CR-39 nuclear track detector for laser-plasma accelerated ions
The polymer polyallyl-diglycol-carbonate (PADC), also known as CR-39, is a material used for ion detection, in particular, for laser-plasma accelerated ions. This detection is based on the analysis of the small tracks generated by the impact of the charged particles onto the PADC sheets that can be visualized with a microscope after an etching process. CR-39 has some interesting advantages over other detectors, for example, its inertness towards electrons and X-rays, its ability to distinguish between different ion species, and its high spatial resolution. To calibrate the response of this material, CR-39 plates have been irradiated with mono-energetic proton and carbon ion beams from a tandem accelerator and we have analyzed the resultant tracks using different microscopes and software to determine their diameters. This procedure of calibration will be discussed by brie y. Our results show that the track diameters depend on the ion energies and the etching conditions fixed the track size doesn’t only depend on these two factors, but the exact composition of the PADC material plays an important role, too. It is known that with ion energy and etching conditions. Nevertheless, the dimensions of the tracks vary between different PADC providers. Furthermore, this aspect also affects the energy range of ions that can be detected. This is the reason why it is important to perform a calibration of the PADC used, as we have done with protons and carbon ions of fixed energies, to determine the useful energy interval and thus choose the appropriate material for our experiments. In our tests, we have used CR-39 from only one provider, which restricts our detection capacities to protons of a few MeV. Therefore, we consider as a future task to examine materials from other providers that allow us to adapt the sensitive interval to the spectral range of our experiments with laser-plasma accelerated ions. CR-39 may not only be applied for determining the energy of the incident ions through the track diameters but also for counting how many ions reach the detector, this is, for measuring the fluence. This measurement is very important, for example, in radiobiological applications where determining the deposited dose is essential. When studying the fluence measurement the possible saturation of the CR-39 chips has to be taken into account. This happens when the amount of particles reaching the detector is so high that the tracks overlap, making it di cult to count them individually. The solution to this problem will be one of the challenges that we will have to face. Finally, we will address the aspects of the experiment that will take place in the Laser Laboratory for Acceleration and Applications (L2A2) at Santiago de Compostela, in which we will use CR-39 detectors to record protons and carbon ions accelerated by laser-plasma interaction.
