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Neutron reference fields from radionuclide sources

The International Organization for Standardization (ISO) recommends different radionuclide neutron sources for the calibration of measuring instruments for use in radiation protection in its standards ISO 8529, part 1-3. An irradiation facility with such sources (252Cf, unmoderated and moderated by 15 cm D2O, 241Am-Be) is available at PTB for calibrations of area monitors as well as calibrations of and comparison measurements for personal neutron dosemeters. The measuring quantities are the ambient and the personal dose equivalent. Furthermore, spectrometers and neutron detectors are examined and calibrated with respect to neutron fluence.

The radiation fields of the radionuclide sources are well characterized. The strengths of the neutron sources were determined at the British metrology institute, NPL, by the primary method manganese bath method. The spectral neutron fluence at the place of measurement was measured with spectrometers and determined by neutron transport calculations. The relative standard uncertainty for the neutron fluence is 0.7 % to 2.3 %, depending on the neutron source. The neutron fluence also serves to determine dose equivalent quantities (e.g., the ambient dose equivalent) using the recommended fluence-to-dose conversion coefficients.

Irradiation facility with radionuclide sources (room size: 7 m x 7 m x 6.5 m):

  • 241Am-9Be(α,n)
  • 252Cf(sf)
  • 252Cf(sf) with D2O moderator

Details of the calibration capabilities with radionuclide neutron sources can be found here.

For further information please contact the Working Group

The irradiation facility with radionuclide sources at PTB with water tank for storage of sources, positioning system for the sources and D2O moderator sphere.

 Spectral neutron fluence rate as a function of neutron energy for the direct and scattered neutrons at the PTB neutron source irradiation facility.


  • Kluge, H (1998):
    Irradiation facility with radioactive reference neutron sources: Basic principles
    PTB-Report N-34. Physikalisch-Technische Bundesanstalt, Braunschweig.