Proposal of measurements of M1 strengths in giant dipole resonance energy region

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The M1 transitions in nuclei have attracted increasing attention in nuclear physics and nuclear astrophysics. In 1957, Agodi predicted that the neutron angular distribution in (gamma, n) reactions with a 100% linearly polarized gamma-ray beam for dipole excitation should be anisotropic and universally described by the simple function of a + b cos(phi) at polar angle of 90 degree, where phi is the azimuthal angle. However, this prediction has not been experimentally confirmed over half a century. We have verified experimentally this angular distribution in the (gamma, n) reaction for Au-197, I-127, natural Cu, Fe-56 targets using linearly polarized laser Compton scattering gamma-rays at NewSUBARU in SPrioing-8. Neutron angular distributions were measured by changing the angle of linear polarization plane of the incident laser. The neutron angular distributions are well described as the function predicted by Agodi.