Electron Absorbed Fractions Based on a New Model of the Anterior Nasal Passage

Abstract

In a previous work we reported that the fraction of the electron energy absorbed in the basal cell layer of the anterior nasal passages was not very sensitive to changes in the surface area or radius of the cylindrical model adopted in Publication 66 of the International Commission on Radiological Protection. These absorbed fraction data are used in calculation of the dose to a 10-microm-thick basal cell layer located at a depth of 40 microm in the epithelial cell layer of the extrathoracic (ET1) region. However, these data may only be applicable to the assumed cylindrical geometry and may not be valid for more realistic ET1 geometries. The nose differs in size and shape from one person to another, its shape is not cylindrical but closer to a truncated elliptical cone, and in most humans the nostrils are elliptical in shape. We propose herein a more realistic geometry model, the frustum of a cone, for the anterior nose region (ET1) as an alternative to the cylinder model provided in ICRP 66. The results of absorbed fraction calculations using MCNP4B with the new model are reported. These absorbed fractions are compared to the values previously obtained using the MCNP4B code and a cylindrical model (10 cm2 surface area). We also investigate the effects of changing the size of the truncated cone to represent variations due to sex and age.

Dust Particle Size Effects on Absorbed Fraction Values in the Anterior Nose

“…1 and 2, for dust particle diameters (d e ) of 2, 10, and 20 m, and in Fig. 3 for dust particle diameters (d e ) of 50 and 100 m. These figures each include, for comparison purposes, absorbed fractions calculated previously (Moussa et al 2004) for a source distribution with no self-attenuation (i.e., curve labeled as "No dust"). In this comparison dust particle sizes are grouped in two groups: a small-sized group that contains dust particles of diameters up to 20 m and a large-sized group that contains dust particle diameters greater than 20 m. In the small-sized group and for electron energies Յ0.1 MeV, the attenuation effects of small dust particle sizes (diameters of 2 m to 20 m) are clearly shown in Fig.…”

“…A truncated cone model, presented previously as an alternative to the ICRP 66 cylinder model (Moussa et al 2004), is used to represent the nasal vestibule (the inner surface area is 10 cm 2 ; upper and lower circular radii are 0.399 and 0.764 cm respectively; and the truncated cone height is 2.55 cm). The materials used in the estimations were air and water (a surrogate for tissue).…”

“…The spherical dust particle's equivalent volume diameter d e ranges from 2 m to 100 m. The number of source electrons generated and followed in each case is 100,000. The electron absorbed fraction is estimated based on the emerging energy spectrum, and compared to the original absorbed fraction values published previously (Moussa et al 2004). The Monte Carlo simulation program was written under the following assumptions: (1) radioactivity is assumed to be uniformly distributed throughout the volume of spherical dust particle; (2) the chemical composition of the dust particles is assumed to be equivalent to reference soil (Eckerman and Ryman 1993) with density of 3 g cm Ϫ3 ; and (3) electrons emitted in the dust particle are assumed to travel in straight-line trajectories to the dust particle surface and lose energy in a continuous manner.…”

“…If an electron moves a distance S in a straight line from its origin to the surface of the sphere, then (following Moussa et al 2004) the distance S can be expressed as:…”

“…where y i is a fraction representing the number of electrons emerging from the dust particle with energy E i normalized to the number of histories used (i.e., 100,000) and AF i is the absorbed fraction (from Moussa et al 2004) corresponding to energy E i .…”