Uranium Detection Using Small Scintillators in a Maritime Environment Page: 4 of 16
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WSRC-CP-2006-00020
environments. The probability of detection is then based on the dose rate of the illicit
source since the background contribution is almost negligible.
For example, to test the ability to detect a significant quantity of HEU (90% 235U) at sea
consider the following two examples:
1. A 5 kg ingot of HEU metal will generate a radiation dose rate field of -6 R/hr at
2 meters from a detector, the approximate center of a cargo container. If the
container is filled with bulk material with average density of 0.5 gm/cm3, the dose
rate drops to a few nR/hr. If the 5 kg sample is low-fired oxide, the dose rate
increases to -30 R/hr at 2 meters with no other materials in the container. These
calculations were performed using the standard dose rate simulation code
MicroShield-4TM
2. A 40 gm sample of HEU inside a 0.25 inch metal can is calculated to generate a
-200 R/hr dose rate at 18 cm. While the 40 gm sample could possibly be
detected on land, the 5 kg sample would probably not trigger a terrestrial alarm at
2 meters.
To resolve unanticipated alarms, a small hand-held RIID with spectroscopic capability is
necessary to determine the radioisotopes responsible for the increased radiation. If the
RIID identifies 235U as a possible radiation source based on a spectrum similar to that
shown above (Figure 1), a suitable follow-on response is initiated.
Most current commercial off-the-shelf (COTS) hand-held radioisotope identifiers (RIID)
contain a small NaI(Tl) scintillator with built-in multichannel analyzer and custom
firmware to identify the isotopes responsible for the increased gamma radiation field.
These detectors are intended to discriminate between nuclear threat materials and
commonly encountered legitimate gamma-ray sources. The detection and identification
of the isotope 235U at levels sufficient to present reasonable cause for continued
investigations is necessary for continued national security. A suite of these COTS
instruments were tested at SRNL in a simulated maritime environment. The performance
of selected instruments has also been field tested in an extended maritime background
study on board ships at a number of maritime ports of entries (3). The results of the study
reported here represent a systematic evaluation of these RIIDs when exposed to 2U
sources as compared to measurements using a portable high resolution high purity
germanium (HPGe) spectrometer.
Instrumentation
Four different RIIDs were tested in this study which represent those commonly used by
US Customs and Border Protection, federal and local law enforcement agents, Port
Security officials and the US Coast Guard. Trained field agents use this equipment to
resolve radiation alarms received by personal radiation pagers or radiation portal
monitors (RPM). The hand-held RIIDs provide the field agents with an initial
identification of the possible source of radiation, i.e, medical, NORM, commercial or3
5/31/2006
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Hofstetter, K.; Donna Beals, D. & Ken Odell, K. Uranium Detection Using Small Scintillators in a Maritime Environment, article, May 12, 2006; [Aiken, South Carolina]. (https://digital.library.unt.edu/ark:/67531/metadc874052/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.