αand2p2nemission in fast neutron-induced reactions onNi60

Abstract

Background: The cross sections for populating the residual nucleus in the reaction A Z X(n, x)A−4 Z−2 Y exhibit peaks as a function of incident neutron energy corresponding to the (n, n ′ α) reaction and, at higher energy, to the (n, 2p3n) reaction. The relative magnitudes of these peaks vary with the Z of the target nucleus.Purpose: Study fast neutron-induced reactions on 60 Ni. Locate experimentally the nuclear charge region along the line of stability where the cross sections for α emission and for 2p2n emission in fast neutron-induced reactions are comparable as a further test of reaction models.Methods: Data were taken using the GEANIE Ge-detector array. The broad-spectrum pulsed neutron beam of the Los Alamos Neutron Science Center's (LANSCE) WNR facility provided neutrons in the energy range from 1 to 250 MeV. The time-of-flight technique was used to determine the incident-neutron energies.Results: Absolute partial cross sections for production of seven discrete Fe γ rays populated in 60 Ni(n, α/2pxnγ) reactions with 2 ≤ x ≤ 5 were measured for neutron energies 1 MeV< E n <250 MeV. Hauser-Feshbach plus pre-equilibrium theoretical calculations are compared to the experimental results.Conclusions: There is good agreement between experimental results and theoretical predictions at lower neutron energies while discrepancies appear at higher neutron energies. The cross section for producing an isotope in fast neutron-induced reactions on stable targets via α emission at the peak of the (n, α) and (n, n ′ α) reactions is comparable to that for 2p2n and 2p3n emission at higher incident energies in the nuclear charge region around Fe. * fotia@lanl.gov

Statistical Hauser-Feshbach model description of $(n,α)$ reaction cross sections for the weak s-process

“…The theory framework outlined in Sec.II is employed in model calculations for a set of nuclei already introduced in s-process network calculations of a massive star, including convective He burning core and shell C-burning [30]. Figure 1 shows the (n, α) reaction cross sections for the following nuclei: 17 O, 18 F, 22 Na, 26 Al, 33 S, 37 Ar, 39 Ar, 40 K, 41 Ca, 59 Ni, 65 Zn, and 71 Ge. For the sake of completeness, we present not only astrophysically relevant low-energy range of the cross sections but a full result.…”

“…In the focus of this study is (n, α) reaction in nuclei of relevance for the s-process nucleosynthesis [30]. For example, 41 Ca(n, α) 38 Ar is considered as the the most important neutron-induced reaction on 41 Ca in the stellar conditions of the weak s-process at temperature about 300 MK [31], i.e., it strongly dominates over the neutron induced γ-emission [32].…”

“…Some of the recent developments in measurements of (n, α) reactions are given in Refs. [31,[36][37][38][39][40][41][42][43]. More recently (n, α) reaction has been measured and analyzed in the s-process branching point for nucleus 59 Ni, in view of considerable differences between model predictions and experimental data [40,44].…”

Feeding of Rh and Ag isomers in fast-neutron-induced reactions

“…[12], and references therein). For more complicated cases, in which the decay scheme involves many more levels, nuclear reaction model calculations were tested and combined with the measured γ-ray data to infer more accurate (n, xn) cross sections (see, for instance, Ref.…”

Advances in nuclear reaction calculations by incorporating information from nuclear mean-field theories

“…CoH 3 is extensively utilized in the nuclear data evaluation above the resonance region at LANL, as well as for the interpretation of experimental data at LANSCE (Los Alamos Neutron Science Center), e.g., the neutron capture measurements with the DANCE detector [9,13], and the γ -ray production measurements with the GEANIE detector [14,15].…”