ISOTOPE SELECTIVE SUPPRESSION OF CONTAMINANT SIGNALS IN PAUL TRAP LASER SPECTROSCOPIC STUDIES

Laser spectroscopy has been carried out on a sample of radioactive Hf- 172 ions in a Paul trap. Laser excitation is on the 5d6s(2)(a(2)D) (J = 3/2)-5d6s(a(3)D)6p(z4(F)) (J = 5/2) transition in the Hf ion (lambda = 340 nm). The fluorescence is observed on the transitions to the two low lying metastable states 5d6s(2)(a(2)D) (J = 5/2) and 5d(2)(a(3)F) 6s(a(4)F) (J = 3/2). The spectra show besides the signal from Hf-172, contaminant signals from stable isotopes present in the sample. Hyperf ine lines from the odd-A Hf isotopes are suppressed by light induced i sotope selective HfH+ formation involving the H-2 buffer gas used for cooling and quenching. The molecule formation leads to an effective lo ss of those isotopes in the sample and allows a better isolation of th e weak signal from Hf-172. The HfH+ formation is from one of the metas table states (mainly 5d(2)6s) which are populated after excitation to the 5d6s(a(3)D)6p(z(4)F) (J = 5/2) state. The molecule formation chann el competes with the decay of the metastable states to the ground stat e through collisional quenching with the H-2 buffer gas. The ratio bet ween HfH+ formation and quenching probability is evaluated to be of th e order of 10(-5).