239Pu[sbnd]Be neutron reference field: Physical and dosimetric parameters

Abstract

This paper presents the establishment of a 239PuBe neutron reference field at the Military Institute for Chemical and Environmental Engineering, Hanoi, Viet Nam. The evaluation of the field parameters due to neutrons of the total component was performed using an in-house developed Bonner sphere spectrometer in combination with the output data from the FRUIT unfolding code. As results, these following field parameters were obtained for neutrons of the total component, at several points of interest: (i) neutron fluence spectrum; (ii) integral neutron fluence rate - ϕ, unit in cm−2s−1; (iii) neutron ambient dose rate (a new operational quantity) - Ḣ∗, unit in μSvh−1; (iv) neutron ambient dose equivalent rate (an old operational quantity) - Ḣ∗(10), unit in μSvh−1; (v) neutron fluence-to-ambient dose conversion coefficient - h∗, unit in pSvcm2; (vi) fluence-averaged neutron energy - E¯, unit in MeV; and (vii) ambient dose-averaged neutron energy - E˜, unit in MeV. The standard combined uncertainties of Ḣ∗ and Ḣ∗(10) due to the total neutron component were estimated within 10%, considered as acceptable for measurements of Ḣ∗ and/or Ḣ∗(10) less than 50 μSvh−1. In addition, the fluence-to-ambient dose equivalent conversion coefficient (h) for the direct neutron component was also deduced. The standard deviation of h between those obtained from this work and from published data was calculated as within 5.7%, acceptable for radiation protection purpose.