Gamow-Teller strength in the ¹⁸O(p, n)¹⁸F reaction at 135 MeV

The distribution of Gamow-Teller strength in the ¹⁸O(p, n)¹⁸F reaction was studied at a bombarding energy of 135 MeV. Five 1⁺, T=0 states are identified below E_x=7 MeV and a concentration of 1⁺ states of presumed T=1 character is observed between E_x=9.5 and 12 MeV. Approximately 82% of the 1⁺ strength is concentrated into the ground-state transition and only 5.5% is seen in the T=1 component. Normalization of the ground-state transition to the known Gamow-Teller matrix element from the analogous beta decay of ¹⁸Ne allows the (p, n) cross sections to be related to the Gamow-Teller strength. The resulting total Gamow-Teller strength observed in the (p, n) reaction is about two-thirds of the minimum value required by the sum rule for a T=1 nucleus. This result is in reasonable agreement with the total Gamow-Teller strength predicted from a shell-model calculation which uses empirically renormalized single-particle Gamow-Teller matrix elements. The concentration of the T=0 strength predominantly into the ground state and the observed ratio of T=1 to T=0 strength also are consistent with these calculations.

NUCLEAR REACTIONS ¹⁸O(p, n)¹⁸F, E=135 MeV; neutron spectra measured in ∼3° steps between 0° and 69°; angular distributions extracted for separate transitions. Strengths of forward-peaked transitions compared with shell-model predictions of Gamow-Teller strength.