Stretched state excitations in (P,N) reactions

Studies of stretched-state excitations with the (p,n) reaction above 100 MeV both complement and significantly extend studies of stretched states performed with other reactions. Because of the isospin selectivity of the (p,n) reaction, it provides a valuable suppression of isoscalar excitations from self-conjugate nuclei. This suppression has been used successfully to identify previously unidentified (f/sub 7/2/, d/sub 5/2/ /sup -1/) 6- fragmented, stretched-state strength in the A = 32 and 40 systems. For target nuclei with a neutron excess, the (p,n) reaction can excite T-1 strength that is unavailable in simple inelastic-scattering reactions. Such excitations include not only ''1 hω'' but also ''0 hω'' stretched-state strength. The latter involves even parity, proton-particle, neutron-hole couplings within the same orbital. The ''0 hω'' excitations dominate the (p,n) spectra at large momentum transfer. Usually they are concentrated in a single state (even in medium- and heavy-mass nuclei) because both the particle and the hole states are at the Fermi level. Normalization factors required for comparison with distorted wave impulse approximation calculations are greater than 0.5 and are significantly larger than those required for similar comparisons with ''1 hω'' stretched-state excitations. We find that large basis shell-model calculations, when available, are able to account for most of the ''missing'' strength in these stretched-state excitations