Hannover 2010 – wissenschaftliches Programm

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MS: Fachverband Massenspektrometrie

MS 4: Beschleunigermassenspektrometrie und Anwendungen I

MS 4.4: Vortrag

Mittwoch, 10. März 2010, 11:30–11:45, F 428

The measured and modeled 36Cl concentration in 100-m long limestone core from Vue des Alpes, Switzerland — •Vasily Alfimov1, Susan Ivy-Ochs1, Peter W. Kubik1, Jürg Beer2, and Hans-Arno Synal11Laboratory of Ion Beam Physics, ETH Zurich, Switzerland — 2EAWAG, Duebendorf, Switzerland

A 100-m long limestone core was sampled in Vue des Alpes (1256.86m, 474’46.8”N, 652’14.70E), Switzerland, and analysed for 36Cl with Accelerator Mass Spectrometry at the Laboratory of Ion Beam Physics, ETH Zürich. The measurements were compared with the theoretical calculation of 36Cl content in the core. The long-lived radionuclide 36Cl (T1/2=301kyr) is produced in limestone by cosmic rays. There are several pathways of 36Cl production in the limestone, and they have different attenuation lengths. At the surface the dominant production pathway is the spallation of Ca by fast neutrons. Under one meter of rock, the slow muon capture on 40Ca starts to take over the lead, while after 10 m depth the fast-muon-induced processes in Ca starts to play a significant role. Three mentioned processes plus U-Th content of the rock also produce thermal neutrons, and these neutrons activate stable 35Cl into 36Cl. These are also important pathways, because concentration of stable chlorine in the sampled core is non-negligible (65 ppm on average). All pathways were combined in a model of 36Cl production and applied to the calculation of 36Cl content of the core. The talk will contain the comparison of the measured and calculated 36Cl profiles, and our conclusions on the parameters included into the model.

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