The ${}^{48}\mathrm{Ca}(\gamma ,n)$ cross section was measured by using $\gamma$-ray beams of energies between 9.5 and 15.3 MeV generated at the Triangle Universities Nuclear Laboratory high-intensity $\gamma$-ray source. Prior to this experiment, no direct measurements had been made with $\gamma$-ray beams of sufficiently low energy spread to observe a structure in this energy range. The cross sections were measured at 34 different $\gamma$-ray energies with an enriched ${}^{48}\mathrm{Ca}$ target. Neutron emission is the dominant decay mechanism in the measured energy range that spans from the threshold, across the previously identified $M1$ strength, and up the low-energy edge of the $E1$ giant dipole resonance. This paper found $B\left(M1\right)=6.8\pm 0.5{\mu }_N^2$ for the 10.23-MeV resonance, a value greater than previously measured. Structures in the cross section have been observed whose magnitudes are in agreement with existing data and that are commensurate with extended random-phase approximation calculations.

• Received 13 January 2011

DOI:https://doi.org/10.1103/PhysRevC.84.044331