Prospects for measuring the 229Th isomer energy using a metallic magnetic microcalorimeter

The Thorium-229 isotope features a nuclear isomer state with an extremely low energy. The currently most accepted energy value, 7.8 +- 0.5 eV, was obtained from an indirect measurement using a NASA x-ray microcalorimeter with an instrumental resolution 26 eV. We study, how state-of-the-art magnetic metallic microcalorimeters with an energy resolution down to a few eV can be used to measure the isomer energy. In particular, resolving the 29.18 keV doublet in the \gamma-spectrum following the \alpha-decay of Uranium-233, corresponding to the decay into the ground and isomer state, allows to measure the isomer transition energy without additional theoretical input parameters, and increase the energy accuracy. We study the possibility of resolving the 29.18 keV line as a doublet and the dependence of the attainable precision of the energy measurement on the signal and background count rates and the instrumental resolution.Comment: 32 pages, 8 figures, eq. (3) correcte

Mesoscale Atlantic water eddy off the Laptev Sea continental slope carries the signature of upstream interaction

A mesoscale eddy formed by the interaction of inflows of Atlantic water (AW) from Fram Strait and the Barents Sea into the Arctic Ocean was observed in February 2005 off the Laptev Sea continental slope by a mooring equipped with a McLane Moored Profiler. The eddy was composed of two distinct, vertically aligned cores with a combined thickness of about 650 m. The upper core of approximately ambient density was warmer (2.6°C), saltier (34.88 psu), and vertically stably stratified. The lower core was cooler (0.1°C), fresher (34.81 psu), neutrally stratified and ∼0.02 kg/m3 less dense than surrounding ambient water. The eddy, homogeneous out to a radius of at least 3.4 km, had a 14.5 km radius of maximum velocity, and an entire diameter of about 27 km. We hypothesize that the eddy was formed by the confluence of the Fram Strait and Barents Sea AW inflows into the Arctic Ocean that takes place north of the Kara Sea, about 1100 km upstream from the mooring location. The eddy's vertical structure is likely maintained by salt fingering and diffusive convection. The numerical simulation of one-dimensional thermal and salt diffusion equations reasonably reproduces the evolution of the eddy thermohaline patterns from the hypothesized source area to the mooring location, suggesting that the vertical processes of double-diffusive and shear instabilities may be more important than lateral processes for the evolution of the eddy. The eddy is able to carry its thermohaline anomaly several thousand kilometers downstream from its source location