What will probably be the most completely equipped laboratory in the world for heavy‐ion research is now operating 20 km from Frankfurt. The laboratory, GSI (Gesellschaft fur Schwerionenforschung), houses UNILAC, a linear accelerator that is expected to be capable eventually of accelerating heavy nuclei, such as uranium to 10 MeV/nucleon and lighter nuclei, such as argon to 14 MeV/nucleon. When it is operating at full energy, for heavy nuclei, it will have the highest energy available in the world, at least for the immediate future. The accelerator is the first to accelerate heavy ions over the full periodic table.

MUCH attention has been given to the origin of ‘giant’ pleo-chroic haloes found in a number of minerals, especially micas1–6. Normal pleochroic haloes are due to the effects of radiation damage from α-particles emitted from small inclusions at the centre of each halo, and the largest radius of the halo is determined by the range of the α-particle of highest energy, which is that from 212Po in the case of a thorium-rich inclusion These have an initial energy of 8.78 MeV. The giant haloes seem to be of two kinds. In Gentry's sample7 ∼40% have a discrete radius ∼ 54 µm and he reports them to be invariably associated with dense thorium haloes. This group appears properly to be associated with production by the well-known but rare (∼ 1.3×10−4) pair of long range α-particle groups from 212Po at ∼ 10.5 MeV. The remaining giant haloes have a monotonic distribution in radius extending up to 110 µm; they have been interpreted in terms of diverse processes such as extinct radiations of higher energy, proton knock-ons by α-particles, knock-ons from neutrons, channelling, migration of the parent radioactive material, but we report one natural and simple explanation which seems not to have been considered.

German heavy‐ion accelerator approaches full energy

Citations

Giant haloes in mica

References

Giant haloes in mica

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