onuclea eac ion 9Be (γ, n), which has a low h eshold, was chosen o neu on gene a ion. Cobal and indium a ge s we e es ed as ac i a ion de ec o s o es ima e he neu on lux densi y. In he cobal a ge , he isome ic s a e o 60mCo wi h an ene gy o 58.6 keV and a hal -li e o 10.5 minu es is well ac i a ed. Two well-known addi ional gamma lines o s anda d cobal sou ce pe mi o cla i y he absolu e alue o he neu on lux. The ac i a ed indium a ge has ou gamma lines bound o he 116mIn isome β- decaying wi h he hal -li e o 54.4 minu es, wha is con enien o measu emen o gamma spec um. Despi e he low ene gy o he ou pu elec on beam, a a beam in ensi y o 5 μA i is possible o ob ain an almos iso opic neu on lux o 107 n/(s∙cm2). Keywo ds — Neu on p oduc ion, mic o on, gamma spec oscopy, neu on ac i a ion de ec o s. I. INTRODUCTION N he mic o on M-10 o Uzhgo od Na ional Uni e si y he e a e ca ied ou expe imen al in es iga ions o pho onuclea eac ions [1] as well as applied s udies o i adia ion in luence on he p ope ies o new echnological ma e ials and elec onical componen s [2]. Fo i adia ion i is possible o use elec ons o ene gies 4-10 MeV and b emss ahlung. Bu i was demons a ed [3] ha low ene gy elec on accele a o mic o on MT-25 wi h 22 MeV ou pu elec on beam can se e as neu on sou ce, which is in e es ing o compa e wi h he gene a ion o neu ons by a p o on accele a o a he same beam ene gies [4]. Neu ons a e unique pa icles ha a e o in e es om bo h a undamen al and an applied poin o iew. O he unsol ed expe imen al undamen al p oblems, we no e he p oblem o neu on li e ime [5], he ques ion o he p esence o he elec ic dipole momen o he neu on [6], and he sea ch o neu on clus e s [7]. In addi ion, neu on egis a ion s ill ep esen s an uneasy p oblem. Among he cu en applied esea ch, we no e he s udy o di e en ypes o s uc u es in he physics o condensed ma e , he s udy o he e ec o neu on luxes on li ing issues and o ganisms, neu on di ac ion analysis [8], neu on ac i a ion analysis. O g ea p ac ical impo ance o ma e ials science is he a ailabili y o accu a e da a on he c oss-sec ions o he in e ac ion o neu ons wi h nuclei. Fo ene gy needs, namely o eac o s con olled by accele a o s, expe imen al da a on neu on gene a ion p ocesses a e equi ed. In his pape , we p esen he esul s o neu on gene a ion on he M-10 mic o on o Uzhgo od Na ional Uni e si y. The expe imen consis o ew s ages – 1) ou pu elec on beam gene a e b emss ahlung spec um in eac ion 𝑒𝑒−+𝑍𝑍 → 𝛾𝛾 + 𝑒𝑒−+𝑍𝑍, 2) neu ons c ea ion in pho onuclea eac ion (γ,n), 3) ac i a ion eac ion (n,γ) and 4) measu ing and analysis o gamma spec a o ac i a ed sample. II. EXPERIMENTAL SET UP A. Schema ic iew The Fig. 1 shows a schema ic o he expe imen . The ou pu elec on beam alls on he b aking ungs en a ge a e which he b emss ahlung beam hi s he be yllium a ge . Neu ons a e c ea ed on a be yllium a ge in eac ion γ+𝐵𝐵𝑒𝑒 9→n + 2𝛼𝛼, (1) s a ing om he h eshold Eγ=1.57 MeV. The in ensi y o gene a ed neu ons is egis e ed by he ac i a ion sample ( a ge ) due o (n, γ) eac ion. Analysis o gamma spec a o he ac i a ed sample (de ec o ) gi es he alue o he neu on lux. Fig. 1. Schema ic o he expe imen : accele a o mic o on M-10, ungs en gamma con e e , he be yllium a ge and he ac i a ion a ge (de ec o ). The main pa ame e s o ou expe imen we e as ollows: he ene gy o he induced elec on beam was 8.7 MeV and a pla e o na u al ungs en o size 93 x 55 x 2 mm ( hickness 2 mm) se ed as a b aking a ge . The size o he be yllium a ge is Ø10 x 14 cm, and i s weigh is 2 kg. To measu e neu ons lux we use 59Co as ac i a ion de ec o s. The cobal de ec o (boxed powde CoCO3*Co(OH)2*nH2O, mass 31 g) was i adia ed du ing 10 min by neu ons Cobal P oduc ion and Moni o ing o Neu on Flux by Ac i a ion De ec o s I an Haysak1, Vasyl Ma ishichkin1, Ye gen Ha apko1, Robe Holomb1,2, and Ka el Ka o sky2 1Uzhgo od Na ional Uni e si y, Uk aine 2B no Uni e si y o Technology, Czech Republic Co esponding au ho : i[email p o ec ed] O © The Au ho s, published by EDP Sciences. 