In April 2005, Seth Putterman's group at UCLA published a paper describing a new method of nuclear fusion based on pyroelectric crystals. In the experiment a pyroelectric crystal, lithium tantalate (LiTaO₃), was heated 25 C in low-pressure (0.7 Pa) deuterium gas generating a potential of 100 kV. The electric field of 25 GV per meter, focussed by a tungsten needle, ionizes the deuterium which is accelerated into a target of erbium deuteride (ErD₂). There the deuterium nuclei fuse about once in every million collisions to produce helium atoms and about 1000 neutrons per second. This device is not capable of producing excess energy, but is considered to be potentially useful in the generation of neutrons.

Observation of nuclear fusion driven by a pyroelectric crystal
B. Naranjo, J.K. Gimzewski and S. Putterman. Nature 434, 1115-1117 (2005)
While progress in fusion research continues with magnetic and inertial confinement, alternative approaches - such as Coulomb explosions of deuterium clusters and ultrafast laser-plasma interactions - also provide insight into basic processes and technological applications. However, attempts to produce fusion in a room temperature solid-state setting, including 'cold' fusion and 'bubble' fusion, have met with deep scepticism. Here we report that gently heating a pyroelectric crystal in a deuterated atmosphere can generate fusion under desktop conditions. The electrostatic field of the crystal is used to generate and accelerate a deuteron beam (> 100 keV and >4 nA), which, upon striking a deuterated target, produces a neutron flux over 400 times the background level. The presence of neutrons from the reaction D + D --> ³He (820 keV) + n (2.45 MeV) within the target is confirmed by pulse shape analysis and proton recoil spectroscopy. As further evidence for this fusion reaction, we use a novel time-of-flight technique to demonstrate the delayed coincidence between the outgoing -particle and the neutron. Although the reported fusion is not useful in the power-producing sense, we anticipate that the system will find application as a simple palm-sized neutron generator.

Details on Pyroelectric Fusion
A Novel Compact Pyroelectric X-ray and Neutron Source. Lead PI: Yaron Danon, Rensselaer Polytechnic Institute
Electron and Positive Ion Beams and X-rays Produced by Heated and Cooled Pyroelectric Crystals such as LiNbO3 and LiTaO3 in Dilute Gases: Phenomenology and Applications. James D. Brownridge and Stephen M. Shafroth
A systematic study has been undertaken of the phenomena associated with the acceleration of nearly monoenergetic high-energy electron and positive ions away from and towards the crystallographic z surfaces of crystals of LiNbO3 and LiTaO3 when they are heated and cooled in a dilute gas. Electron spectra show a multiple peak behavior i.e.peaks of energy E, 2E, 3E are detected. Current vs. time and temperature produced by heated pyroelectric crystals in dilute gas is reported as well as the relationship to x-ray emission. Gas amplification of electron beam energy is described. When the -z surface of a crystal is exposed in dilute gas and the crystal is cooling a self-focusing electron beam is accelerated away from the vicinity of the -z surface. When the +z surface of a crystal is exposed and the crystal in cooling a self-focusing electron beam is accelerated towards the crystal. Conversely when the -z surface of a crystal is exposed and the temperature is raising a self-focusing positive ion beam is accelerated away from the vicinity of the crystal and on cooling the positive ion beam is believed to be accelerated towards the crystal. Self-focused electron beams with energies as high as 170 keV and self-focused positive ion beam with energies as high as 113 keV have been observed. Low temperature behavior of LiNbO3 and LiTaO3 are described and the temperatures where the pyroelectric coefficient goes to zero are reported as 14.09 ± 0.05K and 11.384 ± 0.011K respectively. High temperature behavior up to 200 oC and above where LiNbO3 becomes conducting is reported. The pyroelectric crystals produce high electric fields and the behavior in dilute gases is explained qualitatively. New uses of pyroelectric crystal x-ray generators as portable bremsstrahlung photon fluorescence devices for K x-ray production of high Z up to Bi are described as well as use in teaching x-ray and beam physics. Pyroelectric crystal electron accelerators have been used to excite characteristic K x-rays from tree leaves through out the growing season. Future prospects for pyroelectric crystal research are discussed.

Putterman started this line of research based on a suggestion by Ahmet Erbil.

In March 2005, Geuther and Danon at RPI published a paper describing ion acceleration using pyroelectric crystals. They discuss the possibility of deuterium fusion, but provided no evidence that such a reaction was occurring.

Electron and positive ion acceleration with pyroelectric crystals
Jeffrey A. Geuther and Yaron Danon. J. Appl. Phys. 97, 074109 (2005)
The phenomenon of pyroelectric electron emission has been employed to develop miniature x-ray sources, such as the Cool-X by Amptek (www.amptek.com/coolx.html). The source strength of a pyroelectric x-ray generator is dependent on the emitted electron energy and current. Similarly, the source strength of a pyroelectric neutron generator will be dependent on the energy and production rate of deuterium ions in the fill gas. This paper summarizes our results in experiments directed toward creating high-energy electrons and positive ions with a pyroelectric source. Single-crystal sources are shown to produce positive ions with energies of up to 98 keV and electron energies of up to 143 keV. X-ray spectra are presented as proof that a paired-crystal source can increase electron energy to at least 215 keV. In addition, we offer independent verification of the "bunched" electron emission effect observed by [Brownridge et al., Appl. Phys. Lett. 78, 1158 (2001)].

On February 13, 2006, Rensselaer Polytechnic Institute announced that they had replicated Putterman's work and built an improved double crystal fusion device. The device used two opposing crystals to generate a powerful electric field.

Nuclear Reactions Induced by a Pyroelectric Accelerator
Jeffrey Geuther, Yaron Danon and Frank Saglime. Phys. Rev. Lett. 96, 054803 (2006).
This work demonstrates the use of pyroelectric crystals to induce nuclear reactions. A system based on a pair of pyroelectric crystals is used to ionize gas and accelerate the ions to energies of up to 200 keV. The system operates above room temperature by simply heating or cooling the pyroelectric crystals. A D-D fusion reaction was achieved with this technique, and 2.5 MeV neutrons were detected. The measured neutron yield is in good agreement with the calculated yield. This work also verifies the results published by Naranjo, Gimzewski, and Putterman [Nature (London) 434, 1115 (2005)].

Links

Blob's Discussion of Pyroelectric Fusion
Sonofusion
Wikipedia Article on Pyroelectricity
Wikipedia Article on Pyroelectric Fusion

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