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)(n,\gamma)

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.Comment: 7 pages, 4 figure

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.Comment: 14 pages, 5 figures, 1 tabl

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.Comment: 5 pages, 2 figure

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.Comment: 17 pages, 6 figure

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.Comment: 9 pages,5 figure

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.Comment: 9 pages,4 figure

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.Comment: 12 pages, 6 figures, 1 tabl

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.Comment: 8 pages,5 figure

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.Comment: 11 pages, 13 figure

Calculation of the total gamma-spectra of the fast neutrons capture in the isotopes 117,119Sn for the different parameters of cascade gamma-decay

The gamma-spectra were calculated for the set of different level densities and radiative strength functions. The sufficiently precise reproduction of the experiment is impossible without taking into account the influence of the process of the nucleons Cooper pairs breaking on any nuclei cascade gamma-decay parameters.Comment: 8 pages, 4 figures, 1 tabl