Airport X ray Scanners
It seems the choice de jour for security these days is to use some form of x ray screening at the airport. Our carry-on bags get screened using x rays and sometime get wiped down and checked for chemicals; our checked luggage gets a free CT scan, and we, sometimes, get screened using x rays. It’s called a backscatter x-ray screening device.
Not all airports have these, most use a magnetic field to determine if you have metallic objects on or in you. Many more airports, though, are getting the backscatter x-ray devices. Safe? Not safe? We’ll let you decide and here is some information to do just that.
Let’s compare the technology with that of a standard x ray. With a standard x ray, medium energy x rays go through the body and those that get through create the image that the physician views (those that don’t get through are either absorbed in our body or scattered). The reason medium energy x rays are used is to get a good image of items inside the body. With a backscatter device, low energy x rays come in contact with the body and are mostly scattered back at some detectors – much like me throwing a ball against the wall, it doesn’t go through the wall, but “scatters” back to me.
These low energy x rays penetrate through clothing and some can penetrate beneath the skin, but most are scattered off of the skin. An image is created in just a few second of a body outline that might show explosives, drugs, and anything else that doesn’t belong there. They won’t, however, detect anything deep inside the body – the lack of penetration of the x rays just isn’t good for that. Also, because the x rays don’t penetrate, you need two scans – front and back – which will take about 10 seconds.
So, how much radiation are you exposed to from a backscatter scanner? For this, I’m going to use the unit of effective radiation dose (just like the radiation answers Web site) that is abbreviated rem.
One general use backscatter scan radiation dose = 0.01 mrem
One day of natural background radiation = ~ 1 mrem (10 backscatter scans)
Average commercial airplane flight (one way) = 4 mrem (40 backscatter scans)
Typical chest x ray = 10 mrem (100 backscatter scans)
Typical abdominal x ray = 70 mrem (700 backscatter scans)
Annual maximum permission radiation dose limit for the public = 100 mrem (1,000
Annual maximum permissible radiation dose limit for radiation workers = 5,000 mrem (50,000
Will flying a dozen times a year, getting a backscatter scan each time, cause harmful effects? No.
Will flying a dozen times a year with my children and them getting a backscatter scan each time cause harmful effects in my children? No
Two dozen? No
How many backscatter scans would it take to cause harmful effects? That is difficult to estimate because most of the radiation doesn’t penetrate to sensitive organs. For this example, though, let’s say 5 percent of the x rays actually penetrate to sensitive organs. To accumulate a dose that will cause a clinically observable effect (not harmful, but observable), we would need to have over one million scans in a relatively short period of time (see http://www.radiationanswers.org/radiation-and-me/effects-of-radiation.html).
That gives us an idea of the size of the radiation dose. It’s up to you to decide whether it is safe.