2. Topics Source of x-rays Interaction with matter Detection and Processing Fooling the Detector Health Concerns Source: Towe and Jacobs 1981

3. Source of X-Rays Two guns used in airport detectors Low energy gun is equivalent to CAT scan source High energy gun is stronger than used in a mammogram Can either move the source or the object to be imaged Source: Kaufman and Carlson 2010

4. Compton Scattering U c = K 1 pnf(E) gives the Compton coefficient Ratio of penetration depths between two output fluxes is given by x 2 = x 1 u 2 /u 1 ln(I 2 /I 1 ) Penetration depth depends on energy, intensity, and object density Source: Towe and Jacobs 1981

5. Detecting Backscatter Source: Herr et al 1994

6. Subtraction of Images Source: Towe and Jacobs 1981

7. Modern Backscatter Source: Kaufman and Carlson 2010

8. Fooling the Detector Monte Carlo simulation using parameters from real detectors Cylindrical tissue represents the abdomen Ran simulation four times: No added material 160 g of added tissue 190 g of added TATP explosive 320 g of added PETN explosive Formed cone of material 20 cm in diameter and 1 cm high at center Source: Kaufman and Carlson 2010

11. Health Concerns About 1 μSv dose per exposure. This results in increased cancer risk of 10 -7 per round trip With 1 billion exposures per year, the population risk is no longer minimal Millimeter wave imaging, which is non-ionizing, may provide a viable imaging alternative for airport security Source: Brenner 2011

12. Works Cited