USGS - science for a changing world


Gamma-ray Spectrometer System






The detector assembly (manufactured by Harshaw Chemical Co.) for the gamma-ray spectrometer system consists of a 6" by 6" NaI(Tl) crystal in an aluminum housing bolted to a 10-stage photomultiplier tube (PMT). The detector assembly is connected to an EG&G Ortec ScintiPack photomultiplier base (Model 296) using a standard JEDEC B14-38 socket with 14 pins. The photomultiplier base is 2.2” in diameter by 6.75” in length. The detector assembly with the attached photomultiplier base measures 18.75" high. The photomultiplier base incorporates a low-power, adjustable, high-voltage supply and preamplifier. This is connected by a single cable to an amplifier on an EG&G Ortec MicroACE PCI card installed inside an IBM-compatible 200 Mhz PC running Microsoft’s Windows 98 SE (second edition) operating system.  The photomultiplier base is the brown cylinder with an attached cable. The PMT is inside the dark gray bell-shaped light shield shown in the image below.  The aluminum housing containing the NaI(Tl) crystal (not visible in photo) is located below the PMT.



Photomultiplier Tube Inside Castle


View of Photomultiplier Tube with EG&G

photomultiplier base inside lead castle.

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The detector assembly is held in place by a support assembly made from two 1/2" inch thick aluminum plates, which is located inside an 16" by 16" chamber with 8” thick walls of lead bricks.  In the image below, the PMT is inside the dark gray housing, which is bolted to the aluminum crystal housing extending through holes drilled in the aluminum plates.  Click here for details on the design and construction of the lead castle and of the detector support assembly.  



Photomultiplier Tube in support assembly


Photomultiplier Tube in support assembly.

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For more information about this report contact: Stephen L. Snyder or Joseph S. Duval
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