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Neutron metrology

Working Group 6.42


The working group 6.42 realizes the unit of the flux density (dΦ/dt) of monoenergetic and quasi-monoenergetic neutrons in the energy range from 1 keV to 200 MeV and disseminates it to customers from authorities, industry and research. The neutron reference fields used for this purpose are produced at accelerators facilities using nuclear reactions. The neutron flux density is measured employing various reference instruments which enable the detection of neutrons via scattering of protons or via fission of uranium nuclei. The performance of the procedures for the production and measurement of neutron radiation is regularly checked by participating in the international key comparisons (CCRI, EURAMET) for neutron measurements.

The uncertainty of the measurement procedures used for the realization of the neutron flux density is limited by the uncertainty of the cross sections of the nuclear reactions employed for the detection of the neutrons. Therefore, the working group also participates in experiments which aim at improving the data base of reference cross sections.

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  • Development of neutron detectors and measurement techniques for intermediate and fast neutrons (En = 1 keV - 20 MeV) and for high-energy neutrons (En > 20 MeV)
  • Measurement of cross sections for neutron-producing reactions and for neutron-induced nuclear reactions
  • Monte Carlo simulation of experiments

Scattering chamber used for the production of ‘tagged’ 14.2 MeV neutrons by coincident detection of the kinematically correlated alpha particles produced in the 3H(d,n)4He reaction (top figure).

Experiment for the measurement of the neutron emission delayed by β decays after the neutron induced fission of 232Th (bottom figure).

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