Isospin effect in the (e, e'p) reaction on Zr-isotopes and others

A considerable amount of work concerning 90Zr and 91Zr has been carried out by both the Melbourne and Tohoku groups. This interest largely originated from the observance of marked structure about the giant resonance region in early (p, γ0) experiments on 90Zr. A result of these studies so far is the proposal of a weak coupling core excitation model to explain the change in character of the isotopes 90 and 91. This has been successful with one major exception -- the lack of strength about Ep=7.9 MeV in 91Zr. In order to further test this model and possibly arrive at some explanation for the above mentioned anomaly, the obvious progression to the isotopes 92 and 94 constitutes the basic theme of the present series of experiments. For protons from 92Zr, to determine the nature of the proton groups seen in spectra obtained with Esub(e)=30 MeV, a series of runs with Esub(e) ranging from 22.5 to 15.0 MeV were taken with the end points differing by 0.5 MeV. It should be possible to obtain the estimates of P0, P1, and possibly P2 cross-sections from these data. As to protons from 94Zr, although it was not possible to make the investigation as detailed as that for 92Zr, it will be possible to establish the nature of some of the decay scheme. (Tai, I.)