A radiation dose of between one and two hundred chest X-rays. That is how much radiation frequent passengers or flight crews on the North Atlantic route to New York absorb each year, according to some estimates.
These exposures are related to cosmic rays, high-energy ionising radiation from the sun and from further out in space. There is growing concern about exposures for crews and the air-travelling public. An EU directive to take effect by May 2000 will set limits to these exposures.
Measuring these exposures is another matter. There are large, heavy devices available that can measure high-energy radiation but these are no help in assessing the dose to an individual. The small film badges worn by hospital staff in X-ray departments do not readily record exposures to cosmic radiation, so there are no small, inexpensive devices that can do the job.
The situation could change, however, because of research at the National Microelectronics Research Centre (NMRC) in University College, Cork. A team led by Dr Bill Lane, the centre's assistant director, is developing a solid-state electronic device as small and thin as a credit card that can record high-energy cosmic radiation. It could also be used by radiographers and other medical and industrial staff working around X-ray equipment.
The NMRC employs 230 researchers working in microchip design and manufacture, advanced materials, sensor devices, microsystems and software. It has designed and built radiation detectors for European Space Agency satellites and is working on new devices that will fly on Japanese satellites in 2001, Dr Lane said.
The space agencies "are interested in the radiation coming into their satellites", he said, because high levels could disrupt sensitive equipment. The research on the smart card devices grew out of this work. "The primary aim was to bring them down to personal monitoring" through further miniaturisation but also an increase in sensitivity to record very low radiation doses.
The devices use fairly conventional microchip materials based on silicon dioxide, but they are read in a different way. Chips usually don't do anything useful until a current is applied, but these devices are passive and don't require any power until they need to be read.
Ionising radiation passing through the microprocessor disturbs the chemical bonds in the device. This disturbance changes the way it responds when a current is applied, allowing the chip to respond to both individual heavy cosmic-ray particle impacts but also the general exposure to the flux of lighter particles, gamma and X-rays.
"We have built the basic detector device," he said, involving a chip measuring no more than a tenth of a millimetre square. "We are now working on the electronics that go around it," which will enable the signal delivered by the microprocessor to be read and interpreted. This in turn will have to be linked to software yet to be developed, that will create records and provide an interface for the user.
The object would be to have each member of staff carry a smart card that could be swiped through a reader at the beginning of a shift. The reader would hold files on ongoing exposure levels. At the end of a flight or a day's work in an X-ray department the person would again swipe the card, transferring that day's radiation exposure details into the system.
The system could flag any unusual exposures or warn if the proposed EU radiation action level for flight crews - one millisievert per year, equivalent to about 50 chest X-rays - was being approached. This would mean that crews might have to change to lower altitude flights or spend time working on the ground.
Dr Lane will have three staff working on the electronics this autumn and he hopes to have an early version working by Christmas. The NMRC is not in the business of commercialising consumer software; specialists in this area would take what the NMRC has developed and integrate it into a software product that could be sold to airlines or hospitals.