Ion source with surface ionization for the BESM-2 mass-separator in a heavy ion beam

A surface ionization ion source for a heavy-ion cyclotron beam mass-separation is described. The device has been designed to study radioactive isotopes which are considerably away from the line of beta-stability. The tungsten ionizer has the form of two conjugate cylinders of different diameter. The narrow part of the ionizer faces the extraction electrode and the broad one faces the target and is covered by a thin tantalum foil which is transparent to the recoil nuclei knocked by the beam out of the target. The foil is tightly pressed to the ionizer by a thin-walled tantalum cylinder. Placed inside the ionizer is a tantalum stopper of recoil nuclei. The heating of the ionizer is achieved by bombarding it with an electron beam emitted by two tungsten spiral filaments each with an independent power supply. There is a thermal screen of thin graphite film between the ionizer and the target. The source has been tested for separatino. rare-earth elements. The effectiveness of sorting out dysprosium is 20+-5% at 2600 deg K. The response of the source has been measured for dysprosium and rubidium