Gamow-Teller strength to 38K from the 38Ar(p,n) reaction and 38Ca(β+) decay

Gamow-Teller (1+) strength was studied in 38K with the analog reactions 38Ar(p,n)38K and 38Ca(β+)38K. The (p,n) reaction was performed at 135 MeV using the beam swinger facility at the Indiana University Cyclotron Facility. Excitation-energy spectra were measured at 15 angles between 0 degree and 63 degree. Neutron energies were measured by the time-of-flight method using a large-volume plastic scintillator array at a flight path of 131.0 m. The overall energy resolution was 280 keV. Gamow-Teller (GT) strength was extracted from the measured angular distributions to discrete 1+ final states. The β-decay experiment was performed with the ISOLDE on-line mass separator facility at CERN. The β-decay branching ratios were determined by observing the delayed γ decays of 38K. These decay measurements provide an increased sensitivity over earlier measurements and are able to extract transitions down to ∼ 10-4 of the strongest branches. The B(GT) values obtained from the two experiments are generally in good agreement, except for the transition to the first 1+ state at 0.46 MeV, which is observed to be much weaker in the (p,n) measurements. The β-decay measurements provide good resolution and high sensitivity while the (p,n) measurements extend the β-decay measurements to higher excitation energies. The summed B(GT) strength is ∼50% of the simple Ikeda sum rule. The distribution of GT strength is in reasonable agreement with that predicted from a shell-model calculation using open-quote open-quote effective close-quote close-quote GT operators. copyright 1996 The American Physical Society