Measuring the thermal neutron fluence of NTD-Ge using the self-monitoring method

Thermal neutron irradiation in reactors is widely used in the different frontier fields, including advanced materials and semiconductor devices. The total thermal neutron fluence is a key parameter in various applications. In this paper, we demonstrate a method to determine the total thermal neutron fluence during the manufacture of Neutron Transmutation Doping Germanium (NTD-Ge). The NTD-Ge samples are irradiated at the China Advanced Research Reactor, and their total neutron fluences are measured using the activity of radionuclide 71Ge through the reaction process 70Ge(n,γ)→ 71Ge ⟶EC 71Ga. The activity of 71Ge in a NTD-Ge sample is obtained by measuring the event rates of the gallium KX-rays with energies of 9.2 and 10.3 keV using a Micro-Megas Detector (MMD) and a Silicon Drift Detector (SDD) individually, and incorporating with the correction of detection efficiencies estimated with the Monte Carlo simulation based on the GEANT4 toolkit. The measurements yield the total thermal neutron fluence with high precision, and the results are well consistent with each other between the MMD and SDD method.