Testing the cosmos

Scientists at the Didcot-based

neutron centre have developed instrumentation that enables them to test the effect of cosmic radiation on aircraft electronic systems.

Using a particle accelerator, the scientists can replicate the effect of neutrons on an aircraft’s equipment and simulate the effect of thousands of hours of flying time in just a few minutes.

‘If you were to spend 40,000 hours in the aeroplane, then we can do that in one hour on our instrumentation,’ said Dr Chris Frost, project leader at the ISIS neutron source.

When galactic and sun particles, known as protons, strike the top of the atmosphere, they create huge showers of particles that become greater in number as they fall through the atmosphere. The particles that get to aircraft altitudes (between 30,000ft to 35,000ft) and below are known as neutrons, and these highly penetrating particles can cause a range of damage to an aeroplane’s microelectronic devices.

The scientists generate neutrons by using a particle accelerator to collide very high-energy protons with a lump of metal. Frost said: ‘It’s very akin to what is going on in the atmosphere, where instead of the protons hitting the atmosphere, they are hitting a piece of metal.’

‘Every bit of electronics that does logic or holds things in memory has a degree of susceptibility. Anything from simple memory, SRAM to DRAM, right through to very modern pieces of electronics, such as Staggered Pin Grid Arrays (SPGA),’ said Frost.

‘The neutrons can cause memory to change its state, which means that if you have got something stored, like a bit of information, it could change that. In this case, to fix it, you can rewrite the memory, or change it.

‘A much more permanent problem is if you have to power the device on and off to fix it. And in a third type, they can burn out a device completely, so that it needs to be removed and then put back.’

The testing at ISIS therefore helps avionics manufacturers to make their equipment more robust against the threat of neutrons.

‘There are software things you can do, for example redundancy, so you put in extra circuits and compare the output of the circuits to make sure everything agrees before you go ahead. Also, there may be a particular element in the material that causes a problem, such as boron, so if you detect that this is causing a problem, you could try and remove this from a device,’ said Frost.

Existing instrumentation at the ISIS centre only allows for the testing of individual microelectronic devices, which Frost hopes will change with the completion of a new £140m neutron source alongside the original centre.

‘What usually happens is that five or six different companies will come and do a few days measurements together on one device. But in the new facility, we are aiming to test the whole system in which the devices sit, rather than individual bits,’ said Frost.