The establishment of an absolutely calibrated neutron source

Abstract A 400 me RaBe photoneutron source has been adopted as the national standard source. It has been calibrated by the method of absolute determination of 56 Mn produced in the 55 Mn (n,γ) 56 Mn reaction. The calibration agrees within 1 per cent with an international average. The standard error is ±1 per cent. The error is mainly due to the uncertainty in the knowledge of the manganese and hydrogen thermal neutron capture cross sections. In addition there may be a systematic error not exceeding 1·0 per cent associated with 4πβ proportional counting.