Darmstadt 2008 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 37: Instrumentation und Anwendungen I
HK 37.5: Vortrag
Donnerstag, 13. März 2008, 17:45–18:00, 2C
A Low-Temperature Proton Detector for a Neutron Lifetime Experiment — •Axel Reimer Müller, Igor Altarev, Heinz Angerer, Stefan Materne, Joachim Hartmann, Stephan Paul, and Rüdiger Picker — E18, Technische Universität München
The neutron lifetime τn is a quantity very important for fundamental physics and cosmology. The new experiment PENeLOPE (Precision Experiment on the Neutron Lifetime Operating with Proton Extraction) shall determine τn with a precision nearly one order of magnitude better than previous experiments. In this experiment neutrons will be stored in a magneto-gravitational trap. To measure the time distribution of the decay protons is a substantial part of the experiment. We plan to build a large-area scintillation counter to detect the protons. A thin CsI layer on a UV-transparent light guide will be read out with large-area avalanche photodiodes (LAAPD). The detector arrangement has to work at cryogenic temperatures. Extensive investigations were performed to prove the feasibility of the set-up. In addition to the temperature dependent light output of CsI, we measured the LAAPD gain at temperatures down to 25 K. In contrast to an earlier experiment, which noticed a sharp decrease in the LAAPD gain at 50 K, we observed constant gain down to the lowest temperatures for two different kinds of LAAPD. First results where achieved with evaporated thin-film scintillators. A possible detector scheme was established after light-collection studies from the CsI layer to the LAAPD with the ray-tracing program FRED. This work is supported by the German BMBF, by DFG and by the Cluster of Excellence EXC 153.