States of 5He and 5Li

Abstract

A recent shell model calculation has predicted a low-lying! + level in 5He, in apparent conflict with experimental results. We have confirmed the prediction with an alternative shell model interaction chosen specifically to fit properties of light nuclei. The level is expected to be very broad so that it would not be easily seen in reactions. It should contribute significantly to n-a phase shifts, but did not appear in previous analyses because of the small value of about 3 fm chosen for the channel radius a. A ! + level at the expected energy of about 7 MeV is obtained for a ::::: 5·1 fm. Broad ~ + and ~ + levels are then found at about 14 MeV in agreement with the shell model calculations. Properties of the low-lying ~ - and! - levels in 5He and 5Li are discussed, but the measured values now available do not favour a particular value of the channel radius.