Sih-Hong Doh

Daily intakes of naturally occurring radioisotopes in typical Korean foods

The concentrations of naturally occurring radioisotopes ((232)Th, (228)Th, (230)Th, (228)Ra, (226)Ra, and (40)K) in typical Korean foods were evaluated. The daily intakes of these radioisotopes were calculated by comparing concentrations in typical Korean foods and the daily consumption rates of these foods. Daily intakes were as follows: (232)Th, 0.00-0.23; (228)Th, 0.00-2.04; (230)Th, 0.00-0.26; (228)Ra, 0.02-2.73; (226)Ra, 0.01-4.37 mBq/day; and (40)K, 0.01-5.71 Bq/day. The total daily intake of the naturally occurring radioisotopes measured in this study from food was 39.46 Bq/day. The total annual internal dose resulting from ingestion of radioisotopes in food was 109.83 muSv/y, and the radioisotope with the highest daily intake was (40)K. These values were same level compiled in other countries.

Luminescence properties of a CsI crystal doped with Eu2+ ions

Abstract Optical properties of a CsI crystal doped with Eu 2+ ions are investigated by absorption, emission and excitation spectroscopy. Two absorption bands with a fine structure are observed at 277 and 363 nm, and an emission band is observed at 445 nm. These bands are caused by the electronic transition between 4f 7 and 4f 6 5d configurations. The crystal field parameter 10 Dq of Eu 2+ in CsI is estimated to be 8600 cm −1 . Comparison with the results obtained in other alkali halides is made.

Luminescence and Scintillation Properties of a CeBr

Crystal growth, luminescence, and scintillation properties of a CeBr3 crystal are presented. The crystal was grown with Bridgman method using two-zone transparent furnace and cut to Oslash10 times 10 mm3. The investigation of luminescence and scintillation properties of the CeBr3 was performed under the excitation by ultraviolet and gamma-rays at room temperature. The emission spectrum of the CeBr3 was observed in the range of near ultraviolet to violet, which is due to the 5d rarr 4f transition of Ce3+. The decay time of the Ce3+ emission was measured to be approximately 20 ns. The energy resolution of the CeBr3 single crystal was obtained to be 4.9% for the 137Cs 662 keV gamma-rays. The relative signal of the CeBr3 crystal by the 137Cs gamma-rays is about three times higher than that of a CsI:Tl crystal when a bi-alkali PMT was used. The nonproportionality in the gamma-ray energy of the crystal was also measured. The study showed that the CeBr3 crystal is the promising candidate for the PET application. The CeBr3 crystal with high light output and fast decay time affords its use for the particle detection in a high counting rate environment such as nuclear and high-energy physics.

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Since a double-sided silicon strip sensor provides two-dimensional position information with high resolution, it has been developed for various uses as a medical imaging sensor, radiation detector, sensing detector in space science, and a silicon vertexing/tracking detector in experimental particle physics. We designed and fabricated a double-sided silicon position sensor in a 5 in. fabrication line. Silicon nitride with a silicon oxide layer was used to prevent damage during sensor fabrication. Since the temperature dependences of the silicon nitride and the silicon oxide are different, the thicknesses of the Si3N4 and SiO2 layers were optimized using the ATHENA process simulation to avoid cracks. We present the measurement results of the electrical characteristics of the sensor such as leakage current and capacitance as a function of reverse bias voltage. We performed tests on the sensor using a 90Sr radioactive source and measured the signal-to-noise ratio of the prototype sensor.

Single Crystal

We present the luminescent and scintillation characteristics of CsI:CO3 single crystals. The CsI:CO3 single crystals were grown by using Czochralski method for different concentrations of CO3 from 0.007 to 0.1 mole%. The crystals were cut into a size of 10 mm times 10 mm times 5 mm. The luminescent characteristics were measured with X-rays to study the emission spectra of the CsI:CO3 crystals. The scintillation properties of the CsI:CO3 crystals such as fluorescence decay time, energy resolution, pulse height spectra, proportionality, and relative light output were studied by using various gamma-ray sources with a photomultiplier tube (PMT) at room temperature. The absolute light outputs of the crystals were also measured with an avalanche photo-diode (APD).

Fabrication and beta-ray source test of double-sided silicon strip sensor

The photoluminescence (PL) and photostimulated luminescence (PSL) properties of SrCl2:Eu2+ and SrCl2:Eu2+:Na+ are investigated. A strong PSL emission is observed for SrCl2:Eu2+ and its intensity is enhanced by codoping with Na+ ions. The mechanisms of PL and PSL are discussed in relation to the formation of F centers in SrCl2:Eu2+ and SrCl2:Eu2+:Na+.

The Growth and Scintillation Characteristics of CsI:CO

CsI single crystals doped with lithium, potassium or rubidium were grown by using Czochralski method at Ar gas atmosphere. The energy resolutions of CsI(Li:0.2 mole%), CsI(K:0.5 mole%) and CsI(Rb:1.5 mole%) scintillators were 14.5%, 15.9% and 17.0% for (0.662 MeV), respectively. The energy calibration curves of CsI(Li), CsI(K) and CsI(Rb) scintillators were linear for -ray energy. The time resolutions of CsI(Li:0.2 mole%), CsI(K:0.5 mole%) and CsI(Rb:1.5 mole%) scintillators measured by CFT(constant-fraction timing method) were 9.0 ns, 14.7 ns and 9.7 ns, respectively. The fluorescence decay times of CsI(Li:0.2 mole%) scintillator had a fast component and slow one of

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Single Crystals

The concentrations of natural radioisotopes 230Th and 232Th in Korean foods were measured by the method of calcium oxalate co-precipitation in addition to the conventional anion-exchange method and alpha spectroscopic measurement. The 230Th concentrations(mBq/kg-fresh) in Korean foods were found to be as follows: milk 0.14~2.45, pork 2.98~8.97, beef 1.94~9.80, chicken 1.22~13.0, rice 0.43~2.35, wheat 0.53~14.4, and soybeans, 8.44~91.6. The 232Th concentrations(mBq/kg-fresh) in Korean foods were found to be as follows: milk 0.01~2.46, pork 0.28~9.32, beef 1.02~5.34, chicken 0.56~4.98, rice 0.32~2.54, wheat 0.53~20.0, and soybeans, 2.30~42.2. The annual internal dose of Th was also estimated. The annual internal dose of 230Th and 232Th in milk was about 0.006 uSv/yr and much lower than that of other countries because of the low intake of milk in Korea compared to other countries. The annual internal dose of 230Th and 232Th in the rice was about 0.043 pSv/yr and highest because rice is the staple food of Koreans.

Luminescence and photostimulated luminescence of SrCl2:Eu2+ doped with Na+ ions

crystals were grown by using the Czochralski method, and their scintillation properties were measured. The emission spectrum was located in the range of nm, peaking at about 400 nm. The fluorescence decay time was approximately 75.9 ns for 662 keV -rays excitation. The energy resolution was about 24.4 % for 662 keV -rays, and the ratio to particles from a 5.4 MeV was about 0.25.