Byoung-Jik Kim

Response of six neutron survey meters in mixed fields of fast and thermal neutrons

Calibration neutron fields have been developed at KAERI (Korea Atomic Energy Research Institute) to study the responses of commonly used neutron survey meters in the presence of fast neutrons of energy around 10 MeV. The neutron fields were produced by using neutrons from the (241)Am-Be sources held in a graphite pile and a DT neutron generator. The spectral details and the ambient dose equivalent rates of the calibration fields were established, and the responses of six neutron survey meters were evaluated. Four single-moderator-based survey meters exhibited an under-responses ranging from ∼9 to 55 %. DINEUTRUN, commonly used in fields around nuclear reactors, exhibited an over-response by a factor of three in the thermal neutron field and an under-response of ∼85 % in the mixed fields. REM-500 (tissue-equivalent proportional counter) exhibited a response close to 1.0 in the fast neutron fields and an under-response of ∼50 % in the thermal neutron field.

Synthesis and Characterization of Doped Ceramic Scintillators Based on (Gd,Y)/sub 2/O/sub 3/

From the measured X-ray luminescence spectra, the Gd1.94-x YxEu0.06O3 ceramics with x=0.4 showed the highest emission luminescence. Also both excitation and emission spectra measured at room temperature were higher than that at 11 K. The decay characteristics measured by laser luminescence showed that the decay time was about 1.2 msec at 11 K and it did not change much by increasing ambient temperature. From the results of the X-ray luminescence spectra measurement, it was also found that Eu and Li co-doping certainly increased the light output in the powder form but substantially the light output decreased in the ceramic form, which was considered due to the creation of defects in the sintering process. Therefore a further tuning procedure of the sintering process worthwhile to investigate for making better (Gd,Y)2O3 ceramic scintillator

Fabrication and comparison Gd 2 O 2 S(Tb) and CsI(Tl) films for X-ray imaging detector application

During the last decade, digital X-ray imaging systems have been replacing analog X-ray imaging systems of conventional X-ray film-screen combination for radiography applications. Indirect detection methods consisted of an X-ray converter (or a scintillator film) and photodiode arrays are more widely used in medical diagnoses and industrial fields. Two major scintillation materials such as terbium doped gadolinium oxysulfide (Gd 2 O 2 S:Tb, GOS) and thallium doped cesium iodide (CsI:Tl) are commonly used. In this work, GOS scintillator films were manufactured by mixing and thermal hardening of Gd 2 O 2 S:Tb powder, dispersion agent, hardening agent, and other organic additives. And CsI:Tl scintillator films with columnar structure were also fabricated by the thermal evaporation method. The scintillation properties, such as emission spectrum and light yield etc., of the GOS and CsI:Tl films were measured by X-ray luminescence and photo-luminescence (PL) methods. The maximum luminescent intensity of both scintillators was observed at 540–560nm wavelength. In order to investigate the imaging performances of both GOS and CsI:Tl films as converters of X-ray imaging detectors, both scintillator films were coupled with an CCD sensor. The light response to X-ray dose, signal-to-noise ratio (SNR), spatial resolution were measured and analyzed under the same X-ray conditions. As X-ray dose increases, the SNR curves showed linear relationship. And the spatial resolution of two scintillator films was resolved at 7∼8lp/mm.

Characteristics of airborne radionuclides concentration in a coastal environment.

Airborne radionuclides from the Fukushima nuclear power plant accident in 2011 were measured in 12 regional monitoring stations in Korea. The Gangneung (GN) monitoring station located in a coastal region almost always has a higher radioactivity concentration of airborne radionuclides than any other station. The possible cause of this higher concentration was analysed in terms of the local meteorology and topography. The increase in surface concentrations of radionuclides at the GN region might be attributed to the downslope windstorm, temperature inversion and coupled sea breeze and mountain flows.