Dust Particle Size Effect on Absorbed Fractions Value in the Anterior Nose

Dr. Hanna M. Moussa
University of Tennessee
Department of Nuclear Engineering

Radioactive sources that emit alpha, beta, gamma and electrons are carried in air by dust particles, once air enter the nasal vestibule (the extrathoracic region ET1), the first region in the respiratory system, and this region act as the first filter for the system where the dust particles stopped by the hair and deposited on the anterior surface of the ET1.  for electron emitters, Since the radioactive atom that carried by dust particle decay by electron with a specific energy, the energy lost by the electron is dependent on the position of the atom in the dust particle, and on the energy of the electron and on the dust particle size.  Consequently the absorbed fraction calculated for the Basel cells layer in the ET1 for the truncated cone model will be dependent on the above factor.  In this work we estimated the absorbed fraction for the basel cell layer in the ET1 region given that the electron lost some of its energy after it passing different dust particle sizes by extthe dust particle   of Particle deposition in the respiratory tract, has been, and continues to be an intensive area of radiation research.  Experimental data are available for Caucasian adult males and for a specific range of particle sizes (from about 1 mm to 10 mm aerodynamic diameter) (ICRP 66, 1994).  The aerodynamic diameter dae is the diameter (mm) of a unit density (1 g cm-3) sphere that has the same terminal settling velocity in air or the particle interest.  The radionuclides are carried in the air on dust particles and deposited on the inner surface of the nose.  Therefore, when these radionuclides decay (electron or alpha decay), they lose some of their energy to the carrier (absorption in the dust particle) before entering the nose tissue.  As a result, the electrons or alpha particles enter the nose tissue with less energy and consequently deposit less energy in the target (basal cells).  Absorption in dust particles was not considered at all in ICRP Publication 66.  In this chapter we describe a Matlab® program developed to calculate the energy deposition from electrons inside spherical dust particles.  In the program, the dust particle radii range from 0.5 mm to 50 mm.  The electrons are uniformly generated anywhere within the volume of the dust particle.  Therefore the distance traveled by the electron can range from zero up to the diameter of the dust particle.   The number of source electrons followed is 100,000.  The electron absorbed fraction is estimated based on the energy spectrum.  For comparison, the electron absorbed fraction in ET1 obtained using a 5 mm dust particle radius with the electron generated in the center, and the output from the Matlab® program is made.  The electron is assumed to travel in a straight line to the surface.