239Pu-Be neutron reference field: Physical and dosimetric parameters

This paper presents the establishment of a Pu-239-Be 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 - phi, unit in cm(-2) s(-1); (iii) neutron ambient dose rate (a new operational quantity) - (H)over dot*, unit in mu Sv h(-1); (iv) neutron ambient dose equivalent rate (an old operational quantity) - (H)over dot*(10), unit in mu Sv h(-1); (v) neutron fluence-to-ambient dose conversion coefficient - h*, unit in pSv cm(2); (vi) fluence-averaged neutron energy - (E) over bar, unit in MeV; and (vii) ambient dose-averaged neutron energy - (E) over tilde, unit in MeV. The standard combined uncertainties of (H)over dot* and (H)over dot*(10) due to the total neutron component were estimated within 10%, considered as acceptable for measurements of (H)over dot* and/or (H)over dot*(10) less than 50 mu Sv h(-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.