Solar Particle Event Warning for Pregnant Travelers

[ROBBARISH@aol.com]

Dear Radsafers:

When we were discussing in-flight radiation exposure about a month ago, I 
said that I would be posting a comment about solar particle events in the 
near future. That time has now arrived. 

Let me begin with some background on the phenomenon of Coronal Mass Ejections 
(CME). The plasma at the sun's surface, basically a hot cloud of protons, 
often forms huge arches of flame known as solar prominences.  Collisions of 
blobs of plasma in the sun's outer atmosphere, or corona, often release large 
amounts of energy into space. These are solar flares. In a CME, the release 
also contain billions of tons of the sun itself, and this huge proton cloud 
can interact with the Earth creating energetic secondary particles, 
particularly energetic neutrons, as interactions occur with the atmosphere. 
Like many solar phenomena, the frequency of these events tends to be 
associated with the approximately eleven-year periodicity of the waxing and 
waning of sunspots. These periods are termed solar cycles, and we are now in 
the twenty-third cycle for which detailed observations have been made and 
recorded. Yes, this data is archived back to around 1750!

Considering the ordinary radiation dose received by flight crewmembers and 
passengers, the dominant contribution is made by galactic sources, not our 
own sun. There is generally an inverse relationship between solar activity 
and terrestrial background radiation since the galactic component is 
deflected to a greater or lesser extent from the Earth by a weaker or 
stronger solar wind.  This relationship is quantified in the "heliocentric 
potential" that is a required input parameter in the FAA's CARI computer 
program which can be used to estimate dose from airline travel.

So in addition to the usual doses received at flight altitudes under "normal" 
conditions, passengers and crewmembers who are aloft during some 
charged-particle events can receive doses that are significantly greater than 
usual. Sometimes the radiation levels are elevated to the point that there is 
even a measurable increase in background at the Earth's surface - a so-called 
Ground Level Event (GLE).

In solar cycle twenty-two there were six such events. The radiation level at 
airliner altitudes associated with the event of 29 September 1989 was 
estimated to be 10-15 mrem/hr (100-150 mSv/hr). Ground monitoring stations 
showed an increase of 500% over normal background.  The greatest of all 
particle events occurred in 1956. It is estimated that the dose rate at 
current airliner altitudes was as high as 100 mrem/hr (1 mSv/hr). Although 
such particle events occur suddenly, and the peak level of dose rate is 
reached almost immediately, they substantially decrease in intensity in a 
relatively short period of time, typically several hours.  

The embryo/fetus of a pregnant passenger or flight crewmember may be 
particularly vulnerable to potential harm from such events. It is certainly 
in conformity with the ALARA principle that if a pregnant passenger can avoid 
an exposure of this nature by simply waiting for the next flight, that they 
should strongly consider doing so.

And that is the advice that a pregnant traveler will get if she phones 
1-877-SUNFLARE immediately prior to boarding the aircraft and a particle 
event is occurring. If conditions are normal, she will obviously receive a 
message to that effect. The line will be updated as conditions change, 
insuring up-to-the-minute information.

What I'm doing here is telling you, as my colleagues in radiation safety, 
that I will be implementing this warning system for pregnant travelers in a 
few days time. I expect that there will be media attention, and it is my 
intention to have this subject handled with the utmost objectivity and lack 
of sensationalism by any journalist who displays interest. We are now 
approaching the time (2000-2001) which is projected to be the peak of solar 
cycle 23, and there is every reason to suspect that the next significant 
particle event will occur sometime in the next few months. The last was on 7 
November 1997. It followed several years of minimum solar activity as we made 
the transition from cycle 22 to cycle 23, with "solar minimum" in 1995-96. 

In my paper in The Journal of the American Board of Family Practice which 
initiated the earlier thread on in-flight radiation, I was very careful to 
note the minimal (or zero) risk associated with a pregnant passenger making a 
trip or two to visit relatives, or for a vacation. Under conditions in which 
in-flight radiation levels are "normal," such travel should not be ruled out. 
But there is no good reason to fly during an intense solar particle event if 
it can be avoided by waiting for a few hours. My warning system is, for now, 
the only way in which a pregnant passenger can learn of these events in 
real-time. If your wife or daughter were pregnant, wouldn't you want them to 
have access to this information?

Rob Barish
robbarish@aol.com
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