Search

Two methods were proposed for determining alpha-particle fluence for radiobiological experiments. The first involved calculating the probabilities of hitting the target for alpha particles emitted from a source through Monte Carlo simulations, which when multiplied by the activity of the source gave the fluence at the target. The second relied on the number of chemically etched alpha-particle tracks developed on a solid-state nuclear track detector (SSNTD) that was irradiated by an alpha-particle source. The etching efficiencies (defined as percentages of latent tracks created by alpha particles from the source that could develop to become visible tracks upon chemical etching) were computed through Monte Carlo simulations, which when multiplied by the experimentally counted number of visible tracks would also give the fluence at the target. We studied alpha particles with an energy of 5.486 MeV emitted from an 241Am source, and considered the alpha-particle tracks developed on polyallyldiglycol carbonate film, which is a common SSNTD. Our results showed that the etching efficiencies were equal to one for source-film distances of from 0.6 to 3.5 cm for a circular film of radius of 1 cm, and for source-film distances of from 1 to 3 cm for circular film of radius of 2 cm. For circular film with a radius of 3 cm, the etching efficiencies never reached 1. On the other hand, the hit probability decreased monotonically with increase in the source-target distance, and fell to zero when the source-target distance was larger than the particle range in air., (© The Author 2016. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.)

An analytical analysis of the geometrical efficiency of a circular detector for particles with a finite range, emitted from a point-like source, is given. Several different cases were determined, depending on the particle range, radius of the detector and the position of the source with respect to the detector. These cases were analyzed separately and different expressions for calculating the hit probability were obtained for each of them. Results were compared with Monte Carlo calculations and good agreement was found. The problem considered here might be relevant for alpha-particle detection under specific conditions., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

In determining the etched track rate in solid-state nuclear track detectors, track lengths should be determined accurately. A method based on surface profilometry is proposed to determine the track lengths in CR-39 detectors through measurements of their replicas. Tracks from alpha particles with an incident energy of 4 MeV have been chosen to demonstrate the method. After irradiation and chemical etching, resin replicas were made from the tracks, of which the heights were measured by the Form Talysurf PGI Profilometer. The results showed that the surface of the replicas were smooth and the heights of the replicas were uniform, so the replicating fluid should have filled the tracks completely and the replicas truly reflected the dimensions of the tracks. The heights of the replicas were conveniently determined from the lateral view of the replicas generated by the Form Talysurf PGI Profilometer.

Quality factors of alpha particles emitted by radon progeny in the human lung have been calculated by using the formula recommended by the International Commission on Radiological Protection. Calculations have been carried out for different combinations of sources, energies, and targets. The values obtained are between 20 and 26, with an average of about 24. These are comparable to previously published results for the human lung and for the general consideration of alpha particles emitted in tissue.

A model for bifurcation regions of the human tracheo-bronchial tree was developed. Equations for the surfaces are given to enable calculations of doses from alpha-particles emitted in these regions. It has been found that a bifurcation region is well approximated by a quasi-ellipsoid. The absorbed fractions of alpha-particles emitted in bifurcation regions were calculated by the Monte Carlo method. The average absorbed fraction under the bifurcation geometry is close to that found under the cylindrical geometry in the bronchial region. In the bronchiolar region, the absorbed fractions under the bifurcation geometry are up to 20% larger than those under the cylindrical geometry.

Purpose: To determine the distribution of lineal energy in the target cells and the parameters of distribution for various combinations of sources, targets and energies in the human tracheobronchial tree. Frequency average and average of the square of the lineal energy were also calculated from the lineal energy distribution., Method: A model was created to simulate the geometric distribution of cell nuclei in the airway of the tracheobronchial tree. Propagation of alpha particles in such a model was simulated by the Monte Carlo method. Microdosimetric distributions of lineal energy were calculated., Results: Distributions of lineal energy were substantially different for basal and secretory cells. The frequency average of specific energy was found to be between 0.3 Gy and 0.4 Gy., Conclusions: Interactions of alpha particles with basal and secretory cells show significant differences: events with small energy transfer are dominant for basal cells, while those with large transfer are dominant for secretory cells. This finding can influence dose weightings and yield lower values of the dose-to-exposure coefficient.

