Fission fragment anisotropy for the Am fission isomer by spin exchange pumping with polarized rubidium vapour

The foundations of an experiment have been worked out with which, in principle, the spin, hyperfine constants and the isomer shift of the 14 ms fission isomer ^242mAm can be measured. Such an experiment would be based on the fission fragment anisotropy signal which has actually been observed in this work after spin exchange pumping with polarized rubidium vapour in an optical buffer gas cell. A decrease of the count rate of (12±4)% has been measured at 90% with respect to the quantization axis. From this result it is concluded that the nuclear spin of the ^242mAm fission isomer must be larger than 1. The low-energy fission isomers originating from the ²⁴²Pu(d, 2n)^242mAm reaction have been post-accelerated with the aid of a 6 cm long 100 kV electrostatic accelerator unit in order to implant them through a 0.4 μm thick entrance window into the optical buffer gas cell. A neutralization efficiency of 13% of the americium fission isomers with an energy of about 1 MeV has been determined experimentally.