Hyeonseo Park

Pulse shape discrimination capability of metal-loaded organic liquid scintillators for a short-baseline reactor neutrino experiment

A new short-baseline (SBL) reactor neutrino experiment is proposed to investigate a reactor anti-neutrino anomaly. A liquid scintillator (LS) is used to detect anti-neutrinos emitted from a Hanaro reactor, and the pulse shape discrimination (PSD) ability of the metal-loaded organic LSs is evaluated on small-scale laboratory samples. PSD can be affected by selecting different base solvents, and several of the LSs used two different organic base solvents, such as linear alkyl benzene and di-isopropylnaphthalene. For the metallic content, gadolinium (Gd) or lithium (6Li) was loaded into a home-made organic LS and into a commercially available liquid scintillation cocktail. A feasibility study was performed for the PSD using several different liquid scintillation cocktails. In this work, the preparation and the PSD characteristics of a promising candidate, which will be used in an above-ground environment, are summarized and presented.

Neutron spectrum at the underground laboratory for the ultra low background experiment

We measured the background neutron spectrum using a Bonner sphere spectrometer at the YangYang underground laboratory, where the vertical earth overburden is approximately 700 m. The neutron fluence rate and the energy spectrum were determined through the unfolding procedure. The measured neutron fluence rate was (0.242 ± 0.008) n cm(-2)h(-1) for k=1, and most of the neutrons were below 20 MeV.

Neutron Spectrum Measurement at the Workplace of Nuclear Power Plant with Bonner Sphere Spectrometer

With BSS system, the neutron spectral fluences at the workplace of nuclear power plant at Wolsong were measured. The 9 points at the 4th and 5th floor of the reactor building were selected for the spectrum measurement, where the radiation workers access for the ordinary check of the operation. The spectra show the distribution from the thermal to several MeV, which are composed of the original fission spectrum, scattered fast neutrons and thermal neutrons. The spectral shapes for the places at the same floor are similar to each other. Although the number of data points is limited, we may determine the standard neutron spectrum for each floor and this would help improving the uncertainties of neutron doses. For the comparison, we measured the neutron ambient dose with neutron survey meter (EG&G Ortec, LB6411) and personal dose with TLD on PMMA phantom.

Comparison of fast neutron rates for the NEOS experiment

The fast neutron rates are compared at the site of the NEOS (Neutrino Experiment Oscillation Short baseline) experiment, a short-baseline neutrino experiment located in a tendon gallery of a commercial nuclear power plant using a 0.78-liter liquid scintillator detector. A pulse shape discrimination technique is used to identify neutron signals. The measurements are performed during the nuclear reactor-on and -off periods, and the fast neutron rates are found to be consistent with each other. The fast neutron rate is also measured at an overground site with a negligible overburden and is found to be ~ 100 times higher than that at the site of the NEOS experiment.

DEVELOPMENT OF SIMULATED WORKPLACE FIELDS AT KRISS FOR PERFORMANCE TEST OF NEUTRON PERSONAL DOSEMETERS

Simulated workplace neutron fields have been developed at the Korea Research Institute of Standards and Science (KRISS). An (241)Am-Be neutron source and a cylindrical moderator composed of stainless steel and heavy water were installed in a 10-cm-thick concrete block with dimensions of 150 × 120 × 120 cm(3) The neutron energy spectrum at a distance of 66.5 cm was measured using a Bonner sphere spectrometer and was found to agree with the spectrum obtained from the Monte Carlo N-Particle Extended simulation to within 5 %. The neutron fluence-to-personal dose equivalent conversion coefficients were (20.8-43.6) pSv·cm(2) and were thus in good agreement with those of reactor fields. The results showed that the KRISS-simulated workplace neutron fields can be used for performance tests and the calibration service of neutron personal dosemeters.

Absolute measurement of (198)Au activity in gold foil using plastic scintillators and a well-type NaI(Tl) detector.

A beta-gamma coincidence system has been developed for measuring (198)Au activity in gold foils. The system was validated by Monte Carlo simulations and by measuring the activity of a (60)Co point-source. To study effects such as self-shielding of beta particles in gold foils, (198)Au activity measurements and simulations were performed for various scintillators and foil sizes. The measured (198)Au activities were ~1% above the reference activity, which might be due to self-shielding of beta particles. The measured and simulated (198)Au activities agreed, suggesting feasibility of precise activity measurement.

Measurement of the 250Cf component in a 252Cf neutron source at KRISS

Neutron emission rate measurements have been carried out at the Korea Research Institute of Standards and Science using a manganese sulphate bath system for (252)Cf and (241)Am-Be sources since 2004. The relative measurement method was chosen in 2012, and the neutron emission rates agreed with those by the absolute measurement method within uncertainties. The neutron emission rate of an old (252)Cf source has been measured three times: in 2004, 2009 and 2012. The (250)Cf component was fitted to a double-exponential function of (252)Cf+(250)Cf, and the ratio of the (250)Cf component to the (252)Cf component was estimated to be 7.8 % in 2004 and 46.8 % in 2012. Underestimation of the neutron emission rates of old (252)Cf sources can be corrected if the neutron emission rate of the (250)Cf component is taken into account.

The Determination of Neutron Dose for Accelerator-Produced Neutrons by Using a Bonner Sphere Spectrometer

The spectral fluences of the neutrons from the 18O(p,n)18F reaction were measured at Korea Institute of Radiological & Medical Sciences MC-50 cyclotron. Neutrons were measured with the Bonner sphere spectrometer of Korea Research Institute of Standards and Science. The neutron spectral fluences including the scattered neutrons were evaluated by unfolding together with the initial guess spectrum. The variation of the spectral fluence and the ambient dose equivalent rates were investigated by changing thermal-, intermediate-, and high-energy ratios of the initial guess spectrum. The results show that the spectral fluences and the ambient dose equivalent rates are stable within 2% even though the initial guess spectrum is highly changed. Therefore, if the spectral shape of the initial guess spectrum is chosen properly for the measurement, the spectral fluence of the accelerator-produced neutron can be determined by the unfolding process