1. 1 Study of scintillator/PMT properties for PoGO experiment August 25, 2003@ PoGO Teleconference Tsunefumi Mizuno mizuno@SLAC.Stanford.EDU BGO Transmission efficiency: pp.2-3 Comparison between two PMTs (normal cathode vs. prism one): pp.4-8 Summary: p.9

2. 2 BGO transmission efficiency (1) Lead block 241 Am(59.5keV) Hexagonal plastic scintillator BC404 (fast scintillator) wrapped with VM2000. 20cm long two types of BGO scintillators wrapped with teflon tape. a)manufacture way of polishing; rough surface in sides. Top/bottom surfaces are polished. b)Tune’s proposed way polishing; rough surface in bottom. Other planes are polished. Princeton PMT(H3178) We compared transmission efficiency between two types of BGO scintillators; one is in the original way of polishing and the other is re-polished in the way proposed by Tune.

3. 3 BGO transmission efficiency (2) Spectrum obtained without BGO fitted with gaussian+BG function. Peak~3.15 Through re- polished BGO Peak~2.36 Through BGO in original way of polishing. Peak~2.30 Transmission efficiency: ~75%(re-polished BGO) ~73%(original way of polishing)

4. 4 Comparison between normal cathode and prism one (1) 55 Fe(5.9keV) Hexagonal plastic scintillator BC404 (fast scintillator) wrapped with VM2000. 20cm long Re-polished BGO wrapped with teflon tape Two types of PMTs borrowed from TIT; a) R7899-mod1(normal cathode; S/N AA2190) b) R7899-mod2(prism cathode; S/N ZL1692) We compared the scintillator light yield between normal cathode PMT and prism cathode one in the condition close to PoGO mission(pp.5-6). We also investigated the HV dependence of the light yield(pp.7-8).

5. 5 Comparison between normal cathode and prism one (2) Normalized BG and 55 Fe spectra. (Live time is taken into account) 55 Fe background R7899-mod1 (normal cathode), -1000V BG subtracted spectrum fitted with poisson function. Npe~3.1. Spikes in spectrum are due to the mismatch between histogram binning and ADC resolution. Funny structure seen in ~3.5V needs to be investigated. Single photo-electron events Background is unstable? ???

6. 6 Comparison between normal cathode and prism one (3) Normalized BG and 55 Fe spectra. 55 Fe background R7899-mod2 (prism cathode), -1000V BG subtracted spectrum fitted with poisson function. Npe~3.5. Spikes in spectrum is due to the mismatch between histogram binning and ADC resolution. Funny structure seen in ~3.5V need to be investigated. Single photo-electron events ???

7. 7 Comparison between normal cathode and prism one (4) Normalized BG and 55 Fe spectra 55 Fe background R7899-mod2 (prism cathode), -1500V BG subtracted spectrum fitted with poisson function. Npe~3.6. Spikes in spectrum is due to the mismatch between histogram binning and ADC resolution. Funny structure seen in ~3.5V need to be investigated. Single photo-electron events Background is unstable? ???

8. 8 Comparison between normal cathode and prism one (5) Normalized BG and 55 Fe spectra Background 55Fe R7899-mod2 (prism cathode), -800V BG subtracted spectrum fitted with poisson function. Npe~3.45. Spikes in spectrum is due to the mismatch between histogram binning and ADC resolution. Single photo-electron events Background is unstable?

9. 9 Summary BGO transmission efficiency is ~75%. Although it does not depend on the way of polishing very much, Tune’s proposed way of polishing showed slightly better efficiency. Prism cathode PMT gives a little bit higher light yield (by ~10%) than normal cathode one. Absolute light yield is >=0.5 p.e./keV for 20cm fast scintillator (wrapped with VM2000) with BGO (wrapped with teflon tape). This does not depend on the applied voltage very much.