Measurement and analysis of the excitation function for alpha-induced reactions on Ga and Sb isotopes

Excitation functions for the reactions ⁶⁹Ga({α},xn)^73-xAs, ⁶⁹Ga({α},p3n)⁶⁹Ge, ⁶⁹Ga({α},2p4n)⁶⁷Ga, ⁷¹Ga({α},xn)^75-xAs, ¹²¹Sb({α},xn)^125-xI, ¹²¹Sb({α},p3n)¹²¹Te, and ¹²³Sb({α},xn)^127-xI were obtained from the measurements of the residual activity of stacked foils from threshold to 65 MeV. The excitation functions for the production of ⁷⁴As, ⁷²As, ⁷¹As, ⁶⁹Ge, and ⁶⁷Ga from {α}-induced reactions on Ga and ¹²⁶I, ¹²⁴I, ¹²³I, ¹²¹I, and ¹²¹Te from {α}-induced reactions on Sb are presented.The experimental data are compared with calculations considering equilibrium as well as preequilibrium reaction mechanisms according to the hybrid model of Blann. The high-energy part of the excitation functions are dominated by the preequilibrium reaction mechanism. Calculations were done using the a priori calculational method of Blann. From the reactions ⁷¹Ga({α},3n)⁷²As and ¹²³Sb({α},3n)¹²⁴I, an initial exciton number n₀=4 (nₙ=2, nₚ=2, nₕ=0) with the mean-free-path multiplier parameter k set to 2 has been deduced for both the targets. However, there are a few exceptions. The theory overestimates the cross section for the ⁶⁹Ga({α},2p4n)⁶⁷Ga reaction whereas it underestimates the cross section for the ¹²¹Sb({α},p3n)¹²¹Te reaction and the high-energy tail of ¹²¹Sb({α},2n)¹²³I excitation function. For the ({α},2p4n) reactions on Ga the discrepancy between theory and experiment may be attributed partly to a breakup of the {α} particle and partly to much more complex reaction mechanisms, whereas for the ¹²¹Sb({α},p3n)¹²¹Te reaction two different reaction mechanisms may be attributed.The large discrepancy between theory and experiment for the reaction ¹²¹Sb({α},2n)¹²³I at the high-energy tail of the excitation function may be attributed to emission of more than one preequilibrium nucleon which the theory cannot account for at present. Barring these reactions we have found that the overall agreement between theory and experiment is reasonably good, taking the limitations of the theory into account.