Cosmic rays coming from ultrapowerful sources in the distant universe can pose risks to humans on Earth — particularly frequent air travelers, who are routinely exposed at the high altitudes of commercial flights. Now, astronomers have used low-cost radiation detectors to begin mapping the radiation environment over African skies, in the first steps to protect the safety of airline crews flying over that continent.
Cosmic rays constantly bombard us from every direction in the sky. But the "rays" aren't exactly well named. Although the astronomers who first discovered cosmic rays thought they were a new form of radiation like X-rays and gamma-rays, further investigation revealed that cosmic rays are actually made of subatomic particles traveling at nearly the speed of light.
A typical cosmic-ray particle has the same kinetic energy as a fastball. That may not seem like a lot, but squished down to subatomic levels, that amount of energy packs a real punch. Cosmic rays can scramble electronics, damage data storage devices and even snip apart DNA. When DNA splits, it can cause replication errors and even lead to tumors. Scientists estimate that cosmic rays trigger a few percent of all cancers worldwide.
Thankfully, our planet offers several layers of protection against these threats. The first is Earth's magnetic field — the strongest among the rocky planets in the solar system — that simply deflects the lower-energy cosmic rays. The higher-energy ones barrel right through, however, making their way into our planet's atmosphere.
But once there, the cosmic rays usually strike a molecule of nitrogen or oxygen, releasing their energy in a shower of other particles. At sea level, cosmic rays or their lower-energy showers pass through the human body at a rate of about once every second.
The risks of cosmic rays
That's what happens at sea level; cruising altitude for airline flights is an entirely different matter. Without those tens of thousands of feet to offer protection, passengers and crews suffer far higher rates of cosmic ray bombardment. With higher rates comes a greater risk of DNA or cellular damage, and a corresponding increase in cancer rates.
The metal shell of the aircraft isn't much help in stopping the microscopic damage, either. While the metal will effectively block the cosmic rays themselves, as soon as they strike an atom, they will transform into a shower of subatomic particles that blasts through the cabin. That shower is almost as damaging as the cosmic rays themselves.
The only effective remedy is to limit exposure. Casual airline travelers have nothing to worry about, as their accumulated radiation dose isn't significantly different from what they experience on the ground. But frequent travelers, especially crews, face an increased radiation risk from their time spent at high altitudes.
The governments of the United States and Europe have mandated safety standards that limit the total exposure that airline crews can accumulate in their lifetimes. Combined with frequent monitoring of the radiation environment at high altitudes, airlines can keep their crews safe.
The monitoring must be frequent, because the cosmic-ray environment constantly changes depending on many factors, like Earth's magnetic field, the sun's activity and random cosmic variations.
However, this monitoring program only covers the skies above North America and Europe. We have relatively little knowledge of the radiation environment above Africa. Although fewer flights cross that continent, until we understand the cosmic-ray environment, we cannot quantify the risk posed to airline crews.
A team of astronomers took the first steps in solving this problem, detailing their results in a paper accepted for publication in the Journal of Space Weather and Space Climate. Their setup was incredibly simple. They designed a dosimeter using a Raspberry Pi computer to measure the radiation exposure in any environment. Then, they brought the device on board two long-haul flights — one from Johannesburg, South Africa, to Frankfurt, Germany, and another from Munich to Johannesburg.
The researchers showed that their simple setup could accurately measure the radiation levels during the flight. They hope to expand the deployment of these simple devices to as many passenger aircraft as possible, allowing them to build up a network of monitoring devices that constantly map and update the cosmic radiation environment. From there, they hope to work with African governments to develop safety standards across their airlines.
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Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.
I have no problem with folks mapping cosmic ray intensties as a function of time over various routes used by passenger aircraft.Reply
But, I find it annoying that people publish articles about it in the popular media without actually specifying any radiation dose information. How about providing:
1. the average estimated total radiation dose to people on the ground;
2. the average radiation dose for a flight from Washington DC to LA on San Francisco;
3. the dose limit that applies to flight crews?
That would provide some useful perspective.
And, additional perspective could be provided by telling us the dose rates in terrestrial hot spots, like the one in India, where the does rate is about 10 times the average dose rate for people around the globe. I have not followed this for decades, but the last I read, health effects were not detected in the populations of those unusually high terrestrial radiation areas.
The media tends to get scary numbers by using statistical analyses that show very low additional dose rates to a very large number of people, and multiply those by very low individual risk numbers gleened from linearly extrapolating the effects of high does toward zero dose rate.
On the other hand, I just needed some medical CAT scans, and they gave my eyes 10 times the allowed annual dose to professionals who are monitored for radiation - coming to 75% of the short-term dose that is deterministically known to cause cataracks with about 8 years of lag time. I was scheduled for more x-rays, but asked to be switched to MRIs instead, because I knew the risk. But, you don't read scare stories in the media about medical sources of radiation.
Rather little detail on the detection technique used. I suspect that all is being done is to detect the resulting gamma ray intensity. A much easier thing to do than detect cosmic ray intensity, and not novel. Just take a Geiger counter up with you on your next flight and observe the results. My gamma alarm was set off!! The gamma count was 10 times higher than at sea level.Reply
By the time the "shower" products of cosmic rays that have interacted with matter reach inside the metal cans we call airplanes, I doubt there are any charged particles left to be absorbed by people, just the high energy photons we call gamma rays.Reply
Once these highly charged 'heavy particles' interact with the skin of the aircraft, only about 10% of them are actually absorbed in a dire ct collision, giving off a shower of highly ionized particles measurable by a 'dosimeter'. Of the remainder (90%) are effectively 'slowed down' by their ionic-drag of attracted ions in a comet like trail. Dosimeters are historically 'directional' and only show about half of the total dose, that coming from the Effective Aperture of the material used for detection. A thin sheet of film is mostly effective in a direct or perpendicular direction and the efficiency drops off to Zero in a 90 degree collision. Even Thermo Luminescent Devices (TLD's) display this directivity. Hopefully, these newly developed detection devices have a better cross section capture. But what exactly are they capturing? Gamma? High Speed charged ions? If so, what energy ranges?Reply
I've seen nothing in print on these new devices to be able to pass judgement. I've carried film badges and modern TLD's on 24 hour flights both day and night and have only seen less than 1% of an additional dose that I would have seen on the ground. No doubt, my devices were not very efficient or accurate.
Seems like an old liquid scintillation detector would give the 4 pi detection sensitivity.Reply
Some TLDs I have used were thick crytals, too, so not clear to me that they are not also 4 pi.
But, when looking for cosmic ray dose, it seems that "up" is the prefered direction, anyway.