Measuring Light Reflectance of BGO Crystal Surfaces

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A scintillating crystal's surface reflectance has to be well understood in order to accurately predict and optimize the crystal?s light collection through Monte Carlo simulations. In this paper, we measure the inner surface reflectance properties for BGO. The measurements include BGO crystals with a mechanically polished surface, rough-cut surface, and chemically etched surface, and with various reflectors attached, both air- coupled and with coupling compound. The measurements are performed with a laser aimed at the center of a hemispherical shaped BGO crystal. The hemispherical shape eliminates any non-perpendicular angles for light entering and exiting the crystal. The reflected light is ... continued below

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Janecek, Martin & Moses, William July 28, 2008.

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A scintillating crystal's surface reflectance has to be well understood in order to accurately predict and optimize the crystal?s light collection through Monte Carlo simulations. In this paper, we measure the inner surface reflectance properties for BGO. The measurements include BGO crystals with a mechanically polished surface, rough-cut surface, and chemically etched surface, and with various reflectors attached, both air- coupled and with coupling compound. The measurements are performed with a laser aimed at the center of a hemispherical shaped BGO crystal. The hemispherical shape eliminates any non-perpendicular angles for light entering and exiting the crystal. The reflected light is collected with an array of photodiodes. The laser can be set at an arbitrary angle, and the photodiode array is rotated to fully cover 2? of solid angle. The current produced in the photodiodes is readout with a digital multimeter connected through a multiplexer. The two rows of photodiodes achieve 5-degree by 4-degree resolution, and the current measurement has a dynamic range of 10^5:1. The acquired data was not described by the commonly assumed linear combination of specular and diffuse (Lambertian) distributions, except for a very few surfaces. Surface roughness proved to be the most important parameter when choosing crystal setup. The reflector choice was of less importance and of almost no consequence for rough-cut surfaces. Pure specular reflection distribution for all incidence angles was measured for polished surfaces with VM2000 film, while the most Lambertian distribution for any surface finish was measured for titanium dioxide paint. The distributions acquired in this paper will be used to create more accurate Monte Carlo models for light reflection distribution within BGO crystals.

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  • Journal Name: IEEE Transaction on Nuclear Science; Journal Volume: 55; Journal Issue: 5, part 1; Related Information: Journal Publication Date: October 2008

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  • Report No.: LBNL-1790E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 952861
  • Archival Resource Key: ark:/67531/metadc930068

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  • July 28, 2008

Added to The UNT Digital Library

  • Nov. 13, 2016, 7:26 p.m.

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  • Nov. 18, 2016, 4:21 p.m.

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Janecek, Martin & Moses, William. Measuring Light Reflectance of BGO Crystal Surfaces, article, July 28, 2008; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc930068/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.