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V. A. Khitrov

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

At least 19 recordsLinked to original sources
arXiv2013

New facility for the (n,2g) reaction investigation at the Dalat Reactor

The summation amplitude of coincident pulses (SACP) method which is optimal solution to reduce compton scatter phenomenon and pairs phenomenon in the gamma spectra of nuclei decay gamma cascades was used. In the 1982, in comparision with original method [1], it was improved such as the interfacing techniques, and data analysis with aid of computer [2]. In order to get better, the fast/slow coincidence spectroscopy system was developed into a fast coincidence spectroscopy. It is advantageous and easy operation. The off-line measure results with radioactive source 60-Co and on-line measure results with 35-Cl target on the tangential channel of Dalat Research Reactor were showed the good abilities of this spectroscopy system.

physics.ins-det↗
arXiv2013

The initial results of research on two-step cascades in the Dalat research reactor

By the financial support of Vietnam Atomic Energy Commission and kind cooperation of Frank Laboratory, in the year of 2005 a measure system based on summation of amplitude pulses was established on the tangential channel of Dalat Research Reactor. After a serial of testing, the measure system was explored. In this, we would like to show the initial results were gotten with 36-Cl isotope.

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arXiv2011

Parameters of the best approximation for distribution of the reduced neutron widths. Specificity of full-scale method of analysis

The method is described and tested for analysis of statistical parameters of reduced neutron widths distributions accounting for possibility of coexistence of superposition of some functions with non-zero mean values of neutron amplitude and its arbitrary dispersion. The possibility to obtain reliable values of distribution parameters at variation of number of resonances involved in analysis and change of registration threshold of resonances with the lowest widths is studied.

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arXiv2011

Parameters of the best approximation of reduced neutron widths distribution. Actinides

The data of ENDF/B-VII library on reduced neutron widths for nuclei 231Pa, 232Th, 233,234,235,236,238U, 237Np, 239,240,241,242Pu, 241,243Am and 243Cm (including p-resonances of 232Th, 238U, 239Pu) in form of cumulative sums in function on Gamma0n/ were approximated by variable number K of partial items 0<K<5. Parameters of approximation -- mean value of neutron amplitude, its dispersion and portion of contribution of part of widths of distribution number K in their total sum. The problems of their determination from distributions of different number of squares of normally distributed random values with variable threshold of loss of some part of the lowest widths values were studied. It was obtained for some part of neutron resonances that their mean amplitudes can considerably differ from zero value, and dispersions - from mean widths. And it is worth while to perform any quantitative analysis of widths distributions by means of comparison of different model notions with obligatory estimation of random dispersion of the desired parameters.

nucl-ex↗
arXiv2011

Parameters of the best approximation for distribution of the reduced neutron widths. The most probable density of neutron resonances in actinides

In the frameworks of hypothesis of practical constancy of the neutron resonance number in small fixed intervals of neutron energy, their most probable value was determined for nucleus mass region 230<A<244 from approximation of the reduced neutron widths by superposition of two or four independent distributions. This was done under assumption that a set of the measured neutron amplitudes can correspond to one or to superposition of some normal distributions with non-zero average and dispersion differing from reduced neutron width. The main result of the analysis: the mean spacing and neutron strength function values can be determined only with unknown systematical uncertainty whose magnitude is determined by unknown precision of the Porter-Thomas hypothesis correspondence to concrete experimental sets of resonances and unknown experimental mean neutron widths.

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arXiv2011

Some practical limits on achievable precision of determination of nuclear-physics parameters

The status of experiments on determination of level density and partial widths of the nuclear reaction products emission in diapason of nucleon binding energy is presented. There are analyzed the sources and magnitude of probable systematical uncertainties of their determination. The maximally achievable precision of these parameters is estimated, as well. There is considered ability of new method for determination of distribution parameters of neutron resonances reduced widths in order to distinguish their groups with the same structure of wave functions. It was obtained in both cases that the insufficient value of maximally achievable precision of the parameters of the experimental data analysis does not allow one to obtain reliable and detailed information on the studied nuclear properties -- its entropy, strength functions of nuclear products emission and dominant level structure above 0.5Bn.