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 4.0 (h p://c ea i ecommons.o g/licenses/by/4.0/). EPJ Web o Con e ences 253, 01005 (2021) h ps://doi.o g/10.1051/epjcon /202125301005 ANIMMA 2021 de ec o is ac i a ed by neu ons o bo h 60Co g ound s a e and isome ic le el 60mCo wi h hal -li e 10.47 minu es and ollowing isome ic ansi ion Eγ = 58.6 keV o he g ound s a e. A e β- decay (hal - ime 5.27 yea s) he g ound s a e gi es well-known wo lines Eγ = 1173 keV and Eγ = 1332 keV [9]. As a neu on indica o , we also used an aluminum pla e coa ed wi h indium powde . B. Gamma Spec ome e A NaI(Tl) c ys al scin illa ion de ec o wi h size Ø63 x 63 mm looking h ough by pho omul iplie 19-M and wi h he SBS-40 ampli ude analyze boa d se ed as a gamma spec ome e (Fig. 8). The accumula ion o spec a occu s wi h he help o a specialized compu e p og am AkWin. The numbe o channels o he analyze is a iable and can ake alues om 256 o 8192. Fig. 2. Schema ic o he scin illa ion spec ome e . The measu ed ene gy esolu ion (FWHM) o he spec ome e o calib a ion lines and he simula ed o al peak e iciency ε o he de ec ed gamma lines o he neu on- ac i a ed sample 59Co a e shown in Table I. TABLE I THE EFFICIENCY AND THE ENERGY RESOLUTION OF THE GAMMA SPECTROMETER Eγ, keV 58.6 59.5 661.7 1173 1332 ε × 102 23.2 - - 4.71 4.16 FWHM keV - 16.2(2) 71.2 (3) 82.0(5) 88.8(9) III. BREMSSTRAHLUNG SPECTRUM The gamma- ay spec um c ea ed on a 2 mm hick ungs en a ge in he o wa d di ec ion by a 5 MeV elec on beam is showed a he Fig. 2. The spec um is simula ed by he FLUKA code [10]. The b emss ahlung spec um is a wide peak in he in e al o ene gy Eγ=0.1-5 MeV. In he ene gy egion, less han 0.1 MeV he cha ac e is ic X- ay lines o ungs en a om a e p esen , also he annihila ion line o 0.511 MeV is e iden . Tha is, in a ungs en con e sion a ge wi h a hickness o 2 mm, he e is a signi ican p obabili y o a h ee-s age p ocess, namely, 1) he b aking p ocess on he nucleus e- +Z →γ + e- +Z; 2) o ma ion in he ield o he nucleus o elec on-posi on pai s γ + Z → e+ + e- + Z; 3) he o ma ion o he posi onium a om e+ + e- → Ps; 4) annihila ion o posi onium Ps → γ + γ. The i s wo p ocesses ake place wi h he pa icipa ion o he a omic nucleus, and he las wo a e he a omic p ocesses. Fig. 3. The simula ed b aked gamma spec um o 5 MeV elec on beam in 2 mm ungs en con e e . In Fig. 3 is shown a compa ison o he b emss ahlung spec a simula ed o elec on beam o ene gies 4 MeV, 5 MeV, 8 MeV, and 9 MeV [11]. I is seen ha he shape o he peak is p ese ed, and wi h inc easing elec ons ene gy he yield o gamma quan a is inc eased. In he s udy o nuclea eac ions, only a pa o he gamma spec um wi h ene gy g ea e han he eac ion h eshold "wo ks". In ou case o neu ons gene a ion on a be yllium a ge , i is gamma quan a wi h ene gies g ea e han 1.6 MeV. Bu a a se o he abso bed dose, i is necessa y o conside he whole b emss ahlung spec um. Fig. 4. The simula ed b emss ahlung o di e en elec on beam ene gies 4, 5, 8 and 9 MeV. I should be no ed ha he b emss ahlung spec um depends on bo h he elec on ene gy and he hickness o he b aking a ge and i s a omic composi ion. The pene a ion dep h o a monoene ge ic elec on beam wi h ene gies 3 < Ee <20 MeV in aluminum is well desc ibed by phenomenological o mula 𝑅𝑅= 0.53 ∙ 𝐸𝐸𝑒𝑒−0.106 , (2) whe e R is he dep h o pene a ion in g/cm2, Ee is he elec on ene gy in MeV [12]. Fo o he ma e he pene a ion dep h can be es ima e by co ec ion 2 EPJ Web o Con e ences 253, 01005 (2021) h ps://doi.o g/10.1051/epjcon /202125301005 ANIMMA 2021 𝑅𝑅𝑥𝑥=𝑅𝑅𝐴𝐴𝐴𝐴 (𝑍𝑍 𝐴𝐴 ⁄)𝐴𝐴𝐴𝐴 (𝑍𝑍 𝐴𝐴) ⁄𝑥𝑥 , (3) whe e (Z/A)x is he cha ge o mass a io o he co esponding elemen . The es ima ed pene a ion dep h o an elec on beam o 8.7 MeV in ungs en is 2.8 mm. IV. NEUTRON PRODUCTION The measu ed and e alua ed da a o he ene gy dependence o he