Photon sandwich detectors with WLS fiber readout

Abstract

A photon detector for BNL experiment E949 is described. The detector consists of a lead scintillator "sandwich" of 25 layers of 5 mm thick scintillator BC404 and 24 layers of 2 mm lead absorber. Readout is implemented with 30-60 cm long WLS fibers (BCF 99-29AA) glued into grooves in the BC404. Average yield was measured with cosmic rays to be about 43 p.e./MeV. Extruded plastic scintillation counters developed for sandwich detectors of photons for the KOPIO experiment are also described. For a 7 mm thick counter with 4.3 m long WLS fibers spaced at 7 mm a light yield of 18.7 p.e./MeV and time resolution of 0.71 ns were obtained. A prototype photon veto module consisting of 10 layers of 7 mm thick extruded plastic slabs interleaved with 1 mm lead sheets was tested.

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“…This meant designing curved groove patterns for the fibres to lay in. The fibres have been reported to undergo crazing at a bending radius of 30 mm [15], hence the groove patterns were designed with bending radii of 40 mm in order to eliminate any possibility of this becoming a problem. The location of the grooves were designed to be as uniform, in terms of light collection, as possible across the plate with all of the fibres leaving the same point.…”

“…The sum correction code was used with the 278 keV resonance in 14 Nðp; gÞ 15 O, in addition to the decay of 56 Co.…”

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“…The upstream (downstream) CO detector was located just upstream (downstream) of the ECs [65]. Both of the COs consisted of twenty-four 2-mm thick lead sheets alternating with 25 layers of 5-mm thick Bicron BC404 scintillator sheets, providing about 9 r.l.…”

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