2005 Fiscal Year Final Research Report Summary
Angular Response of Photomultiplier Tubes to Determine Photon Yield in Inorganic Scintillators
| Project/Area Number |
16560047
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied physics, general
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| Research Institution | Saitama Prefectural University (2005)
Saitama Prefectural University. Junior College (2004) |
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Principal Investigator |
SHIBAMURA Eido Saitama Prefectural University, College of Health and Social Services, Professor, 保健医療福祉学部, 教授 (30100605)
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| Co-Investigator(Kenkyū-buntansha) |
SASAKI Shinichi KEK, Radiation Science Center, Associate Professor, 放射線科学センター, 助教授 (80178649)
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| Project Period (FY) |
2004 – 2005
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| Keywords | photomultiplier / scintillation / photocathode / photon yield / angular response / quantum efficiency / reflectance |
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| Research Abstract |
We have measured reflectance and photon-to-electron conversion efficiency of photomultiplier tubes (PMTs ; Hamamatsu R878, R375 and 7696) using three-color LED emitting photons with central wavelengths of 470,525, and 640nm. The use of a light guide with a refractive index similar to that of a photomultiplier window enabled the measurement at the angle of incidence to a photocathode up to 75°. An appreciably large reflectance and conversion efficiency were obtained at the angles of approximately 45 and 60°, respectively. We found that these PMTs work with a higher photon-to-electron conversion efficiency than the quantum efficiency given by the manufacturer in many cases of scintillation counting. The reflectance measured in this study is consistent with that calculated using an optical model, where the photocathode was a thin film with a complex refractive index. For example, photocathode of R878 PMT was 35nm in thickness and the refractive index was 3.0+0i at 470nm, 3.2+0.7i at 525nm, and 2.8+0.3.i. at 640nm.
Using these properties of PMTs, we determined the average energy to produce one scintillation photon W_s for 662keV gamma-rays in NaI(Tl) and CsI(Tl) crystals to be 15.0+/-1.3eV and 13.3+/-1.1eV, respectively, from the absolute numbers of photoelectrons measured for several combinations of a crystal and a PMT used as a vacuum photodiode. The numbers of scintillation photons were obtained by calculating the collection efficiency of scintillation photons at the photo-cathode using Monte-Calro simulations and by determining experimentally the conversion efficiency from photons to photoelectrons at PMT photocathode. The values of W_s determined in the present study are in good agreement with the theoretical values presented recently. The factors affecting energy resolutions were also studied and the calculated resolution agreed well with that obtained experimentally.
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