Identification of high energy ions using backscattered particles in laser-driven ion acceleration with cluster-gas targets

Abstract

A new diagnosis method for high energy ions utilizing a single CR-39 detector mounted on plastic plates is demonstrated to identify the presence of the high energy component beyond the CR-39's detection threshold limit. On irradiation of the CR-39 detector unit with a 25 MeV per nucleon He ion beam from conventional rf-accelerators, a large number of etch pits having elliptical opening shapes are observed on the rear surface of the CR-39. Detailed investigations reveal that these etch pits are created by heavy ions inelastically backscattered from the plastic plates. This ion detection method is applied to laser-driven ion acceleration experiments using cluster-gas targets, and ion signals with energies up to 50 MeV per nucleon are identified.

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“…Etch pit radii indicate that ion species are He and other heavy ions. Detailed microscope investigations show that almost all of the etch pits on the rear surface have elliptical openings (as seen in Figure 13b,c) to demonstrates that laser-accelerated ions with energies up to 50 MeV per nucleon were generated [20]. …”

“…We have demonstrated a new simple diagnosis method for high energy ions utilizing a single CR-39 detector mounted on plastic plates to identify the presence of the high energy component beyond the detection threshold limit of the CR-39 [79]. In addition, we have applied this method to the laser-driven ion acceleration experiments using cluster-gas targets [20].…”

“…Currently, the development of high power femtosecond laser system having a 200 PW level is being pursued through European Extreme Light Infrastructure (ELI) project [13]. This progress in high-field science gives rise to the birth of new applications and breakthroughs which include relativistic particle acceleration [14][15][16][17][18][19][20], bright X-ray source generation [21][22][23][24][25][26][27], and nuclear activation [28,29].…”

Evaluation of dose level in a laser-driven ion accelerator using PHITS code

“…In contrast with these studies, we focused on a cluster target [7] because a cluster is an intermediate state between a solid and gas, and we searched for parameters in that domain. It was succeeded with the accelerated energy of ~50 MeV/nucleon ( 4 He 2+ ) using a CO 2 cluster in helium background gas [8]. Although this experiment was performed in a radiation-shielded room with 1 meter concrete walls, we had to evaluate the shielding Figure 1.…”

“…2+ pits on the CR-39 by the back-scattering method [8]. Because ions penetrate diagonally due to the influence of back-scatter, most of pits are elliptical.…”