Flash Physics: Superfluid helium dark-matter detector, Hinkley C will go ahead, why nanotubes are different

UK’s Hinkley Point reactors get the go-ahead

Artistrsquo;s impression of Hinkley Point C
Ready to go: artist’s impression of Hinkley Point C

Britain’s prime minister Theresa May has approved the planned construction of the £18bn Hinkley Point C nuclear power station in south-west England. May had unexpectedly put the project under review in July, shortly after taking over as prime minister from David Cameron. Comprising two nuclear reactors, the station will be built by the French company EDF with a £6bn investment from China. According to the UK government, new safeguards have been put in place to ensure that Chinese participation in the project does not compromise the national security of the UK. The decision is expected to open the door to Chinese companies, which are keen to build new reactors elsewhere in the UK. There have been concerns about the high cost of electricity from the plant, which is pegged at £92.50 per kilowatt hour and has not been changed by the review. Critics have pointed out that this is much more expensive than energy from a similar facility being built by EDF in France. Hinkley Point C will be based on new European Pressurized Reactor technology, which is being implemented in reactors under construction in Finland, France and China. There is more about Hinkley Point C in the recent Physics World Focus on Nuclear Energy.

Chirality explains why similar nanotubes behave differently

Computer model of a nanotube
Same but different: computer model of a nanotube

Why is it that nanotubes fabricated from seemingly similar nanomaterials exhibit different properties? That is the question asked by researchers at the International School for Advanced Studies (SISSA) in Italy and Tel Aviv University in Israel, who have looked at why materials that have similar structures produce nanotubes that behave differently. For example, while both carbon nanotubes and boron nitride nanotubes are nearly indistinguishable in terms of their structures, they have different responses to frictional forces. The team created computer models of the nanomaterials and studied their characteristics in detail. Team-leader Roberto Guerra says the study showed differences in the chirality of the materials and that this may cause the differences in their properties.

How to detect light dark matter using superfluid helium

Superfluid liquid helium is an ideal medium for detecting low-mass dark-matter particles, according to Katelin Schutz and Kathryn Zurek at the Lawrence Berkeley National Laboratory in the US. While physicists have not been able to detect dark matter directly, several generations of experiments suggest that dark-matter particles have masses below about 10 GeV/c2. As a result, physicists are thinking about how to build detectors that are sensitive to light dark matter at masses as low as 1  keV/c2. This involves looking for extremely rare collisions between dark and ordinary matter in a large detector. The problem is that the dark matter that passes through the Earth is expected to be moving slowly and therefore such collisions will impart tiny amounts of kinetic energy to the detector – making interactions very difficult to see. Schutz and Zurek have calculated that all of the kinetic energy of a dark-matter particle could be absorbed in superfluid helium via the creation of two phonons – particle-like sound waves. These phonons could then be detected using existing technologies. A further benefit of the technique, which is described in Physical Review Letters, is that measurement of the momenta of the two phonons can help distinguish between real dark-matter collisions and background noise. Zurek has a separate paper in the same journal about using superconductors to detect light dark matter.

  • See our video below for more about the nature of dark matter.

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