Nuclear Instruments and Methods in Physics Research B67 (1992) 448-451 North-Holland

Nuclear Instruments & Methods

in Physics Research Sechon 13

The role of fractofusion in the creation of anomalies in neutron production from deuterium-implanted solids

J .S .C . M c K e e , G . R . S m i t h , J . J . G . D u r o c h e r , H . L . J o h n s t o n , M . S . M a t h u r , J .K. M a y e r ,

A . M i r z a i , Y . H . Y e o , A . H e m p e l , H . H n a t i u k a n d S. K i n g

University of Manitoba Accelerator Centre, Department of Physics, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2

K.S. S h a r m a a n d G . W i l l i a m s

Department of Physics, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2

Although most of the evidence for cold fusion has finally proved to be unsupportable, repeated observations of short bursts of neutrons from deuteron-loaded palladium and titanium samples suggest that anomalies exist in the behaviour of deuterium-im- planted solids that may require explafsation. The Manitoba group has seal'ched for anomalous emissions following the direct implantation of palladium, titanium and indium with deuterium, and have observed neutron emissions at a level which may exceed the expectations of standard warm fusion calculations. A specially designed analysis system is now in place to study the behaviour of thin samples of palladium and titanium when implanted with uniquely D~- ions at a concentration of ~ 10 25 per cm 3. The suggestion that the phenomenon of fractofusion may contribute to the cross-section for fusion in these processes is being examined, as it is well known that microcracking in the a phase of palladium is generated by the 13-c~ transformation in that metal. However, until a definlite contribution to the cr~ ss-section for neutron production, additional to that anticipated from standard nuclear reaction calculations is confirmed, the fractofusion process mentioned above cannot be quantified.

1. Introduction

Can deuJterium implanted into palladium, under any circumstances, be expected to undergo significant nu- clear fusion? The purpose of this paper is not only to address this question directly but also to suggest exper- imental measurements that may be helpful in reaching a conclusion on the matter. Some preliminary data will be presented. A priori, however, deuterium fusion in metals seems highly unlikely. To begin with deuterium ions in metals are much further apart than they are in the simple gas phase. In gaseous deuterium, two adja- cent deute:rium nuclei have a separation of about 74 pm. In palladium, the nuclei in the original fcc crystal are 389 pm apart but as deuterium is loaded in their spacing increases to 404 pm in the [~ phase. The deuterium nuclei on the other hand in their octahedral sites, whe~ loaded to the maximum solubility level of around 0.81 are some 285 pm apart, and even if it is possible by ion implantation to reduce this number significantly, the probability of observing nuclear fusion in this situation would normally appear minuscule in the extreme. It is true, of course, that there is still plenty of room within the lattice for additional ions to migrate through it if implantation continues after all normal sites are filled and the maximum concentration possible by electrolysis exceeded. The notion of fracto-

fusion has therefore been introduced as a possible mechanism for the observation of "warm" fusion in such non-equilibrium thermodynamic systems. For fractofusion, to occur in a metal requires two basic conditions to occur. First, fracturing of the material due to excess gas concentration must be possible, and second, at least locally, metal-dielectric transitions within the deuterium-loaded palladium must exist with a lifetime long enough for particle acceleration across the fracture to occur. Let us deal with these two phenomena separately.

2. Fracturing of metals as a result of gas loading

Such fractures are well documented and well stud- ied. Jamieson [1] has demonstrated that fracturing of palladium can occur when cycling between c~ and B phase loading of hydrogen is undertaken at constant pressure and temperature. Of course the swelling of metals loaded with gases for which normal solubility is low, is readily measured, and volume changes of ~ 10% have been reported for hydrogen and deuterium loaded palladium. In addition, acoustic emission methods are now routinely used to monitor crack formation in tri- tium-loaded metals such as tantalum and niobium, and

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helium gas emissions have been measured which corre- late well with fracturing of the materials [2]. Strain gauge measurements of bubble pressures in these ex- periments indicate that pressures in excess of 10 GPa are not unlikely. Such bubble formation appears to lead directly to cracking of the materials involved. Furth [3] and Mayer, King and Reitz [4] have proposed that when a crystal is fractured and charge separation occurs, high electric fields can be generated locally which could accelerate either deuterons or electrons across the gap, always assuming that the charge re- mains in place for a time long enough to ensure that acceleration is completed. Fig. 1 shows a schematic plot of the R C time constant of a crack, assumed to be a shorted parallel plate capacitor for crack separation distances of 0.1 and 1.0 ~m. Crack lengths larger than those indic~i~d by the arrows have sufficient time to fully accelerate the deuterons across a free space gap. While this argument is essentially qualitative, it does appear that high transient potentials have already been measured in mechanically fractured ionic materials. The extension of this result to pure metals however does currently present some difficulty.

