Recent advances in AMS of 36Cl with a 3-MV-tandem

Author(s)

Martin Martschini, Oliver Forstner, Robin Golser, Walter Kutschera, Stefan Pavetich, Alfred Priller, Peter Steier, Martin Suter, Anton Wallner

Abstract

Accelerator mass spectrometry (AMS) of (36)Cl (t(1/2) = 0.30 Ma) at natural isotopic concentrations requires high particle energies for the separation from the stable isobar (36)S and was so far the exclusive domain of tandem accelerators with at least 5 MV terminal voltage. Using terminal foil stripping and a detection setup consisting of a split-anode ionization chamber and an additional energy signal from a silicon strip detector, a (36)S suppression of >10(4) at 3 MV terminal voltage was achieved. To further increase the (36)S suppression energy loss straggling in various counter gases (C(4)H(10), Ar-CH(4) and C(4)H(10)-Ar) and the effect of "energy focusing" below the maximum of the Bragg curve was investigated. The comparison of experimental data with simulations and published data yielded interesting insights into the physics underlying the detectors. Energy loss, energy straggling and angular scattering determine the (36)S suppression. In addition, we improved ion source conditions, target backing materials and the cathode design with respect to sulfur output and cross contamination. These changes allow higher currents during measurement ((35)Cl(-) current approximate to 5 mu A) and also increased the reproducibility. An injector to detector efficiency for (36)Cl ions of 8% (16% stripping yield for the 7+ charge state in the accelerator, 50% (36)Cl detection efficiency) was achieved, which can favorably be compared to other facilities. The memory effect in our ion source was also thoroughly investigated. Currently our measured blank value is (36)Cl/Cl approximate to 3 x 10(-15) when samples with a ratio of 10(-11) are used in the same sample wheel and (36)Cl/Cl approximate to 5 x 10(-16) if measured together with samples with a ratio of 10(-12) or below. This is in good agreement with the lowest so far published isotope ratios around 5 x 10(-16) and demonstrates that 3 MV tandems can achieve the same sensitivity for 360 as larger machines

Organisation(s)

Isotope Physics

External organisation(s)

Eidgenössische Technische Hochschule Zürich

Journal

Nuclear Instruments & Methods in Physics Research. Section B. Beam Interactions with Materials and Atoms

Volume

269

Pages

3188-3191

No. of pages

4

ISSN

0168-583X

DOI

https://doi.org/10.1016/j.nimb.2011.04.016

Publication date

2011

Peer reviewed

Yes

Austrian Fields of Science 2012

103013 Ion physics

Portal url

https://ucrisportal.univie.ac.at/en/publications/7062aace-d73a-4ba8-983d-3153dbc6e2a6