Importance
- 178m2Hf has the highest excitation energy of any comparably long-lived isomer. One gram of pure Hf-178-m2 would contain approximately 1330 megajoules of energy, the equivalent of exploding about 300 kilograms (660 pounds) of TNT. The half-life of Hf-178-m2 is 31 years or 1 Gs (gigasecond, 1,000,000,000 seconds) so that a gram's natural radioactivity is 1.6 TBq (terabecquerels) or roughly 40 Ci (curies). The activity is in a cascade of penetrating gamma rays, the most energetic of which is 0.574 MeV. Substantial shielding is needed before it is safe for people to be around.
- All of the energy released would be in the form of photons of X-rays and gamma rays.
- Discussions also indicate that the energy might be released very quickly, so that Hf-178-m2 could produce extremely high powers (on the order of exawatts).
- The characteristic scales of times for processes involved in applications would be favorable for consuming all of the initial radioactivity. The process for triggering a sample by IGE would use photons to trigger and produce photons as a product. The propagation of photons occurs at the speed of light while mechanical disassembly of the target would proceed with a velocity comparable to that of sound. Untriggered 178m2Hf material might not be able to get away from a triggered event if the photons didn't interact first with the electrons.
- Both the proposal to the NATO-ARW and the fragmentary results from the subsequent experiment indicated that the energy of the photon needed to initiate IGE from 178m2Hf would be less than 300 keV. Many economical sources of such low energy X-rays were available for delivering quite large fluxes to target samples of modest dimensions.
- Samples of 178m2Hf were and remain available at low concentrations <0.1%.
Read more about this topic: Hafnium Controversy
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