Energy dependence of the total reaction cross section of isomeric18Fmon silicon below 400 MeV

Abstract

A 25 MeV/nucleon primary O-17 beam was used to produce an isomeric state F-18(m) beam via the single-nucleon transfer reaction O-17 (C-12, B-11)F-18(m). The total nuclear reaction cross section, sigma(R), of F-18(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 N-14 and O-16 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 F-18(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 N-14, O-16, and F-18(g.s.) cross sections measured in this experiment.