Level Structure of Au¹⁹⁹ from Decay of Pt¹⁹⁹

Abstract

The energy levels of Au¹⁹⁹ are investigated from the decay of 30-min Pt¹⁹⁹. The high-resolution gamma spectra obtained from a Ge(Li) detector have revealed three new gamma transitions of energy 187, 469, and 497 keV. A new energy level at 324 keV has been suggested from the coincidence measurements, carried out with NaI(Tl) and Ge(Li) detectors. The possibility of an 11/2^- isomeric state expected in this odd-mass region of Au isotopes, has been indicated at 549 keV. A study of the internal-conversion-electron spectrum with a surface-barrier detector has clearly shown conversion lines corresponding to 187-, 247-, 318-, and 544-keV gamma transitions, and their K-shell conversion coefficients are obtained as 0.16±0.04, 0.34±0.05, 0.19±0.02, and 0.047±0.004, respectively. These measurements have indicated that the 187-keV transition is almost pure E2 in character, while the 247-, 318-, and 544-keV are mixtures of M1 and E2 in which the E2 component is very much enhanced. The gamma-gamma directional correlation of the 475-318-keV cascade has been found to be W(θ)=1+(0.082±0.01) P2(cosθ)+(0.042±0.03) P₄(cosθ). The half-life of the first excited state at 77 keV has been determined as 1.46±0.12 nsec. Spin and parity assignments to the 77-, 318-, 324-, 544-, 736-, and 794-keV levels are based on these investigations, and the possible nature of these levels is discussed.