No abstract

No abstract

Stimulated by the recent report of Beuhler, Friedlander, and Friedman on the observation of dd fusion under the impact of heavy-water clusters on deuterated solid targets, we undertook a similar study with pure deuterium clusters (D2oo + -D3oo + ) in the same range of incident energy per deuteron (less than 1 keV). We observed no fusion event and our upper limit for the fusion rate is more than 1 order of magnitude below the Brookhaven value. Additional measurements performed with N" + projectiles were not conclusive but showed that beam-contamination problems may be very serious.PACS numbers: 79.20. Rf, 79.90.+b This experimental work was motivated by the recent observation of "cluster-impact fusion" by Beuhler, Friedlander, and Friedman 1 at Brookhaven National Laboratory (BNL). Fusion was claimed to be observed when (D20)" + clusters, with the number n of molecules per cluster ranging from 20 to 1000, accelerated to a total energy of the order of 300 keV, were sent onto a TiD target. The measured maximum fusion rate is more than 10 10 times larger than that expected from isolated deuterons of the same velocity.The cryogenic source of the Lyon accelerator cannot produce water clusters but can deliver deuterium clusters, which allowed us to test the hypothesis that D" + clusters could induce rf(beam)-rf(target) fusion. This paper describes our experimental search for fusion events when 100-150-keV D2oo + -D30o + clusters, carefully mass and energy analyzed after acceleration, bombard deuterated titanium and polyethylene targets. The net result is that we found no evidence for dd fusion.Moreover, we learned that the authors of Ref. 1 also observed fusion when using light-water clusters 2 as projectiles, but with a rate 20 to 50 times smaller. In that case fusion can be due only to rf(target)-rf(target) collisions, which suggests that the oxygen ions of the water projectiles play a major role in the energy deposition process under cluster impact. Minor modifications of our cryogenic cluster-ion source allowed us to produce and accelerate nitrogen clusters (N" + ) depositing about the same amount of energy in the first target layers as with water clusters. Because of the large mass of the projectiles this last experiment was performed with the direct beam. Under these conditions we have not been able to draw conclusions about rf(target)-rf(target) fusion because of the contamination of the incident beam by fast deuterium species.The setup of our experiment is sketched in Fig. 1. After acceleration the incident clusters are selected, first in energy, by a 74° electrostatic analyzer, and then in mass, by a 16° bending magnet, with a mass-energy product of 60 MeVu. The mass resolution (Am/m -3x 10 ~2) is determined by the exit slit of the magnet and an opaque collimator located 44 cm upstream from the target. The distance between the exit slit and the target amounts to 185 cm. The mass selection of the projectiles after acceleration is a major difference between the Lyon and Brookhaven facilities. At BNL the projec...