Operator related attenuation effects in radiometric surveys

Abstract

Radiometric surveys using airborne, vehicular mounted or backpack detector systems are increasingly used to identify and evaluate complex distributions of radioactivity in the environment. The signals detected depend on the energy and spatial distribution of radioactive sources, the material properties of the environment and the specific properties of the detector systems employed. Materials in close vicinity to the detector such as housings, and intermediate materials may have a critical impact on detection efficiency, and must therefore be taken into account in calibration. This study evaluates the effect of shielding by the body of the operator in backpack surveys. Controlled experiments using point sources and absorbers, chosen to represent the form and composition of human tissue, were conducted, and coupled to an analytical radiation transport model to estimate attenuation factors for mapping of 137 Cs. In this way generic factors to correct for this effect using portable spectrometers have been determined. The results compare well with observations at sampled calibration sites in Fukushima and the Solway area in Scotland. Reductions of the 137 Cs fullenergy peak intensity between 20% and 30% may be expected depending on operator stature and the offset position of backpack systems. Similar effects may be present for other radiometric systems carried by a human operator.2 Keywords: Environmental radioactivity, gamma ray survey, attenuation by human operator Highlights:• Evaluation of operator effects on radiometric measurements with backpack systems• Potential for similar effects with other radiometric systems• Count rates for radiocaesium full energy peaks are reduced by 20-30%• Count rates for >450 keV, scaling to dose rate, are reduced by approximately 15%

Using two detectors concurrently to monitor ambient dose equivalent rates in vehicle surveys of radiocesium contaminated land

“…Employing a more controlled calibration environment, where the radiation source type and detector positioning and shielding can be controlled in a systematic way (e.g. Buchanan et al, 2016), would be effective in terms of understanding these factors.…”

“…The H1 results were from a survey with the hand-held instrument conducted on April 16, 2015. The three results were decay corrected to February 9, 2016 for comparison with the DMVj measurements.2.4Measurements to check the effect of vehicle occupant number and fuel levelBuchanan et al (2016) highlighted that vehicle fuel level and number of occupants could present time-varying sources of shielding for radiation detection equipment in vehicle-borne surveys. To check the size of these effects, on 17 th March 2017 we measured De and Hi at four test sites with varying occupant number (0-3 occupants) and…”

Assessment of the calibration of gamma spectrometry systems in forest environments

“…1. Angular response measurements in laboratory conditions using a 137 Cs (662 keV) source predict that this collimator attenuates 42% of radiation from above, and 22% of radiation from the ground in open field conditions (Sanderson et al, 2016;Buchanan et al, 2016).…”

Airborne radiation mapping: overview and application of current and future aerial systems

“…Moreover, this method is only applicable in accessible areas and where data collection is within the safe exposure limits of the operator, which make this method unsuitable for a first response survey due to the unknown intensity. In addition, the operator will attenuate a significant amount of the radiation that would otherwise reach the detector, reducing the measured intensities by 20-35% (Buchanan et al 2016;Jones and Cunningham 1983). Whilst the housing around any detector will also shield radiation, the effect of this is less pronounced, systematically constant, and well constrained in comparison to human shielding -for which currently no comprehensive comparison currently exists for varying body types.…”