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Scintillation Crystals and X-Rays

May 7, 2008

Here are a few photos of inorganic scintillators glowing from exposure to a ~ 300 R / hr x-ray field. These were all long digital exposures, 5-15 seconds, taken last year, and all had to be de-speckled extensively due to radiation noise on the camera CCD.

Bismuth germanate (BGO) crystals from a PET scanner. Lovely cyan glow, not particularly well-matched to photomultiplier tubes but gorgeous to the human eye. Dense, and a wicked photoabsorber of gamma rays, BGO is well-suited to portable homebrew scintillation detectors.

Barium fluoride, a material of choice for fast pulse-mode gamma detectors. Much of the light emission is in the ultraviolet, and to the eye the glow appears a deep purple color. Perhaps there’s a use for this in fast neutron detectors based on inelastic scattering on F-19?

Sodium iodide doped with thallium (NaI:Tl), the old standard for gamma spectrometry and high-class uranium prospecting. This 3″ x 1″ crystal is hermetically sealed because the NaI is hygroscopic. The rich blue glow resulting from exposure to a 60 microcurie radium source is literally bright enough to read by. Next to the x-ray machine, it shines like a spotlight!

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