The COMBAS Fragment Separator

摘要

The basic ion-optical characteristics of the COMBAS fragment separator are analyzed. The momentum distributions of radioactive ~6He, ~8He, and ~9Li nuclei obtained in the reaction (11)~B (33 A MeV, where A is the mass number of a particle) + ~9Be (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 ~6He, ~8He, and ~9Li beams. It has been ascertained that the images of the ~6He, ~8He, and ~9Li 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 ~6He, ~8He, and ~9Li 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.