Nuclear Energy Levels ofTl203

Abstract

Using scintillation spectrometry and coincidence counting techniques, ${\mathrm{Tl}}^{203}$, formed by orbital electron capture in ${\mathrm{Pb}}^{203}$, has been shown to emit gamma rays of energies 280, 403, and 683 kev. The 403- and 280-kev gamma rays were found to be in sequence; the 683-kev gamma ray represents the associated cross-over transition. By energy and conversion coefficient measurements, it has been shown that the same 280\ifmmode\pm\else\textpm\fi{}2 kev level of ${\mathrm{Tl}}^{203}$ is excited in the decay of both ${\mathrm{Hg}}^{203}$ and ${\mathrm{Pb}}^{203}$. A coincidence method for the measurement of the conversion coefficients of the 403-kev gamma rays is described. The $K$-shell conversion coefficient of the 403-kev gamma ray has been measured as 0.076, the $\frac{K}{(L+M)}$ ratio being 3.7. The angular correlation function for the 403-kev---280-kev cascade has the form $W(\ensuremath{\theta})=1\ensuremath{-}(0.152\ifmmode\pm\else\textpm\fi{}0.007){cos}^{2}\ensuremath{\theta}$. For the known multipole mixture of the 280-kev quantum, the correlation measurements indicate the 403-kev transition to be 76 percent $E2$ and 24 percent $M1$. The interference phases of the $E2$ and $M1$ matrices of both transitions are the same in Lloyd's notation. The angular correlation studies and the conversion coefficient measurements indicate the orbitals of the levels of ${\mathrm{Tl}}^{203}$ to be ${d}_{\frac{5}{2}}$, ${d}_{\frac{3}{2}}$, and ${s}_{\frac{1}{2}}$, in order of decreasing excitation energy. The spin of the ground state of ${\mathrm{Pb}}^{203}$ is shown to be $\frac{5}{2}(\ensuremath{-})$.