Introduction

Back in the day when the Cold Fusion was still ‘hot’ Menlove and Prelas reported curious observations of neutron emission associated with the loading of titanium metal with deuterium gas at cryogenic temperature. Specifically, Menlove reported ‘reproducible’ neutron emission coincident with the deuterium loading of titanium sponge at cryogenic temperatures while Prelas reported huge neutron bursts associated with thermal shocking of the cryogenically loaded titanium shavings with hot water.

Both experiments are based on essentially the same idea: once deuterium is absorbed into a titanium lattice, spontaneous lattice deformations (e.g. due to thermal shocking or thermal relaxation) may cause high transient pressures in the dissolved deuterium, which in turn might cause DD nuclear fusion.

Materials and Methods

Due to their simplicity Menlove and Prelas experiments are easy enough to reproduce using the Automated Nuclear Lab and PulseCounter Pro software. For neutron detection I chose 8x ³He-filled proportional counters arranged in a semi-circle. The counters were embedded in HDPE moderator and connected to the ANL as shown on Fig. 1.

The experimental reactor consisted of an aluminum gas cylinder connected to a small vacuum manifold comprising a Pfeiffer APR pressure gauge and a leak valve connected to a deuterium lecture bottle fitted with a regulator. I purchased 1 lb of 325-mesh titanium sponge (Fig. 2) and a lecture bottle of high-purity (99.9% pure) deuterium gas, which I used to load the sponge.

My operating procedure was as follows:

1. After depositing 1 lb of the titanium sponge into the reactor I have evacuated the reactor for several hours under moderate heating (a heating tape was wrapped around the aluminum cylinder housing the sponge) to remove water and any absorbed gases. I quit evacuating when I achieved 1E-6 Torr pressure in the reactor.
2. I filled the reactor with 2000 Torr of deuterium gas by opening the leak valve in the reactor manifold.
3. I dipped the aluminum cylinder into an LN₂ Dewar and allowed it to cool, Fig. 3.

During the cooling the deuterium pressure in the reactor would drop. I did not want the deuterium pressure to drop much below 1000 Torr, so I was periodically opening up the leak valve to admit additional deuterium into the reactor. Because deuterium absorption into titanium is temperature dependent, the most vigorous absorption was evident about 2-3 minutes into the cooling process when the heat from the exothermic deuterium dissolution reaction caused vigorous boiling of LN₂, which was followed by a rapid drop of pressure within the reactor. Eventually the reactor would stabilize with the final deuterium pressure being 850 Torr. The whole process usually took less than 10 minutes although I allowed the cylinder to sit in the reactor for another 30-50 minutes.

Once the titanium sponge was loaded with deuterium I would place the reactor in the counting position as shown on Fig. 1. Sometimes I would pour boiling 100C water into the plastic pitcher housing the aluminum cylinder, which I just removed from the LN₂ Dewar. Other times I would allow the reactor to warm up naturally without using hot water. And one time I have placed the LN₂ Dewar into the counting position to measure neutrons associated with the cryogenic cooling of the titanium sponge as shown on Fig. 3.

Regardless of the procedure, the reactor warm up was always accompanied with the deuterium pressure rise from 850 Torr initially to 2800 Torr at ambient temperature. This pressure change was extremely repeatable and there were no apparent deuterium leaks in the system. I have repeated this protocol several times: I would cool the reactor filled with 2800 Torr of deuterium with LN₂; during the cooling I witnessed the exothermic absorption of deuterium into the titanium sponge, which was evident by the onset of rapid boiling of LN₂; the final pressure in the reactor would be 850 Torr; the warm up to ambient temperature (whether slow / natural or rapid / hot-water-assisted) would result in the final reactor pressure of 2800 Torr consistently.

Results

The resulting neutron counts are shown on Fig. 4.

Each measurement (which corresponds to a vertical bar on Fig. 4) consisted of 10 minutes or 10 CPM count rate samples. The red bars correspond to measurements associated with cooling, while the blue bars correspond to measurements associated with warming up and the background. Even without the color code it is evident that no huge changes in count rates were present during the experiment. The 10-min averaged counts fluctuated between 5 and 8 CPM rather consistently over the span of 160 measurements (1600 minutes total).

More specifically, the first measurement (the first red bar) was captured during the first LN₂ cooling of the titanium sponge followed by thermal shocking with boiling water, which was further followed by cooling to room temperature (measurements 2-22). The resulting P-value trend is characterized by the P-values close to unity, which of course means that there was no significant difference in the count rate between the measurement 1 and the measurements 2 though 22.

The measurements 23-26 (the second group of red bars on Fig. 4) corresponds to the second cooling cycle. The LN₂ Dewar was ~7 feet away from the neutron counters. Although the ~7% count rate increase is evident from the P-value trend, it can hardly be attributed to the neutron flux originating from the cooling of the titanium sponge since the Dewar was far away from the neutron counters. Therefore, the apparent increase in the count rate is likely to be caused by a fluke in the background. This supposition is supported by the P-value trend during the measurements 27 through 70 slowly drifting back up towards unity.

The measurements 71-75 correspond to the third cooling cycle. Here the neutron counts seem to have gone up again. Is this another background fluke? Maybe, but maybe not. Under the hypothesis of the neutrons originating from the cooling titanium sponge, the neutron flux must increase markedly once the Dewar is moved closer to the neutron counters. This is precisely what I did: I placed the Dewar in the counting position as shown on Fig. 3. The resulting measurements are 88-93 (cooling), 94-100 (warming up), 101-105 (cooling again), 106-160 (warming up).

Prior to measurement 88 the P-value was already below 5%. When taken at the face value this meant that the neutron counts during cooling of the titanium sponge in LN₂ were 7% higher compared to the counts associated with the titanium sponge warming up. However, the counts from the Dewar placed right next to the neutron counters were not at all higher than the counts from the Dewar placed 7 feet away from the counting setup. This clearly means that the observed 7% increase in the count rate was not caused by the titanium sponge inside the Dewar.

Conclusion

I did not observe any excess neutron counts associated either with cryogenic loading of titanium sponge in deuterium atmosphere or with thermal shocking of the cryogenically loaded titanium with hot water. As such the results reported by Menlove and Prelas did not check out.

From the philosophical point of view one could never prove a negative, thus it is logically incorrect to state that I have disproved Melove’s and Prelas’s experiments. The correct conclusion is that my replication using the state-of-the-art neutron detection methodology did not reveal any excess neutrons. And the conclusion about no excess counts is a damn solid one.

Another conclusion from this experiment is a pedagogical one: we should not blindly rely on mechanics of statistical analysis and obsess over P-values without conducting additional experiments aimed at bolstering our conclusions. When working with random processes we may (and will!) get results that appear highly statistically significant (P < 5%) purely due to chance or due to systematic errors. However, to prove that these results are meaningful we must demonstrate a causal relationship. In this case there was no such causal relationship as the counts were not changed when the LN₂ Dewar was moved into the counting position from its initial place 7 feet away from the neutron counters. As such the only conclusion that one can derive is that the observed small (~7%) difference in the count rate was likely caused by some unknown systematic, which is most likely to be a natural variation of neutron background.