The fission process induced by gamma quanta up to 25 MeV energy on 238U was analyzed. Experimental observables as cross sections, fragments mass distribution yields of some nuclides of interest and average prompt neutrons multiplicity characterizing 238U photofission process were theoretically evaluated using TALYS 1.9 software. Theoretical evaluations of isomer ratios using Talys supplied by author’s own code as well as experimental isomer ratios obtained at MT - 25

Microtron are presented

Belov, A. G.

Gruia, I.

Gustova, M. V.

Maslov, O. D.

Mihul, A.

Oprea, A. I.

Oprea, C.

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2019-19138-2Colloquia: EuNPC 2018IL NUOVO CIMENTO 42 C (2019) 138Isomers production in 238U photofissionC. Oprea(1), A. Mihul(2), A. I. Oprea(1), I. Gruia(3), O. D. Maslov(1),A. G. Belov(1) and M. V. Gustova(1)(1) Joint Institute for Nuclear Research (JINR) - Dubna, Moscow Region, Russia(2) CERN, CMS - Geneve, Switzerland(3) Faculty of Physics, University of Bucharest - Magurele, Romaniareceived 5 February 2019Summary. — The fission process induced by gamma quanta up to 25 MeV energyon 238U was analyzed. Experimental observables as cross sections, fragments massdistribution yields of some nuclides of interest and average prompt neutrons mul-tiplicity characterizing 238U photofission process were theoretically evaluated usingTALYS 1.9 software. Theoretical evaluations of isomer ratios using Talys suppliedby author’s own code as well as experimental isomer ratios obtained at MT - 25Microtron are presented.1. – IntroductionFission process induced by gamma quanta is of interest for fundamental researchesbecause furnish new data about configuration of fissionable systems near scission point,anisotropy, emitted gamma spectra, fission products ground states, spin distributions,angular momentum dependence of levels density, etc [1], [2]. Photofission is importantalso for applied researches related to transmutation and energy projects, new generationnuclear reactors, isotopes production [3].The fission process induced by gamma quanta up to 25 MeV energy on 238U wasanalyzed. This study represents a research proposal for photofission investigations andisotopes production at the new pulsed Intense Resonant Neutron Source (IREN), fromFrank Laboratory of Neutron Physics (FLNP) at JINR Dubna.2. – Codes and elements of theoryFission observables were evaluated by using Talys 1.9. Main reaction mechanisms areimplemented in this code together with a wide nuclear database for many nuclei [4]. Forthe evaluation of fission cross sections the Hauser - Feshbach approach is applied [4], [5].Fission fragments mass distribution, isotopes yields, prompt neutron distributions wereCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 C. OPREA et al.evaluated using Brosa model [4], [6]. If the incident particles are Bremsstrahlung gammaquanta then the isomer ratios have the form [7]:R = Ym · [Yg]−1 =∫ EmaxEthrN0φ(E)σm(E)dE ·[ ∫ EmaxEthrN0φ(E)σg(E)dE]−1(1a)where: Ym,g = yields of isotope in isomer (m) and ground (g) states; N0 = numberof target nuclei; φ = flux of incident beam; σm,g = production cross section of m andg states respectively; Ethr = threshold energy of emergent particle emission; Emax =maximum energy of incident beam.The incident X - ray flux was evaluated applying the Kramer relation [8]:φ(Eγ) ∼ Ic = ibZ(E0 − Eγ)E−1γ(2a)where: Ic = gamma quanta intensity; ib = electrons beam current; E0 = electrons energy;Z = charge of target stopping element.Isomer and ground cross sections for fission are not provided by Talys and thereforethese values are obtained from a statistical approach and states spin distribution P (J)[9], [10]:P (J) ∼ (2J + 1)Exp[−0.5J(J + 1)(σ + λ)−2(3a)where: J = spin; σ, λ = parameters.3. – Results and discussionsIn Fig. 1 the energy dependences of photofission cross sections and fission fragmentmass distributions are represented. Photonuclear processes (γ,xn), (γ,xp), (γ,np) fol-lowed by fission occur in the interaction of gamma quanta with 238U nucleus togetherwith its photofission. Total photofission cross section represents the contribution of 238U,237U, 236U (see Fig. 1a)) and of other fissile nuclei which can be neglected. In Fig. 1b)experimental data are compared with theoretical evaluation using default Talys input.A satisfactory description of experimental data was obtained. The shapes of both exper-imental and theoretical dependences are similar. Low energy part is well described up to12 - 13 MeV. At higher energies it is necessary to vary Talys input data correlated withanalysis of existing measurements. Experimental data are taken from EXFOR [11].In Fig. 1c) experimental and calculated mass distributions before neutrons emissionare represented for 7 MeV gamma energy. Experimental data were obtained by usinga Bremsstrahlung X - ray source [12]. A very good agreement between theory andexperiment can be observed. In Fig. 1d) evaluated mass distribution of fission fragmentare shown for Eγ = 13 MeV for pre and post neutrons emission. Mass distributiondemonstrates a slowly increasing symmetry with energy.Average prompt neutrons multiplicity, prompt neutrons multiplicity distributions,isotopes yields were also evaluated. In Fig. 2a) the average neutrons multiplicity asfunction of fragment mass for Eγ = 25 MeV, before and after neutrons emission isrepresented. In Fig. 2b) prompt neutrons multiplicity distribution for 13, 19, 25 MeVgamma energy, respectively, are shown. At these energies photofission cross sections areISOMERS PRODUCTION IN 238U PHOTOFISSION 310 15 20 2502040608010012010 15 20 25 300204060801001201401601804321f [mb]Gamma Energy [MeV]b)a)21Gamma Energy [MeV]60 90 120 150 1800.0000.0150.0300.0450.0600.07560 90 120 150 1800.0000.0150.0300.0450.0600.075c)YieldsFragment Massd)Fragment MassFig. 