Presentation Design of the energy spectrometer for laser-accelerated protons using stacked CR-39 detector

Uno, Masataka  ,  Kanasaki, Masato  ,  Fukuda, Yuuji  ,  Yamauchi, Tomoya  ,  Oda, Keiji

In the laser-driven ion acceleration experiment, CR-39 track detectors have been used for the measurement of laser-accelerated ions. This is because CR-39 detectors are insensitive for X-rays and energetic electrons, which are simultaneously generated with ions by the interaction between intense laser pulse and the target material. To evaluate the energy spectrum of laser-accelerated protons, which has the broad energy spectrum, the stacked CR-39 detectors are required because the energetic protons penetrate through the single layer of CR-39. For example, in the case of HARZLAS (TD-1) type CR-39 detector, which can detect up to 20 MeV protons, with the thickness of 0.9 mm, more than 9.63 MeV protons penetrate through the single layer. In other words, the protons with the energies more than 9.63 MeV create the etch pits not only on first layer but also on second layer. In such case, the accurate energy spectrum is not able to obtain by the numbers of etch pits on each layer of CR-39. In the present study, to measure the precise energy spectrum of laser-accelerated protons, we have designed the stacked detector using HARZLAS (TD-1) and energy moderators. Particle and Heavy Ion Transport Code System (PHITS) has been used for the optimization of the thickness of energy moderator and proof-of-principal calculation of the designed detector. We have applied polytetrafluoroethylene (PTFE) as the energy moderators because PTFE has the largest stopping power in the plastics. The thickness of PTFE has been determined as 1.8 mm to avoid a 20 MeV proton entering into the second layer of HARZLAS (TD-1). Therefore, the repetition of 0.9 mm thick HARZLAS (TD-1) and 1.8 mm thick PTFE can obtain the accurate energy spectrum of broad energy spread proton beams. In order to confirm the capability of the designed stacked detector, we have tried to reconstruct the model energy spectrum using the PHITS code simulation. Figure 1 shows the comparison between the model spectrum and the calculated spectrum. From the results of this simulation, the obtained energy spectrum almost reconstructed the model energy spectrum. Thus, the designed stacked detector can be applied to laser-driven ion acceleration experiments as the energy spectrometer for laser-accelerated protons.
The 12th International Workshop on Ionizing Radiation Monitoring

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