Small Deviations Observed in Beta Spectra:Na22

Abstract

The intense positron spectrum of ${\mathrm{Na}}^{22}$ has been carefully measured in a magnetic spectrometer. This transition proceeds from a 3+ to a 2+ level. The observed ${\mathrm{Na}}^{22}$ spectrum has a nonstatistical shape corresponding to an excess of low-energy electrons. The well-measured spectrum of ${\mathrm{Pm}}^{147}$ was reinvestigated and found to have a statistical shape. The many tests of the experimental procedures all indicate that the observed nonstatistical spectrum of ${\mathrm{Na}}^{22}$ is not the result of instrumental distortions. Theoretical refinements for finite de Broglie wavelength, screening, and possible contributions from the twice forbidden matrix elements were considered and found to be much too small to explain the deviation from the statistical shape observed in ${\mathrm{Na}}^{22}$. The Fermi-Kurie plot of ${\mathrm{Na}}^{22}$ can be linearized by a ($1+\frac{b}{W}$) correction factor. This same factor has been used to linearize the Fermi-Kurie plots of ${\mathrm{In}}^{114}$, ${\mathrm{Y}}^{90}$, and ${\mathrm{P}}^{32}$ (in addition to the once forbidden, unique shape factor in the case of ${\mathrm{Y}}^{90}$). In all four cases, the value of the parameter $b$ to yield a linear F-K plot is in the range $0.2lbl0.4$. At present, no theoretical explanation is offered for the correction ($1+\frac{b}{W}$). It may be regarded as an empirical correction capable of explaining the observed shapes in the case of these four Gamow-Teller transitions. A search was also made for negative electrons accompanying the normal positron decay of ${\mathrm{Na}}^{22}$. A weak, low-energy electron distribution was observed. This distribution may be explained by the theory of shake-off electrons.