Neutron generator
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Overview
Neutron generators are neutron source devices which contain compact linear accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deuterium, tritium, or a mixture of these two isotopes into a metal hydride target which also contains either deuterium, tritium or a mixture. Fusion of deuterium atoms (D + D) results in the formation of a He-3 ion and a neutron with a kinetic energy of approximately 2.5 MeV. Fusion of a deuterium and a tritium atom (D + T) results in the formation of a He-4 ion and a neutron with a kinetic energy of approximately 14.1 MeV.
Thousands of such small, relatively inexpensive systems have been built over the past five decades.
Neutron Generator Overview
Sealed Neutron Tubes
Ion Sources
Spark Gap
Cold Cathode (Penning)
Hot Cathode
Microwave
Electron Cyclotron Resonance (ECR)
Radio Frequency (RF)
Targets
High Voltage Power Supplies
One particularly interesting approach for generating the high voltage fields needed to accelerate ions in a neutron tube is to use a pyroelectric crystal. In April of 2005 researchers at UCLA demonstrated the use of a thermally cycled pyroelectric crystal to generate high electric fields in a neutron generator application. In February of 2006 researchers at Rensselaer Polytechnic Institute demonstrated the use of two oppositely poled crystals for this application. Using these low-tech power supplies it is possible to generate a sufficiently high electric field gradient across an accelerating gap to accelerate deuterium ions into a deuterated target to produce the D + D fusion reaction. These devices are similar in their operating principle to conventional sealed-tube neutron generators which typically use Cockcroft-Walton type high voltage power supplies. The novelty of this approach is in the simplicity of the high voltage source. Unfortunately, the relatively low accelerating current that pyroelectric crystals can generate, together with the modest pulsing frequencies that can be achieved (a few cycles per minute) limits their near-term application in comparison with today's commercial products (see below). Also see pyroelectric fusion. [1]
High Voltage Insulation
Other Neutron Generator Technologies
In addition to the conventional neutron generator design described above several other approaches exist to use electrical systems for producing neutrons.
Inertial Electrostatic Confinement/Fusor
- Another type of innovative neutron generator is the inertial electrostatic confinement fusion device. This neutron generator differs from the conventional ion beam onto solid target types because it avoids using a solid target which will be sputter eroded causing metalization of insulating surfaces. Depletion of the reactant gas within the solid target is also avoided. Far greater operational lifetime is achieved. Originally called a fusor, it was invented by Philo Farnsworth, the inventor of electronic television. This type of neutron generator is manufactured by NSD-Fusion. (Note: An extensive discussion of this technology is available in the fusor wiki.)
Dense Plasma Focus
Organizations that manufacture neutron generators
- Adelphi Technology, Adelphi Technology (USA)
- Baker Hughes , Baker Hughes (USA)
- EADS SODERN , EADS SODERN (France)
- Halliburton, Halliburton (USA)
- Hotwell, Hotwell GmbH (Austria) [Using neutron tubes from VNIIA]
- Lawrence Berkeley National Laboratory, Lawrence Berkeley National Laboratory (USA)
- NSD-Fusion, NSD-Fusion (Germany)
- Sandia National Laboratories , Sandia National Laboratories (USA)
- Schlumberger, Schlumberger (USA)
- Thermo Electron Corporation, Thermo Electron Corporation (USA)
- VNIIA, VNIIA All Russia Research Institute of Automatics (Russia)
See Also ...
- Fast neutron
- Nuclear fission
- Nuclear fusion
- Neutron source
- Neutron moderator
- Radioactive decay
- Radioactivity
- Slow neutron
External Links
- Compact Accelerator Neutron Generators, AIP, The Industrial Physicist