LBNL Office of science Department of Energy

Ion Beam Technology Group

Lawrence Berkeley National Laboratory

Accelerator Technology & Applied Physics Division

Neutron and Gamma Generators

Develop methods and instrumentation for quantitatively determining the U, Pu, and transuranic actinide (isotopic) distributions in fuel, product, and intermediate materials in advanced fuel cycles. Study active interrogation methods, utilizing photon or neutron beams, for nuclear safeguards.

schematic of a neutron generator

A schematic of a neutron generator. On the left hand side is an ion source from which a Hydrogen isotope ion beam is extracted. This beam is accelerated with a high voltage towards a target on the right hand side, loaded with Deuterium and Tritium, to produce neutrons in a nuclear fusion process.

Research that began in magnetic fusion energy and was then applied to accelerator-based high energy and nuclear physics has led to a new family of simple, efficient neutron sources. One of them - a simple, reliable ion source that uses radio-frequency power for induction heating of a plasma - has been parlayed into a family of compact, efficient neutron generators. They accelerate deuterium or tritium beams into a target that also contains deuterium or tritium, causing a fusion reaction that gives off neutrons. Several years of R&D increased the neutron output by several orders of magnitude, substantially eclipsing existing commercial products of comparable size. Versatile in size and geometry and able to meet specialized pulse-shape requirements, these neutron generators also have a number of potential homeland security applications, which are being explored in cooperation with government agencies and the private sector.

These sources are of widespread interest because neutrons can probe many properties of materials, including aspects of elemental composition that show the presence of chemical explosives or special nuclear materials.

The Ion Beam Technology group has done and is doing research on various ion source concepts such as Penning, radio-frequency, electron cyclotron resonance, and field ionization. Relevant parameters such as atomic fraction, portability, and power consumption differ among the ion sources; the aim is to provide the optimum ion source for different demands.

neutron generator

This compact and simple device can generate 5e11 neutrons per second by accelerating deuterium or tritium (depending on the desired neutron spectrum) into a deuterated or tritiated neutron production target.

Gamma rays can also be used for such "active interrogation," with the same emphasis on small, simple, reliable, and user-friendly devices. Previous projects include what is believed to be the world's first monoenergetic gamma tube, which uses a nuclear interaction between beam and target materials to produce gammas, and a generator that gives a "white" neutron spectrum from 0 to 9 MeV with an especially fast pulse structure for explosives detection through neutron transmission spectroscopy. Another concept, now being modeled, would use nuclear resonance fluorescence (NRF) techniques for determining the isotopic "fingerprint" of used fuel rods and would be useful for nonproliferation and forensics work.

We are also working with a compact device that generates gamma rays of a single, high energy. This device is conceptually similar to the neutron tubes, but instead of using a deuterium beam and a deuterium target to generate neutrons through fusion, it uses a proton beam and a boron, fluorine, or lithium target (depending on the desired gamma-ray energy) to generate monoenergetic gammas through a nuclear process.

pics/tandem.jpg pics/gamma-reactions.png pics/tandem2.jpg

Colleagues elsewhere are using this gamma source in a system that they hope can detect hidden special nuclear materials with a gamma-ray dose an order of magnitude lower than would be needed if they used bremsstrahlung sources, with their broad distribution of energies. Shown here is a 360-MeV tandem device with a 50-mA H- source