Category Archives: nuclear

Keeping it radioactive: This is how a molten salt nuclear reactor works

Radioactive elements produce heat as they decay. Nuclear plants draw power from this process, and typically stabilize the temperature with water. But during a power outage, H2O—which needs pumps to flow—can’t always prevent meltdowns. Molten salt reactors, which instead control heat with melted lithium and potassium fluorides, have a fail-safe: If the electricity dies, a plug will melt, causing the salts to seep down a safety drain and solidify around the uranium, preventing overheating. After a decades-long lull in development, countries from China to Denmark are building new molten salt reactors.

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The Heidelberg compact electron beam ion traps

Electron beam ion traps (EBITs) are ideal tools for both production and study of highly charged ions (HCIs). In order to reduce their construction, maintenance, and operation costs, we have developed a novel, compact, room-temperature design, the Heidelberg Compact EBIT (HC-EBIT). Four already commissioned devices operate at the strongest fields (up to 0.86 T) reported for such EBITs using permanent magnets, run electron beam currents up to 80 mA, and energies up to 10 keV. They demonstrate HCI production, trapping, and extraction of pulsed Ar16+ bunches and continuous 100 pA ion beams of highly charged Xe up to charge state 29+, already with a 4 mA, 2 keV electron beam. Moreover, HC-EBITs offer large solid-angle ports and thus high photon count rates, e.g., in x-ray spectroscopy of dielectronic recombination in HCIs up to Fe24+, achieving an electron-energy resolving power of EE > 1500 at 5 keV. Besides traditional on-axis electron guns, we have also implemented a novel off-axis gun for laser, synchrotron, and free-electron laser applications, offering clear optical access along the trap axis. We report on its first operation at a synchrotron radiation facility demonstrating the resonant photoexcitation of highly charged oxygen.

 

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Probing Sizes and Shapes of Nobelium Isotopes by Laser Spectroscopy

Until recently, ground-state nuclear moments of the heaviest nuclei could only be inferred from nuclear spectroscopy, where model assumptions are required. Laser spectroscopy in combination with modern atomic structure calculations is now able to probe these moments directly, in a comprehensive and nuclear-model-independent way. Here we report on unique access to the differential mean-square charge radii of 252,253,254No, and therefore to changes in nuclear size and shape. State-of-the-art nuclear density functional calculations describe well the changes in nuclear charge radii in the region of the heavy actinides, indicating an appreciable central depression in the deformed proton density distribution in 252,254No isotopes. Finally, the hyperfine splitting of 253No was evaluated, enabling a complementary measure of its (quadrupole) deformation, as well as an insight into the neutron single-particle wave function via the nuclear spin and magnetic moment.

 

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Revelations from the dissolved 226Ra-228Ra pair distribution in the South East Pacific Ocean

While it is confirmed that 226Ra is an interesting tracer of the water masses encountered along the GP16 US East Pacific Zonal Transect (EPZT) section cruise, 228Ra data coupled to the dissolved iron (Fe), cobalt (Co) and manganese (Mn) ones provide evidence that lateral transport of sediments from continental margins, including shelves and slopes, play an important role in open ocean trace elements and isotopes (TEI) budgets and biogeochemistry.

Indeed, elevated 228Ra activities were measured in the upper 200 m over the entire transect, a distance of 8500 km, as a result of sedimentary inputs from the continental shelf. In addition, a deep 228Ra plume was observed at ~1000–2500 m as far as 600 km away from the margin.

Linear dissolved Mn/228Ra relationship is observed both in shelf and offshore surface waters, suggesting that shelf sediments were likely the main source of dissolved Mn to the upper ocean. A linear dissolved Co/228Ra relationship was also observed in surface waters off Peru but no specific dissolved Co/228Ra trend was seen in shelf waters underlining the more complex behavior of Co in this area. Finally, the dissolved Fe/228Ra gradient suggests a rapid removal of Fe.

These results evidence again the important yet underappreciated role of continental slopes as sedimentary TEI sources to the deep ocean.

18 Sanial

 

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Micro-bubble implosion, a reverse Big Bang

Laser pulse compression technology invented in the late 1980s resulted in high-power, short-pulse laser techniques, enhancing laser intensity 10 million-fold in a quarter of a century.

Scientists at Osaka University discovered a novel particle acceleration mechanism they describe as a micro-bubble implosion, in which super-high energy hydrogen ions (relativistic protons) are emitted at the moment when bubbles shrink to atomic size through the irradiation of hydrides with micron-sized spherical bubbles by ultraintense laser pulses. Their research results were published in Scientific Reports.

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The First Lady of Physics

When her ocean liner, the President Hoover, docked in San Francisco in 1936, Wu Chien-Shiung was surprised to find that discrimination against women was par for the course in the United States. She was told that female students at the University of Michigan, where she was soon to begin as a doctoral student, were not even permitted to use the front entrance of a brand-new student center; they had to scuttle quietly through a side door. It was a problem the “First Lady of Physics” would run up against again and again: when UC Berkeley refused to hire her despite an outstanding performance as a student and researcher, when Columbia University took eight years to promote her, and when the Nobel Prize in physics was given to her two male collaborators for their work in parity nonconservation but not to her.

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Dark Matter Interpretation of the Neutron Decay Anomaly. Is this the solution to a major open problem?

There is a long-standing discrepancy between the neutron lifetime measured in beam and bottle experiments. We propose to explain this anomaly by a dark decay channel for the neutron, involving one or more dark sector particles in the final state. If any of these particles are stable, they can be the dark matter. We construct representative particle physics models consistent with all experimental constraints.

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Accurate measurement of the first excited nuclear state in 235U

We have used superconducting high-resolution radiation detectors to measure the energy level of metastable 235mU as 76.737 ± 0.018 eV. The 235mU isomer is created from the α decay of 239Pu and embedded directly into the detector. When the 235mU subsequently decays, the energy is fully contained within the detector and is independent of the decay mode or the chemical state of the uranium. The detector is calibrated using an energy comb from a pulsed UV laser. A comparable measurement of the metastable 229mTh nucleus would enable a laser search for the exact transition energy in 229Th229mTh as a step towards developing the first ever nuclear (baryonic) clock.

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