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90 A FIRST APPENDIX
A.2 Reports about CsI:Tl detectors
Scintillation detectors are common used detector systems and plenty of
reports describe the assemblies and achieves resolution. With an final
focus on CsI:Tl scintillation detectors of this thesis, mainly reports of
these crystals, comparing between different readout devices, couplings
and crystal wrapping are presented.
For the BARBAR collaboration Brose et al. [39] reported photoelectron
yields of CsI:Tl crystals with different crystal wrapping and readout.
They used crystals of 6x5 cm 2 front face, 6x6 cm 2 rear face and a length
of 36 cm.
The crystal wrapping improved the light yield and uniformity. A crystal
wrapping with two layers of DuPont Tyvek 1056 D (160 µm) or three
layers of 38 µm thick Teflon PTFE improves the light yield by 4 times
compared to no wrapping. One layer Al foil around the two layers
of DuPont Tyvek 1056 D yields an improvement of the light yield of 5
times the light yield without wrapping. The wrapping also improves
the uniformity of light output and reduces cross talk between the crystals.
As readout device, three different systems were used, a PMT, a
PIN diode coupled directly to the crystal and diodes coupled to a wave
length shifter.
The light yields of 74 % for a 5 cm diameter PMT (Hamamatsu R669)
with multialkali photocathode, coupled to the rear face of the crystal
with a minimal air gap, was only given in this article relative to a cubic
CsI:Tl standard crystal (25 mm edge length). They measured the
uniformity of light output for 18 different positions of a 137 Cs source
(662 keV) for the PMT, being within ±2%.
Thereafter two Hamamatsu S2744-08 diodes (10x20 mm 2 active area)
were coupled with optical grease and glue to the rear face of the crystal.
This readout yields around 8500 photoelectrons/MeV with en electronic
noise level of 110 keV at the 1275 keV line of 22 Na. The photo
peak position of a 137 Cs source could not be determined with the diode
readout.
Finally two Hamamatsu S 3588-03 (mod 5400) with 3x3 mm 2 active area
were coupled via a wave length shifter to the crystal rear face. The
wave length shifter consisted of fluorescent dyes, dissolved in 3 mm
thick lucite (PMMA) plates and covered the hole rear crystal surface.
The tested BASF Lumogen F red 300 and Roehm 2466 P have maximum
absorption at 440, 530-540 and 560-570 nm and the fluorescence
emission at around 625 nm, where the quantum efficiency of photodiodes
is higher. The WLS plate was coupled via an air gap of 0.5 mm
to the crystal and one (and later two) S 3588-03 (mod 5400) photodi-