Gamow-Teller strength to ${}_{}{}^{38}{}_{}{}^{}\mathrm{K}$ from the ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ar}$(p,n) reaction and ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ca}$(${\mathrm{\beta }}^{+}$) decay

Gamow-Teller ($1^{+}$) strength was studied in ${}_{}{}^{38}{}_{}{}^{}\mathrm{K}$ with the analog reactions ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ar}$(p,n${)}^{38}$K and ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ca}$(${\mathrm{\beta }}^{+}$${)}^{38}$K. 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° and 63°. 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 ${}_{}{}^{38}{}_{}{}^{}\mathrm{K}$. These decay measurements provide an increased sensitivity over earlier measurements and are able to extract transitions down to ∼ ${10}^{\mathrm{-}4}$ 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 ‘‘effective’’ GT operators. © 1996 The American Physical Society.