Coulomb excitation of elements of medium and heavy mass

Abstract

Yields of gamma rays from thick targets of In, I¹²⁷, Ta¹⁸¹, 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 I¹²⁷ 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 Th²³² and U²³⁸were 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.