Consistent optical potential for incident and emitted low-energy α particles. II. α emission in fast-neutron-induced reactions on Zr isotopes

Abstract

Background: Challenging questions of the α-particle optical-model potential (OMP) are still pointed out by recent high-precision measurements of α-induced reaction data below the Coulomb barrier. Moreover, the reliability of a previous OMP for α-particles on nuclei within the mass number range 45≤A≤209 has been recently proved for emitted α particles as well, but only in the case of proton-induced reactions on Zn isotopes [Phys. Rev. C 91, 064611 (2015), Paper I].Purpose: Analysis of most recent (α, γ) reaction data for Ge and Zr isotopes, which provides an additional validation of the above-mentioned potential, is related to a further account of α-particle emission in neutron-induced reactions on Zr isotopes, at the same time with a suitable description of all competitive processes.Methods: A consistent parameter set, established or validated by independent analysis of recent various data, particularly γ-ray strength functions, have been involved within model calculation of the (α, γ) as well as (n, α) reaction cross sections. The latter are part of the whole analysis of the neutron activation of Zr isotopes, in order to avoid any error compensation or latent ambiguity. Results: The aforesaid potential provides a consistent description of recent α-induced reaction data with no empirical rescaling factors of the γ and/or nucleon widths. On the other hand, its use leads to underestimated predictions of the pre-equilibrium emission and statistical models for the (n, α) reaction cross sections.Conclusions: An optical potential with a volume imaginary component seems to be needed to describe the low-energy α-particle evaporation, while only surface absorption occurs in α-induced reactions at similar energies.

Charged-particle optical potentials proved by first direct measurement of 59Cu(p,alpha)56Ni reaction

“…Moreover, it was validated by the additional reaction data in the meantime [4,5] and especially 64 Zn(p, α) 61 Cu reaction cross sections [6] as well as all similar data for Cu stable isotopes [7]. Indeed, it has provided also discrepant neutron-induced α-emission but concerning an underestimation, namely for Zr isotopes [8]. However, the similar effect for A∼60 mass range has lately been accounted for by a distinct mechanism in addition to HF [3].…”

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

“…The reliability of a previous α-particle optical-model potential (OMP) for target nuclei with mass number 45≤A≤209 [1] was also proved for α-emission in protoninduced reactions on Zn isotopes [2] (Paper I). However, its use led to underestimated predictions of the statistical Hauser-Feshbach (HF) [3] and pre-equilibrium emission (PE) [4] models for neutrons incident on Zr stable isotopes [5] (Paper II). On the other hand, it has recently been shown that this potential can also describe α-emission from excited nuclei in nucleon-induced reactions within the A∼60 range [6,7].…”

“…The so-called α-potential mystery [8] related to the account of both α-emission and absorption by an OMP, of equal interest for astrophysics and fusion technology, thus received an alternate solution. Nevertheless, its support by analysis of more data is imperative, while the case of neutrons incident on A∼90 nuclei [5] is a distinct requisite in this respect.…”

Role of consistent parameter sets in an assessment of the α -particle optical potential below the Coulomb barrier

“…On the other hand, a former OMP [15] concerned only the α-particle emission in neutroninduced reactions, with distinct predictions from potentials for incident α particles [16]. Thus, this OMP [15] was not an earlier version of the above-mentioned ones [8,10,11], while the question on different OMPs for incident and emitted α particles [15,[17][18][19] is still unanswered.…”