The hafnium controversy was a debate over the possibility of "triggering" rapid energy releases, via gamma-ray emission, from 178m2Hf, a nuclear isomer of hafnium. The energy release per event is 5 orders of magnitude (100,000 times) higher than in a typical chemical reaction, but 2 orders of magnitude less than a nuclear fission reaction. In 1998, a group led by Carl Collins in 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 reproduce these results. Peter Zimmerman (an American nuclear physicist and arms-control expert) described claims of weaponization potential as having been based on "very bad science".

Background

178m2Hf is a particularly interesting candidate for induced gamma emission (IGE) experiments, because 178m2Hf's energy is 2.5 MeV per nucleus higher than that of ground-state Hf, and it has a long 31-year half life. If much lower-energy radiation from some agent could "trigger" a release of that stored energy before most of this triggering radiation would be dissipated in competing processes, and if the triggering radiation could be regenerated efficiently by the 2.5 MeV gamma, it might be possible start a cascade of gamma photons. The long half life of 178m2Hf might make it possible to engineer a substance with enough of these energetic nuclei needed for stimulated emission, i.e. a gamma-ray laser. While induced emission of a high-energy photon by a lower-energy photon adds power to a radiation field, stimulated emission adds coherence. With all the caveats about dissipation of the triggering photon, and its efficient recreation by the energetic photon that is being triggered, the process could, in principle, lead to nuclear reaction engines, along with more precise radiometric devices. A proposal to show the efficacy for "triggering" 178m2Hf was approved by a NATO Advanced Research Workshop (NATO-ARW) held in Predeal in 1995. 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 to be extraordinary but were not published. Nevertheless, 178m2Hf was implied to be of special importance to potential applications of IGE. A controversy quickly erupted, mostly between the original proponents of 178m2Hf as having potential military applications as a gamma-ray laser weapon or a non-neutronic but still nuclear-like explosive, and critics who discounted such possibilities due to practical obstacles along the way: 178m2Hf is difficult to make and virtually impossible to separate from the ground-state Hf, the absorption of lower-energy triggering x-rays by the bound electrons around the Hf nucleus, and the minute probability to recreate the trigger-capable x-ray starting with the triggered x-ray itself by multiple random scattering. Still, the military application was enticing enough to try to make 178m2Hf into something useful (rather than an intriguing nucleus suitable for academic study only).

Importance

Chronology of notable events