4 | NewScientist | 17 April 2010

MUON

HADRONS ANDOTHER PARTICLES

MISSING ENERGYIndicates presence of neutrino

INNER TRACKING SYSTEM

CALORIMETER

THE ATLAS DETECTOR IN CROSS SECTION

IF POLITICIANS are serious about nuclear security, they should start listening to scientists. That’s the appeal from scientific groups as world leaders promised better security at a summit in Washington DC this week, but said little about how to achieve it.

At the summit, 47 countries pledged to prevent the theft of fissile material, which could be used to create a nuclear bomb, by securing all stockpiles within four years. Some of the world’s estimated 2100 tonnes of plutonium and highly enriched uranium (HEU) are kept in poorly guarded buildings, and there have been 18 known attempted thefts

since 1993. One crude bomb could cause global economic chaos, a report by nuclear security expert Matthew Bunn of Harvard University warned last week.

Yet there are at present no

Uranium theft risk agreed standards for what is required to make fissile material “secure”, says Ed Lyman, a senior scientist at the Union of Concerned Scientists in Washington DC. The International Atomic Energy Agency has only voluntary guidelines dating from 1999, and efforts to update them in time for this week’s summit failed: national nuclear agencies baulk at the idea of an outside agency imposing, and possibly verifying, expensive security measures. What has been agreed so far, says Lyman, offers little improvement. For instance, nations are still not required to post armed guards at stockpiles of fissile material.

The American Association for the Advancement of Science and the UK’s Royal Society have argued in recent reports that more research could aid international cooperation, as well as improving technology. For example, networks of gamma-ray spectroscopes could help to spot smuggled fissile material; shared databases on stockpiles of fissile materials could make it easier to pinpoint sources; and HEU could be replaced as a fuel.

Laser blastedTHE world’s largest laser is meant to spark off a fusion reaction this year – but don’t bank on it. So says the US government’s watchdog in a critical report about the National Ignition Facility (NIF).

The $3.5 billion laser array at Lawrence Livermore National Laboratory in California is meant to fire pulses from 192 laser beams to trigger nuclear fusion. NIF physicists have said they hope to reach “ignition” – generating as much fusion energy as is

contained in the laser pulse – at a laser energy of 1.2 to 1.3 megajoules, well short of the machine’s 1.8-megajoule capacity.

But the GAO says that many independent researchers think at least 1.8 megajoules will be required, because some laser light could be deflected by the plasma it creates. Firing on full power could also damage high-power optics in the machine, they warn.

An NIF spokesperson told New Scientist that staff are confident they can achieve ignition at no more than 1.5 megajoules.

LHC is on the right track IT’S first blood to the massive Atlas detector at the Large Hadron Collider. Just days after the physics programme started, Atlas has reported its first detection of W boson particles.

W bosons have been seen at other colliders, but before any of the detectors at the LHC can attempt to discover new particles they must “rediscover” established ones. It is “an excellent sign” to spot the particles so soon, says Fabiola Gianotti, who heads the Atlas team. “It demonstrates that both the LHC accelerator and Atlas work extremely well.”

W bosons decay almost instantly into leptons and neutrinos. On two occasions since the machine began collisions at 7 teraelectronvolts last month, the leptons – either a positron

or a muon – have been detected in Atlas’s calorimeter and muon chambers. Neutrinos do not interact with the detector, but their presence was inferred from the imbalance of the decay’s total momentum – its “missing energy” (see diagram, right).

The detection is interesting in its own right as new particles, such as the Higgs boson, have been predicted to decay into W bosons, says Atlas physicist Andreas Hoecker. “W bosons are really very central.”

David Barney, a member of the rival CMS detector collaboration, points to an “element of healthy competition between the two big general-purpose detectors”. He says that many interesting events will be needed from both detectors to produce a complete picture.

“There have been 18 attempted thefts of fissile material documented since 1993”

THE safety of antimicrobial soaps and toothpastes is under review following concerns that they could interfere with hormones in the body.

Last week, the US Food and Drug Administration said it will re-evaluate the safety of triclosan, which is added to plastics, soaps and toothpastes to kill bacteria and fungi. The agency is not yet recommending that consumers avoid such products.

Over the next year, the FDA will look at evidence that triclosan might

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affect the development of the nervous system, in which thyroid hormones play a key role, or the reproductive system. One recent study showed that triclosan lowers levels of thyroid hormones in rats, while a 2008 report found that it boosts the effects of oestrogen and testosterone.

Sarah Janssen of the Natural Resources Defense Council, a US environmental advocacy group, says the announcement is “long overdue”.

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