Hamburg 2009 – scientific programme

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MS: Fachverband Massenspektrometrie

MS 4: AMS-Applications

MS 4.6: Talk

Tuesday, March 3, 2009, 12:00–12:15, VMP 8 R05

The systematics of the ³⁶Cl production rate calculations in limestone — •Vasily Alfimov and Susan Ivy-Ochs — Ion Beam Physics, ETH Zurich, 8093 Zurich, Switzerland

One of the major radionuclides that are measured by Accelerator Mass Spectrometry (AMS) is chlorine-36 (T_1/2 = 301 kyr). It is produced by cosmic rays in the atmosphere and the upper meters of the lithosphere. Since limestone contains no or very little quartz, and hence ¹⁰Be cannot be used, surface exposure dating of this rock type has to be done with ³⁶Cl. There are several production pathways of ³⁶Cl in calcite: spallation of Ca by fast neutrons, capture of slow negative muons on ⁴⁰Ca, fast-muon induced reactions on Ca, capture of thermal and epithermal neutrons on ³⁵Cl, where these neutrons are also produced by several pathways. The complexity of ³⁶Cl production makes it difficult to calibrate each separate pathway and ultimately to use this radionuclide in surface exposure dating. Here we summarize our investigation into the ³⁶Cl production systematics and draw an outline for the recommended calibration constants and calculation procedure.