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SDEX Shared Design Experience

Low Background Well Detector Improvement for Safeguards Measurements

Project Overview

Description:  Gamma spectroscopy with high purity germanium detectors (HPGe) are used to accurately identify radioactive isotopes by quantifying the gamma ray ‘signature’s unique to each radioisotope.   This is especially important for safeguards work and “finger printing” diverted materials.  Detection is relatively easy when the isotope of interest is fairly abundant in the sample.  When the isotope or radionuclides are at very low levels, positive detection can be difficult.  Creating a gamma spectroscopy system with a low background signal is crucial to detect trace levels of radionuclides for safeguards work.  One method for lowering the background on a gamma spectroscopy system is the use of a cosmic veto panel.  The veto panel, made of a scintillating plastic is placed over the radiation detector.  High energy background gamma rays (i.e. cosmic) interact in this veto panel prior to interacting in the HPGe detector.

Issue:  PNNL has a HPGe ‘well’ detector which it operates in the shallow underground laboratory.  The well detector is used to count samples for nuclear forensic and safeguards purposes, looking to detect trace radionuclide that provide an indication of the improper use of nuclear materials.  The system has a frame and veto panel,  however, the veto panel must be moved manually to access the detector.  This is inefficient and could lead to personal injury, damage to the PVT panel, or both.

Solution:  What is desired is modification to the frame holding the veto panel so that the panel would slide back and forth.  In addition, future improvements to the detector may require removal of the cave lid.  It’s desirable to have the frame that holds the PVT panel be robust enough to support upto 1000 pounds.  Considerations for the modified design include:

  • Handle a weight of 1000 lbs
  • Securely hold the veto panel and prevent inadvertent movement
  • Easily move or slide the veto panel and any shielding out of the way so samples can be placed on the detector
  • The panel is expected to be moved or cycled up to 5 times a day for years on end.
  • The materials must be approved for use in a class 10,000 clean room.

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