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A VUV detection system for the direct photonic identification of the first excited isomeric state of 229Th

Abstract

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.

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Correspondence to Benedict Seiferle.

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Seiferle, B., von der Wense, L., Laatiaoui, M. et al. A VUV detection system for the direct photonic identification of the first excited isomeric state of 229Th. Eur. Phys. J. D 70, 58 (2016). https://doi.org/10.1140/epjd/e2016-60653-4

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  • DOI: https://doi.org/10.1140/epjd/e2016-60653-4

Keywords

  • Optical Phenomena and Photonics