Secondary radioactive beams are still a very new tool, but already it has become clear that they provide unique research opportunities (see, e.g., ref.1’2 and references therein). So far, energetic radioactive beams have essentially been made by the use of heavy-ion accelerators in connection with in-flight separation through recoil spectrometers. This technique relies on the forward focusing present in peripheral nuclear reactions. The concept of fragment-separators has been pioneered with relativistic heavy ion-beams at Berkeley using beam-line elements, and later, for intermediate-energy beams, at GANIL, by means of the dedicated doubly achromatic spectrometer LISE. During the last years, new devices for fragment separation have been constructed and put into operation at GSI (“FRS”), MSU-NSCL (“Al200”), RIKEN (“RIPS”) and also a second apparatus at GANIL (“SISSI”). The success of the concept may be evident from the fact that these devices are used during more than 80% of the beam time at the NSCL or at GANIL. The optical quality from secondary projectile-fragment beams is somewhat limited, however, in particular when one aims at high transmission of the fragment separator, privileging its acceptance in solid angle and momentum. Furthermore, it is impossible to attain energies below, say 25 MeV/u, by energy degrading through passage of matter and to simultaneously maintain reasonable optical properties and conserve the intensity. The very elegant technique of cooling and decelerating in a storage ring is also limited by transmission and duty factor and, in particular for short-lived nuclei, by the prohibitive cooling times.
KeywordsHigh Charge State Radioactive Beam Fragment Separator Projectile Fragmentation Unique Research Opportunity
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