Study of the fission isomer 240sup(m)Am (S.F.) using laser-induced nuclear polarization

We have begun a series of in-beam laser experiments intended to determine detailed spectroscopic properties of fission isomeric states. The initial experiment was the measurement of the optical isomer shift of the 1-ms 240sup(m)Am isomer. The technique, Laser-Induced Nuclear Polarization (LINUP), is based on depopulation optical pumping using circularly polarized (sigma+ or sigma-) light. Americium is a good candidate for optical pumping because the ground state, 5f77s28S(7/2), has approximate spherical symmetry, which reduces the collisional relaxation rates, and because the first, excited state arises from the promotion of one 7s electron to the 7p orbital (5f7 7s7p 10P(7/2)). The hyperfine splitting of the atomic ground state is very small (12) (approx. <0.001 cm-1). The total width of the 10P(7/2)-8S(7/2) transition (which is at 6405 Angstroem in 241Am) due to the hyperfine splitting of the 10P(7/2) state is expected to be approx.0.5 Angstroem for reasonable values of the nuclear spin and magnetic moment of the nuclear spin and magnetic moment of the 240sup(m)Am fission isomer. (orig./HSI)