3. Mechanisms of fracturing interbubbie fracture and dislocation loop punching

Much of the work on fracturing in metals has previ- ously been carried out on aging tritides and the evolv- ing 3He bubble formation. However, there is little reason to believe that where bubble formation is due to the continued implantation of deuterons the system should not behave in a similar fashion. H and D implants, as Evans [5] has pointed out, generally give

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bubble and blister formation that is similar to that from helium implantation. There is, however, a likely greater loss of hydrogen and deuterium during implan- tation than from the unimplanted metal tritide mate- rial. Much of our understanding of bubble formation and interbubble fracturing is due to Evans and cowork- ers. Fig. 2 shows schematically the steps involved in pressure buildup, bubble growth, cracking and blister- ing. The generation of microscopic bubbles, two-di- mensional macroscopic discs, and finally surface blis- ters, seem to be well understood in terms of their work. Scanning and transmission electron microscopy have proved invaluable in studying substructure changes in aging tritides [6] and these techniques are of continu- ing value in the examination of implanted metals. Fig. 3 shows a small section of implanted palladium after the onset of blistering. The blister shown is approxi- mately 5 p.m in diameter and basically what one would expect for a uniformly rough or a smooth foil after a certain fluence of implanted ions. This sample was implanted using a 60 keV beam from the Narodny Linear Accelerator at the University of Manitoba. The total fluence was around 102°/cm2. Some time ago, Townsend, Kelly and Hartley [7] studied bubbles and voids and concluded that if a high vacancy concentra- tion is produced in a solid there is a tendency to form large empty volumes or voids. Insoluble gas atoms migrate to these voids and build up bubbles, the shape of which is determined by the surface energy of the walls. This result is, however, questionable as they ignored the existence of self-interstitials.

Because bubble formation requires nucleation, bub- ble density will vary with the density of impurities in the material. An insufficient vacancy supply, however,

Bubble Pressure

Oepth (o} (b)

{c) (d) (e}

Fig. 2. lnterbubble fracture mechanism: (a) high density of overpressurized bubbles; (b) crack formation; (c) bubbles ad- jacent to original crack become involved to widen crack and increase pressure; (d) penny-shaped crack which either ex- tends to cause flaking or (e) forms blister by gas-driven

surface deformation (taken from ref. [I I]).

VII. IMPLANTING, ANNEALING, MIXING

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J.S.C. McKee et al. / Fractofusion in deuterium-implanted solids

of metallic atoms to accumulation on deuterium atoms in the deuterium implanted metal, under conditions of extreme mechanical failure or non-equilibrium loading. Such hydrides would be basically unstable short-lived phases, but this is what may be required.

(b) Solid state zone theory ip.dicates that an in- crease in interatomic distance in crystals leads to a lessening of conductivity zones and expanded band gaps - corresponding to a metal-insulator transition. The observed swelling of hydrogen-implanted palla- dium and titanium suggests that such transitions may play a role.

S. Present and future w o r k at the Acce lerator Centre Univers i ty of Mani toba

Evidence for fractofusion should it exist may bc difficult to find. Neutrons from microscopic "warm" fusion are clearly evident in implantation experiments, but whether or not the numbers are precisely as ex- pected from traditional calculations is difficult to de- termine without precise information as to variation in

Fig. 3. Blister ~ 5 Ixm diameter in implanted Pd. ~oo~

does not necessarily inhibit bubble growth [8]. Pres- sure-driven processes such as interstitial emission and dislocation loop punching are triggered by the implan- tation prcw.ess. Conditions for loop punching by bub- bles as small as 1 nm in diameter have been discussed, and since such a loop originates in the bubble, its radius cannot be much larger than the bubble itself. The details of the loop formation process close to the bubble surface seem not to be well understood.

