Heavy water (deuterium oxide, D2O) is water in which hydrogen atoms (1H, H), one of the constituent elements of water molecules, have been replaced with deuterium (2H, D), a heavier isotope. Heavy water is used in a variety of industries, including semiconductors, nuclear magnetic resonance, infrared spectroscopy, neutron deceleration, neutrino detection, metabolic rate studies, neutron capture therapy, and the production of radioactive materials such as plutonium and tritium. In particular, heavy water is used as a neutron moderator or coolant in nuclear reactors and as a fuel for nuclear fusion energy, methods for measuring heavy water are becoming increasingly important. There are methods with density, mass spectrometry, and infrared (IR) spectroscopy. In this study, Fourier transform infrared spectroscopy (FT-IR) was used, which is commonly used in IR spectroscopy because of its relatively high analytical sensitivity, low operating costs, and easy online analysis. Heavy water was identified in the range of 2,300-2,600 cm-1 wavenumber (O-D) and the range of 1,200-1,300 cm-1 wavenumber (D-O-D), which are known to be the range with strong infrared absorption. As a result, the linearity of infrared absorbance for each heavy water concentration was confirmed within the relative expansion uncertainty (k=2).

Among the test categories of the personal dosimetry performance test in Korea, the reference neutron radiation field used for the mixed neutron-photon radiation field is generated by a D2Omoderated 252Cf source. There are some differences depending on the standards, D2O-moderated 252Cf source consists of the 252Cf source surrounded by the D2O sphere with a diameter of 30 cm, covered with a Cd shell of thickness approximately 0.051 cm ~ 0.1 cm. In order to optimize the design of the D2O sphere and establish the neutron radiation field for the personal dosimetry performance test in Central Research Institute of KHNP, the neutron spectra have been simulated by MCNP 6.2 code by design conditions and evaluated dose conversion coefficients. In the consideration of neutron irradiation facility, the basic design structure was determined a D2O sphere with a diameter of covered with a Cd shell and a cylindrical well is in the middle of sphere. Neutron source transfer tube is inserted into this well-shaped structure and neutron source was withdrawn from the tube. And by changing the following design conditions in detail, the neutron spectra were evaluated; 1) the entire diameter of the D2O sphere (with or without the diameter of 7.5 cm of well-shaped structure) 2) the location of the neutron source (distance from D2O) 3) thickness of Cd shell 4) purity of D2O. As a source spectrum, the spectrum of bare- 252Cf recommended by ISO 8529-1 was adopted and spectra were tallied using F4 tally at a distance of 120 cm from the neutron source. Finally, the fluence to dose conversion coefficients were calculated using the simulated spectra. As a result of the evaluation, in case that an entire diameter of the D2O sphere with a diameter of the source tube is 37.5 cm, the fluence to dose conversion coefficient was evaluated to about 4.4% lower than an entire diameter of the D2O sphere is 30 cm. And in case that the distance between the D2O and the top of the neutron source was about 3.75 cm which is a radius of well-type structure, it was evaluated to about 1.4% larger than the distance was about 1 cm, and when the thickness of Cd was 0.1 cm, it was evaluated to 0.8% larger than when it was 0.051 cm. Finally, when the purity of D2O was 99.99%, it was evaluated 1.5% lower than when it was 99%. Except for the diameter of D2O sphere, the differences on the other conditions are acceptable considering the uncertainty of the simulation. Therefore, the design of D2O-moderated 252Cf source was determined by considering source integrity, economic perspectives, and dose conversion coefficient given in ISO 8529: a D2O sphere with an entire diameter of 37.5 cm, filled with above 99% purity of D2O, and covered with a cadmium thickness of 0.1 cm. The fluence to dose conversion efficient was evaluated as 110.10 pSv cm2 for ambient dose H*(10), 115.21 pSv cm2 for personal dose Hp(10) respectively.