Optical potential for incident and emitted low-energy $α$ particles. III. Non-statistical processes induced by neutrons on Zr, Nb, and Mo nuclei

Abstract

Background: The reliability of a previous α-particle optical-model potential (OMP) on nuclei with mass number 45≤A≤209 was proved for emitted α particles as well, for proton-induced reactions on Zn isotopes [Phys. Rev. C 91, 064611 (2015), Paper I]. However, the same was not the case of neutrons on Zr stable isotopes [Phys. Rev. C 96, 044610 (2017), Paper II].Purpose: A recent assessment of this potential also for nucleon-induced α-emission on A∼60 nuclei, including pickup direct reaction and eventual Giant Quadrupole Resonance (GQR) α-emission, is completed for neutrons incident on Zr, Nb, and Mo stable isotopes. Methods: Consistent sets of input parameters, determined through analysis of independent data, is involved while no further empirical rescaling factors of the γ and nucleon widths have been involved.Results: A suitable account of all competitive reaction channels is confirmed by careful uncertainty analysis, to avoid parameter ambiguities and/or error compensation. Additional validation of this potential is also supported by recently measured (α, γ) and (α, n) cross-sections of Zr and Mo nuclei.Conclusions: An increase of the α-emission beyond the statistical predictions, through consideration of additional reaction channels of the pickup direct interaction and like-GQR decay, makes possible the description of both absorption and emission of α particles by the same optical potential.

Consistent assessment of neutron-induced activation of 93Nb

“…Moreover, the concurrent assessment of all measured excitation functions for various reactions induced by neutrons on 93 Nb, in addition to the results of using default parameters within the worldwide used computer code TALYS-1.96 [14] and the currently related TENDL-2021 evaluation [15], remains an actual goal of further nuclear model analysis. This demand has been confirmed within a recent assessment of the α-particle emission in neutron-induced reactions on Zr, Nb, and Mo stable isotopes [16]. Furthermore, we look for a proper account of all available data for competitive reaction channels to prevent compensation effects of less accurate model parameters.…”

“…This work completes Ref. [16] with reference to the target nucleus 93 Nb, and the only additional HF+PE model parameters for neutron-induced reactions on this nucleus are given in Section 2. Comparison of HF+PE results and all available related data are discussed in Section 3.…”

“…The α-particle transmission coefficients corresponding to the αparticle OMP [18] have just been proved to be well suited for αemission in neutron-induced reactions in the mass range A ~90 including 93 Nb nucleus [16]. A still-open question to be answered in this work may concern only the role of the uncertainties related to the competitive reaction channels (Section 3).…”

“…The HF+PE reaction analysis and collective inelastic scattering crosssection assessment have been carried out using the same models, codes [14,[23][24][25], and previous local approaches [16,26]. Moreover, the same parameters, consistently established or validated by means of distinct data, have been involved for the 1) back-shifted Fermi gas (BSFG) [27] nuclear-level density (NLD), 2) particle transmission coefficients through optical model potentials (OMPs) [18,28], and 3) γ-ray transmission coefficients through radiative strength functions (RSFs) [29,30].…”

“…NLD parameters for the main reaction products concerned in the present work in addition to Ref. [16] are given in (with uncertainties given in units of the last digit in parentheses) in the energy range ΔE above the separation energy S, for target nucleus g.s. spin I 0 , fitted to obtain BSFG level-density parameter a and g.s.…”