Gamma-ray spectroscopic study of the energy level structure of 231Th nucleus

The energy levels of excited states of 231Th are studied from both the alpha decays of 235U and the gamma radiations emitted from the daughter product of 235U. The alpha particle spectrum was measured by means of the Si(Au) surface barrier semiconductor detector with the aid of computer based multichannel analyzer, and seven levels were identified. The gamma radiation spectrum was measured by means of the Ge(Li) detector. Eliminating various contamination of gamma rays and X rays, 39 gamma rays were identified as being radiated from the excited states of 231Th. An attempt was made to construct the energy level scheme of the excited states of 231Th utilizing the present alpha and gamma radiation spectra together with the spectrum lines published by other authors. Energetically 16 energy levels were identified. (Author)