Level Structure ofAu199from Decay ofPt199

Abstract

The energy levels of ${\mathrm{Au}}^{199}$ are investigated from the decay of 30-min ${\mathrm{Pt}}^{199}$. 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 $\frac{11}{2^{-}}$ 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 $E2\mathrm{}$ in character, while the 247-, 318-, and 544-keV are mixtures of $M1\mathrm{}$ and $E2\mathrm{}$ in which the $E2\mathrm{}$ component is very much enhanced. The gamma-gamma directional correlation of the 475-318-keV cascade has been found to be $W\left(\theta \right)=1+(0.082\mathrm{}\pm 0.01)$ $P2\left(cos\theta \right)+(0.042\mathrm{}\pm 0.03)$ $P_4\left(cos\theta \right)$. 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.