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Abstract 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. [ABSTRACT FROM AUTHOR]

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The present work introduced a framework to investigate the effectiveness of proton boron fusion therapy (PBFT) at the cellular level. The framework consisted of a cell array generator program coupled with PHITS Monte Carlo package with a dedicated terminal-based code editor that was developed in this work. The framework enabled users to model large cell arrays with normal, all boron, and random boron filled cytoplasm, to investigate the underlying mechanism of PBFT. It was found that alpha particles and neutrons could be produced in absence of boron mainly because of nuclear reaction induced by proton interaction with 16O, 12C and 14N nuclei. The effectiveness of PBFT is highly dependent on the incident proton energy, source size, cell array size, buffer medium thickness layer, concentration and distribution of boron in the cell array. To quantitatively assess the effectiveness of PBFT, of the total energy deposition by alpha particle for different cases were determined. The number of alpha particle hits in cell cytoplasm and nucleus for normal and 100 ppm boron were determined. The obtained results and the developed tools would be useful for future development of PBFT to objectively determine the effectiveness of this treatment modality. [ABSTRACT FROM AUTHOR]

The CR-39 nuclear track detector is used in many nuclear diagnostics fielded at inertial confinement fusion (ICF) facilities. Large x-ray fluences generated by ICF experiments may impact the CR-39 response to incident charged particles. To determine the impact of x-ray exposure on the CR-39 response to alpha particles, a thick-target bremsstrahlung x-ray generator was used to expose CR-39 to various doses of 8 keV Cu-Kα and Kβ x-rays. The CR-39 detectors were then exposed to 1-5.5 MeV alphas from an Am-241 source. The regions of the CR-39 exposed to x-rays showed a smaller track diameter than those not exposed to x-rays: for example, a dose of 3.0 ± 0.1 Gy causes a decrease of (19 ± 2)% in the track diameter of a 5.5 MeV alpha particle, while a dose of 60.0 ± 1.3 Gy results in a decrease of (45 ± 5)% in the track diameter. The reduced track diameters were found to be predominantly caused by a comparable reduction in the bulk etch rate of the CR-39 with x-ray dose. A residual effect depending on alpha particle energy is characterized using an empirical formula. [ABSTRACT FROM AUTHOR]

The track etch detector, CR-39, in common usage, is highly sensitive to recording charged particles. CR-39 polymer samples were irradiated with alpha particles at different energies (2.17 MeV and 3.95 MeV) followed by chemical etching with different times (1.50, 3.00 and 6.00 h). Tire tracks formed in CR-39 due to irradiations were visualized by using etching technique. The optical properties of the CR-39 polymer before and after the etching processes were studied with ultraviolet-visible (UV-vis) spectroscopy. The optical band gap energy was calculated for the CR-39 polymer samples. The average value of the track diameter of irradiation at 2.17 MeV and etching time 1.5 h is fairly large compared with its value at 3.95 MeV. This is due to the production of defect levels in the band gap of polymer at the 2.17 MeV. The results revealed that the CR-39 samples at 3.00 h are insensitive to the optical variations in the fundamental absorption edge. [ABSTRACT FROM AUTHOR]

The calculating the probability of the cell killing per hit, from radon progeny, requires the development of morphometric model of the human airway system. This study is focused on the different modeling concept. For example, several morphometric lung models have been published which differ in terms of airway structure and lung volume, there by affecting the particle deposition efficiencies. The present variety of modeling concepts suggests that the choice of specific modeling assumptions is as important for dose risk estimates as the choice of proper parameter values. The model of human lung analysed in the present study differ from those employed in the ICRP66 model, dose estimates will consequently differ from ICRP66 predictions, because its included the area of the branching the cylinders (airways tube) in the human lung. A analytical model cylinder bifurcation was created to simulate the geometry of human lung with the geometric distribution of cell nuclei in the airway wall of the tracheobronchial tree. Reported probabilities are calculated for various targets and alpha particle energies in order to show dependence of the probability of cell killing per hit from alpha particle energies and the geometry of tracheobronchial tree for the human lung, created in this study. [ABSTRACT FROM AUTHOR]

