ACCULINNA beam separator is in operation since 1996.
The ACCULINNA fragment separator is in operation since 1996. The achromatic ion-optical system (see Fig.1) is optimized for focusing fragments emerging from the production target, placed in the object plane F1, to the achromatic focal plane F3. The desired secondary beams are separated according to their magnetic rigidity with the aid of magnets D1 and D2. A wedge-shaped degrader installed in the intermediate dispersive focal plane F2 helps to remove background from the selected beam. The separator upgrade (in 2000) caused an extension of the beam line. This was implemented through the use of two doublets and one triplet formed by magnetic quadrupole lensses. The target intended for secondary beams, detectors and electronics were moved from the plane F3 to the plane F4, i.e. beyond the 2-m concrete wall of the U- 400M hall. As a result, the radiation background around the reaction chamber was reduced drastically. An important acquiring was the possibility to work with neutron detectors in the proximity of the reaction chamber. In 2001 a tritium target (gas or liquid) was designed and manufactured to be used in the study of hydrogen and helium isotopes lying beyond the neutron drip line. A 4.0/0.4-mm thick tritium target cell (gas/liquid) was equipped with 10 μm stainless steel entrance and exit windows hermetically welded to the cell body. The diameter of target active area is 22 or 10 mm for the gas or liquid case, respectively.
Radioactive beams available now at the separator are presented in the Table 1.
High intensity (1-5 pμA) primary beams of 7Li, 11B, 13C, 15N and 18O with energies 32 ÷ 50 MeV/nucleon delivered by the U- 400M cyclotron were used for the secondary beams production. Triton beam (1 pnA) with energy 19.3 MeV/n was delivered directly by the U-400M cyclotron. The separator was used in this case for focusing a high quality beam on the physical target.
The typical two dimensional plots of particles identification in the 11B (33 MeV/nucleon) + 9Be reaction are shown in the right corner of Fig.1, the separator was tuned for 6He production, the TOF measurement was provided by pair of plastic scintillators (BC404 type, 0,5 mm thick) coupled with the photomultiplier tubes XP-2252 (two units per each plastic).
Fig.1 "ACCULINNA" fragment separator
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Sergei Anatolievich KRUPKO
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