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Hafnium controversy
The hafnium controversy is a debate over the possibility of 'triggering' rapid energy releases, via gamma ray emission, from a nuclear isomer of hafnium, 178m2Hf. The energy release is potentially 5 orders of magnitude (100,000 times) more energetic than a chemical reaction, but 3 orders of magnitude less than a nuclear reaction. In 1998, a group led by Carl Collins of the University of Texas at Dallas reported having successfully initiated such a trigger. Signal-to-noise ratios were small in those first experiments, and to date no other group has been able to duplicate these results.
==Background==
178m2Hf is a particularly attractive candidate for ''induced gamma emission'' (IGE) experiments, because of its high density of stored energy, 2.5 MeV per nucleus, and long 31-year half life for storing that energy. If radiation from some agent could "trigger" a release of that stored energy, the resulting cascade of gamma photons would have the best chance of finding a pair of excited states with the inverted lifetimes needed for stimulated emission. While induced emission adds only power to a radiation field, stimulated emission adds coherence. The possibility to manipulate gamma ray coherence, even to a small degree, would be interesting.〔Dietrick E. Thomsen (Pumping up hope for gamma ray laser ), Science News, Nov 1, 1986〕 The lifetime of the hafnium isomer is long enough for tractable amounts of material to be collected into experimental targets. Such samples would hold no hazards for personnel working with the material; 1 microgram of 178m2Hf has an activity of .
A proposal to test the efficacy for "triggering" 178m2Hf was approved by a NATO-Advanced Research Workshop (NATO-ARW) held in Predeal in 1995.〔Proceedings of the NATO-ARW are collected in ''Hyperfine Interactions'', 107, pp 3–492 (1997).〕 Although the proposal was to use incident protons to bombard the target, α-particles were available when the first experiment was scheduled. It was done by a French, Russian, Romanian and American team. Results were said 〔(Link to review of "Isomer Triggering history from one participant. )〕 to be extraordinary, but the results were not published. Nevertheless, 178m2Hf was implied to be of special importance to potential applications of IGE. A controversy quickly erupted.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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