JAERI recoil mass separator

A recoil mass separator has been constructed at the JAERI tandem-booster facility. It has a symmetric configuration of Q1Q2-ED1-MD-ED2-Q3Q4-O, where two electric dipoles ED1 and ED2, and the magnetic dipole MD are used to disperse reaction products by their mass/charge ratio (mq) and focus their energies. Two quadrupole doublets (Q1Q2 and Q3Q4) are used for focusing reaction products spread spatially. The octupole magnet O is used to correct a non-linearity of the mq dispersion. The mq and energy acceptances are designed to be ±4% and ±12%, respectively. In order to reduce a background originating from beams scattered from the ED1 anode, the anode is split into two parts, so that the primary beam can pass through without hitting the anode. The performance of the recoil mass separator has been tested by using the 127I and 28Si beams from the JAERI tandem accelerator. The capability of the background suppression at the beam direction is excellent and the obtained mass resolution AΔA ≅ 300.