Study of neutron-deficient polonium isotopes

The topic of this Thesis is the study of neutron-deficient polonium and astatine isotopes with main focus on -ray spectroscopy of isomeric states in ^192;194Po. Investigated isotopes were produced in fusion-evaporation reactions⁵⁶Fe + ¹⁴¹Pr and ⁵¹V + ¹⁴⁴Sm at GSI in Darmstadt (Germany). Reaction products were separated from the primary beam by the velocity filter SHIP and studied using detectors placed at the focal plane of the separator. Four new transitions were attributed to the isomer in ¹⁹⁴Po and coincidences were investigated for the first time for this isomer. The transition, which was in previous experiment suggested to de-excite the isomeric level, was replaced by the new 248 keV transition. Moreover, the spin of the isomer was reassigned from (11..) to (10..), which caused an unexpected change in the chain of isomers in Po isotopes. More precise half-life of 12.9(5) s was determined. Spin and parity (11..) of the isomer in ¹⁹²Po was supported and 14 new transitions were attributed to the isomer. Also for this isomer, coincidences were studied for the first time. De-excitation of the isomeric level by the 733 keV (E3) transition parallel to the 154 keV transition was proposed. Moreover, side-feeding of the ground-state band by the cascade of two transitions was suggested. The Thesis discusses systematics of 11.. isomers and E3 transition strengths in neutron-deficient Po and Pb isotopes in respect to new decay-spectroscopy results. In addition, fine structure in the decay of both ¹⁹²Po and ¹⁹⁴Po was investigated. Previously known fine -decay lines decaying to excited 0⁺ states were identified and upper limits of intensity for additional fine transitions were evaluated. Hint of a new fine transition in ¹⁹²Po was observed. Excitation functions of isotopes ^193..195Po and ^194;195At produced in reaction ⁵⁶Fe+¹⁴¹Pr were evaluated. Results were compared with calculations performed using statistical model code HIVAP. (Author)