Isomeric Cross Section Ratios in Alpha-Particle Reactions

Abstract

Isomeric cross section ratios for reactions Mn⁵⁵(α, n)Co,^58m,g Fe⁵⁶(α, pn)Co^58m,g and Rb⁸⁵(α, 2n)Y^87m,g were measured by the activation method using a stacked-foil technique. The experimental results of the energy dependence of σ_m⁄σ_g for Mn⁵⁵(α, n)Co^58m,g reaction were compared with the calculation using the square-well potential with the interaction radius parameter of r₀=1.7 fermi and the energy level density parameter of a=2 MeV⁻¹ in Fermi gas model.
From the comparison, it seems that as the spin level density parameter either a constant value between σ=3 to σ=4 or the value dependent on nuclear temperature corresponding to 2σ²=14.4T fits comparatively well in experimental results. However, the experimental result on this reaction shows that the σ_m⁄σ_g reaches a maximum value at about 25 MeV and then decrease. This behavior may be interpreted by a mechanism of direct interaction. The energy dependence of σ_m⁄σ_g for Fe⁵⁶(α, pn)Co^59m,g reaction qualitatively indicates that the reaction advances through the compound nucleus formation process, contrary to the results for Co⁵⁹(p, pn)Co^58m,g reaction measured by Meadows et al. in which the same compound nucleus is formed.