Electromagnetic decay of states of high spin and high isospin in fluorine-19

Abstract

The lowest Jπ =11/2+ state and the lowest two T = 3/2 states In 19F have been located among a number of new resonances in the 15 N(α,γ)19F reaction. The spins and radiative widths of these three new levels have been established by measurements of angular distribution and yield of γ-radiation. Their isospin is inferred from their spins, excitation energies, radiative widths and decay schemes. Measured transition matrix elements are compared with those calculated from shell-model wavefunctions which Include all (sd)3 configurations. Disagreements between 3 experiment and theory indicate that the (sd) description is inadequate for some of the positive parity states in 19F above about 4 MeV in excitation. Arguments are presented for the inclusion of (p) -2 (sd) 5 configurations to account for the properties of these states. The new 11/2+ level and the 7/2+ level at 4.38 MeV (whose spin has been definitely established in the course of this work) are discussed also in terms of a simple adiabatic rotational model for 19F. This model is found to account reasonably well for the excitation energies and transition probabilities of the lowest levels of spins 1/2 to 13/2.