Double Valuedness of Specific Luminescence as a Function of Stopping Power

The dependence of specific luminescence on the stopping power of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ions in thin-film plastic scintillators has been determined over a range of incident ion energies which bracket the maximum stopping power. The suggested double-valued dependence of specific luminescence has been confirmed. The pronounced drop in specific luminescence near maximum stopping power is understood in terms of electron pickup by the slowing ion.