The Ca 40(d, α)K 38 reaction and the nuclear structure of K 38

Abstract

Natural Ca-targets were bombarbarded with 7.7 MeV deutereons. Magnetic analysis was used to obtain α-particle spectra at angles of 50°, 70° and 90°. About 35 levels in K 38 were found up to an excitation energy of 4.8 MeV. There are the following low-lying states: ( E exc, Jπ, T) = (0.00 MeV, 3 +, 0); (0.12 MeV, 0 +, 1); (0.43 MeV, 1 +, 0); (1.69 MeV, 1 +, 0); (2.41 MeV, 2 +, 1). They are in agreement with recent intermediate coupling shell model calculations. Most of the levels above 2.5 MeV result from configurations with one or more nucleons raised into the f 7 2 shell. The nuclear temperature derived from an Ericson plot is 1.05 ± 0.15 MeV. Angular distributions for the low excited states were measured from 10° to 165°. The angular distributions and the total cross section show the effect of the ΔT = 0 isobaric spin selection rule which inhibits direct interaction leading to T = 1 final states. Compound nucleus transitions to the T = 1 states take place, however, because of isobaric spin mixing in the intermediate nucleus, and the selection rule seems to be completely violated. The total cross sections are in agreement with the theory of Hauser and Feshbach. This theory also makes it possible to estimate the compound nucleus contributions for the transitions leading to T = 0 states. About 2 3 of the total cross section for these transitions are due to direct interaction, which produces a pronounced structure of the angular distributions in the forward and backward hemisphere. The significance of this structure in terms of the various direct interaction modes is discussed.