  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.
