CHARACTERIZATION OF AN IN-HOUSE DEVELOPED MULTI-CYLINDRICAL MODERATOR NEUTRON SPECTROMETER.

This article describes the characterization of an in-house developed multi-cylindrical moderator neutron spectrometer, which consists of a cylindrical 3He proportional counter and cylindrical moderator shells of different sizes. The response matrix of the spectrometer was calculated by Monte Carlo simulations for neutron energies from 1 × 10-8 to 10 MeV and verified with measurements in 0.144 MeV, 1.2 MeV and 241AmBe neutron standard fields. Influence of scattered neutrons was properly eliminated from the measured response using the shadow cone technique. The calculated and measured responses were in good agreement in most cases. Differences were <10% for all moderated counter configurations, while larger deviations were observed for the bare counter configuration. The performance of the neutron spectrometer in terms of spectrum unfolding was verified in the 241AmBe neutron standard field, showing reliable neutron spectrum and fluence rate in the energy range up to 10 MeV as investigated in this work.

Radiation track, DNA damage and response-a review.

The purpose of this paper has been to review the current status and progress of the field of radiation biophysics, and draw attention to the fact that physics, in general, and radiation physics in particular, with the aid of mathematical modeling, can help elucidate biological mechanisms and cancer therapies. We hypothesize that concepts of condensed-matter physics along with the new genomic knowledge and technologies and mechanistic mathematical modeling in conjunction with advances in experimental DNA (Deoxyrinonucleic acid molecule) repair and cell signaling have now provided us with unprecedented opportunities in radiation biophysics to address problems in targeted cancer therapy, and genetic risk estimation in humans. Obviously, one is not dealing with 'low-hanging fruit', but it will be a major scientific achievement if it becomes possible to state, in another decade or so, that we can link mechanistically the stages between the initial radiation-induced DNA damage; in particular, at doses of radiation less than 2 Gy and with structural changes in genomic DNA as a precursor to cell inactivation and/or mutations leading to genetic diseases. The paper presents recent development in the physics of radiation track structure contained in the computer code system KURBUC, in particular for low-energy electrons in the condensed phase of water for which we provide a comprehensive discussion of the dielectric response function approach. The state-of-the-art in the simulation of proton and carbon ion tracks in the Bragg peak region is also presented. The paper presents a critical discussion of the models used for elastic scattering, and the validity of the trajectory approach in low-electron transport. Brief discussions of mechanistic and quantitative aspects of microdosimetry, DNA damage and DNA repair are also included as developed by the authors' work.

Microdosimetry of the full slowing down of protons using Monte Carlo track structure simulations.

The article investigates two approaches in microdosimetric calculations based on Monte Carlo track structure (MCTS) simulations of a 160-MeV proton beam. In the first approach, microdosimetric parameters of the proton beam were obtained using the weighted sum of proton energy distributions and microdosimetric parameters of proton track segments (TSMs). In the second approach, phase spaces of energy depositions obtained using MCTS simulations in the full slowing down (FSD) mode were used for the microdosimetric calculations. Targets of interest were water cylinders of 2.3-100 nm in diameters and heights. Frequency-averaged lineal energies ([Formula: see text]) obtained using both approaches agreed within the statistical uncertainties. Discrepancies beyond this level were observed for dose-averaged lineal energies ([Formula: see text]) towards the Bragg peak region due to the small number of proton energies used in the TSM approach and different energy deposition patterns in the TSM and FSD of protons.

A Monte Carlo track structure simulation code for the full-slowing-down carbon projectiles of energies 1 keV u(-1)-10 MeV u(-1) in water.

The paper presents a new Monte Carlo track structure code (KURBUC_carbon) for simulations of full-slowing-down carbon projectiles C(0)-C(6+) of energies 1 keV u(-1)-10 MeV u(-1) in water vapour. The code facilitates investigation of the spatial resolution effect for scoring track parameters under the Bragg peak of a carbon ion beam. Interactions of carbon projectiles and secondary electrons were followed interaction-by-interaction down to a 1 keV u(-1) cutoff for primary ions and down to 10 eV for electrons. Electronic interactions and nuclear elastic scattering were taken into account, including charge exchange reactions and double electronic interactions for the carbon projectiles. The reliability of the code was tested for radial dose, range and W-value. The calculated results were compared with the published experimental data and other model calculations. The results obtained showed good agreement in most cases where comparisons could be made. Depth dose profiles for 1-10 MeV u(-1) C(6+) were used to form a spread-out Bragg peak (SOBP) of 0.35 mm width in water. At all depths of the SOBP, the energy distributions of the carbon projectiles varied appreciably with the change in the scoring volume. The corresponding variation was nearly negligible for the track average linear energy transfer (LET), except at the distal end of the SOBP. By varying the scoring slab thickness from 1 to 100 µm, the maximum track average LET decreased by ∼30%. The Monte Carlo track structure simulation in the full-slowing-down mode is a powerful tool for investigation of the biophysical properties of radiation tracks under the Bragg peak and SOBP of a carbon ion beam. For estimation of radiation effectiveness under the Bragg peak the new Monte Carlo track structure code provides yet another accurate and effective dosimetry tool at a single cell level. This is because radiobiology within tissue elements can be understood better with dosimetry at cellular and subcellular level.

EDDIX--a database of ionisation double differential cross sections.

The use of Monte Carlo track structure is a choice method in biophysical modelling and calculations. To precisely model 3D and 4D tracks, the cross section for the ionisation by an incoming ion, double differential in the outgoing electron energy and angle, is required. However, the double differential cross section cannot be theoretically modelled over the full range of parameters. To address this issue, a database of all available experimental data has been constructed. Currently, the database of Experimental Double Differential Ionisation Cross sections (EDDIX) contains over 1200 digitalised experimentally measured datasets from the 1960s to present date, covering all available ion species (hydrogen to uranium) and all available target species. Double differential cross sections are also presented with the aid of an eight parameter functions fitted to the cross sections. The parameters include projectile species and charge, target nuclear charge and atomic mass, projectile atomic mass and energy, electron energy and deflection angle. It is planned to freely distribute EDDIX and make it available to the radiation research community for use in the analytical and numerical modelling of track structure.