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7 Exotic Physics The committee was tasked to review a limited set of more far-term, exotic materials that to date have not been seriously considered by the weapons development community as viable candidate energetic materials. This chapter addresses such materials. CURRENT RESEARCH EFFORTS The committee heard presentations and did a literature search concerning two approaches for storing energy at extremely high densities in antimatter, specifically, as positrons in a Penning traps or possibly as positronium in a standing wave laser trap.2 A positron, the antimatter electron, releases 1 MeV on recombination with an electron. This is about 105 times the energy of TNT on a per-molecule basis. Theoretical calculations indicate that practical devices may have to store about 1022 positrons per liter, which is 109 times greater than concentrations that have been stored to date and exceeds by many orders of magnitude current positron storage capabilities. Extreme technological challenges must be overcome before practical devices based on this or other exotic material will be ready for even exploratory development. These challenges include vastly increased production rates for positrons as well as the development of confinement technologies. The committee also received several presentations on nuclear shape/spin isomers as potential high-density storage media. The second metastable isomer of hatnium, 178m2 Hf. is typical of a limited number of nuclear isomers under consideration as energetic materials. It has been calculated that each atom of 178m2 Hf stores 2.5 MeV, which is about 3 x 105 times the energy/molecule of solid TNT. Preliminary experiments, which are under serious debate, suggest that a 10 key photon might trigger a 178m2 hafnium atom to release this energy; however, the efficiency of the triggering process is unknown and may be too small for practical applications. Many significant uncertainties exist about the relevant fundamentals of isomer selection, production, separation, and triggering and radiation handling. The ~ K.W. Edwards, Eglin Air Force Base. 2001. Presentation to the committee. December 14. 2 J. Ackerman, J. Schertzer, and P. Schmelcher. 1997. Long-lived states of positronium in crossed electric and magnetic fields. Phys. Rev. Lett. 78:199-202. 35
36 ADVANCED ENERGETIC MATERIALS committee has no special expertise in these technology areas. However, the technology of nuclear isomers as energetic materials was reviewed earlier by the JASON Committee, which suggested that this line of research was of exceedingly high risk.3 The JASON report concluded that Before committing resources to such an experimental effort, there must be an adequate existence proof in the form of approximate, order of magnitude, estimates to justify investigating this effect. Without such a defendable order of magnitude estimate of how the reaction rate will be increased to useful values, this approach seems to have no merit at the present time. FINDINGS AND RECOMMENDATIONS With respect to exotic physics, the committee found that The use of both antimatter and nuclear isomers for storing energy for rapid release is at a very early, exploratory predevelopment stage. Moving these technologies to development and to engineering practice is far in the future. The payoffs of successful reduction to practice may be very high for technologies based on exotic physics; however, the technical risks are extremely high. Military applications for devices based on exotic approaches need much further elaboration. With respect to pursuing the development of exotic physics, the committee recommends that . The Department of Defense should continue only small investments in well-focused research projects in the area of exotic physics in order to determine whether these technologies might mature toward proof-of-principle demonstrations. Because of the early stages of research, high costs, and high risks, heavy investments in these technologies seem to be premature at this time. The horizons for their practical applications are many decades away. 3 DoD JASON Committee. 1997. High Energy Density Explosives. JSR-97-110.