PRINCIPLE OF LIGHT-IONS MICROMAPPING AND DOSIMETRY USING A CR-39 POLYMERIC DETECTOR - MODELIZED AND EXPERIMENTAL UNCERTAINTIES

In this paper we propose a model for light ion track etching in CR-39. This model is rigorously applicable to the case of light ions for which the mean latent track core diameter can be considered small compared with one micron. The relations describing the opening of an etch-pit, which can be simulated on a computer screen, are given with their mathematical derivation. The comparison of simulated tracks with experimental tracks has presented good qualitative agreement. It is thus possible to use the theoretical model in order to evaluate the capabilities of CR-39 SSNTD in the field of micromapping or autoradiography. This simulation showed that a single measurement of the minor and major axis of a given etched track, repeated for several etching steps, is sufficient for calculating both energy and incidence angle of the particle. The case of reverse tracks (particle generated in the detector material (n, p) conversion...) is not treated in this paper. The study of critical angle will be treated in another paper. An evaluation of the uncertainty associated with this method is necessary for interpretation of the experimetal measurements. We find that both experimental and simulated data contribute to the uncertainties of the used method. In particular, the necessary use of the optical microscopy is one of the most important sources of uncertainty if we consider that CR-39 SSNTD is an ideal detector (isotropic physical and chemical properties of the bulk material). Considering the mean track diameter distributions and standard deviations for normal incident ions of calibrated energy, such an assumption is realistic at the scale of the micrometer. On the other hand, the non-linear behaviour of the geometrical parameters (diameter, minor/major axis, area....) which were obtained as a function of energy impose the variation of uncertainty with energy. Moreover, this uncertainty also varies with a sequential etching. This can be seen on the experimental plots (energy, diameter) for normal incident alphas or protons. Finally, the average uncertainty for micromapping and autoradiography using CR-39 SSNTD depends principally on the optical measurement device and on the range/energy relation, which is experimentally determined using our method.