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HK: Hadronen und Kerne

HK 56: Postersitzung

HK 56.44: Poster

Wednesday, March 18, 1998, 17:00–19:00, Foyer

Novel large-area, low-pressure MSGC detectors for thermal neutron imaging — •Ch. Schulz, B. Gebauer, and Th. Wilpert — Hahn-Meitner-Institut Berlin, D-14109 Berlin, Germany

A novel type of large-area thermal neutron imaging gas detectors is being developed in order to improve position resolution and count rate capability by about an order of magnitude compared to multiwire chambers using gaseous ³He convertors. A central thin composite ¹⁵⁷Gd/CsI convertor foil is positioned between two fourfold segmented planes of large-area, two-dimensional position-sensitive microstrip gas chambers of novel design, which are optimized for low-pressure, two-stage, high-gain, gas avalanche multiplication. After n-capture in ¹⁵⁷Gd, at the CsI convertor surfaces ≤ 10 well localized eV secondary electrons are emitted, which trigger parallel-plate avalanche multiplication in the adjacent high reduced constant field strength regions, followed by microstrip amplification in the rising fields, generated by the potential differences between the microstrip electrodes. In this two-stage amplification mode total gains of about 10⁶, position resolutions of a few tenths of a mm FWHM for x and y, pulse widths of about 5 ns and very high tolerable local count rates are predicted by extensive model calculations. For the sake of simplicity a delay line based readout technique was chosen, which limits the achievable position resolution, and the count rate capability of the full segmented detector to about 3 Mevents/s.