1. – 238U Cross sections and mass distributions. Cross sections. a) Total fission crosssections 1− > 2 + 3 + 4; 2 - 238U; 3 - 237U; 4 - 236U. b) Comparison between theory andexperiment; 1 - Talys; 2 - experimental data. Mass distributions. c) Eγ = 7 MeV - pre neutronsemission. empty circles - Talys; black squares - experimental data. d) Eγ = 13 MeV - Talys;Neutrons emission: empty circle - pre; black square - post45 90 135 1800123450 2 4 6 8 10 120.00.40.81.21.62.0a)Av.Pr.N.MFragment Massb)321PNMDNeutrons Number5 10 15 20 250.0080.0120.0160.0200.0240.0280.03215 18 21 240.0020.0040.0060.0080.0100.0120.01421YieldsGamma Energy [MeV]d)c)21Gamma Energy [MeV]Fig. 2. – Prompt neutrons and isotopes production. Prompt neutrons. a) Average promptneutrons multiplicity (Av.Pr.N.M.); Eγ = 25 MeV; Neutrons emission: empty circles - pre;black squares - post. b) Prompt neutrons mutiplicity distribution (PNMD). 1 - Eγ = 13 MeV;2 - 19 MeV; 3 - 25 MeV; Isotopes production. c) 132Sb; d) 134I; Neutrons emission; 1 - pre; 2 -postσγf = 90.51, 46.67, 12.68 mb with prompt neutrons mean values νpr = 3.74, 4.68, 5.20,respectively.Yields for 132Sb and 134I isotopes produced in the photofision of 238U are representedin Fig. 2c) and 2d), before and after neutrons emission. These results are obtained withstandard Talys input. For 135I or 135Xe isotopes it is necessary to increase Talys precisionfor yields and cross sections calculations.At Microtron MT - 25 from JINR, isomer ratios for 130Sb, 132Sb, 134I, 135Xe weremeasured using a Bremsstrahlung X - ray source from neutrons threshold up to 16 MeV.Evaluations were realized using cross sections from Talys, relation (1), statistical ap-proach from [10], [12] and incident flux from expression (2). Comparison between exper-imental and theoretical isomer ratios are given in Table 1.For 130Sb nucleus a well agreement was obtained. For 135Xe further analyses arenecessary. For 134I and 132Sb nuclei calculations will be done in the next study. Theerrors appear because the integrals from (1) are sums with a given step (1 keV).4 C. OPREA et al.Table I. – Isomer ratios.Isomer Eγ Rexp RTalys135Xe 16 0.22 ± 0.03 0.43 ± 0.05130Sb 16 0.86 ± 0.15 0.95 ± 0.08134I 16 0.67 ± 0.13 −132Sb 16 0.79 ± 0.13 −4. – ConclusionsIsotopes and isomer production in photofission of 238U was investigated. Cross sec-tions, mass distributions, dependence of average prompt neutrons multiplicity on fissionfragment mass, isotopes production and isomer ratios were obtained for incident neu-trons energy starting from 7 up to 25 MeV. Calculations were compared with existingexperimental data.New photofission experimental and theoretical data are necessary correlated withfuture computer simulations.REFERENCES[1] Krishichayan, Finch S.W., Howel C.R., Tonchev A.P., Tornow W., Phys, Rev. C,98 (2018) 014608.[2] Visan I., Giubega G., Tudora A., Rom. Journ. Phys., 59 3-4 (2014) 272.[3] Salvatores M., Slessarev I., Tchistiakov A., Nucl. Sci. Eng., 309 (1990) 130.[4] Koning A.J., Hilaire S. and Duijvestijn M.C., Proceedings of the InternationalConference on Nuclear Data for Science and Technology, April 22-27, 2007, Nice, France,edited by Bersillon O., Gunsing F., Bauge E., Jacqmin R., Leray S. EDP Sciences(2008) 211.[5] Hauser W., Feshbach H., Phys. Rev, 87, 2 (1952) 366.[6] Brosa U., Grossmann S., Muller A., Phys. Rep., 197 (1990) 167.[7] Tran D.T., Truong T.A., Nguyen T.K., Nguyen T.V., Phan V.C, Belov A.G.,Maslov O.D., Physics of Particles and Nuclei Letters, 6, 2 (2009) 209.[8] Kramers H.A., Philos. Mag., 46 (1923) 836.[9] Huizenga J.R., Vandenbosh R., Phys. Rev., 120 (1960) 1305.[10] Vandenbosh R., Huizenga J.R., Phys. Rev., 120 (1960) 1313.[11] Veyssiere A., Bell H., Bergere R., Carlos P., Lepetre A., Kernbach K., Nucl.Phys, A199 (1973) 45.[12] Goeoek A., Chernykh M., Eckardt C., Enders J., von Neumann-Cosel P.,Oberstedt A., Oberstedt S., Richter A., Nucl. Phys, A851 (2011) 1.

Isomers production in 238U photofission

The fission process induced by gamma quanta up to 25 MeV energy on $^{238}$U was analyzed. Experimental observables as cross sections, fragments mass distribution yields of some nuclides of interest and average prompt neutrons multiplicity characterizing $^{238}$U photofission process were theoretically evaluated using TALYS 1.9 software. Theoretical evaluations of isomer ratios using Talys supplied by author’s own code as well as experimental isomer ratios obtained at MT - 25 Microtron are presented

Oprea, C

Mihul, A

Oprea, A I

Gruia, I

Maslov, O D

Belov, A G

Gustova, M V

CERN Document Server

Isomers production in $^{238}$U photofission

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Isomers production in 238U photofission

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