Estimation of the response function of a PADC based neutron dosimeter in terms of fluence and Hp(10)

Abstract

The UAB PADC-based neutron dosimeter consists of a 500 μm thick Poly Allyl Diglicol Carbonate layer, covered with polyethylene, to originate protons from fast neutrons through elastic (n,p) scattering, with Makrofol, to flatten the energy response of the dosimeter, especially at high neutron energies, and with Nylon, where protons of 626 keV are produced through the 14N(n,p)14C reaction from incident thermal neutrons. Extensive work was performed in the past to characterise the Hp(10) response of this neutron dosimeter, with exposures to reference monoenergetic fields as well as to ISO radionuclide based sources. In the present work, all known information about the dosimeter response R is gathered in order to build the response curves as a function of incident neutron energy in terms of fluence, RΦ(E), and in terms of personal dose equivalent, RHp(10)(E), for normally incident neutrons. Once RΦ(E) is known, the calculated dosimeter readings when exposed to known neutron fields (SIGMA source (IRSN, Cadarache) and several ISO sources) are evaluated and compared to experimental measurements. Calculated and experimental values agree within uncertainties for the SIGMA source and the 241Am–Be and 252Cf sources, while differences about 20% appear for the D2O moderated sources, which have an important contribution of intermediate energy neutrons. An average value of 350 cm−2 mSv−1 for the coefficient K relating dosimeter reading with personal dose equivalent allows determining neutron personal equivalent doses in the range ∼200 keV–12 MeV with an overall standard uncertainty below 50%, as required for routine operational neutron personal dosimetry.