121 research outputs found
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
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
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
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
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
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
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
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
- …