Cosmic Radiation is a constant reality not only in the universe, but also on our own planet. Particles and rays coming from the Sun and the distant parts of the Universe constantly bombard us. As jets and various aircraft go higher and higher, we get more and more exposed to this radiation and it threatens to contribute to health problems. In this article, I wish to discuss the health threats of Cosmic Radiation to passengers and aircrews. I also wish to discuss the use of an established radiation shield, “Polyethylene” that can be used in passenger aircraft.
What is Cosmic Radiation?
Cosmic Radiation is any form of radiation that originates from outer space. (Aircrew Health) It is the radiation left over by supernova explosions, the Big Bang, and all the many processes of the cosmos. A lot of radiation also comes from the Sun; the Sun’s solar flare activity puts out a great deal of energy into the local space. The Earth receives a lot of this radiation as it shoots through space. Cosmic Radiation can come to the Earth in the form of subatomic particles such as protons and gamma rays.
How does Cosmic Radiation Affect Earth?
Cosmic Radiation continually bombards the Earth from all directions. However, Earth’s atmosphere does a good job stopping these rays and particles by absorbing them. For people on Earth, the more air you have between you and the beginning of outer space, the better protected you are from these high energy particles and rays from outer space. People living on a high mountain would naturally get more of a Cosmic Radiation dose than those living at sea level. Some radiation does penetrate to sea level, but not as much as you would receive living on a mountain.
You are at Greater Risk of Cosmic Radiation Exposure when Flying
When travelling at high altitude you are far less protected from Cosmic Radiation, as the air between outer space and the aircraft becomes very thin at 20,000-30,000 feet, where typical passenger aircraft fly. It is not just altitude that determines your exposure to cosmic radiation. Where you fly determines how much radiation you receive. If you were to fly close to the equator, your radiation exposure would be much less than it would be if you flew over the polar regions of the planet. This is because the air is thicker over the equator and thinner over the poles. (Aircrew Health) How long you fly also determines your radiation dose. An overseas international flight will give you more radiation than a domestic half-hour flight. (Aircrew Health) The aircraft itself does block some radiation, but a lot of that radiation is so energetic that it penetrates straight through the aircraft.
The radiation dosage you receive is more nominal when you are an occasional flier, but if you are a crewmember working with an airline company and fly for a living; you take in a lot more radiation than the occasional passenger does. In fact, aircrews are recognized by the FAA as being “Occupationally Exposed” to Cosmic Radiation. (Aircrew Health) In other words, the FAA recognizes radiation as part of the job when it comes to being part of an aircrew. Because of the continual exposure, aircrews are recognized as having a higher potential for cancer. Cancer depends on other factors as well such as genetics, smoking and diet, but Cosmic Radiation can play a contributing role. (Aircrew Health) Radiation during pregnancy is an obvious health hazard to an unborn child. If you are pregnant and on an aircrew, you are urged to bring it to the attention of your supervisor, so that adjustments can be made and perhaps they can put you in a ground-based position for the duration of your pregnancy. (Aircrew Health)
What is being done So Far?
The good news is the Federal Aviation Administration (FAA) has a system in place to monitor Sun activity and can relay information to aircraft so that they may lower their altitude and decrease exposure should the Sun suddenly send out massive amounts of rays and particles. (epa.gov) You may also determine for yourself how much radiation dosage you will receive during a flight using the free radiation calculator available from the FAA:
While Cosmic Radiation can be avoided by things like driving instead of flying and taking shorter flights, the reality of the world is that Cosmic Radiation and aircraft travel go hand in hand. It is not always realistic to change travel plans because of radiation. However, some current research sounds promising in that aircraft and passengers can be better protected from radiation in the future.
Research has shown that molecules that are made of hydrogen and carbon atoms (hydrocarbons) are very effective in absorbing high energy Cosmic Radiation. Polyethylene has been shown to be one of the most effective molecules in radiation absorption. Polyethylene, with the chemical formula (C2H4)nH2, is the most common form of plastic found on earth today. (Wikipedia) We come across polyethylene on a daily basis. It is used to make milk jugs, grocery bags, and almost any kind of packaging you can think of. It is even used in hip and knee replacements. (Wikipedia) In fact, 80 million metric tons of polyethylene is produced annually. (Wikipedia) There are different types and densities of polyethylene that are used commercially.
The Physics and Chemistry behind the Effectiveness of Polyethylene
Polyethylene plastic has been shown to be a much better protector against radiation than metals. Part of this is due to the reason that Polyethylene molecules are composed of lighter atoms than metals and metal alloys. When a Cosmic Radiation particle like a proton strikes an atom, it produces what is called “Secondary Radiation.” What that means is the proton smashes into the atom and breaks it apart into smaller particles, which become the secondary radiation as they shoot out from the original atom. (nasa.gov) If you have a heavier metal atom with many protons, neutrons and electrons, the incoming proton smashes that atom, you get many secondary radiation particles, and some energy released like gamma rays. (nasa.gov) (The concept is the same in nuclear power.) If you have lighter, less atomically massive atoms like carbon and hydrogen, you do not get anywhere near the amount of secondary particles shooting out from the original atom. (nasa.gov)
Hence using hydrogen and carbon in radiation shielding becomes that much more effective in overall radiation protection than you would with a shield made of lead or aluminum. This is the point behind radiation shielding. You “Fragment” the particles coming towards you and minimize their negative effects. Secondary radiation can be worse for health than primary radiation. (nasa.gov) This is why not only the stopping of primary radiation, but the lowest possible reduction of secondary radiation is what researchers seek when making radiation shielding. Polyethylene does just that with its lightweight molecular structure.
