What’s in that bottle? Imaging liquids at airports

Michelle Espy, LANL
 

In August of 2006, an alleged terrorist plot was thwarted in London. The aim was to detonate liquid explosives carried aboard several airliners traveling from the UK to the US and Canada. The alleged plot was discovered by the police before it could be carried out, and as a result unprecedented security measures were immediately put in place. This sudden imposition caused chaos and delayed flights for days. Although the initial measures were somewhat relaxed in the following weeks, the ability of passengers to carry liquids onto commercial aircraft is still limited.
 
After two trials and the largest counterterrorism investigation in Britain’s history, three men were found guilty in September of 2009, and given sentences for life in prison. The bombers’ plan to drain plastic soft-drink bottles with syringes and refill them with concentrated hydrogen peroxide, a bleaching agent also used as a propellant for rockets, led to the new measures prohibiting passengers from carrying all but small quantities of liquids and creams onto flights. Prosecutors said the plot could have killed at least 1,500 people aboard the targeted planes, which by that measure would have made it second only to the September 11, 2001, attacks as the most serious terrorist plot in modern history.
 
The reason for the restrictions on the volume of liquids one can carry aboard aircraft, in the wake of this plot’s discovery, is that there simply is presently no high through-put (fast) and non-contact way to understand the chemical composition of liquids inside bottles. X-ray technology does not assess chemical composition, and other techniques measuring light scattering, electrical properties, mass spectrometry, and fluorescence are all restricted to single bottles and/or may require a physical sample to be present outside the bottle. And so the traveling public must place all liquid items into small (less than 100 ml) bottles contained in one clear quart sized zip-loc baggie.
 
The story we present here is the tale of the three years since that plot’s discovery, and our efforts to convert a technology primarily used for imaging of the human brain (ultra-low field magnetic resonance imaging, or ULF-MRI) into something that can detect liquid explosives in an airport. Our scientific premise is that the ability to detect chemical differences between brain tissue in the MRI might be the same sensitivity required to detect the difference between a benign soft-drink and an explosive liquid. In this Cafe, we discuss the technology of ultra-low field and conventional MRI, applications to imaging brains and bombs, and the adventures of a group of researchers trying to survive the tensions between pure science and the needs of the Department of Homeland Security.
 

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