Gamma-Neutron Reactions in Fluorine

The cross-sectional curves for the reactions ${\mathrm{F}}^{19}(\gamma ,n){\mathrm{F}}^{18}$ and ${\mathrm{F}}^{19}(\gamma ,2n){\mathrm{F}}^{17}$ have been determined by measurement of the induced positron activities. The ($\gamma ,n$) cross-sectional curve rises almost vertically from the threshold to a value of about 2 mb, remains constant for about 3 Mev, and then increases again to a maximum value of 3.48 mb at 20 Mev. The ($\gamma ,2n$) cross-sectional curve has a peak value of 0.66 mb at about 26 Mev. The integrated cross sections for the ($\gamma ,n$) and ($\gamma ,2n$) reactions are 0.039 and 0.0024 Mev-barns, respectively. However, the ($\gamma ,2n$) reaction is evaluated only up to its peak position at 26 Mev. A new value of 60±1 seconds is reported for the ${\mathrm{F}}^{17}$ activity.