Low-level measurement of 63 Ni by means of accelerator mass spectrometry G. Rugel a,b, * , A. Arazi a , K.L. Carroll c , T. Faestermann a , K. Knie a , G. Korschinek a , A.A. Marchetti c , R.E. Martinelli c , J.E. McAninch c , W. R€ uhm b , T. Straume d , A. Wallner a,b , C. Wallner a a Fakult€atf€ur Physik, Technische Universit€atM€unchen, 85747 Garching, Germany b Strahlenbiologisches Institut, Ludwig Maximilians Universit€atM€unchen, 80336 M€unchen, Germany c Lawrence Livermore National Laboratory, Livermore, CA 94551, USA d University of Utah, Salt Lake City, UT 84108, USA Abstract The radionuclide 63 Ni (T 1=2 ¼ 100:1 a) has been proposed as a fluence monitor for fast neutrons in copper samples from Hiroshima. Accelerator mass spectrometry (AMS) represents a powerful tool for the detection of this radionu- clide, provided the isobaric interference of 63 Cu can be sufficiently suppressed. In this paper, we report the first results from a study on the 63 Cu background observed in different sets of control samples, and in a 127-year-old environmental copper sample which was directly exposed to cosmic radiation for about 80 years. The 63 Ni/Ni ratios measured in the blank samples range up to about 2 · 10 13 corresponding to concentrations of a few times 10 4 63 Ni atoms/g Cu. These results provide information on the overall background of the applied methodology and, thus, on the possible sensitivity of 63 Ni measurements in copper samples by means of AMS. In the environmental sample, a 63 Ni concentration of (1.0 ± 0.3) · 10 5 63 Ni atoms/g Cu was observed which is not significantly different from the results obtained on com- mercially available copper material. A similar concentration would be expected in a copper sample located 1300 m from the hypocenter of the Hiroshima atomic bomb. Ó 2004 Elsevier B.V. All rights reserved. PACS: 01.30.Cc; 07.75.+h; 07.77.)n; 29.40.Cs; 82.80.Ms; 87.52.Ga; 87.66.Jj; 89.60.Gg Keywords: Accelerator mass spectrometry; 63 Ni; Hiroshima; Copper 1. Introduction The measurement of radionuclides induced by atomic-bomb neutrons in samples from Hiroshima and Nagasaki has been used extensively to validate the neutron exposures received by atomic-bomb survivors. The significance of those efforts is that the atomic-bomb survivor data serve as the worldwide basis for safety standards and cancer risk estimates for humans exposed to ionizing radiation (e.g. [1,2]). More recently, it has been proposed that fast neutrons which dominate neu- tron doses in Hiroshima and Nagasaki could be * Corresponding author. Address: Garching, Beschleuniger- labor Forschungsgel}ande, 85748 Garching, Germany. Tel.: +49-89-289-14273/14282; fax: +49-89-289-14280. E-mail address: grugel@ph.tum.de (G. Rugel). 0168-583X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.04.144 Nuclear Instruments and Methods in Physics Research B 223–224 (2004) 776–781 www.elsevier.com/locate/nimb