A new use for those ‘unwanted’ neutrons

For more than half a century scientists and engineers have been seeking to generate electricity by taming nuclear fusion, the reaction that powers the sun and the H-bomb. And they have had to put up with constant scoffing from sceptics claiming that commercial fusion power will always lie several decades in the future.

Whatever the outlook for fusion power stations, UK researchers are investing in a more immediate application of nuclear fusion: generating intense beams of neutrons.

Neutrons are the electrically neutral particles that combine with positively charged protons to make up the atomic nucleus – and they are produced in profusion when nuclei of the hydrogen isotopes deuterium and tritium fuse at extremely high temperatures.

For the scientists working on fusion power, such as those involved in the multi-billion-dollar Iter experiment in the south of France, neutrons are a nuisance. But researchers at Culham, the UK centre for fusion technology in Oxfordshire, are designing reactors specifically to make neutrons and have set up a spin-out company called Tokamak Solutions.

The company’s name comes from the ring-shaped tokamak reactor, invented in the Soviet Union in the 1950s, which holds fusion fuel in place as an ultra-hot plasma using powerful magnets. In the 1990s Culham researchers redesigned the reactors into a compact spherical form, much smaller than the huge reactors developed for energy experiments. Tokamak Solutions is now optimising these for neutron production.

Its first reactor, with an outer diameter of 1.5m, could be ready to produce 2MW of neutrons within three years, says David Kingham, the company’s chief executive. The output could be used for scientific research or to prepare medical radio-isotopes, as an alternative to other neutron sources such as particle accelerators.

The second phase will be to generate neutrons that could bombard nuclear waste and transmute the most dangerous isotopes into something easier to handle. Mikhail Gryaznavich, chief scientist at Tokamak Solutions, says isotopes called minor actinides are the most tempting target.

“Burying minor actinides is expensive and risky, as they undergo fissile decay over thousands of years, releasing heat and radioactive fragments, making them difficult to contain,” he says. “Our compact neutron source is the first system based on currently available technology with the potential to produce the neutrons required for this clean-up.”

The most distant – and potentially the most valuable – application will be to use the neutrons as an intense heat source to help generate hydrogen from water as a carbon-free fuel.

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Human stem cell alternative fails to deliver

Many proponents of regenerative medicine have been excited over the past two or three years by the potential of “induced pluripotent stem cells”. iPSCs are made by biochemically reprogramming adult cells to turn their genetic clock back to an embryonic state, from which they could be converted into specialist cells to replace diseased or damaged human tissues.

But there is bad news from California for those who hope that iPSCs could take the place of human embryonic stem cells – derived from early embryos – in regenerative medicine. Researchers at the Salk Institute in San Diego have found that iPSCs actually contain many reprogramming errors and traces of their adult origins.

What’s more, these incompletely or inadequately reprogrammed hotspots are maintained when iPSCs are differentiated into a more specialised cell type. “We can tell by looking at these hotspots whether a cell is an iPSC or an embryonic stem cell,” says Joseph Ecker of Salk.

The researchers reached their conclusions through scrutiny of the “epigenome” – the chemical tags attached to DNA that switch genes on and off, according to the role the cell is playing in the body.

The study, published in Nature, found subtle but extensive epigenetic differences between iPSCs and embryonic stem cells, which had been missed by less thorough analyses.

The discovery does not necessarily mean that it will never be possible to use iPSCs for cell therapy but much more work will be needed to understand the practical significance of the epigenetic differences between them and embryonic stem cells.

If the problem can be overcome, iPSCs will be a more attractive option than embryonic stem cells. This is because they can be custom-made from patients to ensure a perfect match with their immune system and because they can be produced without destroying embryos.

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Secret of the flea jump finally revealed

A 44-year-old mystery – how fleas jump – has been solved. In 1967 the invertebrate biologist Henry Bennet-Clark discovered that fleas store the energy needed to catapult themselves into the air in a pad made of an elastic protein called resilin. But debate raged about exactly how fleas harness this explosive energy – capable of launching them at speeds as high as 1.9m per second.

Bennet-Clark thought that fleas push off with their toes – or the tarsus in zoological terminology. But the naturalist Miriam Rothschild, a noted flea expert, insisted until her death in 2005 that they launch from another part of their complex leg, the trochanter, which is roughly equivalent to our knee.

High-speed photography has finally settled the issue. A paper from Malcolm Burrows and Gregory Sutton at Cambridge University, published in the Journal of Experimental Biology, shows that Bennet-Clark was right.

The Cambridge pair filmed 51 jumps from 10 animals. Although tarsus and trochanter were usually both in contact with the ground for the push-off, sometimes only the tarsus touched the ground. And analysis of the films showed the insects accelerating during take-off when the trochanter was no longer pushing down. Furthermore, electron microscopy showed that the tarsus had claws that provided the grip needed to push off. Finally, a computer model clinched it: trochanter take-off could not provide enough launch acceleration.

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Children’s immunity boosted by infections

Evidence to support the hygiene hypothesis – that exposure to dirt and infections in infancy primes the immune system in a way that reduces allergic and auto-immune disease – is growing. The latest comes from a large clinical trial in Uganda, which shows that treating pregnant women for worms increases their children’s chances of developing eczema.

The study, funded by the Wellcome Trust, involved 2,500 women who were divided randomly into groups either treated for worms during pregnancy or given a placebo treatment. Their babies were twice as likely to develop eczema during the first year of life if they received anti-worm drugs.

The findings, reported in the journal Pediatric Allergy and Immunology, support the hypothesis that exposure to maternal worms during pregnancy, neonatal life and early breastfeeding protects infants against allergy and that killing the worms increases the risk of allergy.

According to senior author Alison Elliott from the London School of Hygiene and Tropical Medicine: “Our study suggests that routine de-worming during pregnancy, in settings where most worm infections are mild, may not be beneficial for the children and may actually cause problems with allergy. However, before we recommend changes to treatment policy, we need to do more work to confirm these findings and better understand what is happening.”

The researchers will follow up the infants to see whether there are long-term effects on allergy, especially asthma, at school age.