[ RadSafe ] Airport x-ray exposure

Jim Hardeman Jim_Hardeman at dnr.state.ga.us
Thu Dec 21 10:06:06 CST 2006

Bob --
It somewhat depends on the individual airport and the type of screening
equipment they use. I typically wear a GammaWatch (thanks Kai!) and
although I don't fly as frequently now as I did a few years back, my
watch still gets run through airport X-ray machines a few times per
year. On several occasions, after retrieving the watch afterwards, I've
watched it trending down from somewhere between 5 and 10 uSv/hr (that's
500 uR/hr to 1 mR/hr - actually, I guess it would convert to urem per
hour - for those folks who can't think in uSv/hr).  Due to the way the
instrument averages exposure rate, the actually exposure rate during the
brief period of the X-ray scan could have been many times that
displayed. I haven't actually gone to the trouble of trying to measure
the DOSE received by the watch during an airport X-ray, and it would be
difficult to do so, as the minimum observable dose increment is 0.001
mSv (0.1 mR). If I remember next time. I'll try to zero the dose right
before I put it through the X-ray machine ...
What I've observed during flight is (of course depending on altitude,
latitude, sun spot activity, etc.) that average gamma radiation levels
once you get above 20K feet are somewhere between 2.5 and 4.5 uSv/hr
(250 - 450 uR/hr).
Not a scientific study by any stretch of the imagination, just my
observations based on my handy dandy GammaWatch, which rarely leaves my
Jim Hardeman
Jim_Hardeman at dnr.state.ga.us

>>> Robert Barish <robbarish at verizon.net> 12/21/2006 01:18 >>>
As a footnote to the story about the infant who received medical
scrutiny following passage through the airport x-ray unit, it may be of
interest to note that in 2002 Jesse Drucker, a reporter from the Wall
Street Journal, flew around the world with radiation measuring
instruments that I suggested to him for an article he wrote on in-flight
radiation exposure. 

He was able to measure both the low-LET components and neutrons with
his instrument package. What makes this footnote relevant is that the
Journal printed a graph of the measured dose rate as a function of time,
showing the smooth rise as the plane reached cruising altitude and the
decline as it descended in its approach to landing. 

What makes this germain to the present incident is the fact that Jesse
had the equipment turned on as it passed through the screening x-ray
unit before he boarded. It is easy to see from the graph that the
measured dose rate was higher while at the airlines cruising altitude
than it was inside the screening x-ray unit at the security checkpoint.
As the transit through the screening machine takes seconds, and the
flight duration could be hours, it's pretty clear where the "risky"
exposure takes place! 

Maybe we should set up medical facilities at airports to check arriving
passengers for the possible harm they suffered from their in-flight
radiation exposure. I'd set the fee low enough so that everyone could
afford it, and high enough to allow me to buy a condo in the recently
renovated Plaza Hotel. 

The Journal article is available online but, unfortunately, it costs
money to read it, as seems to be the practice with many newspaper
stories reprinted online that are more than a week or two old.

Best wishes for the holidays.

Robert Barish, Ph.D., CHP

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