Beta spectrum of F20

The shape of the $\ensuremath{\beta}$-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 $M1$ decay in $^{20}\mathrm{Ne}$ to determine the magnetic form factor we calculate, from conserved vector current theory, a deviation of the $\ensuremath{\beta}$ spectrum from the allowed shape of +1.23\ifmmode\pm\else\textpm\fi{}0.03% Me${\mathrm{V}}^{\ensuremath{-}1}$. Higher order terms reduce the slope to 0.94% Me${\mathrm{V}}^{\ensuremath{-}1}$. The spectrum was measured with an iron-free intermediate-image magnetic spectrometer and the deviation was found to +0.4\ifmmode\pm\else\textpm\fi{}0.5% Me${\mathrm{V}}^{\ensuremath{-}1}$ or somewhat smaller than the conserved vector current prediction.[RADIOACTIVITY $^{20}\mathrm{F}$: measured $\ensuremath{\beta}$-spectrum shape; compared with CVC prediction.]