Energy dependence of the total reaction cross section of isomeric ¹⁸F^m on silicon below 400 MeV

A 25 MeV/nucleon primary ¹⁷O beam was used to produce an isomeric state ¹⁸F^m beam via the single-nucleon transfer reaction ¹⁷O (¹²C, ¹¹B)¹⁸F^m. The total nuclear reaction cross section, σ_R, of ¹⁸F^m (metastable) on silicon was measured using a stack of silicon surface barrier detectors that included a position sensitive silicon detector (PSD). The total reaction cross sections were determined as a function of bombarding energy up to 400 MeV by measuring the energy loss in each detector. The reaction cross sections were measured both for a mixture of metastable- and ground-state ions and for a pure ground-state beam. The reaction cross sections for ¹⁴N and ¹⁶O beams were also measured simultaneously. The reaction cross sections for the metastable beam were deduced from the mixed- and the ground-state cross sections, corrected for the measured purity of the mixed-state beam. The observed reaction cross sections for ¹⁸F^m are larger at low energies than the cross sections measured for the ground state. The isomeric cross sections can be reproduced by an optical model potential having a diffuseness of 0.8 fm, compared to a more conventional diffuseness parameter of 0.5 fm, which is adequate to reproduce the ¹⁴N, ¹⁶O, and ¹⁸F_g.s. cross sections measured in this experiment.