Developments towards detection of ¹³⁵Cs at VERA

Autor(en)

Johannes Lachner, Magdalena Kasberger, Martin Martschini, Alfred Priller, Peter Steier, Robin Golser

Abstrakt

Radioisotopes produced in natural or anthropogenic fission are widely

used for tracer studies of environmental processes, in nuclear

forensics, and are important for nuclear waste disposal. Besides the

well-known ¹³⁷Cs, the longer-lived sister isotope ¹³⁵Cs (T_1/2 = 2.3 Myr)

is also produced, and the combined measurement of the two isotopes

would allow for assessment of contaminating sources. The insufficient

suppression of the stable isobar ¹³⁵Ba presently prevents AMS measurements down to expected natural levels of ¹³⁵Cs/¹³³Cs ≈ 10⁻¹¹.

Via the difference in electron affinities between Cs and Ba further

isobar suppression should be achievable after the installation of the

Ion-Laser-Interaction System (ILIAS) at VERA. We present a preparatory

study on the performance of the 3 MV VERA AMS facility for ¹³⁵Cs concerning ion formation, transmission and detection. Since the usual Cs sputtering would obscure the ¹³⁵Cs/¹³³Cs

ratio of a sample, Rb sputtering was successfully applied and tested

also for various other typical AMS elements. Partial suppression of ¹³⁵Ba is possible with the extraction of Cs⁻ and negative Cs-fluorides. Cs⁻ currents of several 10 nA were extracted over hours from mg amounts of Cs₂SO₄

material. The transmission to various charge states was tested with gas

(Ar, He) and foil stripping. Experiments showed that no suppression in

the detection system is possible at high beam energies with the VERA

facility. For this reason, gas stripping to low charge states (2⁺, 3⁺)

with transmissions up to 30% is favorable to guarantee optimal beam

transport to the detector. In the present setup, utilizing a simple

Bragg-type detector, the blank ¹³⁵Cs/¹³³Cs ratios from chemically pure samples are determined by the ¹³⁵Ba background to a value of (4.0 ± 1.3)·10⁻⁹.

Organisation(en)

Isotopenphysik

Journal

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

Band

361

Seiten

440-444

Anzahl der Seiten

5

ISSN

0168-583X

DOI

https://doi.org/10.1016/j.nimb.2015.01.032

Publikationsdatum

10-2015

Peer-reviewed

Ja

ÖFOS 2012

103013 Ionenphysik

Schlagwörter

ASJC Scopus Sachgebiete

Nuclear and High Energy Physics, Instrumentation

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/b9d380c7-4c72-4c69-b929-b1d7a5acb52f