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Mirion Fast-Track-Fibre™(FTF) Portal Monitor Characterized for Response to Internal and Externally Deposited Radionuclides
Posted on February 20th, 2015

Photon radiation portal monitors are commonly used as an element of radiation protection programs at nuclear facilities worldwide. These radiation monitors are primarily used for personnel monitoring of external contamination, but also have the ability to detect internally deposited radionuclides. Understanding the sensitivity of the radiation portal monitor to both externally and internally deposited radioactivity of single radionuclides or of radionuclide mixtures is an important element in assessing the potential total effective dose equivalent (TEDE) to facility personnel.  

The Mirion, Fast-Track-Fibre™(FTF) portal monitor was characterized for response to internal and externally deposited radionuclides using an anthropomorphic phantom. Detection efficiencies were measured with sources placed at internal and external positions on a phantom, using both static (stationary) and pass-through portal monitor detection modes.

The efficiencies of multiple radionuclides with widely varying photon energies, including Am-241, Co-57, Ba-133, Cs-137, Co-60, Cd-109 and Mn-54, were evaluated in order to determine the FTF’s energy response curve. This response curve, in terms of efficiency as a function of energy, allowed for the calculation of the minimum detectable activity (MDA) minimum detectable intake (MDI), and minimum detectable committed effective dose equivalent (MDCEDE) per alarm for any photon emitting radionuclide mixture. The FTF was also analyzed for activity linearity, background linearity, single detector uniformity and total detector uniformity.

It was found that the minimum detectable activity for internally deposited Cs-137 in the abdomen was approximately ten times higher for pass-through versus static measurements. Additionally, it was found that the minimum detectable activity for Cs-137 in the abdominal region for both internal and external pass-through scenarios are nearly equivalent. In general, if the expected radionuclide source term is primarily non-transuranic, the pass-through mode offers sufficient sensitivity to identify potential overexposures while providing much greater personnel throughput. However, minimum detectable committed effective doses for transuranics such as Am-241, show potential for personnel over exposure if the radionuclide mixture contains a significant fraction of transuranics. It is therefore recommended that nuclear facilities evaluate their radionuclide source term in order to bound potential personnel doses. 

The full report of this research conducted by RSCS was published in Operational Radiation Safety, Vol. 107, No. 3, November 2014.  This report can also be viewed here.

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