Scientists at Berkeley Lab have developed innovative neutron generators that can be tailored to meet a variety of specifications. The generators invented by Ka-Ngo Leung and colleagues are unusual because they are compact, designed to be long-lasting and inexpensive to construct yet capable of using safe deuterium-deuterium reactions to produce a high neutron yield or flux. They can also be designed to use tritium-tritium reactions to generate neutrons across a broad energy spectrum or deuterium – tritium reactions to produce higher energy neutrons.
Neutron generators like these can significantly enhance homeland security. X-ray imaging systems widely used in most airports and cargo inspection stations reveal object shapes and detect metals. Neutron-based techniques, however, are materials specific – they can be used to identify the elemental compositions of shipping and luggage content. Fissile materials, as well as conventional and plastic explosives, can be detected using neutron sources.
The Berkeley Lab neutron generators consist of RF-driven plasma ion sources, extractors of various designs, acceleration electrodes, and titanium covered targets. Conventional generators are usually short-lived because the target’s isotopes are quickly consumed. The target in the Berkeley Lab generators, however, is constantly replenished by ions from the plasma source. These devices may last thousands of hours longer than conventional generators.
The Berkeley Lab portfolio includes a multiple beam system for imaging luggage, small neutron tubes for oil well logging while drilling (LWD), as well as designs suitable for cargo interrogation, tumor therapy, and structural inspection. Because neutron generators can be used for imaging and interrogating so many materials, the applications listed for each invention are not exhaustive.
STATUS: All of the Berkeley Lab neutron generators have patents pending (see individual inventions for patent application numbers) and are available for licensing or collaborative research.
Elements of the following inventions can be combined in a variety of ways.
- Cylindrical Neutron Generator with Nested Option, IB-1764
- Neutron-based System for Nondestructive Imaging, IB-1794
- Mini Neutron Tube, IB-1793a
- Mini Neutron Generator, IB-1793b
Cylindrical Neutron Generator with Nested Option, IB-1764
- Neutron Spectroscopy
- Homeland security: detection of explosives and fissile material in cargo or luggage
- Land mine detection
- Structural evaluation, such as examining the integrity of oil tanker walls and tanks
- Boron neutron capture therapy (BNCT)
- Three orders of magnitude increase in neutron output over conventional neutron generators of similar size
- Safer D-D reactions
- Ion source and target layers can be nested to increase neutron output
- Produces radial neutron output
- Highly scalable
Dr. Leung has developed a coaxial RF-driven plasma ion source for a compact cylindrical neutron generator that operates with high current density and produces high atomic deuterium or tritium ion species. The plasma and extraction electrodes electrostatically control the passage of ions out of the ion source. These electrodes contain longitudinal slots along their circumferences so that the ions radiate out of the source in a full 360 degree pattern.
The single target coaxial neutron generator with dimensions of 26 cm in diameter and 28 cm in length is expected to generate a 2.4 MeV D-D neutron flux of 1.2 x 1012 or a 14 MeV D-T neutron flux of 3.5 x 1014 n/s.
An adaptation of the coaxial generator design uses a versatile nested configuration with multiple plasma and target layers where ion beams can impinge on both sides of the targets to enhance neutron yield. A generator with this nested design and dimensions of 48 cm in diameter and 35 cm long should generate a neutron output 10 times higher than the single target generator described above. Thus, D-D neutron output higher than 1013 n/s and D-T neutron output of 1015 n/s should be attainable.
STATUS: U.S. Patent #6,907,097. Available for licensing or collaborative research
Neutron-based System for Nondestructive Imaging, IB-1794
- Imaging baggage or shipping container content, structures and other materials
- Lower construction costs
- Small source for high resolution images (~2 mm)
- Several objects can be imaged simultaneously
- Produces 3.2 x 1011 T-T n/s output flux for exposure times equivalent to large accelerator systems
The Berkeley Lab radiography system is compact and expected to be less expensive to construct than conventional accelerator systems. It is well suited for homeland security luggage inspection systems because the coaxial design produces multiple beams of fast neutrons, allowing several pieces of luggage on a carousel to be imaged at the same time. Neutrons produced from these T-T fusion reactions range in energy from 1 – 9.4 MeV and therefore can image a wide range of content in a single scan.
Dr. Leung’s generator employs a focused ion beam accelerator with a titanium tubing target that oscillates to minimize heat build-up while maximizing neutron output. The 2 mm neutron source can also be designed to generate monoenergetic D-D or D-T neutrons or large fluxes of thermal neutrons by incorporating a moderating device. This potentially low cost device uses a simple cooling system and can be portable.
Other Berkeley Lab designs can be coupled with elements of this invention for T-T, D-D, or T-D spectroscopic interrogation of luggage or other samples.
STATUS: U.S. Patent #6,870,894. Available for licensing or collaborative research
Mini Neutron Tube, IB-1793a
- Homeland security: detection of explosives and fissile materials in luggage or cargo
- Oil well logging while drilling (LWD)
- Surface analysis
- Extremely compact and portable: < 8 mm in diameter and 2 cm long
- Produces 107 n/s
Dr. Leung and Tak Pui Lou have designed a very compact D-D or D-T fast neutron generator in a capsule configuration that is less than 8 mm in diameter and only 2 cm long. This generator is portable and is ideal for insertion into an oil well logging drill. A larger variation of this invention with a longer target is designed to produce D-D neutron flux higher than 1011 n/s with a modest length and diameter. (See the diagram below.)
STATUS: Published Patent Application. Available for licensing or collaborative research
Mini Neutron Generator, IB-1793b
- Fast neutron brachytherapy
- Mobile and compact
- Radiation dose to healthy tissue is expected to be much less than with external sources
- Clinical personnel should receive no radiation when the source is off
- Delivers ~ 106 n/s with D-D reactions and ~ 108 n/s with D-T reactions
- Drug dose distribution around the tumor region is designed to be tailored or eliminated
Accelerator-based neutron generators have been proposed for treating tumors via brachytherapy but the high energy accelerators necessary for the procedure are typically too large for hospital environments. Dr. Leung has designed a compact D-D or D-T neutron generator specifically for treating tumors less than 5 cm in diameter. The generator is composed of a 2 cm x 2.5 cm plasma source from which deuterium or tritium ions are extracted and then accelerated. The accelerated ion beam is then directed down a 10 cm long needle-like tube (diameter ~ 3 mm) with a titanium target at the end.
The neutron source can be inserted directly into the tumor. This should minimize damage to healthy tissue while delivering a potent dose of radiation to the tumor. In contrast to high-dose rate 252Cf sources, Berkeley Lab’s neutron generator should not generate any dose to clinical personnel when the source is turned off.
Berkeley Lab is seeking a qualified industrial partner(s) to further develop this technology. Please visit the following page for more details: http://www.lbl.gov/tt/collaboration/techs/brachytherapy.html
STATUS: Published Patent Application. Available for licensing or collaborative research.