Lecture 4 - Airports Flashcards
Describe the historical ‘reactive’ nature of airport security.
Initially just a bag and person search of by security personnel for preventing hijackings. Evolved to tackle drug trafficking, contraband, and to improve efficiency for confirming passenger identity. Now, it is at the front line in the battle against terrorism.
Understand the privacy and safety features of airport whole-body scanners.
Privacy - Images viewed in a separate out-of-sight room are immediately deleted. Images can never be stored, and the system operator does not see passengers being scanned. Finer details that can identify a person can also be removed.
Safety - mm waves scanners restricted to produce less energy than a cell phone. Hence, the exposure is insignificant but still a ‘dose’
Convey the mechanism involved in pulse induction used for metal detection systems.
METAL DETECTION
- When metal is present going through the arches the initial pulse creates another
temporary magnetic field in the metallic object but with opposite polarity
- The additional and opposite magnetic field the object prolongs the length of the
reflected pulse»_space; 30 μs - A sampling circuit determines if the reflected pulse takes longer to decay than expected
Appreciate the suitability of various people screening technologies in specific environments and conditions.
There are the whole (full) body scanners: mm waves and backscatter. They produce an image of a person. The detection of contraband hidden in or under clothing. This system cannot detect materials swallowed or hidden in a cavity.
mm, waves are typically the scanners of choice. A lot of organizations have removed Xray body scanners due to privacy and posing of health risk issues.
Describe briefly what can a drug smuggler can do to avoid a small package of cocaine being
detected by a millimeter wave whole body scanner during transportation through an airport?
Transport it internally via swallowing, or hidden inside a body cavity
Describe the operation of a millimeter wave whole body scanner with reference to (a) the
hardware (i.e. antennas), (b) the imaging and (c) threat detection. You may sketch a diagram
to aid you explanation if you wish.
ANTENNAS: Person steps into a booth – surrounded by 2 Antennas (x1 front, x1 back) - Each
antenna is used to transmit and receive mm-waves - rotates around the subject - Protected by a
plastic shield (radome) which is transparent to mm-waves - Antennas are made of many small
elements → Antenna array
IMAGING: Antennas transmit mm-wave which penetrates the subjects clothing - Wave reflects
off the subjects skin and any concealed objects - Rotating antennas allows ‘snapshots’ to be
taken at different angles – Reflected energy is also detected by the antennas - Array
configuration allows the exact location of the reflection points to be determined → Creates a
high-resolution 3D image
THREAT DETECTION: Uses reflected signal strengths: Different materials reflect more/less
of the waves back - Allows discrimination between material types. Uses image analysis
techniques - Shape detection - Pattern matching. Automatic target detection (ATD)
algorithms: Metallic and non-metallic objects; Weapons; Explosives (gels, plastics, powders)
State one advantage and one disadvantage of security screening using metal detectors (not
necessarily in airports).
ADVANTAGES:
Very low cost: under £5k for a walkthrough system and around £100 for a portable system
High throughput screening (~500 people per hour)
Can be setup and deployed easily e.g. I train stations, schools, concerts sports events etc
X-Rays can be categorized as either being soft X-rays or hard X-rays. Soft X-rays have
frequencies in the range between 1016 and 1018 Hz. What is the frequency range of hard Xrays?
1018 and 1020 Hz
A baggage scanning machine transmits X-rays of frequency (f) 3.5 x1018 Hz. Calculate the
energy of the X-ray photons used in the operation of the system. Give you answer in keV
(kilo electron-volts) to 1.dp
E = 14.484561 = 14.5 keV
Attenuation is a process whereby an electromagnetic (EM) waves such as X-rays undergoes
a reduction in its intensity as in encounters and interacts with a material. State the two
process which cause the EM wave to lose some (or all) of its energy.
Scattering (deflection)
Absorption
An 80 keV X-ray airport screening system is being tested against a variety of samples to
examine its ability for discriminating between threat and safe materials. The plastic explosive
known as RDX is one of the materials being tested.
Use the Beer-Lambert Law to calculate the distance in RDX for which the incident X-ray
Intensity halves (i.e. decreases by a fraction of 0.5). Give your answer to 2 dp
0.023104906 = 2.31cm
The image below is a hypothetical X-ray spectra produced by electron bombardment of a
metal target. The continuum of X-rays (labelled as b) is termed Bremsstrahlung radiation.
[a] State the name of given to the peaks of specific (discrete) energy - labelled a (draw it)
[b] Explain in terms of atomic processes how these X-ray peaks are generated.
(a) Lecture 4 page 6 part 3
(b) Lecture 4 page 7 part 3
