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Search for Isobar Nuclei in Mass Distributions of Heavy Fission Fragments of 235U Nuclei by Thermal Neutrons

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Search for Isobar Nuclei in Mass Distributions of Heavy Fission Fragments of 235U Nuclei by Thermal Neutrons International Conference “Nuclear Science and its Application”, Samarkand, Uzbekistan, September 25-28, 2012 SEARCH FOR ISOBAR NUCLEI IN MASS DISTRIBUTIONS OF HEAVY FISSION FRAGMENTS OF 235U NUCLEI BY THERMAL NEUTRONS Abdullaeva G.A., Koblik Yu.N., Nebesniy A.F., Pikul V.P. Institute of Nuclear Physics, Tashkent, Uzbekistan To search for isobar nuclei in mass distributions of 235U nuclei heavy fission fragments (FF) caused by thermal neutrons we used experimental data from [1]. In [1] experimental data of yields for each value of mass number in FF mass numbers range from A=125 to A=155 a.m.u. depending on effective charge state z* are published. In figure 1 such experimental dependence of FF yields Yi (Ai) =f(z*) and processing of this dependence by Gauss distribution with an error to one σ for each z* is presented. The basic difficulty consisted in correct transition from measured z* to charges of heavy fragments at the moment of nuclear fission. For this purpose we used the modified expression from [2] in the form of: k * α k1 i i ii VzV1zz 0 . Here zi* and zi - the measured effective charge of the i-th ion with mass number Ai and a charge of corresponding fragment, Vi - velocity of ion, Vo - average velocity of electrons interacting with fragment in the target matter and influencing to formation of an effective charge of the ion. Velocity Vi was defined with use of measured value Ek for each fragment. Velocity Vo can 8 changes in limits from Vo = 2.2×10 cm/s - electron velocity in the first orbit of hydrogen atom to 3.6×108 cm/s [2], constants: α =0.45 and k =0.6 are taken as from [2]. In Table 1 the results of isobar nuclei estimation for А=125 are presented. Tab.1 0.012 A=125 8 8 Vi×10 , Vo×10 , Isobar z* Ek, MeV zi Y, abs. u. cm/s cm/s nuclei 0.008 125 20±0.51 53.9±0.5 9.11 3.33 49.06 In49 125 22±0.69 59.2±0.6 9.56 3.13 49.96 Sn50 125 0.004 24±0.56 64.6±0.6 9.99 2.97 51.13 Sb51 16 18 20* 22 24 26 Z Fig.1 By using this approach a search for isobar nuclei of 235U nuclei FF caused by thermal neutrons in mass numbers range from A=125 to A=156 is executed. Further, for certain values of isobar nuclei experimental yields are compared with theoretical data [3]. In table 2 results of isobar nuclei yields estimation for А=125 are shown. 175 Section I. Physics of Particles and Nuclei (theory and experiment) International Conference “Nuclear Science and its Application”, Samarkand, Uzbekistan, September 25-28, 2012 Tab.2 Theoretical data from [3] Our experimental data Isobar nuclei Ind. Yield Cum. Yield Y(Ai) Isobar nuclei Yi(Ai) 49 In125-m-12.2 s 4.72E-03 6.39E-03 49 49 In125-2.36 s 4.72E-03 8.61E-03 0.046 In125 0.011 50 Sn125-m-9.5m 1.05E-02 1.80E-02 50 50 Sn125-9.63 d 8.54E-03 1.60E-02 Sn125 0.016 51 51 Sb125-2.758 y 2.74E-05 3.40E-02 Sb125 0.020 Yi(Ai) - yield of isobar nucleus, Y(Ai) - total yield. 1. G.A. Abdullaeva, Yu.N. Koblik, A.F. Nebesniy, V.P. Pikul. Quantitative characteristics of charge and energy yields of 235U fission fragments by thermal neutrons, In this Book of Abstracts. 2. I.S. Dmitriev, V.S. Nikolaev. «Semi-empirical method for calculation of charge equilibrium distribution in fast ion beam», JETP, v.47, ed.8, 1964, p. 615-623.(in Russian) 3. T.R. England and B.F. Rider, Fission Product Yields per 100 Fissions for 235U Thermal Neutron Induced Fission Decay, LA-UR-94-3106, ENDF-34. MULTIPLICITY OF NEUTRON EVENTS SPECTRUM AND TIME DISTRIBUTION OF NEUTRONS REGISTERED IN THE NEUTRON SUPERMONITOR 6NM64 AL-FARABI KAZNU AT 850 M ABOVE SEA LEVEL Chubenko A.P.1, Shepetov A.L.1,2, Oskomov V.V.3, Burtebayev N.T.4, Peterson J.R.5, Saduyev N.O.3, Kalikulov O.A.3 1P.N.Lebedev Physical Institute, Moscow, Russia 2Tien-Shan Mountain Cosmic Ray Station, Almaty, Kazakhstan 3Al-Farabi Kazakh National University, Almaty, Kazakhstan 4Institute of Nuclear Physics, Almaty, Kazakhstan 5University of Colorado, Colorado, USA Neutron supermonitor of KazNU is one standard section with an area of 6 m2, which contains six proportional neutron counters SNM15 type. The peculiarity of the data collection system on the Al-Farabi KazNU experimental setup is that the signals from each of the neutron counters are fed directly to two parallel operating discriminators tuned to different thresholds - low (10 mV in recalculation to counter’s anodic filament) and high (40 mV). The output pulses of both discriminators then formed and registered by data collection system independently from each other. 176 Section I. Physics of Particles and Nuclei (theory and experiment) .
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