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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 (T1/2 = 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.

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