Organ Doses as a Function of Body Weight for Environmental Gamma Rays

Abstract

The organ doses for γ rays from typical environmental sources were determined with Monte Carlo calculations using anthropomorphic phantoms having different body sizes. It has been suggested that body weight is the predominant factor influencing organ doses for environmental γ rays, regardless of sex and age. A weight function expressing organ doses for environmental γ rays was introduced. This function fitted well with the organ doses calculated using the different phantoms. The function coefficients were determined mathematically with the least squares method. On the assumption that this function was applicable to organ doses for human bodies with diverse characteristics, the variances in organ doses due to race, sex, age and difference in body weight of adults were investigated. The variations of organ doses due to race and sex were not significant. Differences in body weight were found to alter organ doses by a maximum of 10% for γ rays over 100 keV, and 20% for low-energy γ rays. The doses for organs located deep inside a body, such as ovaries, differed between a newborn baby and an adult by a maximum factor of 2 to 3. For y rays over 100 keV, the variation was within a factor of 2 for all organs. The organ doses for adolescents more than 12 years agreed within 15% with those of the average adult.

KEYWORDS:

• organ doses
• effective dose equivalent
• body weight
• environment
• gamma rays
• phantoms
• Monte Carlo method
• transport calculation
• energy range
• race
• sex dependence
• adults
• age dependence