It’s an invisible, but looming threat from outer space: distant cosmic events that can cause a computer, or even an aircraft, to crash here on Earth. Concerns have reached the point where a major European effort has been launched to investigate the devastation 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 Organization for Nuclear Research (better known by its French acronym, CERN). We still don’t know what these cosmic accelerators are or where they are located. What we do know is that cosmic rays—made up of subatomic particles—bombard our home world all the time. One source could be dying stars way off in the distance. Another is the “space weather” (solar wind, for example) generated by our local star, the Sun.
A single subatomic particle in a cosmic ray can have the energy of a Concorde jet, reaching speeds approaching that of light itself. These rays pepper the atoms that make up the earth’s upper atmosphere, shattering them and leading to showers of secondary subatomic particles, notably neutrons, which can then wreak havoc on computers down on the planet’s surface.
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 Center’s Weapons Neutron Research Facility in New Mexico, which, at the time, could create the most intense high energy neutron source in any lab environment. They developed a modest steel structure, the ICE House, which in one hour could replicate what would happen to a memory chip that experienced 100 years of exposure to the fallout of cosmic rays at cruising altitudes. They did this by subjecting each chip to a million neutrons per square centimeters per second.The result: the average ICE house chip suffered 1,200 errors per hour
Now, a second dedicated facility is being commissioned. Britain has built the $8.5 million “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. It should provide Europe’s gold standard for screening microchips. China also plans its own facility — the China Spallation Neutron Source in Dongguan — to cook microchips with neutrons. It’s currently under construction, and is set to be up and running by 2018.
The European instrument effort, led by Chris Frost, has been funded by the U.K.’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 pass through materials unhindered. 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 doesn’t really 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 passengers and nine 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 bringing the $1 billion Cypress Semiconductor Corporation factory to a halt. And now the potential havoc caused by this invisible threat is growing as more airborne microchip-based devices are used in drones, aircraft, spacecraft and satellites every year. The threat increases with altitude. At cruising altitudes of 10,000 meters, some 2,000 neutrons per second of various energies penetrate each square meter of an aircraft’s surface, passing through the hull, passengers, seats and electronics. As a consequence, the rate of errors at this altitude is hundreds of times that seen at sea level.
But the threat on the ground is growing too, as we build more servers to store our data, rely on more routers to send more of it worldwide and keep shrinking transistor sizes to cram billions into a single microchip. There is a seemingly endless densification of transistors in electrical circuits — Moore’s law, for example, has observed that the number of transistors that can be crammed into a single circuit doubles about every two years. That has driven the relentless advance of computing power—along with our growing dependence on silicon chips for purposes spanning communications, banking, medicine, GPS and more.
Some fear that Moore’s Law will soon break down — not because of a limit in our ability to make ever-smaller transistors at the scale of tens of nanometers (billionths of a meter) or less, but because of the neutron threat. As transistors shrink, errors can be caused by much smaller bursts of charge arising from neutrons. With higher densities, higher speeds and lower power consumption, microchip manufacturers are seeing neutron-induced soft errors occur more frequently.
When Chipir goes into action in the next month or two, circuits used in life-critical systems (like plane autopilot systems) 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 particles with about 207 times the mass of an electron, that could have similar effects as the neutrons.
Meanwhile, computers continue to 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.
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