On neutron-induced reaction mechanisms at medium energies

Abstract

Abstract. Recent accurate data obtained for the isomeric cross section of the 197 Au(n, 2n) reaction provides an effective opportunity to consider the question of the effective moment of inertia of the nucleus within a consistent model analysis of all available reaction data for the 197 Au target nucleus. Moreover, since the corresponding model assumptions are better validated by analysis of the data above 20-30 MeV where only several data with large uncertainties are known, the usefulness of further measurements to be performed at large-scale facilities as SPIRAL-2 and n TOF, for incident energies up to 40 as well as 100 MeV, are underlined.

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

“…The results of our previous calculations [18] at the higher as well as lower α-particle energies, using the same SM parameters and obviously the unchanged α-particle potential [8], are compared with the measured data in Second, the measured (α, n) reaction cross section at the higher incident energy is described in the limit of 2σ uncertainty [ Fig. 2(b)] while the concurrence provided by the nucleon OMPs of Koning and Delaroche [55] at lower energies is not confirmed by the proton OMP analysis [18] as well as the Gyürky et al data [53]. On the other hand, while use of the a-values for 67 Ga corresponding to the fit of D exp 0 error-bar limits (Table I) leads to NLD effects within 3.5% of the calculated (α, p) cross sections, a similar statement may concern 67 Ge a-value but not its ∆ parameter.…”

“…Second, limits of the insight of M 1-radiation upbend-function f up (E γ ) have been additionally assumed. Therefore, we have considered an upper limit C=3×0.77×10 −8 MeV −3 , using a multiplying 61,62,63,64,65 Cu, 64,66 Zn, 69 Ga [38][39][40][41][42][43] and 76 Ge nuclei [44], and the sum of calculated γ-ray strength functions of the SLO model for M 1 radiations (shortdotted curve), and E1-radiation models SLO (dashed curve), GLO (dash-dotted curve), EGLO (short-dashed curve), as well as the sum (solid curve) of the M 1 component including the upbend to zero energy (dotted curve) and EGLO, for 68 Ge nucleus. Uncertainties corresponding to those assumed (see text) for E1-radiation EGLO/GDR parameters (gray band) and, in addition, for the M 1-radiation upbend (light-gray band) are shown too; s-wave average radiation widths Γγ (in meV, also in Table I) are deduced from systematics [32] or correspond to either M 1 and each of above-mentioned E1 models, or the upbending M 1 and EGLO models.…”

“…Therefore its population follows the side feeding and continuum decay, being particularly determined by the α-particle OMP, nuclear level density, and RSF. While proved the appropriate assumptions for the latter quantities [65], the effective nuclear moment of inertia I which is most important for the isomeric cross section estimation may still be uncertain. Thus, although neutron-induced data analysis suggested a constant I r value for the effective I of 198 Au [21], more recent RSF and (n, γ) reaction data suggest that levels in the quasicontinuum are dominated by lower spins [63].…”

“…Color online) Comparison of measured[1, 28,53], evaluated within TENDL-2017 library[33] (short-dotted curves), and calculated cross sections of α-induced reactions on 64 Zn using the electric-dipole RSF models SLO (dashed curves), GLO (dash-dotted curves), EGLO (short-dashed curve) models along the SLO model for M 1 radiation, as well as EGLO and the M 1-radiation upbend (solid curves) for 68 Ge nucleus, with the proton OMP of Ref. [18] and the alternate involvement of Ref [55]. (dash-dot-dotted curves), versus laboratory energy of α-particle (bottom) and corresponding ratio of the center-of-mass energy and Coulomb barrier B[56] (top); uncertainty bands correspond to (b) NLD parameters for 67 Ge (light-gray band), and (c,d) those assumed for EGLO and M 1-upbend RSFs (gray band) and, in addition, for NLD parameters of 68 Ge nucleus (light-gray band); Γγ values (in meV) are either based on data systematics[32] or corresponding to above-mentioned RSF models for E1 radiation; (d) comparison of presently calculated (α, γ) cross sections and χ 2 -based assessment of Mohr et al[2] for χ 2 /F <15 per data point (solid squares), and results[2] using the α-particle potentials of Refs [8].…”