Solar Radiation - How many transatlantic trips are safe?
Based on the following information, how many trips across the pond are considered safe and how many do you actually do?
I figure that we can only fly a maximum of about ten a year based on the information below... I am on my third already this month! Interestingly, latitude has a lesser effect than I thought.
But with further reading it gets worse. As radiation is present at all areas around the globe why do we only concentrate on transatlantic crossings? Surely the information below is related to any area and consequently at an average of 700 flying hours a year we are being exposed to levels as high as 4400uSv per annum, 4.4 times the recomended maximum for a ground based worker exposed to radiation at work. And we do this for careers as long as 40 years? With global terms and conditions reducing, why are we even considering doing this job anymore?
Q: When flying on a commercial jet airliner at high altitudes (i.e. transcontinental or transatlantic), what is the x-ray exposure per hour?
A: The radiation exposure to passengers and crew in high-flying aircraft is caused not only by x rays (photons) but also by a variety of energetic particles such as neutrons, protons, electrons, muons, and pions. These radiation types are produced as a result of the interaction with the Earth's atmosphere of high-energy particles (primarily protons and alpha particles) that come from a variety of cosmic sources in our galaxy, with a lesser contribution from our own sun. The galactic component of this incoming cosmic radiation is always present; the solar contribution varies in intensity over an approximately eleven-year cycle. In fact, the galactic component is greatest at solar minimum and is reduced at solar maximum by solar particle interactions with irregularities in the magnetic field associated with the "solar wind." Additionally, there is a significant variation of dose rate with altitude and to a lesser extent with geomagnetic latitude. During the last period of "solar minimum," at an altitude of 30,000 feet, the dose rate was about 4 uSv per hour at the latitudes of North America and Western Europe. During solar maximum, which is occurring now, the dose rate fell to around 3 uSv per hour. For the higher altitude of 40,000 feet, the dose rates were about 8 uSv per hour at solar minimum and now are about 6.5 uSv per hour. To put this into perspective, the legal value of "maximum permissible dose" for members of the public exposed to radiation originating from ground-based industrial or medical facilities is 1,000 uSv per year. So an airline passenger flying at an average altitude of 35,000 feet for a period of about 160 hours (75,000 miles) during solar minimum would receive an exposure at about the limit of the current acceptable level. Of course, most people who fly 75,000 miles a year or more do so because of their professional responsibilities as business travelers. It is my contention that the almost 450,000 individuals in the United States who fall into that category should be classified formally as occupationally exposed workers and that they should receive appropriate education about their exposures, particularly if they may be, or are about to become, pregnant. In addition to the general cosmic-ray "background" discussed above, there are rare solar particle events ("solar storms") that can significantly elevate the dose rates at airliner altitudes. The National Oceanic and Atmospheric Administration (NOAA) estimates that in an eleven-year solar cycle there could be up to three events that might produce a dose rate of up to 200 uSv per hour for a few hours at airliner altitudes. The most recent significant particle event occurred on July 14, 2000. Although an exact value of the maximum dose rate has not yet been established, my estimate is that it was at least 50 uSv per hour extending over the relatively long period of almost a full day. Robert J. Barish, Ph.D., CHP, DABR, DABMP, FAAPM