Investigation of High-Lying States Using Single Nucleon Transfer Reactions.

The reactions (^7Li, ^6Li), (^7Li, ^6He), (^7Li, ^8Li), (^{12}C, ^{13}N) and (^ {12}C,^{13}C) have been measured at 30 MeV/n on the targets ^{90}Zr, ^{91 }Zr, ^{89}Y, ^{208}Pb, ^ {209}Bi and ^{207 }Pb in order to investigate high lying states. Particles were analyzed using the S320 magnetic spectrograph. In each reaction, the measured spectra were plotted both as a function of the reaction Q-value and as a function of the excitation energy. A preference for the excitation of high spin states with no spin flip was observed. Broad resonance like peaks were observed in both proton and neutron stripping reactions at excitation energies close to the excitation energy of the giant quadrupole resonance. Comparison of reaction Q-values and the excitation energy spectra suggests that these broad peaks are due to the excitation of single particle states rather than a collective giant resonance. The existence of an extra particle or hole outside closed shell nuclei does not change the strengths of these broad peaks significantly, but does change the excitation energies significantly in some cases. Shell model calculations carried out in the ^ {208}Pb region support this conclusion. Substantial backgrounds were observed in these stripping reactions. Calculations of these underlying backgrounds were carried out with the Serber model and with a semi-classical theory developed by Brink and Bonaccorso. The Serber model calculations do not match the shape of the experimental spectra except at the very high excitation energies (>35 MeV) in proton stripping. The Brink-Bonaccorso model, does match the shape of the experimental spectra for neutron stripping reactions very well although it does not agree with the shape for the proton stripping case. The Brink -Bonaccorso model, also, predicts that for these bombarding energies, only 20% of the continuum arises from projectile breakup and 80% arises from the excitation of compound states in the residual nucleus. Strong peaks observed the (^{12}C,^ {13}C) reaction on both ^ {90}Zr and ^{208} Pb region targets appear to arise from the mutual excitation of bound 2s_{1/2}, 1p_{3/2} and 1d _{5/2} excited states in ^{13}C along with low lying states of the residual nuclei. Broad peaks are observed for the (^{12}C,^ {13}N) reaction on the ^ {208}Pb, ^{209} Bi and ^{207}Pb targets at excitation energies about 18 MeV. The origins of these structures are not understood clearly.