中子俘获瞬发γ射线数据评价(英文)

简要地介绍了中子俘获瞬发γ射线数据及其衰变纲图的评价方法技术、主要程序及其功能、数据评价流程、强度平衡检验，以及对A=1-44的稳定核素和A>190的部分稳定核素的热中子俘获瞬发γ射线数据及其衰变纲图评价的具体应用.The method of prompt γ-ray data evaluation for neutron capture and how to calculate the prompt γ-ray intensities of neutron capture have been briefly presented. The prompt γ-ray data of thermal-neutron capture of some stable nuclei for A=1-44 and A>190 have been evaluated. The ENSDF format has been adopted. The checks of intensity balance and format have been made. The examples are given to illustrate its application.     

Investigation of condensed matter by means of elastic thermal-neutron scattering

The application of elastic thermal-neutron scattering in investigations of condensed matter that were performed at the Institute for Theoretical and Experimental Physics is described. An account of diffraction studies with weakly absorbing crystals, including studies of the anomalous-absorption effect and coherent effects in diffuse scattering, is given. Particular attention is given to exposing the method of multiple small-angle neutron scattering (MSANS). It is shown how information about matter inhomogeneities can be obtained by this method on the basis of Molière’s theory. Prospects of the development of this method are outlined, and MSANS theory is formulated for a high concentration of matter inhomogeneities.     

A MODEL OF FISSION

Mass and kinetic energy distribution of fragments in thermal-neutron in-duced fission of ²³⁵U are calculated by a α decay-like model. Besides Coulomb andnuclear interactions, the deformation and intrinsic excitation energies of fragments arealso taken into account.     

Coordination number in liquid argon

Structure of liquids is discussed in terms of Voronoi figures and Delaunay polyhedra. Equations of the respective models and precise experimental data recently available for argon lead to calculated values of the coordination number z and the geometric parameter μ. The relation between z and μ is thus found empirically. Further, calculated values of coordination numbers are compared with those coming from thermal-neutron and X-ray scattering data. A selection among the existing methods of obtaining z from the radial distribution function g(R) is made. The method chosen enables one to find z[g(R)] corresponding to the Voronoi structure.     

Neutron sensitivity and detection efficiency of <Superscript>3</Superscript>He and <Superscript>10</Superscript>BF<Subscript>3</Subscript> counters

An analytic relationship between the efficiency, sensitivity, and the coefficient of working-isotope utilization is established for gas-filled cylindrical thermal-neutron counters. This dependence is expressed in terms of the ratio of the characteristic length of a counter to its diameter. The characteristic size is introduced as the ratio of the total absorption cross section to the length of the counter. The parameters of basic ³He and ¹⁰BF₃ counters used in NM-64 neutron monitors are calculated.     

A multisectional annular thermal-neutron detector for the study of diffraction on microsamples in axial geometry

A new gaseous annular sectional thermal-neutron detector for the new neutron diffractometer at the IBR-2 reactor has been designed and manufactured at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research (JINR). The detector is designed to study small-volume samples at high pressure and consists of 16 sections, each one of which is divided into six independent detector elements. We present the main design features of the detector, detecting electronics, data-acquisition and visualization software, and software system for experiment management. The results of the first neutronographic experiments that were carried out with the use of the detector are also presented.     

The effective absorption cross-section of thermal neutrons in a medium containing strongly or weakly absorbing centres

The structure of a heterogeneous system influences diffusion of thermal neutrons. The thermal-neutron absorption in grained media is considered in the paper. A simple theory is presented for a two-component medium treated as grains embedded in the matrix or as a system built of two types of grains (of strongly differing absorption cross-sections). A grain parameter is defined as the ratio of the effective macroscopic absorption cross-section of the heterogeneous medium to the absorption cross-section of the corresponding homogeneous medium (consisting of the same components in the same proportions). The grain parameter depends on the ratio of the absorption cross-sections and contributions of the components and on the size of grains. The theoretical approach has been verified in experiments on prepared dedicated models which have kept required geometrical and physical conditions (silver grains distributed regularly in Plexiglas). The effective absorption cross-sections have been measured and compared with the results of calculations. A very good agreement has been observed. In certain cases the differences between the absorption in the heterogeneous and homogeneous media are very significant. A validity of an extension of the theoretical model on natural, two-component, heterogeneous mixtures has been tested experimentally. Aqueous solutions of boric acid have been used as the strongly absorbing component. Fine- and coarse-grained pure silicon has been used as the second component with well-defined thermal-neutron parameters. Small and large grains of diabase have been used as the second natural component. The theoretical predictions have been confirmed in these experiments.     