Recycling Polyethylene for use in Passenger Aircraft
Polyethylene does not biodegrade very well at all. It is very tough, especially the higher density polyethylene. It can sit in a landfill for centuries without decomposing at all. This is where I think that polyethylene can be utilized after being used for everyday applications like grocery bags. Polyethylene can be taken from landfills and recycled into radiation shielding, thus protecting the environment and saving on manufacturing costs.
Use in Passenger Aircraft
With Polyethylene being much better than metal at absorbing high-energy radiation, I believe the use of recycled Polyethylene in aircraft fuselages becomes somewhat of a necessity. In fact, a NASA researcher named Raj Kaul has been researching using a special type of reinforced Polyethylene for use in spacecraft so astronauts can be better protected from Cosmic Radiation. (NASA Science) His reinforced Polyethylene is made using heat and pressure acting upon pre-layered Polyethylene fiber sheets. The result is a brick of reinforced Polyethylene that weighs about half as much as a similar piece of aluminum and much stronger. (NASA Science)
Polyethylene does not have to be a brick. The fibrous nature of Polyethylene makes it so that it can molded around components like a drape or sheet. This is where it may become practical for use in passenger aircraft. A layer of reinforced Polyethylene covering the fuselage tube in between the outer skin of the aircraft and the passenger compartment would make for a big increase in radiation protection for passengers and crew. It is not a complete solution, as many Cosmic Radiation particles are so high energy that they pass straight through Polyethylene. Of course the thicker the layer of Polyethylene the better the shielding will be. The fact remains however that Polyethylene is 50 percent more effective at blocking radiation than aluminum, which is the current shielding of choice for spacecraft.
The fact that Polyethylene is so much lighter than metals like aluminum make it very practical for use in passenger aircraft. Adding a layer of Polyethylene to the aircraft structure will not significantly add to the overall aircraft weight like another layer of metal shielding would. This is also the reason it is being researched for use in spacecraft. Rockets will have an easier time lifting this material into space than metal radiation shielding. In fact, the reinforced Polyethylene is already being utilized in military aircraft as a ballistic shield. (NASA)
The Flammability Problem
Pure Polyethylene is very flammable. (NASA Science) This might pose a problem in aircraft where you are already sitting on a large quantity of jet fuel. In the event of an accident, radiation protection does not make much sense when the entire fuselage can catch fire. However, this is not a cause to give up on the idea of Polyethylene layering for radiation protection. In my research for this article, I came across several companies that offer flame retardant polyethylene sheeting. Mostly this means that there is a flame retardant film laminated over a Polyethylene sheet. This lamination or something equivalent could be used in aircraft, but the flame retardant lamination would have to be of a heat resistance so as to not allow the Polyethylene layer to catch fire in an accident. Likewise, the lamination would have to be tear resistant so as not to expose the Polyethylene during or before an accident. In fact, the co-researcher of the reinforced Polyethylene Nasser Barghouty states that more research will be required so that the reinforced Polyethylene does not melt when exposed to sunlight in space. (nasa.gov) I believe that in the coming years more research will make it so that the reinforced Polyethylene will be much more flame proof than it currently is, at which point it will be even more suitable for aircraft radiation protection. It would be more sensible to make the Polyethylene itself flame retardant than to use a flame retardant lamination film.
A cost-to-benefits analysis will have to be conducted to determine how practical it will be to use polyethylene shielding in current aircraft and aircraft currently being manufactured. One problem that I can foresee is that the shielding will break down over time with exposure to radiation. The atoms in the shielding will degrade and compromise the shielding. This might make it necessary to replace the polyethylene layer in an aircraft after several years. That replacement cost will have to be factored in as well. I am the type of political scientist that puts people’s health and safety above cost, but the cost does have to be considered, and if a cheaper more effective solution is available than it should be pursued, but so far this solution seems to be promising.
We live in a world where flying high is routine, and unfortunately with that routine comes the exposure to the properties of the universe. This is just another problem in our technical lives that we have to overcome. When considering the costs of health care for flight crews and frequent fliers, radiation shielding becomes a method of reducing health care problems as people age and will help to protect the health of aircrews. Health insurance might become cheaper for people working in the airline industry when there is better shielding against cosmic radiation in aircraft. The engineering and cost of a polyethylene shield in an aircraft will have to be assessed. Polyethylene shielding is something we might see in the distant future. For now, more research in anti-flammability will have to be conducted. On a physics level, I can certainly see this working and I hope that it will be explored for the entire aerospace industry.
Plastic Spaceships – NASA Science
Fire Away, Sun and Stars! Shields to Protect Future Space Crews – NASA
Polyethylene – Wikipedia
Aircrew Exposure to Cosmic Radiation – Aircrew Health
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