Mössbauer Effect in Ru⁹⁹

Abstract

The 90-keV transition in Ru⁹⁹ is a very interesting, but as yet little exploited, case for recoilfree resonance studies. The multipolarity of the transition is a mixture of magnetic dipole and electric quadrupole, with a mixing ratio δ² = 2.7. The half life of 20 nsec results in a linewidth to gamma-energy ratio which is somewhat smaller than that for the case of Fe⁵⁷. The level in Ru⁹⁹ is fed in the decay of 16-day Rh⁹⁹ which is produced by p,n reaction on Ru⁹⁹. A source host of ruthenium gives an unsplit emission line with a recoilfree fraction of ~15% at 4.2°K. By bombarding enriched isotope and doing a chemical separation, high specific activity sources in the several millicurie range can be prepared. The complex magnetic hyperfine spectrum of 18 lines resulting from the 3/2 → 5/2 transition can be completely resolved in the 500 kG_.field which acts on the ruthenium nucleus situated in an iron host. By making use of accidental separation of left and right circularly polarized hyperfine components, it is possible to measure the sense and magnitude of relatively small aligned fields acting on the ruthenium nuclei. Details of source and absorber preparation are presented.

Work performed under the auspices of the U.S. Atomic Energy Commission.