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V. A. Khitrov

Publications and source records attributed to V. A. Khitrov.

34 records · Page 2Linked to original sources
arXiv2005

Partial level density of the n-quasiparticle excitations in the nuclei of the 39< A <201 region

Level density and radiative strength functions are obtained from the analysis of two-step cascades intensities following the thermal neutrons capture. The data on level density are approximated by the sum of the partial level densities corresponding to n quasiparticles excitation. The most probable values of the collective enhancement factor of the level density are found together with the thresholds of the next Cooper nucleons pair breaking. These data allow one to calculate the level density of practically any nucleus in given spin window in the framework of model concepts, taking into account all known nuclear excitation types. The presence of an approximation results discrepancy with theoretical statements specifies the necessity of rather essentially developing the level density models. It also indicates the possibilities to obtain the essentially new information on nucleon correlation functions of the excited nucleus from the experiment.

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arXiv2005

Parameters of the 125Te compound state cascade gamma-decay

Reliable information on level density and radiative strength functions for the excitation energy region with density of excited states more than 100 levels per 1 MeV and higher can be obtained now only by its model-free extraction from intensities of two-step cascades proceeding between compound states and few low-lying levels. Full model-free determination of these parameters in any method is possible only if one can extract from additional experimental information about general trend in dependence of ratio of strength functions of emitted reaction products of a given type on excitation energy of the nucleus under study. Analysis of the available experimental data for 125Te shows that the peculiarities observed earlier in other nuclei are also inherent to this nucleus.

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arXiv2005

Some problems in determining level density and radiative strength functions in light and near-magic nuclei

The values of some functional dependencies of level density and radiative strength functions that reproduce the experimental intensities of the two-step gamma-cascades to the ground and first excited states of 28Al have been determined. It was shown that the assumption about independence of the dipole cascade transitions radiative strength functions on energy of decaying level leads to rather essential error in observation of both level density and radiative strength functions.

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arXiv2005

Level Density and Radiative Strength Functions in Light Nuclei: 60Co as an Example of the Method for Determination and their Reliability Verification

Up to now, level density for some nuclei (close to construction materials of nuclear reactors with respect to their mass) was determined only from the evaporation nucleon spectra. All its energy dependences obtained are smooth enough functions and are usually reproduced in the frameworks of generalized model of the superfluid nucleus with the use of the phase transition energy of infinite and homogeneous macrosystem. The same data obtained from 59Co(n,2gamma) reaction demonstrate the presence of two clearly expressed step-like structures. This fact corresponds to the analogous data for other nuclei studied in the same way. Level density and radiative strength functions derived from two-step cascade intensities provide more precise reproduction of the total gamma-spectrum than conventional nuclear models.

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arXiv2005

Probable Level Densities and Radiative Strength Functions of Dipole gamma-Transitions in 57Fe Compound Nucleus

From the published results of experimental research of 56Fe(n,2gamma) reaction carried out in Budapest, the values of the most probable densities of cascade intermediate levels with 1/2, 3/2 spin and radiative strength functions of cascade E1 and M1 transitions in 57Fe compound nucleus have been determined. These results correspond to analogous data for other nuclei studied by us and contradict to predictions of conventional models.

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arXiv2005

Level Density and Radiative Strength Functions of Dipole gamma-Transitions in 163Dy

Using our early experimental data on the cascade gamma-transitions from the 162Dy(n,2gamma) reaction, we determined dependence of the cascade intensity on the energy of their intermediate levels, and then - level density and radiatibe strength functions which allow precise reproduction of the experimental two-step cascade intensities and total gamma-width. Level density in this nucleus (like in other earlier studied even-odd nuclei) in the interval 1 to 3 MeV is considerably less than that predicted by Fermi-gas model. Enhancement of the radiative strength functions, caused by strong correlations of parameters, most probably, relates with the change in ratio between the quasi-particle and collective component of the wave functions of the cascade intermediate levels in the region of most strong change in their density.

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arXiv2005

Level Density and Radiative Strength functions of Dipole gamma-Transitions in Ba-139 and Dy-165

Level density and radiative strength functions which allow precise reproduction of the two-step cascade intensity, gamma width of compound state and cascade population of levels up to excitation energy of about 3.5 MeV were determined using experimental data on the (n,2gamma) reaction. Level density in these nuclei (like in other even-odd nuclei studied earlier) in wide excitation energy interval is considerably less than that predicted by Fermi-gas model. Enhancement of the radiative strength functions, caused by strong correlations between cascade gamma-decay parameters, most probably, relates with the change in ratio between the quasi-particle and collective components of the wave functions of the cascade intermediate levels in the region of most strong change in their density.

