Radiation detection based on noble-gas scintillation

Arktis’ platform technology for gamma and neutron radiation detection exploits the phenomenon of noble gas scintillation detection. Our technology is suitable both for gamma and neutron radiation detection. One of the unique features offered by our technology is its capability to measure fast neutron radiation directly – without the need for a moderator.

Noble gases as excellent alternative

Noble gas scintillation properties

The Arktis platform technology uses compressed noble gas as a medium for gamma and neutron radiation detection. Noble gases are an abundantly available, low-cost, and safe ressource. They present an excellent alternative to He-3, BF3, Li-6.

Arktis designs and manufactures detectors using Xenon, Argon, and natural Helium as a detector medium. All of these materials allow very powerful discrimination between gamma and neutron radiation, nevertheless, they have different unique properties:

  • Xenon, with an atomic number of 54, has very high charge density, making it well suited for high resolution gamma detection.
  • Argon, at a cost of about $1/kg is perhaps one of the most cost effective detector materials on earth.
  • Natural Helium (He-4), with an atomic number of 2, has very low charge density, making it virtually immune to gamma radiation.

Arktis He-4 based fast neutron detection

Motivation 

Fast neutron detectors have a higher detection potential in passive applications. They provide a unique tool to defeat configurations of heavy shielding. By virtue of He-4's unique physical properties, Arktis' He-4 based neutron detectors may well be the best of breed of fast neutron detectors.

Detection Performance

Two aspects contribute to achieving strong detection performance:

a) High detection efficiency
The probability of detecting a radiation source can be maximized with a scalable system in which detector modules of high intrinsic efficiency can be integrated into a compact array. Scalability must be possible both from a physics point of view, as well as from an availability and cost point of view.

b) Low background
It is easier to hear a whisper in a quiet room than a shout in a train station. The same principle applies to radiation detection, the lower the background, the more easily a signal can be detected. The natural neutron background has a 1/Energy dependence, making it more intense at low energies than at high energies. Thermal neutron detectors are sensitive to the entire background, leading to background count rates of the order of counts per second. Fast neutron detectors can focus on the energy range of interest (from ~400 keV to ~6 MeV) in which fission neutrons are emitted. In this range, the natural background is substantially weaker, of the order of several counts per hour.

Defeating Shielded Sources 

Plot shows, as a function of shielding thickness, which fraction of neutrons escaping from a shielded fission source are actually fast neutrons. Note that shielding significantly attenuates the total flux of neutrons. For example, 75 cm of borated polyethylene shielding suppresses the emitted neutron radiation by a factor 2*10-4. Such weak signals are easily below the natural background count rate detected by thermal neutron detectors. Since the fast neutron background is substantially lower, detection of such a source may still be possible with fast neutron detectors, especially considering that  almost 90% of the egressing neutrons are of high energy. 

Advantages

Advantages of Arktis fast neutron detection

  • Higher sensitivity: Measured in MDL (Minimum Detectable Limits), Arktis technology is capable of detecting weaker radioactive threats at larger distances.
  • Better capability of defeating shielding: Heavily shielded nuclear materials that elude conventional detection with thermal neutron detectors can still be detected with Arktis technology.
  • These performance improvements are achieved without an increase in false alarms.