Abstract
Five neutron-deficient isotopes of thorium lighter than mass 218 were studied at the Berkeley Heavy Ion Linear Accelerator by bombardment of enriched with . Silicon (Au) surface-barrier detectors were used in on-line measurements performed to determine -decay characteristics. Mass-number assignments of through were made on the basis of excitation functions and systematic trends in -decay properties. Half-lives and -particle energies were determined. New information was also obtained about the -decay characteristics of , , , and . Systematic occurrence of complex structure in the decay of even- 125-neutron nuclei is discussed, and spins and parities are suggested for three lowest-energy levels of , , and . Systematic occurrence of isomerism in odd- 127-neutron nuclei is also discussed, and spins and parities are suggested for several levels. On the basis of the extreme regularity of the experimental energies, predictions are made for the energies of several unknown neutron-deficient isotopes of thorium, protactinium, uranium, and neptunium. In the experimental work, the helium-jet transport method was used to remove the -emitting products from the target region. Technical details concerning the application of the method to millisecond activities are discussed.
- Received 14 June 1968
DOI:https://doi.org/10.1103/PhysRev.176.1377
©1968 American Physical Society