Two-proton pickup in the zirconium region using the ( 6Li, 8B) reaction

Abstract

Spectra at θ lab = 8° have been measured for the 92, 94, 96, 98, 100Mo( 6Li, 8B) 90, 92, 94, 96, 98Zr and 90, 92, 94Zr( 6Li, 8B) 88, 90, 92Sr two-proton pickup reactions at 90 MeV. The strongest transitions to levels in the Zr isotopes are the 0 + → 0 + transitions to the g.s. and first excited 0 + states. The salient feature of the five Zr spectra is the large increase in 0 + 2 transition strength relative to that of the g.s. which is observed in the two heaviest isotopes, 96, 98Zr. In 90Zr, the 0 + 2 transition is weak whereas it is the dominant transition in 98Zr with twice the g.s. strength. These large variations in relative cross section, which are reproduced by DWBA calculations, are attributed to changing g.s. proton configurations in Zr. In the Sr spectra, which are distinctly different from the Zrspectra, the strongest transitions to excited states are to 2 + rather than 0 + states. The ( 6Li, 8B) reaction seems to be adequately described as a one-step cluster transfer of a T = 1, S = 0 proton pair. The suitability of this reaction for measurements of two-proton pickup is discussed.