Evaluation of conversion coefficients from measurable to risk quantities for external exposure over contaminated soil by use of physical human phantoms |
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Authors: | V Golikov E Wallström T Wöhni K Tanaka S Endo M Hoshi |
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Institution: | Institute of Radiation Hygiene, Mira str. 8, St Petersburg, Russia. bazil@SG5816.spb.edu |
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Abstract: | Conversion coefficients from measurable quantities such as air kerma free-in-air or personal dose equivalent to effective
dose were determined by phantom experiments. Heterogenic anthropomorphic phantoms representing children of one and five years
age, and a Rando phantom representing an adult were exposed in the open field contaminated by different levels of radiocesium
in the upper soil layer, in a forest site and inside a wooden house. LiF thermoluminescent (TL) detectors were used inside
the phantoms for the estimation of organ doses and effective dose. Personal dosimeters similar to those used in radiation
protection for individual dose measurements were placed onto the phantom surface (chest area). The ratios of dose values in
separate organs to air kerma free-in-air varied from 0.69 to 1.15 for the children phantoms, and from 0.55 to 0.94 for the
adult phantom, respectively, when irradiated in the open field. Body size (weight) was found to be the most important factor
influencing the values of the conversion coefficients. The differences observed can reach approximately 40% when comparing
conversion factors from air kerma free-in-air to effective dose for adults and newborns. For conversion coefficients from
personal dose to effective dose, these differences can reach approximately 15%. The dependences of the various conversion
coefficients on body mass were quantified by regression analysis. The results were compared with those calculated for a plane
mono-energetic photon source having an energy of 700 keV and being located in the ground at a depth of 0.5 g cm−2. Calculated and measured conversion coefficients from air kerma free-in-air to effective dose agreed within 12%. |
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