Angular Distributions of Conversion Electrons from OrientedCe137mNuclei

Abstract

The angular distributions of $K$- and of ($L+M$)-conversion electrons from oriented ${\mathrm{Ce}}^{137m}$ nuclei were observed. Precise simultaneous intensity measurements of conversion electrons and $\gamma$ rays from the same sample provided an accurate, direct determination of the particle parameters $b_2$ associated with the 255-keV isomeric transition in ${\mathrm{Ce}}^{137}$. The $K$-electron result, $b_2=1.061\mathrm{}$ (18), is in excellent agreement with a theoretical prediction based on a "point nucleus" model. Techniques and parameters in this experiment, the first of its kind, are discussed. A more careful determination of the temperature dependence of anisotropy of the 255-keV $\gamma$ ray yielded the value $A=0.0147\mathrm{}$ (7) ${\mathrm{cm}}^{-1\mathrm{}}$ for the hyperfine structure constant of ${\mathrm{Ce}}^{137m}$ in neodymium ethylsulfate. This is slightly higher than the older value of 0.0129 (12) ${\mathrm{cm}}^{-1\mathrm{}}$ found in this laboratory and is to be preferred on the basis of internal evidence. Using Bleaney's value of ${〈r^{-3\mathrm{}}〉}_{4f}=4.44\mathrm{}$ au, the derived magnetic moment is changed from 0.96 (09) nm to 0.89 (05) nm. Other radial integrals give different values. A possible discrepancy in the magnetic temperature scale for neodymium ethylsulfate is discussed.