The COMBAS fragment separator

The basic ion-optical characteristics of the COMBAS fragment separator are analyzed. The momentum distributions of radioactive 6 He, 8 He, and 9 Li nuclei obtained in the reaction 11 B (33 A MeV, where A is the mass number of a particle) + 9 Be (332.6 mg/cm 2 ) have been investigated in forward-angle measurements on the COMBAS fragment separator. The momentum and angular (horizontal) acceptances of the COMBAS separator have been measured using the 6 He, 8 He, and 9 Li beams. It has been ascertained that the images of the 6 He, 8 He, and 9 Li nuclear beams in final achromatic focus of the separator F a approximately twofold exceed the size of the beam on a producing target (input focus F 0 ), at which the primary beam has a diameter of 6 mm. The intensities of 6 He, 8 He, and 9 Li beams obtained at a 5-μA intensity of the primary 11 B beam are 6.9 × 10 5 , 2 × 10 4 , and 4.7 × 10 5 particles/s, respectively. These values are sufficient for use in spectroscopic measurements. It is proposed that time-of-flight analysis of nuclear reaction products at the exit from the COMBAS separator will be used not only to measure the energy of transported particles over the whole operating range of the momentum acceptance, but also to identify them by mass A and charge Z without loss of these particles. The problem of reducing the count rates of detectors and further improvement of their energy resolution for detected particles can be solved by placing a high-resolution magnetic spectrometer past the second target accepting the secondary radioactive nuclear beams.