W. Kutschera

Measurement of 129I concentrations in the environment after the Chernobyl reactor accident

Abstract The Chernobyl nuclear reactor accident which occurred on April 26, 1986 is known to have injected into the atmosphere a pulse of a large number of radionuclides. The activities of several radionuclides present in the subsequent fallout have been measured in different locations throughout Europe by gamma-ray and beta counting. We present here measurements of concentrations of the long-lived radionuclide 129I ( T 1 2 = 1.6 × 10 7 yr ) in environmental samples collected in Israel and Europe following the nuclear reactor accident. The measurements were performed by accelerator mass spectrometry, using the 14UD Rehovot Pelletron Accelerator. Concentrations of 129I in rainwater samples collected in the Munich (West-Germany) area and in Israel during the fallout period were measured to be 2.6 × 1010 and 1.2 × 109 atoms I respectively, while a 1982 rainwater sample from Israel shows a 129I concentration of 8.2 × 107 atoms I . Three measurements of the ratio 129I/131I gave a mean value of 21, from which an effective operating time of the reactor of 1.5 to 2 yr prior to the accident can be estimated. The possible use of anthropogenic 129I as a tracing tool for global environmental processes is discussed.

Calcium-41 concentration in terrestrial materials: prospects for dating of pleistocene samples

Calcium-41 has been suggested as a new tool for radiometric dating in the range of 105 to 106 years. The concentration of cosmogenic calcium-41 in natural samples of terrestrial origin has now been determined by high-sensitivity accelerator mass spectrometry after pre-enrichment in calcium-41 with an isotope separator. Ratios of calcium-41 to total calcium between 2 x 10-14 and 3 x 10-15 were measured for samples of contemporary bovine bone and from limestone deposits. Some prospects for the use of calcium-41 for dating Middle and Late Pleistocene bone and for other geophysical applications are discussed.

Abundance of live 244Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis

Half of the heavy elements including all actinides are produced in r-process nucleosynthesis, whose sites and history remain a mystery. If continuously produced, the Interstellar Medium is expected to build-up a quasi-steady state of abundances of short-lived nuclides (with half-lives ≤100 My), including actinides produced in r-process nucleosynthesis. Their existence in today’s interstellar medium would serve as a radioactive clock and would establish that their production was recent. In particular 244Pu, a radioactive actinide nuclide (half-life=81 My), can place strong constraints on recent r-process frequency and production yield. Here we report the detection of live interstellar 244Pu, archived in Earth’s deep-sea floor during the last 25 My, at abundances lower than expected from continuous production in the Galaxy by about 2 orders of magnitude. This large discrepancy may signal a rarity of actinide r-process nucleosynthesis sites, compatible with neutron-star mergers or with a small subset of actinide-producing supernovae.A. Wallner, 2, ∗ T. Faestermann, J. Feige, C. Feldstein, K. Knie, 5 G. Korschinek, W. Kutschera, A. Ofan, M. Paul, F. Quinto, † G. Rugel, ‡ and P. Steier Department of Nuclear Physics, Research School of Physics and Engineering, The Australian National University, Canberra, Australia VERA Laboratory, Faculty of Physics, University of Vienna, Währinger Strasse 17, A-1090, Austria Technische Universität München, D-85747 Garching, Germany Racah Institute of Physics, Hebrew University, Jerusalem, Israel GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstr. 1, 64291 Darmstadt, Germany

Half-life of 60Fe

Abstract The half-life of 60Fe has been measured to be T 1 2 = (1.49 ± 0.27) × 10 6 a, significantly longer than the one previous measurement of Roy and Kohman which reported a value of 3 × 105 a uncertain by a factor of 3. The present value was obtained from measurements of specific activity and radioisotope concentration in a material produced by spallation of copper with 191 MeV protons. 60Fe/Fe ratios in the range of 10−8 were measured with the Argonne FN tandem-superconducting linear accelerator system in conjunction with an Enge split-pole spectrograph. The specific activity of 60Fe in Fe was measured through the grow-in of the 1.332 MeV gamma-ray line of the 60Co daughter activity.

