Effective dose equivalent and effective dose for photon exposures from point and disk sources on the floor.

Abstract

A complete set of H(E) and E values were calculated for photon exposures from point and disk sources on the floor using the MCNP code and a "hermaphroditic" phantom. It was found that a male can receive a higher H(E) or health risks than a female by a factor of two from an identical point source on the floor when source distance is less than 50 cm. Conversely, if the source distance becomes larger than 100 cm, the female receives H(E) higher than the male by up to 40%. For identical sources, both the male and female experience significantly higher H(E) from front-located sources than from back- or side-located sources. For a 100-cm source distance, male H(E) from a front-located source is greater than that from a side-located source by factors of 4, 3, and 2 for 0.08, 03, and 1.0 MeV photons, respectively. In the female cases, the differences are somewhat smaller but still differ by factors of 3, 2, and 1.7. It was also found that both the highest male and female H(E) values occur when a source is within 40-60 cm in front of the phantom. The maximum male H(E) is 1.8 x 10(-18), 6.6 x 10(-18), and 2.1 x 10(-17) Sv per photon emission for 0.08, 03, and 1.0 MeV photons, respectively. For females, these maximum values are slightly smaller, 1.4 x 10(-18), 5.3 x 10(-18), and 1.9 x 10(-17) Sv/photon, respectively. Tissue kerma free-in-air at 100 cm above a disk source (Ktissue) was found to greatly overestimate H(E) if the source radius is less than 200 cm. For radii larger than 200 cm, the Ktissue gives a relatively better estimate of H(E), overestimating by not more than 100%. The point source H(E) values were directly integrated to estimate H(E) for simple non-self-shielding sources such as disk, circle, and line sources. This simple approach was found to overestimate H(E) by less than 10% for these irradiation geometries. Finally, the comparison of H(E) and E showed that for most cases these values are almost identical. For point sources, when source distance is larger than 50 cm, the difference between H(E) and E was always less than 23% over photon energies between 0.08 and 1.0 MeV. For disk sources of radius larger than 50 cm, the difference was even smaller (<12%).