Compton suppression system at Penn State Radiation Science and Engineering Center |
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Authors: | N Ö Çetiner K Ünlü J S Brenizer |
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Institution: | (1) Penn State Radiation Science and Engineering Center, University Park, PA 16802, USA |
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Abstract: | A Compton suppression system is used to reduce the contribution of scattered gamma-rays that originate within the HPGe detector
to the gamma-ray spectrum. The HPGe detector is surrounded by an assembly of guard detectors, usually NaI(T1). The HPGe and
NaI(T1) detectors are operated in anti-coincidence mode. The NaI(T1) guard detector detects the photons that Compton scatter
within, and subsequently escape from the HPGe detector. Since these photons are correlated with the partial energy deposition
within the detector, much of the resulting Compton continuum can be subtracted from the spectrum reducing the unwanted background
in gamma-ray spectra. A commercially available Compton suppression spectrometer (CSS) was purchased from Canberra Industries
and tested at the Radiation Science and Engineering Center at Penn State University. The PSU-CSS includes a reverse bias HPGe
detector, four annulus NaI(T1) detectors, a NaI(T1) plug detector, detector shields, data acquisition electronics, and a data
processing computer. The HPGe detector is n-type with 54% relative efficiency. The guard detectors form an annulus with 9-inch
diameter and 9-inch height, and have a plug detector that goes into/out of the annulus with the help of a special lift apparatus
to raise/lower. The detector assembly is placed in a shielding cave. State-of-the-art electronics and software are used. The
system was tested using standard sources, neutron activated NIST SRM sample and Dendrochronologically Dated Tree Ring samples.
The PSU-CSS dramatically improved the peak-to-Compton ratio, up to 1000:1 for the 137Cs source. |
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