ONE OF the problems with radioactive contamination is that it is invisible.
Smoke blackens, oil stains, chemicals discolour, but you can鈥檛 actually see
dangerous ionising radiation with the naked eye.
But now a British company is working on a system that shows up radioactivity
as a glow in the dark. With a pair of modified military night-vision goggles,
scientists monitoring radioactive contamination at the scene of a possible spill
would be able to spot smears of alpha-emitting radionuclides such as
plutonium.
The radiation goggles designed by British Instrument Consultants (BIC) in
Warrington, Cheshire, are based on an old technique. Early last century, nuclear
pioneer Ernest Rutherford saw the flashes of light given off by zinc sulphide
when it is struck by alpha particles. The effect, known as scintillation, is
commonly used in radiation monitors which convert the flashes of light into
electronic signals.
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BIC wanted to find a way of boosting the weak flashes given off by low levels
of radioactivity until they鈥檙e visible to the human eye. To do this, the company
took a pair of night-vision goggles and tuned them to highlight light
wavelengths emitted by scintillating zinc sulphide.
The result, according to BIC spokesman Mike Scott, is that you can see alpha
contamination as low as 30 becquerels per square centimetre as an intense glow
on the goggles鈥� green monochrome screen. 鈥淭he main advantage is being able to
measure contamination of unusually shaped objects,鈥� he says. 鈥淲ith standard
probes it鈥檚 very difficult to get into nooks and crannies.鈥�
The goggles, which have been tested at the University of Liverpool, would
also enable staff monitoring an area to keep well away from contamination. One
disadvantage, though, is that you have to spray zinc sulphide onto the area
under investigation. And you can only use the goggles out of doors at night
because daylight swamps the sensitive electronics, though filters might make it
possible to see the glow in ambient light, Scott says.
Nevertheless, Scott says some of the major players in the nuclear industry,
including the UK Atomic Energy Authority (UKAEA) and British Nuclear Fuels
(BNFL) have already expressed an interest. The goggles could be useful in
identifying hot spots of plutonium contamination at the nuclear plants being
decommissioned at Dounreay in Caithness and Sellafield in Cumbria, he
argues.
Scott, a physicist who has specialised in radiation measurement, accepts some
people would prefer a device that could detect lower levels of contamination and
other forms of radioactivity. But he is confident that he can improve his design
to highlight contamination down to 10 becquerels per square centimetre. He is
also planning to investigate other materials such as plastics that are
susceptible to scintillation from beta, neutron and gamma radiation.
Peter Burgess from Britain鈥檚 National Radiological Protection Board says that
while BIC鈥檚 idea is a clever notion, he is worried that spraying potentially
contaminated areas with zinc sulphide might send radioactive particles into the
air and worsen the clean-up problem. But the UKAEA believes the technology
鈥渟ounds very interesting鈥� and could be useful. 鈥淏ut we need to reserve judgement
until we have seen it demonstrated,鈥� a spokesman says. BNFL takes a similar
tack, arguing that the goggles are the 鈥渟park of an idea鈥� that needs more work
and testing before they would be willing to use them.