pho onuclea eac ion c oss-sec ion σ(γ, abs) o be yllium, is as ollows Fig. 4. Fo elec on ene gy o 8.7 MeV(and maximal ene gy o gamma), he c oss-sec ion is abou 1.5 mb. Up o h eshold ene gy o channel (γ, p) 16.89 MeV he e a e open channels (γ,nx) whe e x a e 2α o 8Be Fig. 5. The measu ed and he model calcula ion o he o al c oss-sec ion o pho oabso p ion eac ion 9 Be(γ,abs) [13]. in he g ound o exci ed s a es ( he h ee lowes well-sepa a ed le els o 8Be a e 3.04, 11.4, and 16.6 MeV). The h esholds o hese channels a e indica ed in Table I. So o elec on beam 8.7 MeV he h ee channels o eac ion 9Be(γ,n) a e opened. TABLE II THE THRESHOLD ENERGIES FOR DIFFERENT REACTION CHANNELS Th eshold ene gies (MeV) γ, n+2α γ, n+8Be γ, n+8Be*(3.04) γ, n+8Be*(11.4) 1.57 1.67 4.71 13.1 Analysis o he kinema ics o he 9Be(γ, n)8Be eac ion shows ha he kine ic ene gy o a neu on is weakly dependen on i s emission angle. Fig. 5 gi en he dependence o he neu on kine ic ene gy dis ibu ion e sus he angle o he ou going neu on ela i e o he gamma beam di ec ion o ene gies o gamma quan a 8, 6, 4, and 2 MeV. Howe e , he shape o he angula dis ibu ion can be de o med by he dynamics (ma ix elemen ) o he nuclea eac ion. Fig. 3 shows ha he in ensi ies o he co esponding ene gies o gamma quan a di e by an o de o magni ude. Tha is, one can conclude ha he eac ion (γ, n) o ming an almos iso opic dis ibu ion o neu ons in he whole ene gy egion om ze o up o 6 MeV. Bu in he be yllium a ge i sel , neu ons a e mode a ed by elas ic mul iple sca e ing on be yllium nuclei. The e o e, he spec um o neu ons ou side he be yllium a ge will be much so e . Fig. 6. The angle dependence o kine ic ene gy o ou going neu ons o eac ion γ + 9Be → n + 8Be a ene gy Eγ=8, 6, 4 and 2 MeV ( iole , ed, yellow, and g een line espec i ely). V. ACTIVATION DETECTORS We chose samples o 59Co and na u al indium as ac i a ion de ec o s which ha e sa is ac o y a e ac i a ion and disin eg a ion cons an s. The ac i a ion sample was loca ed close o he side su ace o he be yllium cylinde . A. Cobal sample The e ec i e c oss-sec ion o he eac ion 59Co(n,γ) is shown in Fig. 6. In he egion om he mals up o 6 MeV neu ons, he c oss-sec ion belongs o in e al 2-40 ba ns [14]. Fig. 7. The ene gy dependence o c oss-sec ion o eac ion n + 59Co → γ + 60g,m Co [14]. Neu on ac i a ion o 59Co leads o he o ma ion o 60gCo in he g ound s a e and in he isome ic s a e 60mCo. The decay schemes o cobal om he g ound (T1/2=5.27 yea s) and isome (T1/2=10.47 minu es) s a es [9] a e shown in Fig. 7. Isome s a e has wo decay modes – 99.76% isome ic gamma ansi ion wi h Eγ=58.59 keV and 0.24% β- decay. The g ound s a e is a well- known s anda d cobal -sou ce which a e β- decay gi es wo 0 50 100 150 0 1 2 3 4 5 6  ,deg ee Tn,MeV The kine ic ene gy o neu ons s.angle  E  8, 6, 4and 2MeV  3 EPJ Web o Con e ences 253, 01005 (2021) h ps://doi.o g/10.1051/epjcon /202125301005 ANIMMA 2021 gamma lines 1333 keV and 1173 keV. B. Indium sample Na u al indium consis o 113In(4.29%) and 115In(95.7%) iso opes [15]. A e ac i a ion by neu ons in eac ion (n,γ) isome 116mIn is c ea ed which a e β- decay wi h hal -li e 54.29 m ans o ms in o 116Sn in exci ed s a es wi h gamma lines Eγ=417, 1097, 1293 and 2112 keV. The c oss-sec ion o eac ion 115In(n,γ) is nea 200 ba n [14]. Fig. 8. The decay schemes o cobal g ound and isome s a es [8]. VI. RESULTS AND CONCLUSIONS A be yllium a ge and ac i a ion samples we e i adia ed o 10 minu es wi h a b aking beam o gamma quan a ob ained on a ungs en con e sion a ge by an elec on beam wi h an ene gy o 8.7 MeV and an in ensi y o 5 μA. Fig. 9 shows he gamma spec a om samples o indium, cobal , and backg ound. The isome ic cobal line is no shown because i is loca ed nea channel 20 whe e he backg ound is e y high. Fig. 9. The gamma spec a om ac i a ed 59Co and 115In samples and backg ound spec um. 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