Jeff Buske Rocky Flats Gear 2011

Much mystery and controversy surrounds the airport security dose.  X-rays are short wavelength high energy photons that occupy the upper region of the electromagnetic spectrum.  Terahertz/mm-wave scanners use radiation below visible and just above microwaves.  We can see only a tinny sliver of the spectrum as visible light as shown in Fig 1.


FIG. 1 Electromagnetic Spectrum

 

FIG. 2  Radiation  Wave and Particle 

For our simple demonstration we use a common red laser pointer to visualize and simulate the X-ray pencil beam emitted from backscatter systems.

Similar to x-ray measurements for dose or exposure we use a light meter to read intensity or brightness.  The measurement principles are the same for microwave, light photons or x-rays.  Initially the x-ray/laser is off and we read background radiation or room light, in this case about 10 Lux.

FIG. 3 X-ray/Laser off Background Radiation Level.

Scanning is simulated by rapidly sweeping the laser pointer from side to side.  Backscatter systems use a rapidly rotating slotted disk with a complex mechanism to  sweep the beam over the whole body.  The scanning process over-scans the target (your body) and spray the security area and beyond making the area radioactive.[2]  The scattered dose to security workers as measured by John Hopkins University should classify staff as radiation workers and be issued dosimeters.

As indicated in FIG. 4  the average dose is small due to the energy being spread over a larger area.  In this example dose is only 4 times the background radiation.


FIG. 4 Simulated backscatter X-ray scanning.

Stopping or a failure of the mechanical scanner will deliver a large dose as shown in figure 5.  The light sensor below assumes uniform illumination over the white sensor area. You can see only a small fraction of the sensor is exposed. If the beam (red area) covered the full sensor (white area) the reading would be about 20x greater than displayed.  This would make in this example true dose rate approximately 2,000 times the average reading during the scan.  The back-scatter measurement were done in using a similar method resulting in deceptively low dose readings.

In this case the actual stopped beam reads 100 times the scanned average. The instantaneous DOSE that your tissue cells and DNA sees is perhaps 1000-2000 times the averaged value.

FIG. 5 Scanner failure/scan stopped beam intensity measurement.

The bright X-ray pencil beam emitted by the backscatter scanner creates a local region of intense radiation.  This intense radiation spot is quickly moved over the full body from head to toe. The skin and underlying organs see this much larger instantaneous dose.  Remember the free radical damage is done in as little as 0.000001 second, a 6 second scan breaks lots to things from head to toe on  both sides of your body.  Most of the damage is repaired in few minutes some is never repaired serious double DNA breaks can cause cancer and be passed to your children. 

FIG. 6 Visualize x-ray tissue absorption and scattering

A large percentage of the x-rays also miss the target person and are beamed into the open security area and beyond irradiating bystanders and security personnel with direct and scattered x-rays.  A significant amount is also scattered off the person giving a significant dose to unshielded security personnel standing nearby.

X-rays have been known for 100+ years to be damaging to tissue, so ignorance is no excuse.  Radiation induced damage to critical cellular machinery such as DNA is done on a molecular level in a few billionths of a second.  Remember the free radical damage is done in a flash the repair time is a few minutes to forever with serious double DNA breaks.  This is a serious issue to the 5% of the population with DNA repair issues from a defect in the BRCA1 gene on chromosome 17 as shown in Fig. 8 below.

FIG. 8 BRCA1 Gene and double DNA break.