4. M a i n t a i n i n g charge separat ion across a fracture

In order to establish an electric field capable of accelerating deuterium ions or electrons, rapid conduc- tion of charge from a site must be inhibited. For such to be the= case the material under implantation must exhibit dielectric properties, at least on the local scale. Chechin :rod Tsarev [9] have discussed this problem in relation to basically non-ionic dielectric materials such as metals and metal hydrides.

In order to increase the dielectric properties of the materials one of two novel explanations must be in- volved:

(a) In a similar way to which hydrides of rare earth metals range from less saturated metal hydrides to more saturated ionic or ion covalence hydrides, it may be possible to direct a number of the valence electrons

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Channel No. Fig. 4. Top: X-rays from deuterium-implanted Pd; short inter- val ( ~ l0 min) at 9 h, flux 1016 cm -2 s- l ; K, and Kp X-rays from Pd clearly visible. Bottom: X-rays from deuterium-im- planted Pd; short interval ( ~ 10 min) at 23 h, flux 1016 cm -2 s- t ; K, and Kt3 X-rays from Pd clearly visible. Source

of additional X-rays unknown.

J.S.C. McKee et aL / Fractofusion in deuterium-implanted solids

concentration and temperature with film depth, and loss of deuterium gas from the material as a whole, see McKee et al. [10]. If accelerating fractures do exist, and evidence for that is forthcoming, it is most likely that evidence from accelerated electrons will be more read- ily available. In a recent high-fluence experimental run in which deuterium ions were implanted into a 25.4 mm square, 1 mm thick palladium sheet, K X-ray pro- duction was monitored for a period of 24 h. The spectrum was recorded event by event having previ- ously been calibrated using 241Am as an appropriate source. K X-rays from Pd were constantly observed and the peak heights for a given integrated beam current stayed fairly constant. Other X-rays, however, made their appearance from time to time, often below but sometimes above the Pd energies. Indeed as time of implantation increased, there was a tendency for X-rays to be generated with an energy at least equal to the maximum possible on the basis of implantation energy. The random nature of the additional compo- nent to the X-ray spectrum and the constancy of other features indicates to us that further detailed study of this phenomenon is appropriate. Fig. 4 shows data for two different time intervals within the experiment.

At the present time, further experiments using the implanter are planned in which we will measure di- rectly, in addition to neutron production and X-ray production, onset of blistering, resistivity and resist- ance of each sample, sample temperature, and hope- fully acoustic emission and bubble pressure. The new

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analyzed beam facility funded by Manitoba Hydro will enable a unique species of ion to be selected for each experiment. It is expected that much of this work will be completed in 1992.

References

[1] H.C. Jamieson, G.C. Weatherly and F.D. Manchester, J. Less-Common Met. 50 (1976) 85.

[2] T. Schober, J. Golczewski, R. I_~sser, C. Dieker and H. Trinkaus, Z. Phys. Chem. (Frankfurt am Main) 147 (1986) 161.

[3] H. Furth, comment at APS meeting, Baltimore, 1989. [4] F.J. Mayer, J.S. King and J.R. Reitz, paper presented at

the Workshop on Cold Fusion Phenomena, Santa Fe, NM, 1989, to be published.

[5] J.H. Evans, private communication (1991); J. Nucl. Mater. 76 & 77 (1978) 228.

[6] T. Schober, H. Trinkaus and R. L~isser, J. Nucl. Mater. 141-143 (1986) 453.

[7] See: P.D. Townsend, J.C. Kelly and N.E.W. Hartley, Ion Implantation, Sputtering and their Applications (Aca- demic Press, London, 1976).

[8] H. Trinkaus and W.G. Wolfer, J. Nucl. Mater. 122 & 123 (1984) 552.

[9] V.A. Chechin and V.A. Tsarev, Preprint 172 (Lebedev Physical Institute, USSR Academy of Sciences, 1990).

[10] J.S.C. McKee et al., Proc. Int. Workshop on Anomalous Nuclear Effects in Deuterium/Solid Systems, ed. S. Jones, AIP Conf. Proc. 228 (1991) p. 275.

[11] J.H. Evans, J. Nucl. Mater. 68 (1977) 129.

VII. IMPLANTING, ANNEALING, MIXING