The shape of the $\beta$-ray spectrum of ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ has been investigated as a test of the weak magnetism prediction of the conserved vector current theory. Using the radiative width of the analog $M1\mathrm{}$ decay in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ to determine the magnetic form factor we calculate, from conserved vector current theory, a deviation of the $\beta$ spectrum from the allowed shape of +1.23±0.03% Me${\mathrm{V}}^{-1\mathrm{}}$. Higher order terms reduce the slope to 0.94% Me${\mathrm{V}}^{-1\mathrm{}}$. The spectrum was measured with an iron-free intermediate-image magnetic spectrometer and the deviation was found to +0.4±0.5% Me${\mathrm{V}}^{-1\mathrm{}}$ or somewhat smaller than the conserved vector current prediction.

[RADIOACTIVITY ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$: measured $\beta$-spectrum shape; compared with CVC prediction.]

• Received 29 November 1976

DOI:https://doi.org/10.1103/PhysRevC.17.730