Detection of explosives in baggage using tomographic reconstruction and image analysis February 16, 2010 Purdue University Aziza Satkhozhina

A BRIEF HISTORY OF EXPLOSIVES Gunpowder by Chinese alchemist 618/907 In the Tang Dynasty, China The shooting fire weapon Huo Chong 1271 – 1368 In the Yang Dynasty

High Explosives Dynamite = nitroglycerine + kieselguhr 1866 Alfred Nobel Plastic explosives 1939, during Second World War II Interesting fact: some of them are edible

What is an explosive? An explosive material, also called an explosive, is a substance that contains a great amount of stored energy that can produce an explosion, a sudden expansion of the material after initiation, usually accompanied by the production of light, heat, and pressure. Explosive material. (2007). In Wikipedia. Retrieved February 2, 2010, from

Classification of explosives Propellants / low explosives contain oxygen needed for the combustion and produce gas which produces explosion ( black powder, smokeless powder) Primary explosives/initiators are very sensitive and explode when they are heated or subjected to shock, often used as detonators (lead azide, nitrogen sulfide etc). High explosives are less sensitive than primary explosives, detonate under the influence of the shock of the explosion of a suitable primary explosive (nitroglycerin, acetylene, ammonium nitrate etc) Airport security is threatened by High Explosives (HE) Davis, T. (1972). Chemistry of Powder and Explosives. Angriff Press.

How do they work?

What kind of explosives do terrorists like to use? IED (improvised explosive device ) – homemade bombs constructed and deployed in ways other than in conventional military action. Often used for suicide terrorism. IED usually consists of an explosive charge, a detonator and an initiation system. Classified by trigger mechanisms: - Command wire IED (CWIED) – the wire connected to IED - Radio controlled IED (RCIED) – controlled by radio link. (can be triggered from car alarm, cell phones, pagers etc) - Cell phone RCIED – modified cell phone is connected to an electrical firing circuit - Victim operated IED (VOIED) - functions upon contact with a victim.

On average one busy international airport 60 departures per hour 200 passengers for each flight 12,000 pieces of baggage to check each hour! Riveros, E. G. (2002, December 22). The digital radiographic and computed tomography imaging of two types of explosive devices. International Journal of Radiation Applications and Instrumentation, Retrieved February 15, 2010, from D&_user=29441&_coverDate=12%2F31%2F2002&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId= &_rerunOrigin=google&_acct=C &_version=1&_urlVersion=0&_userid=29441&md5=8b3ba91f68f01bd9cf71e317403ff406

Properties of explosives that help explosive detection Elemental composition: many explosives contain large amount of oxygen and nitrogen Density: most explosives have higher material density than other objects. Typical explosives that terrorists use fall in the range between 1.2 and 1.6 g/cm^3.

CT images Spreading streaks in CT images – star artifacts Mathematical distortion of the image when significant amount of impedance is mismatching Appears when a high density object surrounded by low- density object Riveros, E. G. (2002, December 22). The digital radiographic and computed tomography imaging of two types of explosive devices. International Journal of Radiation Applications and Instrumentation, Retrieved February 15, 2010, from D&_user=29441&_coverDate=12%2F31%2F2002&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId= &_rerunOrigin=google&_acct=C &_version=1&_urlVersion=0&_userid=29441&md5=8b3ba91f68f01bd9cf71e317403ff406