It is an invisible threat from outer space: -distant cosmic events that can cause a computer, or even an aircraft, to crash here on Earth. The idea may sound more science fiction than fact but concerns have reached the point where a major European effort has been launched to investigate the havoc that can result from cosmic rays, wiping a device's memory or damaging safety-critical aircraft electronics.
Dotted across the cosmos are particle accelerators that are tens of millions of times more powerful than the Large Hadron Collider atom smasher at the Geneva-based European Organisation for Nuclear Research, known by its French acronym CERN. We still don't know what these cosmic accelerators are or where they are located. Dying stars may be one source of the cosmic rays' subatomic particles that bombard our home world. Another is the space weather generated by our local star, the Sun.
A single subatomic particle in a cosmic ray can have the energy of Andy Murray?s second serve, reaching speeds approaching that of light itself. These rays pepper the constituent atoms of the upper atmosphere, shattering them and leading to showers of secondary subatomic particles, notably neutrons.
For more than two decades, the aerospace and computer industries have been aware of the threat. In the early 1990s, the aircraft manufacturer Boeing approached Los Alamos National Laboratory's Neutron Science Centre's Weapons Neutron Research Facility in New Mexico, which, at the time, was the most intense source of high energy neutrons. They developed a modest steel structure, the ICE House, which in one hour could produce the same number of errors as 100 years of exposure to the fallout of cosmic rays at cruising altitudes. In the ICE House, a -typical memory chip will suffer roughly 1,200 errors per hour when subjected to a million neutrons per square centimetre per second.
Now, a second dedicated facility is being commissioned. Britain has built the 5m Chipir at the powerful ISIS neutron source, operated by the Science and Technology Facilities Council at the Rutherford Appleton Laboratory in Didcot, near Oxford. This will dramatically speed electronics testing with a measurement of just one hour being equivalent to exposing microchips to high-energy neutrons over hundreds of years of flying time, providing Europe's gold standard for screening microchips. China also plans its own facility to cook microchips with neutrons.
The European instrument effort, led by Chris Frost, has been funded by the UK's Technology Strategy Board. Working with experts in Italy, they have found ways to trace a pencil beam of neutrons over a chip, or flood a rack of electronics with neutrons.
Usually neutrons go unhindered when they pass through materials. Not always. When a high energy neutron strikes a silicon atom in a microchip, it can trigger a burst of electric charge that causes what is known as a ?single-event? upset or effect. This is a so-called "soft" error, when a 0 changes to a 1 in a logic circuit, or vice versa, or a transistor flips from an ?on? state to the ?off?. If it just means a video skips a beat it does not matter. But it could prove fatal if the autopilot goes haywire.
This is what was thought to have happened on October 7th, 2008, when an Airbus A330-303 operated by Qantas Airways, en route from Perth to Singapore, suffered a failure. When incorrect data entered the flight control systems, the plane suddenly and severely pitched downwards, injuring 110 of the 303 passengers and 9 of the dozen crew members.
Neutrons have been blamed for thousands of extra votes being recorded by a voting machine in Schaerbeek, Belgium, in 2003, supercomputer errors, and for repeatedly halting a $1bn factory. The potential havoc caused by this invisible threat is ramping up as more airborne microchip-based devices are used in drones, aircraft, spacecraft and satellites. The threat increases with altitude. At cruising altitudes of some 10,000 metres, some 2,000 neutrons per second of various energies penetrate each square metre of an aircraft?s surface, passing through the hull, passengers, seats, and electronics. As a consequence, the rate of these errors rises to hundreds of times that seen at sea level.
But the threat on the ground is growing too, as more servers store our data, routers send more of it worldwide and transistor size continues to shrink to cram billions into a single microchip. The seemingly endless rise in the density of transistors in electrical circuits is known as Moore's Law and has driven the relentless advance of computing power, along with our dependence on silicon chips, whether in communications, banking, medicine or GPS.
Some fear that Moore's Law will break down, not because of a limit in our ability to make ever smaller transistors at the scale of tens of nanometres (billionths of a metre) or less, but because of the neutron threat. As transistors shrink, much smaller bursts of charge arising from neutrons can trigger errors. With higher densities, higher speeds and lower power consumption, microchip manufacturers are seeing soft errors occur more frequently.
When Chipir goes into action in the next month or two, safety critical circuits will be put through their paces and engineers will be able to test ways to deal with rays, from novel transistor designs to error-correcting software and redundant systems. ?Overcoming the neutron threat will require ingenuity as we scale transistor sizes down,? says Frost. He adds that, as electronics become more sensitive, they will have to start studying the effects of other fallout from the impact of cosmic rays: muons, heavy electrons.
Meanwhile, computers play a more central role in everyday life, guiding trains, planes and automobiles, warming our homes and moving our money. With luck, the global semiconductor industry will be able to keep Moore's Law going for at least another decade. For the next few years, at least, the world should remain one step ahead of cosmic gremlins.
