Gamma-Neutron Reactions in Fluorine

The cross-sectional curves for the reactions F¹⁹(γ,n)F¹⁸ and F¹⁹(γ,2n)F¹⁷ have been determined by measurement of the induced positron activities. The (γ,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 (γ,2n) cross-sectional curve has a peak value of 0.66 mb at about 26 Mev. The integrated cross sections for the (γ,n) and (γ,2n) reactions are 0.039 and 0.0024 Mev-barns, respectively. However, the (γ,2n) reaction is evaluated only up to its peak position at 26 Mev. A new value of 60±{}1 seconds is reported for the F¹⁷ activity.