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arXiv2011

On problems of experimental determination of reliable values of nucleus parameters at low excitation energy - Ni-60 as an example

The reanalysis of the published experimental data from reaction Co-59(p,2gamma)Ni-60 was performed. The region of the most probable values of level density and radiative strength functions of cascade gamma-transitions was determined. The obtained data were rather precisely approximated by the V.M. Strutinsky model and semi-phenomenological model - for strength functions. The region of appearance and magnitude of maximal errors of the calculated cross-section of nucleon emission in evaporation spectra in traditional methods of their analysis were determined as well. There was for the first time obtained methodically correct information on the radiation strength function of primary gamma-transitions in diapason of neutron binding energy with averaging over large set of initial levels.

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arXiv2010

Estimation of maximum permissible errors in the total gamma-spectra intensities at determination from them of level density and radiative strength functions

From a comparison of the total gamma-spectra calculated for different functional dependencies of level density and radiative strength functions, there were obtained both their square root relative differences and analogous data for the used parameters. The analysis of these data showed that the total uncertainty in determination of gamma-spectra intensities which is necessary to obtain reliable values of parameters of cascade gamma-decay, most probably, must not exceed one percent.

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arXiv2009

Possibility of Experimental Determination of Reliable Parameters of the Compound-State Gamma-Decay and Some Errors of Analysis: Mo-96 as an Example

Comparison between potential possibilities and inevitable systematic errors of one- and two-step reactions for obtaining of maximum reliable data on level density and radiative strength functions after decay of excited levels of complicated nuclei has been performed. It was shown that the use for this aim of two-step reactions instead of one-step reactions provides for potential possibility to decrease systematical errors of mentioned nuclear parameters, as minimum, by several times.

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arXiv2009

Level Density and Radiative Strength Functions of the $^{237}$U Nucleus from the $(\overline{n},γ)$ Reaction

The independent analysis of the published data on the intensities of the primary gamma-quanta following resonance neutron capture in $^{236}U$ has been performed. Distribution of these intensities about the mean value was approximated in different energy intervals of the primary gamma-transitions and neutrons. Extrapolation of the obtained functions to the zero registration threshold of the primary gamma-transition intensity allowed us to estimate (independently on the other experimental methods) expected level number of both parities for spin values J=1/2, 3/2 and sum of radiative widths for both electric and magnetic dipole gamma-transitions to levels with excitation energy up to $\approx 2.3$ MeV.

nucl-ex↗
arXiv2009

Parameters of Cascade Gamma-Decay of Compound-Nuclei Nd-146, Gd-156, Yb-172, Ta-182, W-184, Os-191, Th-231,233, U-239, Pu-240 from Experimental Data of Reaction $(n,γ)$

Re-analysis of experimental data on primary gamma-transitions averaged over some energy intervals of neutron resonances has been performed. Approximation of their cumulative sums together with extrapolation of the obtained distribution to zero value allowed us to determine mean intensities of of E1- and M1-transitions, their probable number and total dispersion of intensity deviations from the mean value. The level density and sum of radiative strength functions determined in this way confirm main peculiarities of these nuclear parameters determined from intensities of the two-step gamma-cascades.

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arXiv2009

Parameters of Distribution of the Primary Gamma-Transition Intensities Following Resonance Neutron Capture and Some Properties of Compound Nuclei $^{157,159}$Gd

The re-analysis of the published experimental data on the primary gamma-transition intensities following neutron capture in different groups of neutron resonances in $^{156,158}$Gd has been performed. There are determined the most probable values of sum of E1 and M1 primary transitions, numbers of excited by them levels of both parities, ratios of radiative strength functions k(M1)/k(E1), dispersions of deviations of random values of intensities from the average and ratios of mean intensities of primary transitions to levels J=5/2 with respect to analogous data for J=1/2 and 3/2 (capture of the 24 keV neutrons) in narrow excitation energy intervals. All the data on level density and sums of radiative strength functions confirm the presence of clearly expressed step-like structure in level density below 3 MeV and general trend in change in strength functions as changing primary gamma-transition energy. Variations of distribution dispersions and, especially, ratio k(M1)/k(E1) (or $k(E1)/k(M1)$) at changing excitation energy point to strong change in structure of these nuclei above 1.0-1.5 MeV.

nucl-ex↗
arXiv2008

Reanalysis of the process of the cascade gamma decay of compound state of $^{198}$Au

