Measurements of ⁵⁹Ni in meteorites by accelerator mass spectrometry

Isotopic abundances of the radionuclide ⁵⁹Ni (T _{1 2 = 76000} yr) were measured by accelerator mass spectrometry with the 14UD Pelletron tandem accelerator at the Australian National University and a detection system solely based on a multianode ionization chamber. The sensitivity limit in the measurement of ⁵⁹Ni isotopic abundances is 5 × 10^-13, as determined by residual interferences from isobaric ⁵⁹Co and isotopic ⁵⁸Ni ions. Cosmogenic ⁵⁹Ni abundances ⁵⁹Ni Ni = (8-20) × 10^-12 were measured in four samples prepared from the metal phase of two meteorites (mesosiderites). The ratio of the ⁵⁹Ni abundances to those measured for ⁴¹Ca in the silicate phase of the same samples, is in fair agreement with the ratio of the production rates via thermal-neutron capture on ⁵⁸Ni and ⁴⁰Ca.