The present work aims to develop a semi-analytical method to calculate the absorbed dose delivered by alpha particles in a cylindrical geometry. This method will be employed to reproduce the dose conversion coefficients or absorbed fraction of alpha particles in sensitive cells of the tracheobronchial tree obtained by NRC and ICRP, respectively. The difference caused by using water stopping power and tissue stopping power will also be investigated. Linear stopping powers for alpha particles in tissue and air were calculated, and the dependences of stopping powers on the traveled distance were established. A geometry model is set up for our calculations, and two different cases have been considered, namely the near-wall and far-wall cases. The total energy imparted to a unit-diameter sphere around a point is shown to be obtainable from a triple integral, which can be solved numerically. The absorbed dose is found to be independent of the diameter of the sphere being considered and additional assumptions about its diameter were not needed. The results obtained are in good agreement with those obtained previously by NRC and ICRP66. Using the semi-analytical method developed in the present work, the dose conversion coefficients or absorbed fraction previously obtained by NRC and ICRP, respectively, have been satisfactorily reproduced. Using the tissue stopping power instead of the water stopping power can slightly lower the values for dose conversion coefficients in the bronchial region.

The purpose of the present work was to calculate the specific energy distribution in sensitive cells of the human lung. Specific energy distributions were calculated by applying Monte Carlo methods and the ICRP 66 model of the human respiratory tract. Specific energies were calculated at various depths in the epithelium and combined according to the relative cell abundance. Distributions are given for various combinations of sources, alpha-particle energies, targets and regions of the lung. The chord length does not follow the triangular distribution when the particle range is comparable to the diameter of the target. The notion of "effective volume" is introduced and defined, which is needed for estimation of hit frequency in some particular targets. It has been shown that basal cells are subjected to a larger proportion of alpha-particle hits with small energy transfer than secretory cells. Small energy transfer events that lead to minor damage of the DNA are more efficient in cancer induction than are hits with large energy deposition that lead to cell killing.

The sensitivity to different relevant parameters of the absorbed fraction of alpha particles emitted from the 222Rn chain in sensitive cells of the tracheo-bronchial tree have been investigated. The structure of the airway wall given by ICRP (ICRP66) has been adopted and employed in the present calculations. The source thickness (mucous gel and sol + cilia), target layer thickness and the depth of the sensitive layers have been varied within reasonable ranges around the default values recommended by ICRP66. The results have shown that the depth of the sensitive layers is the most important parameter in calculating the absorbed fraction. In addition, dose conversion coefficients were calculated and presented along with the absorbed fractions.

Purpose: To calculate the hit probabilities by alpha-particles emitted by radon progeny for basal and secretory cell nuclei in the epithelium of the human tracheobronchial tree., Materials and Methods: The equilibrium activities on the surface of airway tubes were calculated using the ICRP66 model. The stopping-power and ranges of alpha-particles in tissue were adopted from ICRU49. A semi-analytical method for determining the alpha-particle fluence rate in tissue was applied. The distributions of secretory and basal cells throughout the tracheobronchial tree were as given by Mercer et al. (1991)., Results: The probability to hit basal cell nuclei is three-to-four times smaller than for secretory cell nuclei in the bronchial region (BB). However, the total number of traversed basal cell nuclei is greater because of the larger volume abundance of basal cells in BB. The total number of secretory cell nuclei hit in the bronchiolar region (bb) is larger than that in BB because the volume abundance of secretory cells in bb is larger than that in BB., Conclusions: Basal cells are more sensitive to alpha-radiation than secretory cells. This finding is based on the analysis of the relative number of cell hits and the relative frequencies of lung cancer induction in BB and bb.