Evolution of neutron transmutation doped germanium in research reactor HANARO

Abstract

Research on neutron transmutation-doped germanium (NTD-Ge) is underway in the High-flux Advanced Neutron Application Reactor (HANARO) with the aim of developing sensor materials for bolometers used in rare-event experiments such as neutrino-less double beta decay and dark matter searches. In the initial phase, disk-shaped germanium samples from a high-purity germanium (HPGe) crystal were irradiated at the HANARO neutron irradiation facility. The thermal responses and dose rates of the samples were monitored to assess their operational safety. Radioisotopes produced through neutron activation and their characteristic gamma-rays were identified using HPGe gamma-ray spectroscopy. To obtain the quantitative relationship between the neutron fluence and dopant incorporation, the doping concentration of the NTD-Ge samples was assessed through Hall effect measurements. The results showed that the mechanical and electrical integrity of the samples remained stable during irradiation. The gamma spectra of the activated samples were comprehensively analyzed. A doping concentration of approximately 10¹⁵ cm⁻³ was achieved at a neutron fluence of 10¹⁷ n/cm². This study explains the doping behavior and activation characteristics of NTD-Ge samples, thereby supporting the development of high-performance thermistors for low-temperature particle physics detectors.