Neutron source



Neutron source is a general term referring to a variety devices that emit neutrons, irrespective of the mechanism used to produce the neutrons. Depending upon variables including the energy of the neutrons emitted by the source, the rate of neutrons emitted by the source, the size of the source, the cost of owning and maintaining the source, and government regulations related to the source, these devices find use in a diverse array of applications in areas of physics, engineering, medicine, nuclear weapons, petroleum exploration, biology, chemistry, nuclear power and other industries.

There are several kinds of neutron sources:

Contents

Small Sized Devices

Radioisotopes Which Undergo Spontaneous Fission
Certain transuranic element in a nuclear reactor, where neutrons are absorbed in the starting material and its subsequent reaction products, transmuting the starting material into the SF isotope. Cf-252 neutron sources are typically 1/4" to 1/2" in diameter and 1" to 2" in length. When purchased new a typical Cf-252 neutron sources emit between 1×107 to 1×109 neutrons per second but, with a half life of 2.6 years, this neutron output rate drops to half of this original value in 2.6 years. The price of a typical Cf-252 neutron source is from $15,000 to $20,000.
Radioisotopes Which Decay With Alpha Particles Packed In A Low-Z Elemental Matrix
Neutrons are produced when lithium (AmLi).
Radioisotopes Which Decay With High Energy Photons Co-located With Beryllium or Deuterium
Gamma radiation with an energy exceeding the neutron binding energy of a nucleus can eject a neutron. Two examples and their decay products:
  • 9Be + >1.7 Mev photon --> 1 neutron + 2 4He
  • 2H (deuterium) + >2.26 MeV photon --> 1 neutron + 1H
Sealed Tube Neutron Generators
Some accelerator-based tritium ions and metal hydride targets which also contain these isotopes.

Medium Sized Devices

Plasma Focus and Plasma Pinch Devices
The tritium gas is heated to temperatures sufficient for creating fusion.
Light Ion Accelerators
Traditional particle accelerators with hydrogen (H), deuterium (D), or tritium (T) ion sources may be used to produce neutrons using targets of deuterium, tritium, lithium, beryllium, and other low-Z materials. Typically these accelerators operate with voltages in the > 1 MeV range,
High Energy Bremsstrahlung Photoneutron/photofission Systems
Neutrons (so called photoneutrons) are produced when photons above the nuclear binding energy of a substance are incident on that substance, causing it to undergo giant dipole resonance after which it either emits a neutron or undergoes fission. The number of neutrons released by each fission event is dependent on the substance. Typically photons begin to produce neutrons on interaction with normal matter at energies of about 7 to 40 MeV, which means that internal conversion, and thus produce neutrons by a mechanism similar to that of photoneutrons. [1]

Large Sized Devices

Nuclear Fission Reactors
Nuclear fission which takes place within in a reactor produces very large quantities of neutrons and be used can be used for a variety of purposes including power generation and experiments.
Nuclear Fusion Systems
National Ignition Facility in the USA and the recently started ITER experiment in France.
High Energy Physics Accelerators
A spallation source is a high-flux source in which protons that have been accelerated to high energies hit a target material, prompting the emission of neutrons.

Neutron flux

For most applications, a higher neutron flux is always better (since it reduces the time required to conduct the experiment, acquire the image, etc.). Amateur fusion devices, like the fusor, generate only about 300 000 neutrons per second. Commercial fusor devices can generate on the order of 109 neutrons per second, which corresponds to a usable flux of less than 105 n/(cm² s). Large neutron beamlines around the world achieve much greater flux. Reactor-based sources now produce 1015 n/(cm² s), and spallation sources generate greater than 1017 n/(cm² s).

See also

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Neutron_source". A list of authors is available in Wikipedia.