Randall S. Caswell

A consistent set of neutron kerma coefficients from thermal to 150 MeV for biologically important materials

Neutron cross sections for nonelastic and elastic reactions on a range of elements have been evaluated for incident energies up to 150 MeV. These cross sections agree well with experimental cross section data for charged-particle production as well as neutron and photon production. Therefore they can be used to determine kerma coefficients for calculations of energy deposition by neutrons in matter. Methods used to evaluate the neutron cross sections above 20 MeV, using nuclear model calculations and experimental data, are described. Below 20 MeV, the evaluated cross sections from the ENDF/B-VI library are adopted. Comparisons are shown between the evaluated charged-particle production cross sections and measured data. Kerma coefficients are derived from the neutron cross sections, for major isotopes of H, C, N, O, Al, Si, P, Ca, Fe, Cu, W, Pb, and for ICRU-muscle, A-150 tissue-equivalent plastic, and other compounds important for treatment planning and dosimetry. Numerous comparisons are made between our kerma coefficients and experimental kerma coefficient data, to validate our results, and agreement is found to be good. An important quantity in neutron dosimetry is the kerma coefficient ratio of ICRU-muscle to A-150 plastic. When this ratio is calculated from our kerma coefficient data, and averaged over the neutron energy spectra for higher-energy clinical therapy beams [three p (68) + Be beams, and a d (48.5) + Be beam], a value of 0.94 +/- 0.03 is obtained. Kerma ratios for water to A-150 plastic, and carbon to oxygen, are also compared with measurements where available.

Interaction of neutrons and secondary charged particles with tissue: secondary particle spectra

Theoretical calculations have been made of the secondary particle spectra for p, d, α,

Modeling energy deposition and cellular radiation effects in human bronchial epithelium by radon progeny alpha particles.

{}^{9}{\rm Be},{}^{11}{\rm B},{}^{12,13,14}{\rm C},{}^{14,16}{\rm N}

On the Accuracy of the Adiabatic Separation Method

, and16 O produced ...

Neutron‐Insensitive Proportional Counter for Gamma‐Ray Dosimetry

Energy deposition and cellular radiation effects arising from the interaction of single 218Po and 214Po alpha particles with basal and secretory cell nuclei were simulated for different target cell depths in the bronchial epithelium of human airway generations 2, 4, 6, and 10. To relate the random chord lengths of alpha particle tracks through spherical cell nuclei to the resulting biological endpoints, probabilities per unit track length for different cellular radiation effects as functions of LET were derived from in vitro experiments. The radiobiological data employed in the present study were inactivation and mutation (mutant frequency at the HPRT gene) in V79 Chinese hamster cells and inactivation and transformation in C3H 10T1/2 cells. Based on computed LET spectra and relative frequencies of target cells, probabilities for transformation, mutation, and cell killing in basal and secretory cells were computed for a lifetime exposure of 20 WLM. While predicted transformation probabilities were about two orders of magnitude higher than mutation probabilities, they were still about two orders of magnitude lower than inactivation probabilities. Furthermore transformation probabilities for basal cells are generally higher than those for secretory cells, and 214Po alpha particles are primarily responsible for transformations in bronchial target cells.

Radon progeny microdosimetry in human and rat bronchial airways: the effect of crossfire from the alveolar region

Numerical experiments performed for a model of two strongly coupled oscillators indicate that the adiabatic separation method yields accurate results even where the condition of adiabaticity is violated to a very high degree, except in those cases where two levels are degenerate in the adiabatic approximation. An accurate solution for those cases can be obtained by diagonalizing the 2 × 2 Hamiltonian submatrix built on the two degenerate adiabatic states. It is conjectured that the adiabatic separation method can be expected quite generally to yield highly accurate results, at least for states belonging to the discrete spectrum.

Effects of track structure on neutron microdosimetry and nanodosimetry

A gamma‐ray dosimeter with low sensitivity to neutrons has been developed for radiation dosimetry in mixed fields of neutrons and gamma rays. Neutron sensitivity in a 2.5‐ to 3‐Mev H2(d,n)He3 neutron field has been shown experimentally to be ≤1.2% on the basis of first collision dose in tissue. Gamma‐ray sensitivity is independent of energy to within ±5% from 1.25 Mev (Co60) to 200 kev and to within ±20% down to 47 kev. The instrument is a proportional counter which may be used as a dosimeter for gamma rays in the presence of neutrons by pulse‐height integration of the small pulses due to secondary electrons produced by gamma rays and rejection of the large pulses due to heavy particle recoils from neutrons.

Track Structure Predictions of Radon-Induced Biological Effects in Human Bronchial Epithelium

The objectives of the present study were (1) to present a comprehensive analysis of the microdosimetric quantities in both human and rat bronchial airways and (2) to assess the contribution of the crossfire alpha particles emitted from the alveolar region to bronchial absorbed doses. Hit frequencies, absorbed doses and critical microdosimetric quantities were calculated for basal and secretory cell nuclei located at different depths in epithelial tissue for each bronchial airway generation for defined exposure conditions. Total absorbed doses and hit frequencies were slightly higher in rat airways than in corresponding human airways. This confirms the a priori assumption in rat inhalation experiments that the rat lung is a suitable surrogate for the human lung. While the contribution of crossfire alpha particles is insignificant in the human lung, it can reach 33% in peripheral bronchiolar airways of the rat lung. The latter contribution may even further increase with increasing alveolar 214Po activities. Hence, the observed prevalence of tumors in the bronchiolar region of the rat lung may partly be attributed to the high-linear energy transfer crossfire alpha particles.

Nuclear data for biomedical applications

Abstract The process by which neutrons transfer their energy to tissue is described, including the deposition of energy by secondary charged particle tracks in small sites; that is, microdosimetry and nanodosimetry. Three approximations are considered in order of increasing amounts of information on track structure: the continuous slowing-down approximation (CSDA), the straggling approximation, and the delta-ray approximation. Although simple approximations sometimes work quite well, much work remains to be done for very small sites, and for the inclusion of the effects of “passer” in the calculations.

Monte Carlo and Analytic Methods in the Transport of Electrons, Neutrons, and Alpha Particles

Abstract The formalism of track structure theory was used to predict the probabilities of different cellular radiation effects in basal and secretory cells of the bronchial epithelium exposed to radon progeny alpha particles. Cellular radiosensitivity data applicable to the prediction of carcinogenic response consists of in vitro data on oncogenic transformation and survival in C3H10T1/2 cells, mutation and survival in V79 Chinese hamster cells, and chromatid aberrations and survival in CH2B 2 cells. Energy spectra of 218 Po and 214 Po alpha particles were computed for cell nuclei located at varying depths in the bronchial epithelium of different airway generations. Applying track structure theory, the number of observable inactivations, chromatid aberrations, transformations, and mutations can be calculated for a given alpha particle energy spectrum. The computed effect probabilities are then weighted by the depth-density distributions of basal and secretory cells. The track structure predictions for airway generation 4 suggest that cellular radiation effects are rather uniformly distributed within the bronchial epithelium and that the lung cancer risk per unit exposure at low exposure levels is either constant or increases slightly, and then decreases at high cumulative exposures.