Nuclear Structure ofSn12050

Abstract

The radiations from 5.8-day ${\mathrm{Sb}}^{120m}$ have been investigated in detail, using sector-type double-focusing magnetic spectrometers and scintillation counters. The following measurements were performed: coincident gamma-ray spectra, directional correlations of 1.18 Mev $\gamma$—1.03 Mev $\gamma$, 1.03 Mev $\gamma$—0.20 Mev $\gamma$, 1.18 Mev $\gamma$—0.20 Mev $\gamma$, 0.20 Mev $\gamma$—0.09 Mev $\gamma$, 0.20 Mev ${\mathrm{Ke}}^{-}$ -0.09 Mev $\gamma$ and 0.20 Mev $\gamma$—0.09 Mev ${\mathrm{Ke}}^{-}$. The 1.18 Mev $\gamma$—1.03 Mev $\gamma$ polarization direction correlation, the conversion electron spectra, and the mean lives of the 2.41- and 2.50-Mev levels have also been investigated. The decay scheme of 5.8-day ${\mathrm{Sb}}^{120m}$ proposed by McGinnis, which gives the following assignments to the excited states in ${\mathrm{Sn}}^{120}$, 1.18 Mev(2+), 2.21 Mev(4+), 2.41 Mev(6+), and 2.50 Mev (7-), has been confirmed uniquely. These levels have been interpreted as arising from the neutron configurations ${\left(2\mathrm{}{d}_{\frac{3}{2}}\right)}^2{\left(1\mathrm{}{h}_{\frac{11}{2}}\right)}^2$ and ${\left(2\mathrm{}{d}_{\frac{3}{2}}\right)}^3{\left(1\mathrm{}{h}_{\frac{11}{2}}\right)}^1$. The lifetimes of the 2.41-, 1.18-, and probably 2.21-Mev levels are shorter by a factor 3-4 than those expected for single-proton transitions and may be explained by the neutron transition, assuming a somewhat larger effective charge of neutron in spherical nuclei. The high forbiddenness of the 0.09-Mev $E1+M2\mathrm{}$ transition is ascribable to the simultaneous $j$- and $l$-forbidden transition between the states involving ${\left(2\mathrm{}{d}_{\frac{3}{2}}\right)}^3{\left(1\mathrm{}{h}_{\frac{11}{2}}\right)}^1$ and ${\left(2\mathrm{}{d}_{\frac{3}{2}}\right)}^2{\left(1\mathrm{}{h}_{\frac{11}{2}}\right)}^2$ configurations.