Feasibility of 129I groundwater dating calibrated by both 81Kr and 4He for the assessment of deep geological repositories in Japan.

Iodine-129, which is a promising tracer for dating old groundwater, has been used as a tracer for deep upwelling groundwater. The nuclide is expected to be one of the key factors for site selection for high-level radioactive waste disposal, which is a global societal issue. The pre-anthropogenic 129I/127I ratio for marine iodine is (1.50 ± 0.15) × 10-12, which could be considered the initial value for 129I dating. This study identifies the challenges in groundwater age dating using 129I/127I. We measured the ratios of 129I/127I and 81Kr/Kr and concentration of 4He in groundwater from boreholes on the northern coast of Japan. The 129I dating results were not coincident with the other groundwater dating results. The iodine in the groundwater was inferred to be released in situ from marine organisms in sediments of various ages. We estimated that the primordial iodine ratio originating from seawater was ~ 1 × 10-13 (8 × 10-14 ~ 2 × 10-13). The groundwater age deduced from the 129I/127I ratio using this value agrees with other groundwater dating results.

Dual-band frequency reconfigurable metasurface antenna for millimeter wave joint communication and radar sensing systems.

This paper introduces an innovative, compact, and high-gain metasurface antenna, covering both the 24 GHz millimeter wave (mmWave) radar band and the 5 G n257 and n258 bands. The proposed metasurface antenna consists of a wideband stacked patch antenna and a dual-layer metasurface to focus its radiation beams for multiple mmWave bands. The operating frequency can be slightly shifted by altering the distance between the feeder and the metasurface. The distribution of the metasurface unit cells is designed based on a simplified phase compensation formula. The dimension of the fabricated feeder is 6 mm × 6 mm, and the metasurface occupies a 65 mm × 65 mm radome area. Experimental results demonstrate a wide bandwidth from 23.5 GHz to 29.1 GHz for the feeder, and impressive maximum gains of 19.7 dBi and 19.5 dBi for the lower band and higher band of the metasurface antenna are achieved simultaneously. The frequency reconfiguration ability was characterized by a 750 MHz frequency shift with every 1 mm distance adjustment. The compact size and high gain performance of the proposed design underscore its potential for practical applications in millimeter wave joint communication and radar sensing systems.