M. P. R. Waligorski

The radial distribution of dose around the path of a heavy ion in liquid water

Abstract Monte Carlo calculations of the radial distribution of dose in liquid water, incorporating energy deposition due to primary excitations and ionizations, have been performed for protons of energy 1, 10, 20, 50 and 100 MeV. By combining these results with earlier semi-empirical formulae used in track structure theory calculations, a corrected analytic formulation has been developed which on radial integration closely reproduces the value of stopping power for protons in the energy range 0.1–1000 MeV. After including a β-dependent ‘effective charge’ formula, this corrected formulation is tested against all published measurements of radial distribution of dose from energetic ions in gaseous media. Though some inconsistencies at the closest and the farthest reaches of the radial distribution of dose remain, the overall agreement is very satisfactory, indicating that the ‘effective charge’ Z∗, and Z∗2/β2 scaling are phenomenologically valid concepts for describing the radial dose from heavy ions of energies above ∼ 0.5 MeV/amu.

Supralinearity of peak 5 and peak 6 in TLD-700

Abstract Track theory has been applied to calculate the response of peak 5 and peak 6 in LiF (TLD-700) for H, He, C, O and Ne bombardment. Calculations reproduce experimental features of the heavy-ion response of TLD-700 and provide means of connecting the gamma and high-LET responses in thermoluminescent dosimeters.

The response of the alanine detector after charged-particle and neutron irradiations

Abstract Radiosensitivity parameters of track structure theory, representing alanine as a one-hit detector, have been fitted for this free-radical amino-acid system on the basis of the available experimental data on the relative effectiveness of alanine after charged particle and neutron irradiations. The experimental data set can be reproduced by theoretical calculations, roughly to within experimental accuracy. A charged-particle “equivalent radiation” is introduced which can mimic the response of alanine to neutron irradiations. Implications of the results of model calculations for alanine on the shape of the radial distribution of σ-ray dose postulated by track theory, are discussed.

Radiosensitivity parameters for neoplastic transformations in C3H10T1/2 cells

We have evaluated radiosensitivity parameters for cellular transformation from published experimental data on neoplastic transformations induced in C3H10T1/2 cells by BEVALAC ions. The measured RBE values are well reproduced by a track theory calculation using sets of m-target parameters with either m = 2 or m = 3, suggesting a quadratic or cubic extrapolation to low doses of gamma rays. Using track theory one is thus able to predict transformation frequencies in those cells after an arbitrary radiation field, under known or assumed conditions of exposure, in a manner shown earlier for cellular survival. Extension of these calculations to interpret cancer incidence in vivo is also discussed.

The Fricke dosimeter as a 1-hit detector

A fit to the experimental data for the response of the Fricke dosimeter to energetic heavy ions is obtained using a calculation of the relative effectiveness of a 1-hit detector, from track theory. We use 2 fitted parameters, the target size, α0, which may be thought to represent a ‘diffusion length’, and E0, the dose of gamma-rays at which there is an average of one hit per target (the D-37 dose), and a new algorithm for the average radial distribution of dose in liquid water from the passing ion. The G value for ions is then given as the product of the calculated relative effectiveness and the experimental G value for gamma rays.

Inactivation of Dry Enzymes and Viruses by Energetic Heavy Ions

Abstract A newly developed corrected formula for the distribution of dose (RDD) has been used to calculate cross sections for the inactivation of dry enzymes and viruses by heavy ranging from 42He to 4018Ar of energies ca 10 MeV/a.m.u., spanning a range of LET of ca 5–2000 MeV cm2g-1. In comparison with earlier “point-target” calculaions of Butts and Katz where a linear range-energy relationship for electrons (σ-rays) was used, and with “extended-target” calculations of Zhang Dunn and Katz where a power range-energy law and an “uncorrected” RDD formula were applied, the present calculations reproduce all the 72 experimentally measured cross sections and values of the D-37 dose (where available) much more accurately, essentially to within experimental errors. This agreement supports the validity of our phenomenological correction of the RDD formula, suggesting that the theory should rather be tested in the highly structured “thindown” region, at ion energies below ca 0.5 MeV/a.m.u.

Application of the finite-difference approximation to electrostatic problems in gaseous proportional counters

Abstract The basic principles of the finite-difference approximation applied to the solution of electrostatic field distributions in gaseous proportional counters are given with the aim of making this method more popular with authors dealing with electrostatic problems. When this method is used, complicated two-dimensional electrostatic problems may be solved, taking into account any number of anodes, each with its own radius, and any cathode shape. A general formula for introducing the anode radii into the calculations is derived and a method of obtaining extremely accurate (up to 0.1%) solutions developed. Several examples of potential and absolute field distributions for single rectangular and multiwire proportional counters are calculated and compared with exact results according to Tomitani, in order to discuss in detail errors of the finite-difference approximation.