https://doi.org/10.1140/epjd/e2016-60653-4
Regular Article
A VUV detection system for the direct photonic identification of the first excited isomeric state of 229Th
1
Ludwig-Maximilians-Universität München,
Am Coulombwall 1,
Garching,
Germany
2
GSI Helmholtzzentrum für Schwerionenforschung GmbH,
Planckstr. 1,
Darmstadt,
Germany
3
Helmholtz Institut Mainz, Johann-Joachim-Becherweg 36, Mainz, Germany
a
e-mail: benedict.seiferle@physik.uni-muenchen.de
Received: 17 November 2015
Received in final form: 1 February 2016
Published online: 15 March 2016
With an expected energy of 7.6(5) eV, 229Th possesses the lowest excited nuclear state in the landscape of all presently known nuclei. The energy corresponds to a wavelength of about 160 nm and would conceptually allow for an optical laser excitation of a nuclear transition. We report on a VUV optical detection system that was designed for the direct detection of the isomeric ground-state transition of 229Th. 229(m)Th ions originating from a 233U α-recoil source are collected on a micro electrode that is placed in the focus of an annular parabolic mirror. The latter is used to parallelize the UV fluorescence that may emerge from the isomeric ground-state transition of 229Th. The parallelized light is then focused by a second annular parabolic mirror onto a CsI-coated position-sensitive MCP detector behind the mirror exit. To achieve a high signal-to-background ratio, a small spot size on the MCP detector needs to be achieved. Besides extensive ray-tracing simulations of the optical setup, we present a procedure for its alignment, as well as test measurements using a D2 lamp, where a focal-spot size of ≈100 μm has been achieved. Assuming a purely photonic decay, a signal-to-background ratio of ≈7000:1 could be achieved.
Key words: Optical Phenomena and Photonics
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2016