It sounds like magic: long-lived radioactive waste made harmless by a laser beam. Now, for the first time scientists have managed to pull it off, transmuting iodine-129, one of the bad boys of nuclear waste, into the much more benign isotope iodine-128.
Found extensively in radioactive waste, iodine-129 is born inside nuclear reactor fuel rods during the fission of uranium atoms. With a half-life of 15.7 million years, iodine-129 likes to hang around, emitting beta particles as it decays. Radioactive iodine has been associated with thyroid problems, including cancer of the thyroid, the region of the body where ingested iodine-129 tends to concentrate.
In a report published 22 August in the Journal of Physics, researchers describe a technique for converting iodine-129 into iodine-128, an isotope with a half-life of only 25 minutes. Ken Ledingham, a laser nuclear physicist at the University of Strathclyde, U.K., and colleagues, focused a huge laser on a lump of gold. For just a fraction of a picosecond they crammed the equivalent of 1000 times all the electrical power in the United States onto a spot the diameter of a human hair. This generated a stream of gamma rays, which the team trained on a sample of iodine-129, where they knocked out a neutron and created iodine-128.
Until now, such transmutation has required large particle accelerators coupled to nuclear reactors. "This shows there is possibly another way of doing this using lasers, and this sort of transmutation could be a big player in the nuclear industry in 20, maybe 30 years time," says Ledingham.
Using laser transmutation to get rid of nuclear waste is a "a hot topic" says Paul Ewart, a laser physicist at the University of Oxford, U.K. Although Ewart considers it "an exciting prospect," he points out that the process is likely to be expensive and difficult to employ widely. If it can be scaled up, however, it would provide an environmentally friendly alternative to the present iodine disposal method: burial deep in the ground. The technique could also offer a plentiful source of radioisotopes used in hospital PET scanners.