Performance of a Characteristic X-ray Camera to Identify Contamination of Radioactive Cesium

The lightweight, high sensitivity and low-price camera to image Cs-137 contamination in environment has been developed. These three merits have not been realized by recent gamma cameras and Compton cameras. The camera images Cs-137 distribution by detecting the characteristic X-rays from it instead of gamma-rays. We have investigated the performance of the characteristic X-ray camera (CXRC) in detail and the specification is summarized

Characteristic X-ray detector with a large sensitive area: Its sensitivity to environmental radioactive cesium and imaging performance as confirmed in an area of Fukushima

An X-ray detector which we call the characteristic X-ray detector (CXRD) with a large sensitive area of 199 cm2 was studied as a candidate imaging device with high sensitivity, light weight and low-cost features to visualize environmental 137Cs deposited after the Fukushima Dai-ichi Nuclear Power Station accident. The CXRD has a directionality for its sensitivity and it is able to visualize a spatial distribution of 137Cs by scanning the flux of 32 keV characteristic X-rays due to disintegration of 137Cs instead of imaging the 662 keV gamma-rays from 137Cs. Our experimental results showed that the counting efficiency of the CXRD was 105 counts per second for a 1 MBq 137Cs source at a distance of 1m and the CXRD had a very high counting efficiency for a certain direction. We estimated the potential sensitivity of the CXRD when it was used in the scanning mode to image an area of 2π sr. The CXRD was tested in a contaminated forest in Fukushima Prefecture and images of the spatial distribution of 137Cs in the forest were successfully obtained. We found that most of the 137Cs was present in the forest floor and no 137Cs was detected in the atmosphere and the tree canopy. The CXRD is useful because of its low cost, light weight and high sensitivity as a 137Cs imaging device for monitoring post devices in forests and as a portable imaging device to confirm the effectiveness of decontamination work

Trace-Level Mercury Ion (Hg²⁺) Analysis in Aqueous Sample Based on Solid-Phase Extraction Followed by Microfluidic Immunoassay

Mercury is considered the most important heavy-metal pollutant, because of the likelihood of bioaccumulation and toxicity. Monitoring widespread ionic mercury (Hg²⁺) contamination requires high-throughput and cost-effective methods to screen large numbers of environmental samples. In this study, we developed a simple and sensitive analysis for Hg²⁺ in environmental aqueous samples by combining a microfluidic immunoassay and solid-phase extraction (SPE). Using a microfluidic platform, an ultrasensitive Hg²⁺ immunoassay, which yields results within only 10 min and with a lower detection limit (LOD) of 0.13 μg/L, was developed. To allow application of the developed immunoassay to actual environmental aqueous samples, we developed an ion-exchange resin (IER)-based SPE for selective Hg²⁺ extraction from an ion mixture. When using optimized SPE conditions, followed by the microfluidic immunoassay, the LOD of the assay was 0.83 μg/L, which satisfied the guideline values for drinking water suggested by the United States Environmental Protection Agency (USEPA) (2 μg/L; total mercury), and the World Health Organisation (WHO) (6 μg/L; inorganic mercury). Actual water samples, including tap water, mineral water, and river water, which had been spiked with trace levels of Hg²⁺, were well-analyzed by SPE, followed by microfluidic Hg²⁺ immunoassay, and the results agreed with those obtained from reduction vaporizing–atomic adsorption spectroscopy