Heidelberg 2015 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 6: Structure and Dynamics of Nuclei 1

HK 6.2: Vortrag

Montag, 23. März 2015, 15:00–15:15, T/HS2

A VUV detection system for the direct identification of the fluorescence radiation of ^229mTh * — •Benedict Seiferle, Lars v.d. Wense, and Peter G. Thirolf — LMU Munich

In the whole landscape of atomic nuclei, ²²⁹Th has the lowest transition energy to its first excited state. The transition energy was indirectly measured to be 7.8(5) eV, which corresponds to ≈160 nm and conceptionally allows to get optical access to the transition. This talk will report on a VUV detection system that aims on the direct detection of the fluorescence radiation of ^229mTh. The setup consists of two annular parabolic mirrors (made of MgF₂-coated aluminum) and a phosphorous screen behind a CsI-coated MCP, monitored by a CCD camera. ^229(m)Th will be populated via the α decay of ²³³U. Therefore a ²³³U α-recoil source is placed in a buffer-gas stopping cell, where a continuous ion beam is produced by a subsequent RFQ. By using a quadrupole mass separator, ^229(m)Th ions are then separated from other short lived daughter nuclei. The ^229(m)Th ions are collected on a point-like micro electrode (50 µm in diameter) that is placed in the focal spot of the annular parabolic mirror (f=10 mm) which collimates the fluorescence radiation. The parallelized light is then focused by a second annular parabolic mirror (f=2 mm) onto the MCP. To get a high signal to noise ratio, it is important to achieve a small focal spot size on the MCP. Since the optical axis is blocked by the collection electrode, also the alignment of the optics poses a special challenge. The alignment method as well as results from first test measurements will be presented. *Supported by the DFG Grant TH956/3-1