Monday, 5 September 2005 - 1:40 PM

This presentation is part of: Ion Sourcery (optics, modeling, performance, etc)

The problem of background reduction for noble-gas AMS in ECR sources

Philippe A. Collon1, Youssef El Masri2, R. Golser3, C. L. Jiang4, M Gaelens2, A. Heinz5, D. Henderson4, W Kutschera3, P Leleux2, M Loiselet2, R. C. Pardo4, Michael Paul6, K. E. Rehm4, G Ryckewaert2, R. H. Scott4, and R. Vondrasek4. (1) Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556, (2) Université Catholique de Louvain, Institut de Physique Nucléaire, Chemin du Cyclotron 2, Louvain-la-Neuve, Belgium, (3) Vienna Environmental Research Accelerator (VERA), Universität Wien, Währinger Strasse 17, Vienna, Austria, (4) Physics Division, Argonne National Laboratory, , 9700 S. Cass Avenue Argonne, Argonne, 60439, (5) Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520, (6) Racah Institute of Physics, Hebrew University, Jerusalem, 91904 , Israel

The development of a viable AMS method for noble gasses (in particular 81Kr and 39Ar) has been underway for several years using positive ion accelerators with Electron Cyclotron Resonance (ECR) ion sources [1]. One of the main problems linked to the measurement of low isotopic ratios (atmospheric values are 81Kr/Kr = 5.3x10-13, and 39Ar/Ar = 8.2x10-16) has been linked to the high background created by the presence of stable isotope interference present in the ion source (81Br and 39K, respectively).

In particular in the case of the development of an AMS counting technique for 39Ar, where a clear 39Ar has been detected using the Enge split-pole spectrograph operating in the gas-filled mode [2], measurement are hampered by the intensity of the interfering 39K isobar in the source. Our group has investigated the sources of 39K in ECR sources as well as potential reduction methods of 39K drawing on both our previous experience with 81Kr [1] as well as results from investigations both at Argonne National Laboratory and Louvain-la-Neuve. Using some of the techniques developed we have been able to reduce the 39K background by a factor of ~100 opening the possibility of measuring 39Ar from ocean water samples [2]. However measurements are at present hampered by the intensity of the argon beam current. Any increase of the argon beam, a necessity if these measurements are to become a viable measurement technique, must be made without increasing the amount of 39K. Possible specific source requirements for this type of application will be discussed.

Possible improvements as well as the application of some of these background reducing techniques to other isotopes (i.e. 63Ni) will be discussed.

[1] P. Collon, Z-T. Lu, W. Kutschera, Tracing Noble Gas Radionuclides in the Environment, Annu. Rev. Nucl. Part. Sci. 54 (2004) 39-67. [2] Ph. Collon, M. Bichler, J. Caggiano, L. DeWayne Cecil, Y. El Masri, R. Golser, C.L. Jiang, A. Heinz, D. Henderson, W. Kutschera, B.E. Lehmann, P. Leleux, H.H. Loosli, R.C. Pardo, M. Paul, K.E. Rehm, P. Schlosser, R.H. Scott, W.M. Smethie Jr., R. Vondrasek, Development of an AMS method to study oceanic circulation characteristics using cosmogenic 39Ar, Nucl. Instrum. Meth. 223-224 (2004) 428- 434.


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