Coulomb Excitation of Elements of Medium and Heavy Mass

Abstract

Yields of gamma rays from thick targets of In, I 127 , Ta 181 , Re 185,187 , Ir 191,193 , Hg 198,199,200,202 , Th, and U were investigated under proton or alpha-particle bombardment in the energy range 2 to 4 Mev. By using the theory for electric excitation, reduced matrix elements for all electrically excited radiations were computed and compared with single-particle estimates. The results are interpreted in terms of the strong-coupling collective model of Bohr and Mottelson and compared with the systematic trends in the region of the closed shell at 126 neutrons. A 512-kev gamma ray excited in In by proton bombardment must result from a nuclear reaction. From excitation curves, gamma rays in I 127 at 60, 208, 392, 438, 631, 751, and 941 kev appear to arise from Coulomb excitation. No cascade radiations are observed. The radiations from Ta, Re, Ir, and Hg show the effects of a transition from the strong collective rotational motion to a collective vibrational nuclear motion or single-particle excitation as one approaches the closed neutron shell. Only the first excited states of Th 232 and U 238 were excited with alpha particles. No evidence for other levels was observed with proton excitation. The results agree within experimental error with other excitation measurements and with radiative lifetime measurements.