Intercomparatives study of the detection characteristics of the CR-39 SSNTD for light ions: Present status of the Besancon-Dresden approaches

For the last few years, the Besancon and Dresden teams have been working in a parallel way on light ion (protons and alphas) registration characteristics for the CR-39 SSNTD. Even if the two groups use different approaches, the main part of both investigations concerns the study of the track etch rate (VT) and the consequences of the obtained results, which have provided us with greater understanding of detection limits. After recalling the methods used to determine the VT from both teams, we will show how fundamental data related to the registration properties of the CR-39 detector can be extracted. Indeed, the knowledge of an analytical relation for the VT enables the relationship between this velocity and the primary deposited energy to be examined with respect to the same spatial variable (the instantaneous depth of penetration (x) of the incoming particle). According to experimental uncertainties, the Bragg peak of the primary ionization coincides within a very close range with the maximum of the VT. Moreover, if increasing the etching parameters (C, T) increases the maximum VT value, these changes do not affect its position with respect to the instantaneous depth of penetration. Taking into account the reduced etch rate, the Dresden team found that both protons and alphas exhibit the same behavior when this rate is plotted versus the primary energy deposition rate. As a consequence, the corresponding reduced etch rate is always identical no matter what type of particle deposits a given amount of energy (e.g. proton or alpha). The Besancon team has corroborated the results obtained by the Dresden group for alphas and have extended the study to various etching conditions. From these results, the sensitivity of the CR-39 SSNTD is obtained in terms of critical LET and leads to a very low energy threshold for alpha particles. We will see throughout this paper that the lower threshold does not seem to depend on the etching parameters