Neutron standards

World-leading facilities for measuring neutron source emission rates

Our work ensures the continued availability of national standards of neutron fluence and dose equivalent quantities. These standards are essential for calibrating and checking radiological protection instruments and dose meters. We provide an extensive range of accelerator- and source-based calibration fields.

The manganese bath is the primary standard for neutron emission rate at NPL. It measures the number of neutrons per second emitted by sealed radionuclide neutron sources such as ²⁴¹Am-Be and ²⁵²Cf. The sources can then be used to calibrate neutron sensitive devices, such as area survey instruments and personal dose meters.

We are experts at producing well-characterised neutron fields via our neutron facilities, including:

• Radioisotope sources – providing fields that have a broad energy spectrum and a very predictable intensity with emission rates up to 10⁷ neutrons per second
• Monoenergetic neutron fields – produced by our Van de Graaff accelerator, at energies from the keV region to just below 20 MeV. This includes ISO standard monoenergetic neutron fields from 144 keV to 5 MeV.
• Other characterised fields, including high intensity and multi-energy fields, produced via the accelerator
• A thermal neutron facility consisting of a large graphite pile used to thermalise fast neutrons, providing an accelerator-based thermal neutron field.