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

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