A very low background HPGe detector operating deep underground at 4800 m water equivalent.
A very low background HPGe detector has been installed in the Fréjus underground laboratory in order to investigate radioactive contaminations. The main features and capabilities of the detector are described here.
Development of a HPGe shielding system for radioactivity measurements at Cheongpyeong Underground Radiation Laboratory
We constructed an underground laboratory called Cheongpyeong Underground Radiation Laboratory (CURL) for measuring the radioactivity levels of various samples by using HPGe detectors. CURL is located underground at a depth of 1000-m water equivalent in the Cheongpyeong Pumped Storage Power Plant. We developed a shielding system, which consists of 15-cm-thick Pb blocks and 5-cm-thick Cu blocks and completely surrounds a 100% HPGe detector. We measured the background radiations and the gamma peaks from sources with and without the shield. The shielding efficiencies were also estimated using MCNP5 simulations, and they were compared to our measured data. The shielding system blocked more than 99.99% of gamma rays with energies up to 3.0 MeV. The HPGe detector with the shielding system at CURL blocked both high-energy cosmic rays and background radiation from surrounding rocks and materials. Our CURL detector system was optimized for gamma-ray measurements of meterials with ultra-low radioactivity.
The potential vorticity flux through the Yucatan Channel and the Loop Current in the Gulf of Mexico
Two‐year‐long time series of current and density structure measurements across the Yucatan Channel's main section allow the calculation of the time‐dependent potential vorticity flux between the Gulf of Mexico and the Caribbean Sea, which is characterized by alternating periods of positive (cyclonic) and negative (anti‐cyclonic) vorticity influx. Periods of negative cumulative vorticity influx are related to the Loop Current extending into the Gulf of Mexico, whereas periods of positive cumulative vorticity influx relate to a Loop Current retraction, sometimes coincident with the shedding of an anti‐cyclonic eddy.