The recent discovery of new superheavy transuranic nuclei has reawakened interest in the possibility of an “island of stability” inhabited by quasi-stable nuclei. These exotica are produced by bombarding a suitable nuclear target with a high-energy beam of specially prepared nuclei and studying the resulting decay chains in a suitable detector.
The discovery of these nuclei is a major accomplishment for the accelerators that handle the beams and is a tribute to the expertise of the scientists at the three traditional world centres for this work Dubna near Moscow, the GSI heavy-ion Laboratory in Darmstadt and the US Lawrence Berkeley Laboratory, where transuranic nuclei were first discovered by McMillan and Abelson 60 years ago. The detectors (the SHIP velocity filter at Darmstadt and gas-filled separators at Dubna and Berkeley) also play a vital role.
However, given the minuscule production rates of the new nuclei (roughly one every two weeks), a prerequisite for achieving anything at all is to be able to supply enormous doses (1018) of ions to feed the accelerators in a reasonable time. Moreover, the ions required are highly charged: krypton-19+ at Berkeley, calcium-5+ at Dubna and nickel-9+ at Darmstadt. The supplied beams also have to be well defined so that no precious particles are lost downstream in the acceleration and transport stages. The standard source that meets all of these demanding criteria is the electron cyclotron resonance ion source (ECRIS), which is capable of supplying adequate doses nonstop over several weeks.
The ATLAS muon detection system will cover 17 000 m3. Its production is being shared between 46 institutions around the world, with strict quality control procedures at each.Chambers will be arriving at CERN over the next four years, with the full detector being ready for installation by early 2004.
Prof. Floratos is accompanied by members of the team that established the Greek production line, which began in August.
ECRIS uses neither cathodes nor arc discharges. The cavity is filled with vapour and subjected to microwave oscillations in a magnetic field. Ionization electrons in the vapour see the source as a miniature cyclotron, whirling round and acquiring energy. These high-energy electrons trigger a plasma breakdown and in turn rip out more electrons, thus ionizing the vapour to high charge states.
Owing to the absence of electrodes, these sources are very reliable and can provide virtually unlimited amounts of ions. Darmstadt is now equipped with its CAPRICE ECR source, Dubna with ECR4M and Berkeley with ECR-U, all of which are operating at 14 GHz.
Incidently, CERN’s new heavy-ion linac, commissioned in 1994, also uses a 14 GHz ECR ion source (supplied by France) and produces lead-27+ ions at 2.5 KeV per nucleon to feed CERN’s programme of research using beams of heavy ions.
