Levels inZr90: Experimental

Abstract

The levels in ${\mathrm{Zr}}^{90}$ have been studied by analyzing the radiations of ${\mathrm{Nb}}^{90}$ in magnetic and scintillation spectrometers employing various coincidence techniques. Multipolarities of most of the transitions have been determined from internal conversion coefficients and $K\ensuremath{-}L$ ratios. A decay scheme (I) for ${\mathrm{Nb}}^{90}$ has been proposed which assigns the following excited states in ${\mathrm{Zr}}^{90}$: 1752 kev (0+), 2182 kev (2+), 2315 kev (5-), 3081 kev (4+), 3453 kev (6+), and 3595 kev (8+). Evidence has been discussed for a few weak additional transitions potentially involving three additional levels (decay scheme II). Following the suggestion of Ford, the levels in decay scheme I have all been interpreted as arising from the proton configurations ${({p}_{\frac{1}{2}})}^{2}$, ${({g}_{\frac{9}{2}})}^{2}$, and (${g}_{\frac{9}{2}}{p}_{\frac{1}{2}}$). The half-life of the 3595 kev 8+ state has been experimentally determined as 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ sec, in good agreement with the half-life expected for a 141.5-kev $E2$ transition between 8+ and 6+ states, each involving a ${({g}_{\frac{9}{2}})}^{2}$ configuration.The relative population of the two 0+ states of ${\mathrm{Zr}}^{90}$, both by de-excitation of the 2+ state of that nucleus and by the beta decay of ${\mathrm{Y}}^{90}$, indicates that these states result from highly mixed ${({p}_{\frac{1}{2}})}^{2}$ and ${({g}_{\frac{9}{2}})}^{2}$ configurations.Hindrance factors for several transitions indicate that the other positive parity states are largely generated from the ${({g}_{\frac{9}{2}})}^{2}$ configuration.