Track Structure Effects Research Articles

Radical and molecular yields in the radiolysis of water with carbon ions

The radiation chemical yields of H 2 and H 2O 2 molecules and OH radicals have been determined with carbon ions at energies of a few to 35 MeV. With increasing carbon ion energy, the yields of H 2 and H 2O 2 decrease by 6 and 10% respectively whereas the yield of OH radicals almost doubles. The differential yields have been determined from the observed energy dependences and combined with previous studies on the production of H atoms and HO 2 radicals to give a complete set of radiation chemical yields for the primary species produced in the carbon ion radiolysis of acidic aqueous solutions. The effects of track structure on radiolytic yields is discussed and simulated using a numeric diffusion-kinetic model.

Track structure effects at p- n junctions in microelectronic circuits

Accurate predictions of the soft error rates in microelectronic circuits exposed to energetic charged particles require the ability to predict charge collection at a junction as a function of the LET of the traversing particle, and the ability to predict the response of the circuit to the resulting voltage swing across the junction. Detailed modeling of charge collection will require quantitative information on the distribution of charges about the particle trajectory as a function of time from the initiation of the track until the charge is collected across the junction. Track structure models may contribute to quantitative explanations of the shape of the dependence of the soft error cross section on LET and the frequency of multiple upset events in VLSI circuits.

The Relative Biological Effectiveness of 670 MeV/A Neon as a Function of Depth in Water for a Tissue Model

Linear energy transfer (LET infinity) spectra of identified charge fragments and primaries, produced by nuclear interactions of 670 MeV/A neon in water, were measured along the unmodulated Bragg curve of the neon beam. The relative biological effectiveness (RBE) values for spermatogonial cell killing, as reported on the basis of weight loss assay of mouse testes irradiated with beams of approximately constant single LET infinity, were summed over the particle LET infinity spectra to obtain an effective RBE for each charged-particle species, as a function of water absorber thickness. The resultant values of effective RBE were combined to obtain an effective RBE for the mixed radiation field. The RBE calculated in this way was compared with experimental RBEs obtained for spermatogonial cell killing in the mixed radiation field produced by neon ions traversing a thick water absorber. Discrepancies of 10-40% were observed between the calculated RBE and the RBE measured in the mixed radiation field. Part of this discrepancy can be attributed to undetected low-Z fragments, whose contribution is not included in the calculation, leading to an overestimated value for the calculated RBE. On the other hand, calculated values 10% greater than the measured RBE are explained as track structure effects due to the higher radial ionization density near neon tracks relative to the ionization density near the silicon tracks used to fit the RBE vs LET infinity data.

Theoretical consideration of the chemical pathways for radiation-induced strand breaks

A theoretical approach to the understanding of the biochemical mechanisms of indirect action of ionizing radiation on SV40 DNA in aqueous solution is presented. The extent of OH attack on the sugar moiety and bases has been calculated. A realistic model for the DNA (in B form) based on available X-ray diffraction data is used and specific reaction sites for the OH radicals are obtained. A Monte Carlo scheme is used to follow the diffusion and reaction of the OH radicals. Effects of track structure have been considered and the single strand break D 37 values for 14 MeV electrons (low-LET) and 670 MeV/u and 40 MeV/u neon particles are presented. Calculated results are in agreement with available experimental data. It has been found that regardless of the qualities of radiation, 80% of the OH attack on DNA is on the bases and 20% is on the deoxyribose. From probability considerations only, it appears that the number of double strand breaks varies linearly with dose.