Separation of an isotope as a precursor of a gamma-raylaser medium

The nuclear isomer ¹⁷⁸Hf^m2, expected to be the most promising candidate for the gamma-ray medium, is rather difficult to produce in large quantities. There are a few ways to create this isomer, such as the irradiation of ¹⁷⁹Hf with high-energy neutrons through the (n,2n) reaction, the irradiation of ¹⁷⁶Yb with high-energy α particles through the (α,2n) reaction, the irradiation of ¹⁸¹Ta with protons through the (p,2p2n) reaction. In some of these reaction schemes the isotopically pure target works better than the natural one from the viewpoint of spectroscopic purity, handling of radioactive materials and productivity. However, isotope separation of heavy elements for producing a precursor as a target material is difficult in terms of cost/effectiveness. The atomic vapor laser isotope separation (AVLIS) method is expected as the most efficient way compared with the normal electromagnetic separation method. This revised version was published online in August 2006 with corrections to the Cover Date.