P4_3

	To IPPE /


MAIN	STAFF	VANT	PUBLICATIONS	CODES	DATA	LINKS

VANT 1997 rev.1(Voprosi Atomnoy Nauki i Techniki)



NEUTRON CONSTANTS AND PARAMETERS INVESTIGATION OF RESONANCE STRUCTURE AND TEMPERATURE DEPENDENCE OF Pu-239 NEUTRON CROSS SECTIONS *Yu.V. Grigor’ev, V.V. Sinitsa* *Institute of Physics and Power Engineering, Obninsk, Russia* *N.A. Gundorin* *Joint Institute of Nuclear Research, Dubna, Russia* The measurements of full transmissions and self-indication functions in the plutonium-239 fission cross-section were measured at the 60m, 123m and 1006m flight paths of IBR-30. A low-efficiency He-3,B-10 counters and an ionization fission chamber with plutonium-239 (1.6 g) were used as detectors. Metal plutonium-239 disks with diameter 45 mm served filter samples-filters, which cooled to the temperature of liquid and heated to 293K. The measurements have been taken with 7 thickness of the samples-filters. From transmissions and self-indications, by using the method of subgroups, the group meen cross-sections and self-shielding resonance factors in the energy range from 4.65 eV to 200 keV with error of 3-10% have been received. Analogous resonance characters were calculated on the base of the BROND-2, ENDF/B-6 and JENDL-3 evaluated data libraries by means of the GRUCON computer program. (206kb) (in Russian) PHOTOFISSION CROSS-SECTION OF URANIUM-234 IN THE ENERGY REGION FROM 5 TO 9 MeV AND ITS COMPARISON WITH THE DATA FOR THORIUM-232 AND NEPTUNIUM-237 IN SUBBARRIER REGION *A.S. Soldatov* *Institute of Physics and Power Engineering, Obninsk, Russia* The measurements were performed by relative method in a bremsstrahlung beam from microtron with an energy step of 25 keV in subbarier section (below 6 MeV) in the frame of one experiment with nuclei ²³²Th and ²³⁷Np. The table-data for the ratio of yields of (g ,f)-reaction for nuclei ²³⁴U, ²³²Th and ²³⁷Np to yield for ²³⁸U (standard) are presented. The photofission cross sections are reconstructed from these data and are presented in the tables. The resonance structures of photofission cross sections of three nuclei are compared with each other. The resonance structure with an average spacing of about 0.1 MeV is confirmed. The angular components of the photofission cross section for ²³⁴U were calculated. The energy dependence of the quadrupole component shows on the manifesting of fission channel with quantum characteristics Jp =2+ and K=1. (274kb) (in Russian) MEASUREMENTS OF RELATIVE ABUNDANCES AND PERIODS OF DELAYED NEUTRONS FROM FAST NEUTRON INDUCED FISSION OF ²³⁷Np *V.M. Piksajkin, Yu.F. Balakshev, S.G. Isaev, G.G. Korolyov, N.N. Semyonova, A.I. Sergachyov, M.Z. Tarasko* *Institute of Physics and Power Engineering, Obninsk, Russia* Relative abundances and periods of delayed neutrons have been measured by the method based on periodic irradiation of ²³⁷Np sample by neutrons generated from T(p,n) reaction and measurements of delayed neutron activities. The measured data are given in the six group presentation. (234kb) (in Russian) ABSOLUTE MEASUREMENTS OF THE EFFICIENCY OF 4p DELAYED NEUTRON DETECTOR *V.M. Piksajkin, S.G. Isaev, V.V. Korobejnikov, G.G. Korolyov, N.N. Semyonova, M.Z. Tarasko* *Institute of Physics and Power Engineering, Obninsk, Russia* The absolute energy dependent efficiency of delayed neutron detector has been determined in the energy range 0.01-10 MeV using the measurements of the average number of prompt neutrons from ²⁵²Cf spontaneous fission and Monte-Carlo calculations. An activation technique on the basis of ⁵¹V(p,n)⁵¹Cr reaction has been used for measurements of the absolute efficiency of neutron detector at the neutron energy of 0.430 MeV. (285kb) (in Russian) FACTORS DETERMINING THE ENERGY DEPENDENCE OF DELAYED NEUTRON YIELDS IN NEUTRON INDUCED FISSION *V.G. Pronyaev, V.M. Piksajkin* *Institute of Physics and Power Engineering, Obninsk, Russia* The scheme of parametrization of the energy dependence of delayed neutron yields (DNY) in neutron induced fission is proposed. It is based on "microscopic" approach, where the DNY for each precursor is obtained as a product of cumulative yield (CY) of this precursor on neutron emission probability Pn. The dependence of cumulative yields from incident neutron energy can be obtained from independent yields calculated with account of the following factors having a physical sense: i) contributions from different chances of fission; ii) variation of mass independent yields with energy due to variations of contributions of different modes of fission (Symmetric, Standard I and Standard II); iii) washing out of even-odd effects in charge distribution of fission fragment yields with increase of the neutron energy; iv) shift of distribution of fragment mass yields for a given isotope formed after emission of prompt neutrons because of variation of number of prompt neutrons with energy. The analysis was done for the energy region of the first fission chance of ²³⁵U and ²³⁷Np nuclei (neutron energy below 5.5 MeV). The different experimental data were used for a choice of parameters. It is shown, that DNY for fissioning nuclei with even and odd Z have rather different energy dependence and general decrease of DNY is explained mainly by variation of number of prompt neutrons with energy. (561kb) (in English) EVALUATION OF CORRECTIONS FOR SPHERICAL-SHELL NEUTRON TRANSMISSION EXPERIMENTS BY THE MONTE-CARLO TECHNIQUE *B.V. Devkin, M.G. Kobozev, S.P. Simakov* *Institute of Physics and Power Engineering, Obninsk, Russia* *U. Fischer, F. Kappler, U. von M*o llendorff Forschungszentrum Karlsruhe GmbH, Institut fur Neutronenphysik und Reaktortechnik,Karlsruhe, Germany** The influence of some experimental factors on the measured quantities in neutron spherical-shell transmission benchmark experiments was estimated by simulating the corresponding components of the set-up (materials near the neutron source, collimator and shield of the detector etc.) as well as the specific measuring technique (time-of-flight spectrometry) in Monte-Carlo calculations. The calculations were performed by the MCNP code with nuclear data from the EFF-1 and FENDL-1 libraries. The corrections describing the effects of several distinct experimental details were evaluated. (489kb) (in English) ABSOLUTE LEVEL DENSITY FROM ANALYSIS OF COMPLETE SET OF PARTIAL CROSS SECTIONS *V.G. Pronyaev, V.P. Lunev, S.P. Simakov* *Institute of Physics and Power Engineering, Obninsk, Russia* Absolute level density for ⁵²Cr and ⁵⁶Fe nuclei in excitation energy range between 5 and 20 MeV was determined from description of the partial cross sections of neutron induced reactions, evaluated on the base of all available experimental data. The numerical value of the level density for a last bin on excitation energy accessible in inelastic scattering channel has been varied for each incident neutron energy starting from threshold of continuum of the levels to obtain the best description of the evaluated partial reaction cross sections with predominant contribution of discrete channels. The comparison of the obtained absolute level densities with different model predictions was done. (489kb) (in English) THE CONSISTENT EVALUATION OF THE (n,p) AND (n,a ) REACTION CROSS SECTIONS FOR Y, Zr, Nb, Mo ISOTOPES *A.I. Blokhin, V.N. Manokhin, S.M. Nasyrova* *Institute of Physics and Power Engineering, Obninsk, Russia* An analysis of all experimental data and calculated excitation functions of the (n,p) and (n,a ) reactions on Y, Zr, Nb, Mo isotopes is made and new consistent evaluations of these reactions are given on the base of the empirical systematics of excitation functions. (111kb) (in English) ACTINIDE NEUTRON DATA FROM FOND AND ABBN LIBRARIES *S.V. Zabrodskaya, G.A. Korchagina, V.N. Koshcheev, M.N. Nikolaev, A.M. Tsybulya* *Institute of Physics and Power Engineering, Obninsk, Russia* The questions of updating of ABBN93 group constant system for Minor Actinide (Z=89-99) are discussed. The MA group constants are produced on the basis of updated evaluated neutron data library FOND. The cross sections are presented as MF9 tables according to the new ABBN system format. (108kb) (in Russian) NUCLEAR REACTOR DATA SHIELDING REQUIREMENTS FOR THE TRANSPORT OF NUCLEAR WARHEAD COMPONENTS UNDER DECOMMISSIONING *Luisa F. Hansen* *Lawrence Livermore National Laboratory, Livermore, USA* The requirements to carry out accurate shielding calculations involved with the safe off-site transportation of packages containing nuclear warhead components, special assemblies and radioactive materials are discussed. The need for: a) detailed information on the geometry and material composition of the packaging and radioactive load, b) accurate representation of the differential energy spectra (dN/dE) for the neutron and gamma spectra emitted by the radioactive materials enclosed in the packaging, c) well-tested neutron and photon cross section libraries, d) and accurate three-dimensional Monte Carlo transport codes are illustrated. A brief discussion of the need for reliable dose measurements is presented. (93kb) (in English) ANALYSIS OF DISCREPANCY BETWEEN MEASURED AND CALCULATED PHOTONS SPECTRA LEAKING FROM REACTOR BUILDING MATERIALS *L.A. Trykov, V.A. Chernov* *Institute of Physics and Power Engineering, Obninsk, Russia* . The paper is devoted to the problem of gamma-ray transport in the most used reactor building materials. Now there are considerably discrepancy between measured and calculated gamma-ray spectra leaking from iron, lead and chromium specimens with neutron source in the centre. Shown that discrepancies may be caused by constants errors of photons transport, radiative neutrons capture and nonelastic neutrons scattering. To provide support these assumptions it is necessary to investigate the energy-angular photons spectra at neutrons capture end nonelastic neutrons scattering for variety of materials and different neutrons spectra. (353kb) (in Russian)