Date of Award

6-2005

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Larry W. Burggraf, PhD

Abstract

The purpose of this research is to improve the ability to image Special Nuclear Material (SNM) using a High Purity Germanium Double Sided Strip Detector (HPGeDSSD) for use in the field of nuclear nonproliferation. When used for gamma spectrometry, HPGe detectors can efficiently distinguish various isotopes because of their good energy resolution. The detector used for this research is a liquid nitrogen cooled germanium detector with five charge collection strips on each face. The strips are orthogonal to each other, creating a five by five array of data collection pixels. When the 25 mm by 25 mm detector array is coupled to a converging collimator an imaging system is achieved which provides the ability to image SNM sources which are larger than the detector crystal. For this work, an ideal converging collimator was designed, built and employed. The new collimator provided proper spatial resolution of all sources tested while still providing sufficient efficiency for imaging. Another system improvement is the addition of an OR gate which provides proper timing information, resulting in the ability to image using three strip events for the first time. A new image processing code was developed which employs the ability to use three strip events while reducing the time required to produce an image from approximately five hours down to less than a minute. Additionally, the new code demonstrates the ability to distinguish between multiple isotope sources in a single image through the simultaneous use of multiple energy windows. The system improvements developed during this work combine to improve the overall efficiency and flexibility of the imaging system. The capability to distinguish a point source from a distributed source, with proper spatial resolution, was demonstrated. This ability is the primary goal for developing this technology.

AFIT Designator

AFIT-GNE-ENP-05-09

DTIC Accession Number

ADA437935

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