An allene-doped liquid argon ionization chamber for O and Ne ions at 100 MeV/n

An allene-doped liquid al argon ionization chamber with a sensitive volume of 48 mm x 48 mm x 40 min has been constructed and investigated for precise measurement of the heavy ion energies at around 100 MeV/n. An energy resol ution of 1% (full width at half maximum [FWHM]) was achieved for the 99 MeV /n O-16 and 125 MeV/n Ne-20 ion beams. However, the energy resolution was f ound to deteriorate as the beam intensity increased. To understand this phe nomenon, a simple model is proposed, in which a space-charge electric field due to the positive ions left along the track of an incident ion is taken into consideration. The estimated electric field is strong enough to worsen the energy resolution when the incident beam intensity is only 100 particl es/s.