Preparation of a 60 Fe target for nuclear astrophysics experiments D. Schumann a,Ã , J. Neuhausen a , I. Dillmann b , C. Domingo Pardo b , F. K¨ appeler b , J. Marganiec b , F. Voss b , S. Walter b , M. Heil c , R. Reifarth c , J. Goerres d , E. Uberseder d , M. Wiescher d , M. Pignatari d,e a Laboratory for Environmental and Radiochemistry, Paul Scherrer Institute Villigen, 5232 Villigen PSI, Switzerland b Forschungszentrum Karlsruhe, Institut f¨ ur Kernphysik, Postfach 3640, D-76021 Karlsruhe, Germany c GSI Helmholtzzentrum f¨ ur Schwerionenforschung GmbH, Planckstrasse 1, 64291 Darmstadt, Germany d University of Notre Dame, Department of Physics, Notre Dame, IN 46556, USA e Keele University, Keele, Staffordshire ST5 5BG, UK article info Available online 9 October 2009 Keywords: Nuclear astrophysics Radio-chemical separation Neutron capture cross-section abstract An 60 Fe target for studying the 60 Fe(n, g) 61 Fe cross-section at stellar energies was prepared using radio- chemical separation techniques. In total, 7.8  10 15 60 Fe atoms (777 ng) were separated from a copper beam dump for the 590 MeV proton beam of the high intensity accelerator at PSI. The final target was prepared by evaporating the iron-containing aqueous solution onto a graphite backing. With this sample the keV neutron capture cross-section of 60 Fe has been measured at FZ Karlsruhe. The work is part of the ERAWAST-initiative (Exotic Radionuclides from Accelerator WAste for Science and Technology) which is aimed at extracting rare valuable radionuclides from accelerator waste by chemical means. & 2009 Elsevier B.V. All rights reserved. 1. Introduction The isotope 60 Fe, with a half-life of 1.5  10 6 yr, plays a key role in tracing the history of the early Solar System (ESS). Current comprehensive attempts at reconstructing the inventory of short- lived isotopes in the mass region between Fe and Pb that were found to be present in the ESS [1,2] showed that 60 Fe (together with 107 Pd, 41 Ca, 36 Cl, 26 Al, and 10 Be) must be considered as a late addition to the protosolar nebula. Whether this material stems from a supernova or a nearby asymptotic giant branch (AGB) star is still an open question. Reliable values for neutron capture cross-sections are required for calculating production of 60 Fe via the s-process. The stellar (n, g) rates for the unstable isotopes, 59 Fe and 60 Fe, which govern the stellar production and destruction of 60 Fe, are presently obtained by theoretical calculations using the Hauser–Feshbach statistical model, which exhibits typical uncertainties of 30–50% for the resonance dominated cross-sections in the mass region around Fe [3], whereas the results from calculations of the 60 Fe cross-section with the statistical model codes NON-SMOKER [4] and MOST [5] differ by a factor of three. Because the s-process abundances are directly determined by the respective stellar (n, g) rates, the present cross-section uncertainties translate into uncertainties in the calculated 60 Fe yields of more than a factor of two, thus obscuring the abundance predictions of the stellar models. Thus, experimental solutions to this problem are urgently needed. Precondition for such an experiment is the availability of a sufficient amount of 60 Fe as sample material. One of the very few possibilities for gaining such rare isotopes is the exploitation of activated components available from accelerator facilities at the Paul Scherrer Institute (PSI). The work is part of the (ERAWAST)-initiative [6], aimed at extracting scientifically interesting isotopes, e.g. 44 Ti, 26 Al, 10 Be, 60 Fe, 182 Hf, from beam stops, targets, and shielding materials. The activated components from the PSI high-power accelerator facilities were shown to contain considerable amounts of these valuable isotopes [7]. The project covers both development of separation methods at the production site and application in various scientific fields, for example in nuclear astrophysics, fundamental nuclear physics, pharmaceutical chemistry, accel- erator mass spectrometry, and nanotechnology. 2. Source of 60 Fe The 60 Fe was separated from copper chips, which were drilled out from cylindrical beam-dump pieces 8 cm in diameter. The piece shown in Fig. 1 is part of a beam dump that had been irradiated at the PSI 590 MeV ring cyclotron for 12yr with a total dose of 0.1 Ah. In a first step, a complete radio-chemical analysis of the entire beam dump had been carried out to determine the radial and axial activity profiles. This information allowed us to identify the most active regions. Details of this analysis results can ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2009.09.072 Ã Corresponding author. E-mail address: dorothea.schumann@psi.ch (D. Schumann). Nuclear Instruments and Methods in Physics Research A 613 (2010) 347–350