Evaluation of a microdosimeter designed for measurement of neutrons dose-equivalent in mixed neutron-gamma fields

In the present work a microdosimeter designed for measurement of neutrons dose-equivalent, is evaluated in the mixed neutron-gamma fields of 241Am-Be and 252Cf sources. The microdosimeter is considered as an array of 259 similar sensitive volumes to increase the sensitivity to neutrons. Each sensitive volume is a cylinder of 5 mm in diameter and height filled with the tissue-equivalent gas at 0.11 atm pressure to simulate 1 µm of tissue. Dose-equivalent values of neutrons are determined using the microdosimetric distributions calculated by Geant4 simulation toolkit and also considering the separation limit of 3.5 keV/µm between the neutron and gamma contributions in these distributions. Obtained results reveal that the dose-equivalent values of above sources deviate by 9% and 17% from H*(10) values, respectively. Paying attention to the no need for dose calibration of microdosimeters separately in different fields and their trustworthy responses in unknown fields, it can be concluded that the designed microdosimeter can be used in every mixed neutron-gamma field with the maximum energy of 11 MeV in order to measure the dose-equivalent of neutrons.