Alpha-induced reactions on cobalt

Alpha-induced reactions on the target element cobalt were investigated in the energy region from 25 to 172.5 MeV using the stacked foil technique. Twenty excitation functions were measured for the production of ⁶¹Cu, ⁵⁷Ni, ^60m+gCo, ^58m+gCo, ⁵⁷Co, ⁵⁶Co, ⁵⁵Co, ⁵⁹Fe, ⁵²Fe, ⁵⁶Mn, ⁵⁴Mn, ^52m+gMn, ⁵¹Cr, ⁴⁸V, ⁴⁷Sc, ^46m+gSc, ^44mSc, ^44gSc, ⁴³K and ⁴²K. Only for ⁶¹Cu, ⁵⁸Co, ⁵⁷Co and ⁵⁶Mn were cross sections available earlier, which, however, were limited to α-energies ≦ 41 MeV. The experimental data are compared with calculations considering equilibrium as well as preequilibrium reactions according to the hybrid model of Blann. The excitation functions of half the product nuclides are dominated by preequilibrium effects over wide energy ranges. From the reaction ⁵⁹Co(α, 2n)⁶¹Cu an initial exciton number between n₀ = 4 (2n-2p-0h) and n₀ = 5 (2n-3p-0h) or (3n-2p-0h) is deduced. However, the theoretical analysis reveals several severe shortcomings, e.g. the underestimation of the excitation functions for ^60m+gCo, ^58m+gCo and ⁵⁹Fe for up to 2 orders of magnitude. For ^60m+gCo the discrepancy between theory and experiment can be attributed to break-up reactions of the α-particle, whereas for the two other product nuclides even more complex reaction mechanisms have to be assumed. Moreover, the strong contributions of preequilibrium emission of α-particles observed for (α,2pxn) and (α, 4pxn), which are not accounted for by the program OVERLAID ALICE, indicate that the initial reaction phase for α-induced reactions is more differentiated than is supposed by the present form of the hybrid model.