Yong Joon Park

Rapid sequential determination of Pu, 90Sr and 241Am nuclides in environmental samples using an anion exchange and Sr-Spec resins.

This paper presents a quantitative and rapid method of sequential separation of Pu, (90)Sr and (241)Am nuclides in environmental soil samples with an anion exchange resin and Sr Spec resin. After the sample solution was passed through an anion exchange column connected to a Sr Spec column, Pu isotopes were purified from the anion exchange column. Strontium-90 was separated from other interfering elements by the Sr Spec column. Americium-241 was purified from lanthanides by the anion exchange resin after oxalate co-precipitation. Measurement of Pu and Am isotopes was carried out using an α-spectrometer. Strontium-90 was measured by a low-level liquid scintillation counter. The radiochemical procedure of Pu, (90)Sr and (241)Am nuclides investigated in this study validated by application to IAEA reference materials and environmental soil samples.

Oxidation State Shift of Uranium during U(III) Synthesis with Cd(II) and Bi(III) in LiCl–KCl Melt

Synthesis of U 3+ with Cd 2+ or Bi 3+ was investigated in a LiCl―KCl eutectic melt at 500°C by using cyclic voltammetry (CV) and ultraviolet-visible (UV-vis) spectroscopy. CV results showed that the equilibrium potentials of the species are larger in sequence of U 0/3+ < Cd 0/2+ < U 3+/4+ < Bi 0+/3+ . UV-vis spectroscopy results exhibited that U 3+ was directly produced in the eutectic melt containing Cd 2+ . In BiCl 3 , U metal was oxidized to U 4+ by Bi 3+ , and then U 4+ was reduced to U 3+ by additional U. From these results, the reaction mechanisms taking place during the synthesis are proposed.

Classification of materials for explosives from prompt gamma spectra by using principal component analysis

Data from the elemental composition-ratios and experimental prompt gamma spectra of samples were used to develop suitable discriminant classes for suspect samples. The collected data and gamma spectra were applied to principal component analysis (PCA) to discriminate explosives from non-explosive materials.

Explosives Detection Using Deuterium-Deuterium Neutron Generator

Gamma spectra of general and explosive materials were obtained by using the developed neutron induced prompt gamma-ray spectrometry system containing a neutron generator, where the neutron source was created from a deuterium-deuterium reaction, and they were examined to establish whether the samples were explosives or not by using the pattern recognition method. When the gamma spectra of real explosives (or general materials) were projected into the already prepared training set for the pattern recognition, they were placed in the categories of explosives (or general materials) properly.

Thickness measurement of organic films using Compton scattering of characteristic X-rays

An X-ray scattering method is presented for determining the thickness of an organic film placed on a steel substrate. The strong peaks of characteristic X-rays are taken as an advantage to measure the intensity of backscattered photons. It is shown that the intensity of Compton scattering of characteristic X-rays is proportional to film thickness, up to the thickness of 250 μm of acrylic adhesive layers. In addition, the measurement time was 300 ms, providing a simple and convenient method for on-line for thickness monitoring.

DETERMINATION OF THE 129I IN PRIMARY COOLANT OF PWR

Among the radioactive wastes generated from the nuclear power plant, a radioactive nuclide such as 129 I is classified as a difficult-to-measure (DTM) nuclide, owing to its low specific activity. Therefore, the establishment of an analytical procedure, including a chemical separation for 129 I as a representative DTM, becomes essential. In this report, the adsorption and recovery rate were measured by adding 125I as a radio-isotopic tracer (t1/2 = 60.14 d) to the simulation sample, in order to measure the activity concentration of 129 I in a pressurized-water reactor primary coolant. The optimum condition for the maximum recovery yield of iodine on the anion exchange resins (AG1 x2, 50-100 mesh, Cl- form) was found to be at pH 7. In this report, the effect of the boron content in a pressurized-water reactor primary coolant on the separation process of 129 I was examined, as was the effect of 3H on the measurement of the activity of iodine. As a result, no influence of the boron content and of the simultaneous 3H presence was found with activity concentrations of 3H lower than 50 Bq/mL, and with a boron concentration of less than 2,000 μg/mL.

Radioisotopic neutron transmission spectrometry: Quantitative analysis by using partial least-squares method

Neutron spectrometry, based on the scattering of high energy fast neutrons from a radioisotope and slowing-down by the light hydrogen atoms, is a useful technique for non-destructive, quantitative measurement of hydrogen content because it has a large measuring volume, and is not affected by temperature, pressure, pH value and color. The most common choice for radioisotope neutron source is (252)Cf or (241)Am-Be. In this study, (252)Cf with a neutron flux of 6.3x10(6)n/s has been used as an attractive neutron source because of its high flux neutron and weak radioactivity. Pulse-height neutron spectra have been obtained by using in-house built radioisotopic neutron spectrometric system equipped with (3)He detector and multi-channel analyzer, including a neutron shield. As a preliminary study, polyethylene block (density of approximately 0.947g/cc and area of 40cmx25cm) was used for the determination of hydrogen content by using multivariate calibration models, depending on the thickness of the block. Compared with the results obtained from a simple linear calibration model, partial least-squares regression (PLSR) method offered a better performance in a quantitative data analysis. It also revealed that the PLSR method in a neutron spectrometric system can be promising in the real-time, online monitoring of the powder process to determine the content of any type of molecules containing hydrogen nuclei.

Use of pluronic F108 as a cosurfactant in a synthesis of mesoporous silica microspheres with bimodal pore size distribution.

Large mesoporous silica microspheres with bimodal pore size distributions will be very promising in a special application. Silica microspheres of 10-100 microm in size were synthesized using n-dodecylamine and polymeric surfactant as co-templating agents at room temperature. Surface area and large pore volume of the mesoporous silica microspheres were 884-1009 m2/g and 1.25-1.68 cm3/g, respectively, depending on the reaction conditions. Mesoporous silica microspheres prepared using a short-chained alkylamine surfactant and a long-chained polymeric surfactant exhibited distinct bimodal pore size distribution, that is, small (< 3 nm) and large mesopores (> 20 nm). Pluronic F108, which is a poly(ethylene glycol)-poly(propylene glycol) triblock copolymer, played an important role in the formation of the large mesopores as well as the formation of stable silica microspheres without strong aggregation between particles.