Interstitial-impurity reactions during stage I of platinum alloys after thermal and fast-neutron irradiation

Recovery spectra of pure platinum and selected dilute platinum alloys are compared to equivalent induced resistivities following either fast- or thermal-neutron irradiation at 4.4 K. Annealing during stage I (7–30 K) was significantly retarded due to the fast-neutron irradiation. Although a reduction in recovery due to alloying impurities was observed, it appears that due to the highly-localised defect concentration, interstitial-interstitial reactions were predominant during annealing of the fast-neutron defects, whilst in the case of the thermal neutrons, due to the generalised low defect concentration, interstitial-impurity reactions were more important.     

Calculated beta-ray spectra from decay of fission products produced by thermal-neutron fission of 235U

Beta-ray spectra from decay of fission products created by thermal-neutron fission of ²³⁵U have been calculated using summation techniques and using an independently created beta-ray data file. The calculated beta-ray spectra are in very good agreement for E_β ? 1 to 8 MeV with recently measured specta of beta rays for two very different exposure and counting time conditions: (a) an “instantaneous” spectrum following a 1.5 day exposure, and (b) an 8 s counting-time spectrum obtained 1.7 s following a 1 s exposure of ²³⁵U by thermal neutrons.     

Nuclear charge distribution of heavy fission fragments from thermal-neutron-induced fission of235U

Fragments from thermal-neutron induced fission of²³⁵U have been separated by a mass spectrometer with respect to their masses and kinetic energies within 1 μsec. The separation principles are briefly described. For masses 130 to 139 amu the charge distributions have been determined by counting the number of beta tracks emitted from the individual mass selected fission fragments in a nuclear photographic emulsion. In another method, the average number of beta particles for each fragment mass is determined by use of a 4π-proportional counter. The mean nuclear charge as a function of mass is compared with other experimental results and theoretical curves. Contradictory to the radiochemical results, this experiment yields a dip in the mean nuclear charge versus mass curve at mass 132 amu corresponding to the doubly magic nucleus (N=82,Z=50)¹³²Sn. Recent theoretical calculations of Nörenberg are in agreement with this finding.     

Richtungs- und Temperaturabhängigkeit der Lichtimpulse von Anthrazenkristallen bei Anregung mit α-Teilchen

The spectrum of internal conversion electrons emitted by Ag¹¹⁰ after thermal-neutron capture was measured with the beta spectrometer at the research reactor near München. 45 conversion lines corresponding to 34 transitions were found between 0 keV and 300 keV. The multipolarities of 19 transitions were determined. The low-energy gamma radiation was investigated between 10 keV and 600 keV by means of a Ge(Li)-detector. A partial level scheme containing the most intense transitions is proposed.     

Systematics of neutron emission probabilities from delayed neutron precursors

A simple correlation based on the gross theory ofβ-decay is derived between the neutron emission probabilitiesP _n of delayed neutron precursors, theirβ-decay energies and the neutron binding energies of the daughter nuclei. The correlation is shown to be valid for delayed neutron precursors among the fission products. TheP _n-values of several expected but still unidentified neutron precursors are estimated together with their contributions to the delayed neutron groups in thermal-neutron induced fission of²³⁵U. Some aspects of theβ-strength function for transitions into highly excited states are discussed.     

Thresholds for the Break of Nucleon Cooper Pairs and Special Features of the Decay of the <Superscript>172</Superscript>Yb Nucleus in the Reaction <Superscript>171</Superscript>Yb(<Emphasis Type="Italic">n</Emphasis><Subscript>th</Subscript>,2γ)

The reaction ¹⁷¹Yb(n_th,2γ) was studied with the aim of extending the experimental database of intensities of cascades of two photons emitted sequentially after radiative thermal-neutron capture. An analysis of these cascade intensities permitted revealing the change in the structure of observed levels of the ¹⁷²Yb nucleus versus the excitation energy and determining probable thresholds for the break of four Cooper pairs of neutrons below the neutron binding energy.     

