This research investigates the use of G-M counters to triage the individuals who have been exposed to a Radiological Dispersal Device (RDD). Upon being exposed to an RDD, inhalation of the airborne radionuclide is a method which someone can receive a considerable amount of dose. Bioassay via analysis of excreta is a commonly used method of determining the dose received, yet it would be cumbersome if there are a large number of people needing to be screened. An in vivo method must be considered so that a non-intrusive and more efficient triaging method can be implemented. Whole body counters are commonly used in counting facilities as an in vivo bioassay method, yet they are limited in number and not easily portable. Therefore, a more portable and more common detection device should be considered. G-M survey meters are common devices that are highly portable, making them ideal candidates to fulfill this necessity. The ease of use contributes to the viability of the device as a portable, in vivo screening device. To analyze this detector, a Monte Carlo model of the detector was created to be used in simulations with the Medical Internal Radiation Dose phantoms. The detector was placed in a few locations on the phantoms. Four locations were strategically chosen for detector placement: the posterior upper right torso, the anterior upper right torso, the lateral upper thigh, and the anterior of the neck. Six phantoms were considered: Reference Male, Female, Adipose Male, Adipose Female, Post Menopausal Adipose Female, and a Child. Six radionuclides were investigated: Am-241, Co-60, Cs-137, I-131, Ir-192, and Sr-90. The nuclides were distributed throughout the phantoms according to Dose and Risk Calculation Software, a code that determines how a radionuclide is distributed over time upon inhalation, ingestion, or injection. A set of time dependent guidelines were developed, determining the count rate per unit dose inhaled for each detector location and phantom type.

The detonation of a radiological dispersion device (RDD) may result in a situation where many individuals are exposed to contamination due to the inhalation of radioactive materials. Assessments of contamination may need to be performed by emergency response personnel in order to triage the potentially exposed public. The feasibility of using readily available standard 2x2-inch sodium-iodide detectors to determine the committed effective dose to a patient following the inhalation of a radionuclide has been investigated. The 2x2-NaI(Tl) detector was modeled using the Monte Carlo simulation code, MCNP-5, and was validated via a series of experimental benchmark measurements using a polymethyl methacrylate (PMMA) slab phantom. Such validation was essential in reproducing an accurate detector response. Upon verification of the detector model, six anthropomorphic phantoms, based on the MIRD-V phantoms, were modeled with nuclides distributed to simulate inhaled contamination. The nuclides assessed included Am-241, Co-60, Cs-137, I-131, and Ir-192. Detectors were placed at four positions on the phantoms: anterior right torso, posterior right torso, anterior neck, and lateral left thigh. The detected count-rate varied with respect to detector position, and the optimal detector location was determined on the body. The triage threshold for contamination was set at an action level of 250-mSv of intake. Time dependent biokinetic modeling was employed to determine the source distribution and activity in the body as a function of post-inhalation time. The detector response was determined as a function of count-rate per becquerel of activity at initial intake. This was converted to count-rate per 250-mSv intake for triage use by first responders operating the detector to facilitate triage decisions of contamination level. A set of procedure sheets for use by first responders was compiled for each of the phantoms and nuclides investigated.