S. Starke

Dependence of the etch rate ratio on the energy loss of light ions in CR-39

Abstract Mathematical simulation of the etch pit evolution requires the knowledge of the relationship between the etch rate ratio and the restricted energy loss of charged particles. Whereas a unique correlation of both quantities independent of the kind of particle and its initial energy was found for protons, deuterons and alpha particles the results of the depth-dependent track etch rates for 7 Li , 11 B and 12 C ions indicated a different behaviour for heavier ions. A detailed analysis of the etch rate ratio in dependence on the restricted energy loss confirmed the existence of specific relationships for ions of different kind and initial energy. The spread of the corresponding curves is explained by the gradual increase of the track etch rate over a certain distance from the detector surface. The speed of this increase is the higher the lower the restricted energy loss is.

Variation of the track etch rate along the trajectories of light ions in CR-39

Abstract The track etch rate has been found to be described by a generalised function of the restricted energy loss in good approximation along the trajectories of protons, deuterons and alpha particles. Extending the studies to tracks of 7 Li , 11 B and 12 C ions, curves for the track etch rates as a function of the depth within the detector were obtained the shape of which is like that of the Bragg curve in principle. In detail, however, systematic deviations from a unique correlation of the track etch rate with the restricted energy loss are observed which are more distinct the heavier the ion and the lower its initial energy. This effect is explained by a gradual increase of the track etch rate to the value expected at a given restricted energy loss. At the beginning of the etching process the track etch rate is, therefore, lower than the value observed for larger depths when the same restricted energy loss is presumed.

Studies of SSNTDs made from LR-115 in view of their applicability in radiobiological experiments with alpha particles

Radiobiological studies on cell monolayers irradiated by charged particles need to determine the number and position of particle traversals. Solid state nuclear track detectors used as basic substrate for the cell layers are in principle suitable for this purpose. The detector foils must be as thin as possible but still guaranteeing mechanical stability. Two types of LR-115, red coloured and colourless, were tested in the present work. The studies aimed at optimisation of the etching conditions and determination of the registration efficiency for alpha particles in a wide range of energies and angles of incidence. Specific requirements have to be fulfilled for application of the detector foils under the environmental conditions of radiobiological experiments. Most important are biocompatibility between detector and cells and registration properties insensible against special treatments, as UV sterilisation and cell plating prior to irradiation as well as cell incubation after the irradiation. The experimental studies performed with alpha particles showed that environmental conditions of radiobiological experiments do not change the registration properties of LR-115 detectors significantly.

Computation of etched track profiles in CR-39 and comparison with experimental results for light ions of different kinds and energies

Abstract Computation of etched track profiles needs the knowledge of the variable track etch rates along the ion trajectories. Using the depth-dependent track etch rates experimentally determined for perpendicularly incident protons, deuterons and alpha particles as well as 7 Li , 11 B , 12 C , 14 N and 16 O ions of different energies simulations of the track development were performed. Two models of track etching were applied for that purpose recently published in literature. Although the models are based on the same physical fundamentals the results are slightly different. The reasons of the discrepancies were found by analysing the algorithms in detail. Comparison of the calculated track profiles with those determined experimentally from longitudinal sections of the etch pits showed good agreement for non-overetched as well as overetched tracks. The consistency of the whole experimental data set was checked by analysing the correlation of the track etch rates with geometric track parameters for all kinds of ions and etching times covered by the experiments.

3D computation of the shape of etched tracks in CR-39 for oblique particle incidence and comparison with experimental results

Abstract Computation of the shape of etch pits needs to know the varying track etch rate along the particle trajectories. Experiments with alpha particles and 7 Li ions entering CR-39 detectors under different angles showed that this function is not affected by the inclination of the particle trajectory with respect to the normal on the detector surface. Track formation for oblique particle incidence can, therefore, be simulated using the track etch rates determined for perpendicular incidence. 3D computation of the track shape was performed applying a model recently described in literature. A special program has been written for computing the x,y,z coordinates of points on the etch pit walls. In addition, the etch pit profiles in sagittal sections as well as the contours of the etch pit openings on the detector surface have been determined experimentally. Computed and experimental results were in good agreement confirming the applicability of the 3D computational model in combination with the functions for the depth-dependent track etch rates determined experimentally.

A new approach to characterising the etch rate ratio in CR-39 using a function of two variables

Abstract The formation of etched tracks in solid-state nuclear track detectors is usually described assuming an unequivocal correlation of the etch rate ratio with the energy loss of charged particles. For protons, deuterons and alpha particles this assumption could be verified within the scatter of the experimental data. Experimental studies with 7 Li , 11 B and 12 C ions yielded, however, systematic deviations from the expected results. Analysing the complete experimental data set for CR-39, a dependence of the etch rate ratio was found not only on the particles energy loss, but also on the depth within the detector where this energy loss occurs. Arranging the etch rate ratio as a function of both these variables all experimental results appear without inconsistencies. The etch rate ratio represented by a two-dimensional matrix can be used, then, for characterising the etch kinetics along the trajectories of charged particles of different kinds and initial energy.

Track etch rates along the trajectories of nitrogen and oxygen ions in CR-39

Abstract Experimental studies on track etch rates in CR-39 performed with protons, deuterons and alpha particles as well as 7 Li , 11 B and 12 C ions were extended to 14 N and 16 O ions. The results are compatible with the general systematics found for the dependence on the kind of ion and its initial energy. Analysing the etch rate ratios as function of the restricted energy loss (REL), the non-existence of a unique relationship has been confirmed. However, assuming a dependence of the etch rate ratio not only on REL, but also on the depth within the detector where a given REL value occurs, all experimental data could be adjusted. The experiments with 14 N and 16 O ions allow extension of the REL range studied up to about 14 000 MeV / cm . The whole area relevant to neutron-induced charged particles generated within the CR-39 detectors is covered thereby. Having added the data for 14 N and 16 O ions, the array of curves for the etch rate ratio could be expanded up to 14 000 MeV / cm without inconsistencies, demonstrating the compatibility of the new data set also quantitatively.

Thickness measurements on cell monolayers using CR-39 detectors

Interpretation of radiation effects on living cells requires the determination of the absorbed dose. Dosimetry in cell monolayers irradiated by charged particles needs the knowledge of the mean cell thickness. Thickness measurement was made utilising the energy alteration of alpha particles traversing the cell monolayers. The reduced energy was determined from diameters or lengths of etched tracks produced by the penetrating alpha particles in CR-39. The experiments were performed using 3T3 cells grown directly on the CR-39 surface. The reliability of the method has been studied by means of a detailed error analysis. The total thickness errors are composed of the measurement uncertainty and the fluctuations of the cell thickness within the monolayers.