Neutron transmutation doping in semiconductors: Science and applications

Different aspects of neutron transmutation doping (NTD) of silicon and germanium are considered, with a special emphasis on the contribution by scientists of the Ioffe Physicotechnical Institute, Russian Academy of Sciences, to the solution of these problems. Fundamental studies related to determination of the cross sections of thermal-neutron capture by isotopes of semiconducting materials, annealing of radiation defects produced by fast reactor neutrons, and the use of NTD for probing the structure of the Ge impurity band are reviewed. Problems involved in industrial-scale production of NTD-Si, application of NTD-Si and NTD-Ge to fabrication of power thyristors, nuclear-particle and IR detectors, deep-cooled thermistors, and bolometers are discussed. The paper concludes with a consideration of prospects in the application of NTD-Si and NTD-Ge based on the use of materials with a controlled isotopic composition. Fiz. Tverd. Tela (St. Petersburg) 41, 794–798 (May 1999)     

Potential of present-day experiments for determining the parameters of the gamma decay of compound states of heavy nuclei in a model-independent way

Experimental data on two-step cascades initiated by thermal-neutron capture in ^184,186W and ^190,192Os nuclei are analyzed from the point of view of prospects for improving the reliability of a model-independent determination of the density of levels in a given interval of J ^π and the radiative strength functions for E1 and M1 transitions exciting these levels in the region E _exc≤B _n .

     

The thermal-neutron-induced alpha-accompanied fission of235U investigation of the low energy part of the alpha spectrum

The energy spectrum of the α-particles emitted in the thermal-neutron induced fission of²³⁵U was measured from 11.5 MeV down to 2 MeV using the parabola mass spectrometer Lohengrin at the I.L.L. high flux reactor. This low energy part of the energy spectrum presents a smooth connection with the energy spectra which have been recently reported above 7 MeV. The overall energy spectrum, which is known to be quasi-gaussian above 12 MeV, is slightly asymmetric at low energy, where the observed particles are 6% more than expected from a gaussian shape. As a consequence, all the values reported for²³⁵U for the rate of α-accompanied fission compared to binary fission have to be multiplied by 1.06. This asymmetry is about 2 times less important than the one reported for²⁵²Cf. No evidence was seen for any intense low energy component as reported before. The possible reasons for the existence of this asymmetry are discussed.     

Magnetic state of a Zn<Subscript>1 −<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se bulk crystal

The spin system of a Zn_{1 ?x} Cr _x Se bulk crystal (x = 0.045) was studied using thermal-neutron diffraction and magnetic measurements. Previously, it was reported in the literature that thin films (～200 nm thick) of this type of semiconductors exhibit a ferromagnetic order. In this study, the ferromagnetic order is found to be absent in the bulk crystal.     

Delayed-neutron emission from short-lived Br and I isotopes

Rapid radiochemical separation techniques have been used to investigate the delayed-neutron emission from bromine and iodine isotopes produced by thermal-neutron induced fission of ²³⁵U. The nuclides 0.63 sec ⁹¹Br, 0.26 sec ⁹²Br and 0.41 sec ¹⁴¹I have been identified as delayed-neutron precursors. Relative neutron abundances of these and of the known precursors ^87–90Br and ^137–140I have been measured and absolute neutron abundances and neutron emission probabilities have been deduced. The P_n values are discussed within a simple semiempirical picture.     

Radiation-induced formation of ZnO nanoparticles on the ZnSe single-crystal surface

The possible formation of ZnO nanocrystals was studied as a result of radiolysis of a ZnSe crystal surface exposed to zinc vapor and irradiated with gamma rays and in producing ZnSe-ZnO heterostructures. Under ⁶⁰Co gamma radiation in air, nanocrystals ～27 nm in size are formed from nanoscopic ZnO nuclei. Under a mixed flux of gamma rays and thermal-neutron radiation, a twin structure is formed in the host ZnSe lattice and ZnO is removed. The oxide layer is also destroyed under proton irradiation in vacuum. It is found that the growth of ZnO nanocrystallites causes a manyfold increase in the luminescence intensity in the ～600-nm band and in microhardness and also a decrease in the resistance and blocking and threshold voltages irrespective of polarity. Thus, gamma irradiation brings about the formation of light-emitting ZnSe-ZnO: Zn semiconductor structures with a p-n junction.