Hyperfine structures of the resonance line of the arc spectra and nuclear quadrupole moments of the isotopes 135 and 137 of barium

Abstract

The h.f.s. of the resonance line of the arc spectra of 135 Ba and of 137 Ba- have been determined by observing the absorption of atomic beams enriched in one or other of these isotopes; the recently developed technique (Jackson 1961) of operating the atomic beam between the plates of the interferometer enabled strong absorptions to be obtained over long periods, at high collimation, with the limited quantities of enriched isotopes available. In both cases the h.f.s. consists of three components, with intensity ratios of 3 : 2 : 1 (in order of increasing wave number); their positions relative to the single line of 138 Ba are: 137 Ba 2.1 8.7 18.5 mK 135 Ba 3.5 10.2 17.8 mK. The probable error is ±0.2 mK . From the intervals between these components, the magnetic moment splitting factor, A , and the quadrupole moment coupling factor, B , of the term 6 s 6 p 1 P 1 are found; the ratios of the values of these factors for the two isotopes are in good agreement with those found by nuclear resonance methods. The isotope shifts of 137 Ba and 135 Ba relative to 138 Ba derived from these measurements are respectively 7.0 ± 0.3 and 8.1 ± 0.3 mK. A brief announcement of these results has already been made (Jackson & Duong 1963 a ). The values of Q , the nuclear quadrupole moment of 137 Ba and of 135 Ba, are derived from the values found for the coupling factors, B . The isotope shifts of 136 Ba and of 134 Ba relative to 138 Ba have also been measured by this method, for samples enriched in one or other of these isotopes and in 138 Ba; they are respectively 4.2 ± 0.2 and 4.6 ± 0.1 mK.