© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

6.3.7.3 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 M_e is replaced by a heavier negatively charged particle such as a muon (M_muon ~ 207 M_e), 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 (M_tauon ~ 3500 M_e) 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 loadings^1610-1612 may give rise to significant concentrations of PdD_x (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