Neutron Metrology
Neutrons have many uses in a wide range of environments. Their ability to induce nuclear fission makes them fundamental to nuclear power, and their penetrating nature makes them useful probes into the composition and structure of materials and artefacts. In addition to their industrial uses they also have some medical applications, such as isotope production. In all cases, it is important to know how many neutrons there are, and what risk they pose to anyone present.
NPL hosts a world-leading facility for measuring the neutron emissions from radionuclide sources.
To support these services extensive research is carried out to improve not only the standards but also the basic techniques used to measure neutron fluence and dose equivalent. An increasingly powerful tool in this research is the use of computer codes to simulate neutron sources, detectors and even whole facilities.
Several radionuclide sources (with broad energy spectra) are available, as are monoenergetic neutrons derived from the section's 3.5 MV Van de Graaff accelerator.
Another key area of the NM section’s capabilities is the range of field instruments available for use. These include active and passive systems to measure neutron fluence rates and energy spectra, as well as instruments for performing neutron dosimetry, including cosmic ray dosimetry for air crew. The fields generated are representative of those found in workplaces around nuclear facilities.
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- Collaborative work in the Neutron metrology area is undertaken with a number of organisations.
- The manganese bath is the primary standard for neutron emission rate at NPL.
- The primary objective of this work is to ensure the continued availability of national standards of neutron fluence and dose equivalent quantities.
- NPL has a suite of neutron spectrometers that are used for characterising workplace fields in the nuclear industry or anywhere neutrons are a hazard. The devices are also used to derive knowledge about the spectra of standard neutron fields used for calibration and type testing.
- NPL can undertake on-site spectrometry measurements which, in addition to providing information for radiation protection applications, can also be used, for example, to determine the neutron output from a range of devices.
Neutron Metrology products & services
- NPL is one of the few laboratories in the UK that can offer performance testing of dosimetry services for fast neutron radiation.
- Radiation levels at aircraft cruising altitudes are twenty times higher than at sea level. The main source is galactic cosmic radiation, primarily generated by exploding stars within our own galaxy.
- Microdosimetry is a useful tool in the measurement of radiation levels in the workplace and has one distinct advantage over other techniques: it records a spectrum that can be analysed to give separate photon and neutron dose rates and dose equivalent rates in a single measurement.
- NPL is one of the few national standards laboratories worldwide that offers an absolute measurement of the total emission rate of a radionuclide neutron source into 4π steradians.
- At NPL well-characterised mono-energetic neutron fields covering the greater part of the energy range 70 keV to 5 MeV are routinely available for the calibration of neutron sensitive devices or for irradiation purposes.
- NPL has particular expertise both in the measurement of neutron fields and in calculations with neutron transport codes. This expertise is available to customers in a variety of ways depending on the scope and nature of the work.
- NPL can undertake on-site spectrometry measurements which, in addition to providing information for radiation protection applications, can also be used for example to determine the neutron output from a range of devices.
- A variety of radionuclide neutron sources are available to provide, at NPL, well-characterised neutron fields for calibrating neutron sensitive devices or for irradiating samples.
- Well characterised thermal neutron fields are available at NPL for the calibration of neutron measuring devices e.g. area survey instruments or personal dosemeters, and for irradiation purposes.
- The transfer standard for thermal neutron fluence is based on the activation of gold foils and the subsequent measurement of the induced activity. The activity is directly proportional to the fluence but also depends on the neutron spectrum.
- Minutes of the 2010 Neutron Users Club meeting.
- The Neutron Users Club acts as a focal point for discussion of the production, use and metrology of neutron fields.
- Resources to find nuclear data.
- The UK Nuclear Science Forum (UKNSF) covers the measurement and evaluation of nuclear data for applications in the nuclear industry, nuclear medicine and protection of the environment.