Evidence for anM1giant resonance inBa138

The $M1\mathrm{}$ strength function was measured in ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ at an excitation energy of approximately 8.6 MeV throughout the neutron energy region 9-60 keV using the threshold photoneutron technique. A method was developed for extracting the dipole strength even though the first excited state of the daughter nucleus, ${}_{}{}^{137}{}_{}{}^{}\mathrm{Ba}$, is only 281 keV above the ground state. The photoneutron spectrum was measured at laboratory angles of 90° and 135° with high resolution (0.5 ns/m) using the time-of-flight spectrometer associated with the Argonne high current linac. The $M1\mathrm{}$ strength function for ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ was found to be anomalously large at 8.6 MeV. In addition, the $E1\mathrm{}$ dipole strength function was estimated at this excitation energy.