Long-lived noble gas radionuclides

Abstract The first AMS measurements of 39Ar and 81Kr have been performed by combining positive-ion production in an ECR ion source with acceleration to 6 MeV/A in the ATLAS linear accelerator and detection in a gas-filled spectrograph. Sensitivities of 39Ar/Ar = 8 × 10−16 (natural argon), and 81Kr/Kr = 2 × 10−10 (neutron-activated krypton) were achieved. A full-stripping experiment for 81Kr-81Br separation at 45 MeV/A was performed with the MSU K1200 cyclotron. Substantial contributions from nuclear reactions in a Be stripper foil were observed, in the attempt to detect 81Kr36+ ions in the A1200 recoil separator. The general situation for the detection of noble gas radionuclides is discussed.

Selective suppression of negative ions by lasers

Abstract A method of selective suppression of negative ions by electron photodetachment with a laser beam is investigated. The interaction of 532 nm photons from a Nd:YAG laser with negative ions of 32 S, 37 Cl and 40 Ca 16 O was studied. A strong depletion of 32 S − and 40 Ca 16 O − beam intensities, but no effect on 37 Cl − ions, was observed. Photodetachment cross sections of (1.0±0.2)×10 −17 cm 2 and (7±3)×10 −17 cm 2 were measured for 32 S − and 40 Ca 16 O − , respectively. Implications for accelerator mass spectrometry measurements are discussed.

Study of laser interaction with negative ions

Abstract Negative ions can be neutralized by detaching their additional electron through interaction with a laser beam. By properly choosing the laser wavelength, the process is highly selective; it can in principle enhance the discrimination power of an accelerator mass spectrometry system for ions of different elements (e.g. isobaric background) by allowing their separation prior to their injection into a tandem accelerator. We demonstrate this process in the case of the 59 Ni- 59 Co pair with the AMS system based on the Rehovot 14UD Pelletron accelerator and a pulsed Nd-YAG laser at the fundamental wavelength (1064 nm). A photodetachment cross section of (0.6 ± 0.3) × 10 −17 cm 2 was measured for 59 Co − and a suppression factor of 125 for the 59 Co isobaric background was achieved in a 59 Ni AMS measurement. The duty factor due to the pulsed laser was about 10 −4 . The laser-AMS system was also applied to the study of rare negative ions in the actinide region. Preliminary results on the laser interaction with uranium negative ions are reported.

Accelerator mass spectrometry: A versatile tool for research

Abstract A review of measurements with accelerator mass spectrometry is presented. Emphasis is placed on the use of long-lived radioisotopes and the versatility of the method. Although necessarily incomplete, this paper is intended to convey some feeling for the enormous breadth of AMS measurements and its prospects for future research.

Half-life of41Ca

The half-life of41Ca has been redetermined to be (1.01 ±0.10)×105 yr from the specific activity of a sample of enriched calcium material and its41Ca concentration. The activity was measured with a Si(Li) detector via the 3.3-keV X rays emitted in the electron capture decay of41Ca to41K. The41Ca concentration was measured by mass spectrometry. Since our result agrees well with the two most recent half-life measurements of Mabuchi et al. (1974), (1.13±0.12)×105 yr, and Klein et al. (1990), (1.03±0.07)×105 yr, we recommend the weighted mean of these three measurements, t1/2=(1.04±0.05)×105 yr, as the most accurate value of the half-life of41Ca.

Accelerator mass spectrometry at ATLAS

Abstract The special conditions required to run AMS experiments at a large heavy-ion accelerator such as ATLAS are discussed. Operational schemes for the current tandem-linac combination and their application to measurements of the long-lived radioisotopes 41 Ca, 60 Fe and 126 Sn are described. A brief outlook of future possibilities for AMS experiments with the new positive ion injector of ATLAS is presented.