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arXiv2004

Two Regions of a Possible Drastic Change in the Structure of the Excited States of Any Nuclei

From a comparison of the absolute intensities of individual two-step cascades with known intensities of their primary and secondary transitions following thermal neutron capture the cascade and total population abilities of up to \~100 levels of each of the nuclei: 40K, 60Co, 74Ge, 114Cd, 118Sn, 124Te, 137,138Ba, 150Sm, 156,158Gd, 165Dy, 168Er, 175Yb, 181Hf, 183,184,185,187W, 196Pt and 200Hg have been determined. These experimental data as well as the intensities of two-step cascades to the low-lying levels of these very nuclei can be restored within an accuracy of experiment if only the level densities with a clearly expressed "step-like" structure are used and a considerable local increase of the radiative strength functions of secondary transitions to the levels situated close to the breakpoints on the energy dependence curve of level densities and their quite significant decrease to the low-lying levels of the nucleus are taken into account.

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arXiv2004

On correctness of some processing operations for two-step cascade intensities data from the (n,2gamma) reaction

An influence of some incorrectness of analysis on the level densities and radiative strength functions derived from the experimental gamma-spectra is considered. It was shown that the obtaining of reliable data from the reaction (n,2gamma) requires one to derive dependence of the two-step cascade intensities on their primary transitions energy. The influence of some conditions of an analysis of the experimental gamma-spectra from reaction (3He,alpha) on the expected value of both level density and radiative strength functions was estimated. The ways to decrease these uncertainties are suggested.

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arXiv2004

Cascade population of levels and probable phase transition in vicinity of the excitation energy ~0.5Bn of heavy nucleus

From the comparison of absolute intensities of the two-step gamma-cascades and known intensities of their primary and secondary transitions, the cascade and total population of about ~100 levels of 181Hf and 184,185,187W excited in thermal neutron capture was determined. These experimental results and intensities of two-step cascades to the low-lying levels of mentioned nuclei were reproduced in calculation using level densities with clearly expressed step-like structure. Radiative strength functions of the primary transitions following gamma-decay of these compound nuclei to the levels in the region of pointed structure are considerably enhanced. Moreover, population of levels below 3 MeV can be reproduced only with accounting for local and rather considerable increase in radiative strength functions of the secondary transitions to the levels in vicinities of break points in energy dependence of level density and significant decrease of that to lower-lying states. Simultaneous change in both level density and strength functions in the same excitation region of a nucleus corresponds to the definition of the second-order phase transition.

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arXiv2004

Estimation of the value and localization of possible systematic errors in determination of level density and radiative strength functions from the (n,2gamma) -reaction

Systematic error in determination of the absolute intensities of the two-step gamma-cascades after the thermal neutron capture and its influence on the value and localization of extracted from (n,2gamma)-reaction probable level densities and radiative strength functions of dipole gamma-transitions have been analysed. It was found that this error in limits of its possible magnitude cannot change made earlier conclusions about the radiative strength functions of E1- and M1- transitions at Egamma ~ 3 MeV and level density of heavy nucleus below ~0.5Bn.

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arXiv2003

Main parameters of the 118Sn compound-state cascade gamma-decay

Main properties of the excited states of $^{118}$Sn manifesting themselves in cascade gamma-decay of its compound state were studied. As in other heavier nuclei studied earlier, qualitative interpretation of the totality of the observed properties of this nucleus is impossible without accounting for coexistence and interaction of quasi-particle and collective nuclear excitations and their considerable influence on the main parameters of the process under study.

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arXiv2003

Intense two-step cascades and gamma-decay scheme of the Sn-118 compound nucleus

Transition energies and intensities of 454 two-step cascades following thermal neutron capture in Sn-117 have been measured. These data allowed us to make more precise and considerably extend the earlier obtained decay scheme of the Sn-118 nucleus. Autocorrelation analysis of the excitation spectrum of intermediate levels of the most intense cascades allowed us to determine the most probable period of their regularity. Besides, the analysis showed impossibility quantitatively to reproduce the total cascade intensity with accounting only for the excitations of the fermion type. This resulted into a conclusion that the excitations of a probable vibrational type in Sn-118 also considerably influence the cascade gamma-decay process practically up to the neutron binding energy.

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arXiv2001

New Technique for a Simultaneous Estimation of the Level Density and Radiative Strength Functions of Dipole Transitions at Eex < Bn-0.5 MeV

The new, model-independent method to estimate simultaneously the level densities excited in the (n,gamma) reaction and the radiative strength functions of dipole transitions is developed. The method can be applied for any nucleus and reaction followed by cascade gamma-emission. It is just necessary to measure the intensities of two-step gamma-cascades depopulating one or several high-excited states and determine the quanta ordering in the main portion of the observed cascades. The method provides a sufficiently narrow interval of most probable densities of levels with given J,pi and radiative strength functions of dipole transitions populating them.

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