Development of the Environmental Radiation Survey Program and Its Application to In Situ Gamma-Ray Spectrometry.

An environmental radiation survey using a gamma-ray spectrometer is used to rapidly detect radioactive contamination over a wide area of ground that was released from nuclear events. For the successful application of a gamma-ray spectrometer to the calculation of the radioactivity concentration in the ground and the dose rate at 1 m above the ground, it is necessary to build a calibration procedure to obtain the counting efficiency at the in situ measurement, which means in situ calibration factor to report the calculation results from the measured net count rate according to the diverse detection geometries. This study is focused on the development of a program to calculate the in situ calibration factor and report the survey results in the environmental radiation surveys using three kinds of gamma-ray spectrometers, which have been widely used in the field of in situ measurements: a coaxial HPGe detector, cylindrical NaI(Tl), and rectangular NaI(Tl). The program is based on the results of diverse theoretical calculations of the unscattered photon fluence at the detector height, detector responses of three detectors, and their angular corrections. The developed program was successfully applied to the estimation of the radioactivity concentration of nuclides in the ground and the dose rate at 1 m height above the ground induced from them.

Photocatalytic enhancement of cesium removal by Prussian blue-deposited TiO2.

After the Fukushima nuclear accident, tremendous efforts were made to treat radiocesium, radiostrontium, and other radioactive materials. For the first time, we demonstrate that a TiO2 photocatalyst can significantly enhance Cs adsorption by Prussian blue-deposited TiO2 (PB/TiO2) under UV irradiation. In this study, we synthesized PB/TiO2 using the photodeposition method. After the Cs ions were adsorbed on the PB/TiO2 in darkness, we then exposed the PB/TiO2 to UV light irradiation. This resulted in a further increase in Cs ion adsorption of more than 10 times the amount adsorbed in darkness. This photocatalytic-enhanced adsorption of Cs ions was not observed on PB mixed with SiO2, nor under visible light irradiation. We investigated the effects of PB concentration, PB/TiO2 concentration, and gas purging on both dark and photocatalytic-enhanced adsorption of Cs ions by PB/TiO2. Based on the results, we suggest that the photocatalytic-enhanced adsorption of Cs ions on PB/TiO2 is due to photocatalytic reduction of PB, which leads to additional adsorption of Cs ions. The change in solution color before and after the reaction, and the change in solution pH in the dark and during UV irradiation strongly support this suggestion. The photocatalytic-enhanced adsorption of Cs ions was equivalent during radioactive 137Cs removal, indicating important applications for pollutant removal from contaminated water.

Rapid removal of radioactive cesium by polyacrylonitrile nanofibers containing Prussian blue.

After the Fukushima Daiichi Nuclear Power Plant disaster in Japan in 2011, the demand drastically increased for efficient technology for the removal of radioactive cesium. Prussian blue (PB) nanoparticles have shown excellent adsorption ability toward Cs. In this study, we synthesized PB nanoparticles incorporated polyacrylonitrile nanofiber (PB/PAN). PB/PAN has the porous structure of nanofibers, with diameters of several hundred nanometers. PB nanoparticles can be incorporated successfully into the PAN matrix without any change to their intrinsic crystallinity and structure. The mesoporous structure of PB/PAN and the incorporation of PB nanoparticles led to an increase in the Brunauer-Emmett-Teller surface area and pore volume. In addition, PB/PAN exhibited excellent wettability with water. With simple filtering for the removal of radioactive cesium, PB/PAN showed high removal efficiency (87 ±â€¯3%) within 10 s for 10 mL of 137Cs solution (1000 Bq L-1). In addition, the 137Cs removal by PB/PAN showed high removal efficiency (70 ±â€¯2%, after 1 h), even in the actual seawater medium (1000 Bq L-1 of 137Cs). Therefore, PB-incorporated PAN nanofibers can be considered useful in the practical application of Cs removal from radioactive wastewater.

A New Approach for the Determination of Dose Rate and Radioactivity for Detected Gamma Nuclides Using an Environmental Radiation Monitor Based on an NaI(Tl) Detector.

To expand the application of dose rate spectroscopy to the environment, the method using an environmental radiation monitor (ERM) based on a 3' × 3' NaI(Tl) detector was used to perform real-time monitoring of the dose rate and radioactivity for detected gamma nuclides in the ground around an ERM. Full-energy absorption peaks in the energy spectrum for dose rate were first identified to calculate the individual dose rates of Bi, Ac, Tl, and K distributed in the ground through interference correction because of the finite energy resolution of the NaI(Tl) detector used in an ERM. The radioactivity of the four natural radionuclides was then calculated from the in situ calibration factor-that is, the dose rate per unit curie-of the used ERM for the geometry of the ground in infinite half-space, which was theoretically estimated by Monte Carlo simulation. By an intercomparison using a portable HPGe and samples taken from the ground around an ERM, this method to calculate the dose rate and radioactivity of four nuclides using an ERM was experimentally verified and finally applied to remotely monitor them in real-time in the area in which the ERM had been installed.

Simultaneous Determination of the Depth of an Embedded Source and its Radioactivity in the Medium.

The simultaneous determination of the depth of an embedded source and its radioactivity in the medium at the environmental surveys is a very useful and advisable method for an in-situ gamma-ray measurement with respect to the time and cost constraint. An algorithm for the determination of the source depth and its radioactivity in the medium was developed using the information on the uncollided photon fluences and measured net count rates, which mean not scattered fluences and background subtracted count rate, at the detector positions. Uncollided photon fluences were calculated at several source depths in the medium as well as at detector positions from the Monte Carlo N-Particle (MCNP) simulation. The results were then used to establish a database to output their values according to the source depth in the medium by inputting the photon energy and detector position from the medium. A simple program about the simultaneous determination of two variables was applied to the results on a task to find out the depth and activity of Cs and Cs at in-situ gamma-ray spectrometry. Less than 10% and 15% differences compared with the real values at the source depth and radioactivity, respectively, were achieved using the developed program.