Magneto-optic trapping of beta-decaying K-38(m), K-37 from an on-line isotope separator

A magneto-optic trap (MOT) can provide-a well-polarized, backing-free, localized source of radioactive atoms for beta-decay experiments. We have trapped approximately 6000 atoms of K-38(m) (t(1/2) = 0.925 s) and 2000 atoms of K-37 (1.226 s) produced at the TRIUMF on-line separator TISOL in a vapor-cell MOT. We have measured optical isotope shifts and deduced the nuclear charge radii, which show an unusual lack of change at the neutron number N = 20 shell closure. Plans include a search for scalar contributions to the beta(+)-nu correlation in the 0(+) --> 0(+) decay of K-38(m).