Modern status of photonuclear data Varlamov, V. V.; Ishkhanov, B. S.
Physics of atomic nuclei,
09/2017, Letnik:
80, Številka:
5
Journal Article
Recenzirano
The reliability of experimental cross sections obtained for (γ, 1
n
), (γ, 2
n
), and (γ, 3
n
) partial photoneutron reactions using beams of quasimonoenergetic annihilation photons and ...bremsstrahlung is analyzed by employing data for a large number of medium-heavy and heavy nuclei, including those of
63,65
Cu,
80
Se,
90,91,94
Zr,
115
In,
112−124
Sn,
133
Cs,
138
Ba,
159
Tb,
181
Ta,
186−192
Os,
197
Au,
208
Pb, and
209
Bi. The ratios of the cross sections of definite partial reactions to the cross section of the neutron-yield reaction,
F
i
=
σ
(γ,
in
)/
σ
(γ,
xn
), are used as criteria of experimental-data reliability. By definition, positive values of these ratios should not exceed the upper limits of 1.00, 0.50, 0.33,... for
i
= 1, 2, 3,..., respectively. For many nuclei, unreliable values of the above ratios were found to correlate clearly in various photon-energy regions
F
i
with physically forbidden negative values of cross sections of partial reactions. On this basis, one can conclude that correspondent experimental data are unreliable. Significant systematic uncertainties of the methods used to determine photoneutron multiplicity are shown to be the main reason for this. New partial-reaction cross sections that satisfy the above data-reliability criteria were evaluated within an experimental–theoretical method
σ
eval
(γ,
in
) =
F
i
theor
(γ,
in
) ×
σ
expt
(γ,
xn
) by employing the ratios
F
i
theor
(γ,
in
) calculated on the basis of a combined photonuclear-reaction model. It was obtained that cross sections evaluated in this way deviate substantially from the results of many experiments performed via neutron-multiplicity sorting, but, at the same time, agree with the results of alternative activation experiments. Prospects of employing methods that would provide, without recourse to photoneutron-multiplicity sorting, reliable data on cross sections of partial photoneutron reactions are discussed.
We developed a cluster model which allows to take into account both shape deformation parameters and cluster degrees of freedom. The important ingredient of the model is the dinuclear system concept ...in which the wave function of the nucleus is treated as a superposition of a mononucleus and two-cluster configurations. The model is applied to describe the multiple negative-parity bands in the deformed actinides.
Investigations of superheavy elements (SHE) have received much attention in the last two decades, due to the successful syntheses of SHE. In particular, α-decay of SHEs has a great importance because ...most synthesized SHE have a-decay and the experimentalists have evaluated the theoretical predictions of the a-decay half-life during the experimental design. Because of this, the correct prediction of α-decay half-life is important to investigate superheavy nuclei as well as heavy nuclei. In this work, artificial neural networks (ANN) have been employed on experimental a-decay half-lives of superheavy nuclei. Statistical modeling of a-decay half-life of superheavy nuclei have been found as to be successful.
An asymmetric system of colliding copper and gold nuclei (Cu + Au) has a specific overlap geometry when compared to symmetric systems (Au + Au, Cu + Cu). Studying asymmetric heavy systems allows us ...to obtain additional restrictions for existing models and more accurate descriptions of the processes of parton energy loss in hot and dense QCD matter produced in collisions of heavy nuclei. This work reports nuclear modification factors for neutral pions in Cu + Au, Сu + Cu, and Au + Au collisions at an energy of 200 GeV, measured in the PHENIX experiment on the RHIC.
Optical model analyses were carried out using the coupled-channels method over various medium and heavy nuclei for incident neutrons and protons in the energy region from 1 keV to 200 MeV. Global ...systematics were consequently obtained for the optical potential parameters with simple functional forms. It was confirmed that coupled-channels analyses were indispensable to achieving a global description of experimental data for wide ranges of energies and mass numbers (50 ≤ A ≥ 240). It was also found that the parameter set obtained would be useful for nuclear data evaluations of fission-product nuclei for which available experimental data are scarce.
A spectrum of cosmic rays within energy range 10 super(15) - 3 x 10 super(17) eV was derived from the data of the small Cherenkov setup, which is a part of the Yakutsk complex EAS array. In this, ...work a new series of observation is covered. These observations lasted from 2000 till 2010 and resulted in increased number of registered events within interval 10 super(16)-10 super(18) eV, which in turn made it possible to reproduce cosmic ray spectrum in this energy domain with better precision. A sign of a thin structure is observed in the shape of the spectrum. It could be related to the escape of heavy nuclei from our Galaxy. Cosmic ray mass composition was obtained for the energy region 1016-1018 eV. A joint analysis of spectrum and mass composition of cosmic rays was performed. Obtained results are considered in the context of theoretical computations that were performed with the use of hypothesis of galactic and meta-galactic origin of cosmic rays.
The spectra of
p
,
d
, and
t
charged particles produced in stopped-pion absorption by nuclei are analyzed. Respective measurements were performed for 17 nuclei by means of a semiconductor ...spectrometer. A phenomenological model developed previously for medium-heavy and heavy nuclei was applied to describing the spectra and yields of charged particles originating from light nuclei (
6,7
Li,
9
Be,
10,11
B, and
12
C). The contribution of intranuclear clusters (such as
pp
and
3,4
He) to pion absorption was estimated.
Activities performed in preparation for the search for ternary fission of heavy nuclei and the analysis of fragment angular correlations with nuclear track emulsion and an automated microscope are ...detailed. Surface irradiation of nuclear emulsion by a Cf source was initiated. Planar events containing nothing but fragment triples were found and studied.
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