Nanomedicine, Volume I: Basic Capabilities
© 1999 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999
184.108.40.206 Exothermal Nuclear Catalysis
One solution to low nuclear reaction probability and a poor energy balance is to employ a nuclear catalyst. A number of possibilities have been investigated, as described below.
In principle, the two deuterons in a deuterium molecule can spontaneously fuse to form tritium + proton or He3 + neutron, liberating 4 Mev of energy. The two electrons in the D2 molecule act as a catalyst, holding the deuterons together so they can react. According to quantum mechanics, the deuterons can tunnel toward each other through the classically forbidden region of repulsion until they get so close (~2 x 10-15 m) that the strong force dominates and fusion occurs.605
In practice the rate of this reaction is very small, ~10-74 molecule-1 sec-1.609 But if an electron of mass Me is replaced by a heavier negatively charged particle such as a muon (Mmuon ~ 207 Me), forming a muonic molecule, the required tunneling distance shortens by the ratio of the masses -- in this case, from 5 x 10-11 m to 2 x 10-13 m, making penetration of the barrier much more likely and dramatically raising the reaction rate to ~106 molecule-1 sec-1.607
Muon catalysis of the proton-deuteron reaction, initially proposed theoretically by Frank in 1947,606 was first observed experimentally in 1957 by Alvarez.604 It has since been shown to be an effective means of rapidly inducing fusion reactions in low-temperature (<1200 K) mixtures of hydrogen isotopes, with D-T reaction rates of ~109 sec-1.608,610,611 The field has had its own technical journal, Muon Catalyzed Fusion, since 1987, and there are excellent recent review articles.663,664 But muon catalysis has long been considered impractical for large-scale fusion reactors because the muon is relatively short-lived (2 microsec) and is quickly captured by a helium nucleus formed in a fusion reaction.*605 Typically the number of fusions catalyzed by a muon during its lifetime is ~150 in liquid D2/T2, but ~1000 are needed to achieve energy breakeven given the energy cost of artificial muon production.664 More than 70% of the cosmic ray flux at Earth's surface consists of positive and negative muons, but the cosmic-ray induced fusion rate is still impractically low, ~10-26 watts/micron3 in liquid deuterium targets.665
* In 1975 an even heavier negatively-charged lepton was discovered, the tauon. The internuclear tunneling distance for a hypothetical tauonic deuterium molecule (Mtauon ~ 3500 Me) is only ~10-14 m, which should catalyze fusion almost instantaneously. Unfortunately the tauon is shorter-lived than the muon (~10-11 sec), a lifetime much closer to the typical nuclear reaction time range of 10-13 - 10-21 sec.
It has also been demonstrated experimentally that various changes in chemical composition, pressure, or electric fields can also act as nuclear catalysts, increasing the rates of nuclear transformations:
A. Chemical Composition -- The rate of electron capture for Be7 is 0.08% greater in BeF2 than in metallic Be.390
B. Mechanical Pressure -- The electron capture (EC) decay rates of Tc99 and Ba131 are measurably altered at a pressure of 100,000 atm.612 At 230,000 atm there is a 0.35% increase in the electron density at the nucleus of the free Be atom; the observed increase in the EC decay constant of Be7 oxide with pressure is so linear that it may be used as a method of pressure measurement in diamond anvil experiments in which optical access is impossible.612 It has been suggested that very high pressures could induce fusion.609,933 One experiment in which Pd and Ti immersed in D2O were bombarded with intense ultrasound apparently produced above-background levels of He4, an expected endproduct of D-D fusion processes.1289
C. Fracture Deformations -- Fracto-fusion621 experiments have detected neutron emission when a crystal of lithium deuteride or heavy ice is mechanically fractured, believed to be the consequence of deuteron acceleration by >10 KeV electric fields generated by a propagating crack in the crystal, consistent with D-D fusion.614,620,1009 Heating, cooling, or fracturing metal specimens exposed to high-pressure D2 (e.g., deuterated titanium) frequently produces statistically significant bursts of neutrons and emission of charged particles, rf signals and photons. It is proposed that crack growth results in charge separation on the newly formed crack surfaces, accelerating D+ ions in the electric field across the crack tip to energies >10 KeV sufficient to significantly raise the D-D fusion probability.618 Neutrons are reportedly generated when fragments of titanium are crushed with steel balls in a bath of heavy water.619 It has also been speculated that the core of the spherical acoustic shock wave generated during sonoluminescence, if it remains stable to a 10-nm radius, might reach temperatures appropriate to fusion >~106 K.716,933
D. Electric Fields -- Claytor et al at Los Alamos National Laboratory passed a current of 2.5 amperes at 2000 volts through 200-micron diameter palladium wires in a glow discharge tube of D2 gas at 0.3 atm for ~100 hours apparently producing ~10 nanocuries of tritium, with great care being taken to eliminate possible sources of contamination.613 Deuterium-saturated LiTaO3 crystals in a 75 KV/cm AC field exhibit elevated neutron emission attributed to D-D fusion.2344 Wires of LiD exploded by high current pulses also emit fusion neutrons.622
E. Metallic Deuterides -- Most controversial is the speculative possibility of metallic deuteride catalyzed fusion at temperatures between 300 K1100 K,615-617,624,740,3438 first reported (then later partially retracted!) in the years 1926-27.666 Positive results are reported for a comprehensive series of experiments conducted at SRI International for the Electric Power Research Institute (EPRI) during 1989-94,676,677 and for another comprehensive series of experiments conducted by the U.S. Naval Air Warfare Center at China Lake during 1989-96,1275 and U.S. patents have been issued for such devices (e.g., Patterson and Cravens, U.S. #5,607,563 on 4 March 1997). In another class of experiments [Edmund Storms, personal communication, 1996], a hydrogenophilic metal such as palladium is loaded with deuterium at effective pressures ~10-100 atm, giving molecular loadings of D/Pd = 85%-95%. Palladium deuteride normally exists either as Pd2D or PdD, but it is believed that the highest loadings1610-1612 may give rise to significant concentrations of PdDx (x = 1-2), asserted to be the "nuclear active phase." Superstoichiometric palladium hydride (x = 1.33) at ~50,000 atm has been observed experimentally in X-ray diffraction studies,667 although preliminary molecular simulation studies of deuterium-entrained metal lattices have given pessimistic results.668
Upon applying a current of ~1 nanoampere/micron2 at ~1-10 volts to a superstoichiometric metallic deuteride, significant heat energy in excess of the electrical input is said to be developed as the deuterium is consumed, on the order of 106-109 watts/m3. He4 is claimed to be produced at the expected rate of ~1011 He4 atoms/sec-watt,1275 with neutrons, tritons (tritium nuclei), g-rays and X-rays missing or detected in amounts far too small to account for the excess energy, which is asserted to be evidence of a catalyzed D-D aneutronic process at work. If the results of these experiments were confirmed, it might become possible to use diamondoid pistons to maintain continuously high deuterium loadings in an active catalytic crystal and thus to develop 1-1000 pW of aneutronic thermal energy in a precisely nanomanufactured porous 1 micron3 metal-deuteride reactor with He4 (23.85 MeV) as the principal (and benign) effluent, achieving storage densities >1016 joules/m3 which would allow a completely self-contained >10 year fuel supply to be carried aboard a 10 pW nanorobot in a ~1 micron3 fuel tank.
Last updated on 19 February 2003