To further study the "pygmy" resonance phenomena in the photon strength function, we reanalyzed the two-step cascade data for the target nucleus $^{197}$Au using the Dubna group approach. The range of obtained values allows for meaningful conclusions: the level density at low excitation energy shows a step-like behavior; the electric dipole photon strength function has a broad maximum around $E_γ=5$ MeV and is not typical of a "pygmy" resonance; the level density below $B_{n}$ also demonstrates step-like behavior.

nucl-ex↗
arXiv2008

Approximation of Sums of Experimental Radiative Strength Functions of Dipole Gamma-Transitions in the Region $E_γ\approx B_n$ for the Atomic Masses $40 \leq a \leq 200$

The sums k(E1)+k(M1) of radiative strength functions of dipole primary gamma-transitions were approximated with high precision in the energy region of $0.5 < E_1 < B_n-0.5$ MeV for nuclei: 40K, 60Co, 71,74Ge, 80Br, 114Cd, 118Sn, 124,125Te, 128I, 137,138,139Ba, 140La, 150Sm, 156,158Gd, 160Tb, 163,164,165Dy, 166Ho, 168Er, 170Tm, 174Yb, 176,177Lu, 181Hf, 182Ta, 183,184,185,187W, 188,190,191,193Os, 192Ir, 196Pt, 198Au, 200Hg by sum of two independent functions. It has been shown that this parameter of gamma-decay are determined by the structure of the decaying and excited levels, at least, up to the neutron binding energy.

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arXiv2008

Problems of experimental determination of parameters of nucleus and applicability of the Bohr-Mottelson hypothesis

Population of a number of excited levels of 51V and 57Fe has been determined from the data of the ENDSF file up to the excitation energy of about 7 and 5.2 MeV, respectively. It cannot be reproduced in the region of their maximal energies in the framework of assumption on the independence of partial radiative widths on the structure of decaying level and excited one, at least, lower than 0.5Bn. Therefore, it is impossible to estimate the actual degree of reliability of data on the level density and radiative widths of cascade gamma-transitions in light spherical nuclei obtained from the spectrum analysis of nuclear reactions, which do not take into account this circumstance.

nucl-ex↗
arXiv2007

Possibilities to verify the level density and radiative strength functions, extracted from the two-step gamma-cascade intensities

The direct determination of the excitation level density and radiative strength functions of their exciting gamma-transitions is impossible for the larger part of the stable and long-life radioactive target nuclei. This circumstance is uniquely determined by the fact, that the level spacing much less than the resolution of the existing spectrometers of gamma-rays and charged particles. The extraction of these parameters of nucleus in this situation can be executed by their only fitting to the most probable values, reproducing the measured in the nuclear reactions spectra and sections. This inverse problem of mathematical analysis of its nature is principally ambiguous. Moreover, system of equations, those connecting the number of excitable levels and probability of the emission of charge particles are assigned usually within the framework of some assumptions about the mechanism of nuclear reaction and factors, determining the dynamics of the studied process. The verification of these parameters can be partially executed by the calculation of total gamma-spectra for their different sets. As, in particular, the results of this analysis show, the calculation of the structure of the excited levels to a change in the form of the energy dependence of radiative strength functions most likely must be considered to the neutron-binding energy. It is not possible to exclude the possibility of that, that also radiative, and neutron strength functions depend on the structure of neutron resonance and for the higher excitation energies.

nucl-ex↗
arXiv2007

On the correctness of various approaches in the extraction of the nucleus parameters on example of analysis of the two-step gamma-cascades in 163Dy compound nucleus

The model-free analysis of experimental data in the intensities of two-step cascades into 163Dy shows, that the basically special features of the cascade gamma-decay of its compound-state completely correspond to those observed in other nuclei. Thus, the density of the levels in this nucleus with good precision it is reproduced as sum of three, five, seven-quasiparticle excitations with the tenfold, as the minimum, by an increase due to vibration type excitations. The greatest changes in the sum of the radiation strength functions of dipole primary gamma-transitions correlate with a change in the number of excitable quasi-particles. Accordingly, model presentations about the radiation strength functions of larger, than for those existing, accuracy must consider as a quantity of excited quasi-particles, so the presence of the vibration type excitations of all possible types. Moreover, the reliable picture of the studied process can be obtained only from the approximation of the distributions of the intensities of cascades in the function of energies of their primary gamma-transitions.

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