X-ray Backscatter Detectors

By Mark Guseman

TopicsSource of x-rays

Interaction with matter

Detection and Processing

Fooling the Detector

Health Concerns

Source: Towe and Jacobs 1981

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

Compton ScatteringUc = K1pnf(E) gives the Compton coefficient

Ratio of penetration depths between two output fluxes is given by x2 = x1 u2/u1ln(I2/I1)

Penetration depth depends on energy, intensity, and object density

Source: Towe and Jacobs 1981

Detecting Backscatter

Source: Herr et al 1994

Subtraction of Images

Source: Towe and Jacobs 1981

Modern Backscatter

Source: Kaufman and Carlson 2010

Fooling the DetectorMonte 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

Source: Kaufman and Carlson 2010

Source: Kaufman and Carlson 2010

Health ConcernsAbout 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

Works Cited