Accelerator Mass-Spectrometry Of Ni-59 In Extraterrestrial Matter

Cosmic-ray produced Ni-59 (t1/2 = 76000 years) was detected in meteoritic and lunar material by AMS with fully stripped ions. At 641 MeV beam energy, a clean separation of Ni-59(28+) ions from Co-59(27+) background was achieved with a magnetic spectrograph. A background limit of Ni-59/Ni < 7 X 10(-14) was determined with a blank Ni sample. A Ni-59/Ni ratio of (2.3 +/- 0.4) x 10(-11) was measured in a sample from the Admire stony-iron (pallasite) meteorite, corresponding to a specific activity of 280 +/- 50 dpm/kg meteorite. In a surface layer of Apollo 16 lunar rock 68815, a Ni-59/Ni ratio of (8.8 +/- 3.3) x 10(-13) was measured (diluted with Ni carrier), corresponding to a specific activity of 4.1 +/- 1.5 dpm/kg rock. This result compares well with values calculated by Reedy from the (Fe(alpha, n)Ni)-Fe-56-Ni-59 reaction induced by solar cosmic ray alpha particles. Methodological aspects of the full-stripping technique and future possibilities of Ni-59 measurements in lunar materials are discussed.