User:ObsidianOrder/Cold fusion redux

History

Early work

• Paneth
• Tandberg
• Palmer

Pons and Fleischman

See full article [Pons and Fleischman cold fusion experiment]

• rationale for the experiment: combination of monoatomic absorption and high conductivity in deuterated palladium

• setup: D2O electrolysis to load up palladium cathode with monoatomic deuterium produced in situ
• cell dimensions of ?? ml, current ?? mA, applied power ?? mW, excess power claimed ?? mW
• open-type indirect isoperibolic calorimeter
• water bath kept at constant temperature, compensating heater keeps interior at constant temperature as well, difference between inside and outside temperature is constant. excess power is derived from measuring the power applied to the compensating heater and subtracting that from the known (calibrated) heat flow.
• mixing by gas sparging with a time constant on the order of ?? seconds. no active mixing.

Controversy

• numerous attempts to reproduce, starting immediately after the announcement
• some were claimed as successfull (source), some were claimed as not (source). (list) (summary)
• early experiments, including P&F and attempts to reproduce, have been criticised as being poorly conducted in later analyses (source)
• at least some of the failed reproductions can be explained by factors which are now known or suspected to affect the results (source)
• P&F criticised for not making available all necessary information to reproduce the experiment (source)
• the debate quickly turned acrimonious, with a flurry of charges of incompetence, countercharges, press conferences, and numerous articles in the popular press. (source) eventually some (source) started making charges of fraud.

Ban

• the outcome was after several negative reports (ERAB/DoE), prominent scientists (list) and publications (list) took the stance that cold fusion was pathological science
• journals that will officially not publish cold fusion related articles include: (list)
• however a number of scientists, particularly from teams that had performed successful reproductions of P&F, continued work. (list)
• several publications devoted to publishing cold fusion papers have sprung up
• there is a semi-annual international conference on cold fusion

Theoretical objections

Insufficient energy to bring nuclei together

• in hot fusion, D nuclei require ?? MeV to overcome the electrostatic repulsion and bring them together. that corresponds to an effective temperature of ? degrees K. it is unclear how any process can concentrate that much energy in a single deuterium atom in an electochemical cell, or inside the palladium metal lattice, at room temperature.
• average distance between nuclei of atomic deuterium absorbed in Pd is 0.17nm (source) which is actually greater than in a D2 molecule (?? nm). this is much higher than that required for fusion, on the order of ?? nm (source)

Lack of expected isotopic products

• in hot fusion D+D produces either T+p or 3He+n (roughly equal ratios).
• although some reports of T and 3He production exist (source), they are not in a quantity consistent with the energy output.
• it has been proposed that the predominant reaction pathway is D+D -> 4He+gamma (source), which is a very rare reaction pathway in hot D+D fusion (1 in ??).
• 4He has been reported in quantities consistent with the energy output (source), but the corresponding gamma rays are largely absent.

Lack of energetic protons, neutrons and gamma rays

• the level of neutron radiation from D+D->3He+n corresponding to the excess energy output (?? W per W of output) seen in cold fusion is high enough to be dangerous to anyone in the vicinity (?? rad/second for a person 1m away from a cell with 0.1W excess power). it should also be very easy to detect.
• while that level of radiation is not seen, there are reports of very low neutron emissions (close to background levels)( source?).
• the other proposed pathway D+D->4He+gamma, should produce a high level of gamma rays, which would also be very easy to detect. those are not seen either, although again there are reports of very low levels of gamma ray emissions (source).

Conversion of energy to heat

• in hot fusion, a large fraction of the total energy output is carried away as high-energy particles as described in the last section. since those are mostly absent, cold fusion requires a highly efficient mechanism to convert fusion energy directly to heat, presumably by some means of coupling the fusing nuclei to the palladium lattice. at present there is no theory that can explain such a mechanism.

Practical difficulties

Problems with reproduction

• some Pd samples work, some don't
• long (and apparently random) delay until heat production, needs to run without interruptions
• water vapor (from the atmosphere) kills the effect
• heat is produced in bursts

There is clear unrefuted evidence that the work by Fleischman and Pons generated excessive heat - more than can be explained by a chemical reaction. Rather than given recognition for that fact, they were utterly attacked by the elite scientific community. Tritium was also produced which is a clear indication of a nuclear event and contradicts a chemical reaction.

Calorimetry difficulties

• different kinds of calorimeters: open/closed, isoperibolic, Seebeck, flow
• factors affecting accuracy

Isotopic contamination

• 4He in particular is present at relatively high levels in air (~5ppm) and can contaminate gas samples.
• electrochemical isotopic enrichment has been proposed as an explanation for some of the isotope finds, in particular on electrode surfaces.

Proposed mechanisms

There are three elements of cold fusion which would require a new theoretical explanation:

• the way in which the coulomb barrier can be overcome at low temperatures
• the radically changed branch probabilities of the nuclear reaction, and
• the way in which energy is converted entirely to heat and not to energetic particles

Bose condensation-like

• theoretical work (source) suggests that deuterons in shallow potential wells such as may be found in a palladium metal lattice may exhibit a cooperative behaviour similar to a bose condensate. this would allow nuclei to react despite the coulomb barrier, due to tunneling and superposition. however, traditional bose condensates only occur at much lower temperatures (close to absolute zero).
• "ion band states", Bloch condensates (source)

Mossbauer effect-like

• theoretical work (source) suggests that in the energy of fusion can be transmitted to the entire metal lattice rather than a single atom, preventing the emission of gamma rays. it is interesting to compare this to the mossbauer effect, in which the recoil energy of a nuclear transition is absorbed by a crystal lattice as a whole, rather than by a single atom. however, the energy involved must be less than that of a phonon, on the order of ?? keV, compared with ?? MeV in cold fusion.

Current research

Groups

• SRI (partly funded by EPRI)
• Naval Research Laboratory
• China Lake Naval Weapons Laboratory(?)
• Mitsubishi
• Centro Ricerche di Frascati, ENEA

• Bhabha Atomic Research Centre (BARC) - active until ??
• Technova - active until ??

Different forms of the experiment

• electrolysis using electrodeposited Pd on carbon electrodes
• suspension of Pd
• D2 gas passage through thin Pd films
• glow/arc discharge

Improvements in reproducibility

factors affecting reproducibility center on the physical and chemical structure of the Pd cathode, and the maximum degree of D loading which can be obtained. several techniques are reported to improve reproducibility:

• cold-working (cite)
• oxidation in air followed by electro-reduction (cite)
• certain additives such as boron in the palladium (cite)
• using electrodeposited cathodes, which have a preductable structure and which can be co-deposited with D to produce an already loaded cathode, eliminating the delay to fusion (cite)
• certain additives such as aluminum ions (cite)

it is important to monitor the D/Pd ratio since cold fusion only appears to occur above a ratio of 0.85-0.9, and possibly even higher.

Other kinds of cold fusion

Locally cold

• muon-catalyzed fusion

Locally hot

• sonoluminescence
• pyroelectric
• farnsworth-hirsch fusor
• antimatter-initialized
• cluster impact