The response of CR-39 nuclear track detector (TasTrak®) to protons in the energy range of 0.92-9.28 MeV has been studied. Previous studies of the CR-39 response to protons have been extended by examining the piece-to-piece variability in addition to the effects of etch time and etchant temperature; it is shown that the shape of the CR-39 response curve to protons can vary from piece-to-piece. Effects due to the age of CR-39 have also been studied using 5.5 MeV alpha particles over a 5-year period. Track diameters were found to degrade with the age of the CR-39 itself rather than the age of the tracks, consistent with previous studies utilizing different CR-39 over shorter time periods. [ABSTRACT FROM AUTHOR]

Biological effects of radiation in terms of their effect on living cells are considered in this work. In dosimetry of the human lung exist the need to include the influence of the biological effects. The aim of this work is to calculate the probability of biological effects (transformation cell and production of lesion) per hit induced by alpha particle radiation on sensitive cells of human lung. Probability was calculated by applying the analytical model cylinder bifurcation (Nikezić et al., Int J Radiat Biol 79(3):175-180, ; Nikezić and Yu, Radiat Environ Biophys 42:49-53, ) which was created to simulate the geometry of human lung with the geometric distribution of cell nuclei in the airway wall of the tracheobronchial tree. This analytical model of the human traheobronchial tree represent the exstension of the ICRP66 model, and follows it as much as possible. Reported probabilities are calculated for various targets and alpha particle energies in order to show dependence of the probability of biological effects (transformation cell and production of lesion) per hit from alpha particle energies and the geometry of tracheobronchial tree for the human lung. [ABSTRACT FROM AUTHOR]

In the present technique, an amount of radon gas (2210 ± 5.1 Bq/m3) is collected in a tight PVC chamber equipped with two sources of radium (5 μCi). Blood samples and the pieces of CR-39NTDs are exposed (together) to a known radon concentration for different periods of exposure. Complete blood test and the computer scanning for each piece of CR-39NTDs before and after exposure are carried out. The results show a 95% retention of radon gas in the present technique during the exposure. Thus, the present technique is considered a better technique in terms of conservation of gas, because of the low rate of loss of the gas (4.915%), and this is the advantage of the present technique: keeping the concentration of gas during periods of exposure as much as possible. Deposition of the alpha particles, which are emitted from radon daughters, has reduced the number of platelets in both gender, and this is dependent on the energies of the alpha particles. Exposure time and the energy loss of the alpha particles within the target (blood and CR-39) through the atomic displacements are considered important parameters in the changes of platelet count. At 20-minute exposure time, the rate of absorption dose is 2.255 ± 0.11 μSv and the platelet count reduces rapidly. [ABSTRACT FROM AUTHOR]

The ‘proxy equilibrium factor’ (Fp) method has been developed for long-term determination of airborne radon progeny concentrations using LR 115 solid-state nuclear track detectors. In this paper, the effects of 220Rn on the Fp method have been studied. The correction to the track density was related to a parameter α which was the ratio of the sum of activity concentrations of alpha-particle emitting radionuclides in the 220Rn decay chain to the activity concentration of 220Rn alone. Under commonly encountered circumstances, α could not be smaller than 2. An attempt was made to verify this using the exposure chamber at the National Institute of Radiological Sciences (NIRS), Chiba, Japan. A most interesting observation of α < 2 for very high 220Rn concentrations and very low equilibrium factors for 220Rn in the exposure chambers was made. A possible explanation was the substantial deposition of 216Po under the extreme conditions inside the exposure chambers. [ABSTRACT FROM PUBLISHER]

Solid-state nuclear track detectors have found wide use in various domains of science and technology, e.g. in environmental experiments. The measurement of alpha activity on sources in an environment, such as air is not easy because of short penetration range of alpha particles. Furthermore, measurement of alpha activity by most gas ionization detectors suffers from high background induced by the accompanying gamma radiation. Solid state nuclear track detectors (SSNTDs) have been used successfully as detecting devices and as a passive system to detect alpha contamination on different surfaces. This work presents the response of CR-39 (for two types) to alpha particles from two sources, 238Pu with energy 5 MeV and 241Am with energy 5.4 MeV. The methods of etching and counting are investigated, along with the achievable linearity, efficiency and reproducibility. The sensitivity to low activity and energy resolution are studied. [ABSTRACT FROM AUTHOR]

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 0.4Gy. 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. [ABSTRACT FROM AUTHOR]

Purpose: To calculate the hit probabilities by α-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 α-particles in tissue were adopted from ICRU49. A semi-analytical method for determining the α-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 α-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. [ABSTRACT FROM AUTHOR]