- 1705 - Radiation. Energy in the sub-atomic world can come in waves or particles. How much radiation is needed before it is harmful to your health? How will radiation affect spaceflight? Can the risk be measured?
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--------------------------- 1705 - Radiation
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- Radiation can hurt you. Yes, or it can help you if you need an X-ray, or some medical treatment. Radiation in the form of electromagnetic waves covers the spectrum of 24 orders of magnitude. That is 10 times 24 times magnitudes of energy. In electron volts it ranges from:
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---------- 3 hertz electric power ---------- 0.00000000000000 249 electron volts
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------------------- Gamma Rays ---------------- 2,490,000,000 electron volts
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- In between these extremes of long wavelengths to short wavelengths we have a spectrum of wavelengths:
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------------------------ Radio
------------------------ Microwaves
------------------------ Infrared
------------------------ Visible red -- 700 nanometers ---- 0.356 electron volts
------------------------ Visible blue --400 nanometers ----- 0.624 electron volts
------------------------ Ultraviolet
------------------------ X-Rays
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- The shorter the wavelength , the higher the energy.
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- Radiation can also be particles. Cosmic Rays are not rays, ( a misnomer ) they are subatomic particles, mostly protons.
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- These high energy waves and high velocity particles can break atoms apart. Atoms that hold your body together. Radiation can damage genes, and can cause cancer, the mutations of cells.
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- Most of the radiation we experience comes from our Sun. But, it can come from radioactive dirt, elements like Uranium. Or, the potassium in bananas. Or, it can come from outside our Solar System, from supernovae, exploding stars, or, from Blackholes.
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- We are very fortunate that Earth’s atmosphere blocks most of the harmful radiation before it reaches the surface.
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- To quantify radiation we will introduce a unit of radiation called “ millirems” One “rem” carries a 0.055% chance of eventually developing cancer. A “millirems” is 1/1000th of a rem. ( See footnote ( ))
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- The average person receives 360 mrem per year. In the U.S. the average is 610 mrem. The additional radiation in the U.S. comes form X-rays, CAT Scans, and radon gas oozing out of the ground.
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- Hard to believe but you get 0.010 mrem for eating one banana. The potassium is good for you, but, it comes at a price.
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- If you lived 50 miles from a nuclear power plant you could receive 0.009mrem per year. More if you eat a lot of bananas.
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- If you frequent high elevations like airplane pilots and flight attendant you have a 1% greater occurrence of cancer compared to surface dwellers.
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- A whole body CT scan can give you the same amount of radiation as a survivor of the atomic bomb blast at Hiroshima, one mile from ground zero.
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- Astronauts on excursions on the Moon received radiation without an atmosphere for protection. They reported seeing flashes and streaks crossing their field of vision. Actually these were Cosmic Rays, mostly protons, ripping through their brains.
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- We were a week on the Moon. What is going to happen to astronauts on a one year trip to Mars?
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- We have some data from the spacecraft that delivered the Curiosity Rover to Mars. The results of radiation measured was equivalent to getting a whole body CT scan every 5 days for a year. This is the same as being a Hiroshima survivor , one mile from ground zero, 24 times over a year. The same bomb goes of twice a month.
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- A round trip mission to Mars would have the radiation exposure of 66,240 mrems.
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- This is equivalent of an average persons exposure over a 184 year lifetime. In the U.S. it would be a 107 year lifetime. ( 66,240 / 620 = 107 years ). A trip to Mars would increase the risk of dying form cancer by 4%. And, this exposure that was measured did not include any major solar flares occurring. And, it did not include any time on the Martian surface. It was only the trip there and back. It assumes astronauts could find caves or shelter of some sort to protect themselves from radiation once on the surface.
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- Mars has magnetosphere, or appreciable atmosphere to protect the surface from radiation from space. But, astronauts could become cave dwellers like we started out on this planet.
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- Radiation is a problem that needs to be solved if we are going to have safe space exploration. It is not enough to restrict bananas from astronauts diets. We need technology to again come to the rescue. We have a few years to work on it. A trip to Mars is a few decade in our future, if we don’t blow ourselves up with atomic bomb radiation in the meantime.
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- Stay tuned, there is still more to learn.
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- (1) See Cosmic Rays:
- #1659 - Cosmic Rays are ionized atomic nuclei traveling at near light speeds. the energy of Cosmic Rays spread over 12 order of magnitude from 10^8 to 10^20 electron volts.
- #1624 - Cosmic Rays coming from supernovae explosion and their accelerating shockwaves.
- #1568, #1496, #1377 - Cosmic Rays and Gamma Rays
- #810 - Sunspots and Cosmic Rays
- #709 - The risks of space travel.
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- (2) Here is how radiation causes damage to your body. Energy is absorbed when ionization occurs. Ionization is when a neutral charge separates into a positive charge and a negative charge, a free proton and free electron.
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- Chemical bonds are broken when this energy is absorbed destroying needed substances in a living cell. The ions may induce abnormal chemical reactions in the cell. The cell could just die. The cell could become a cancer. The gene may be mutilated causing an abnormal offspring. Cells in the body that reproduce rapidly are the most susceptible to this radiation damage.
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- (3) Radiation effects is an inexact science. When the body absorbs an ionized radiation particle or wave it is “ one dose of radiation”. How many doses are harmful? It is nearly impossible to quantify the effect of a “ dose “ of radiation on the human body. There are too many variables . A single alpha particle could cause more damage that 1,000 X-rays. It just depends.
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- How do you measure it? Science has come up with several measurement units: Roentgens, Grays, Sieverty, Rads, Rems. 1 Gray = 1 Joule / kilogram. The rem, or millirems is the one selected in this review.
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- (4) When you get down to the subatomic level particles and waves are the same thing. Their behavior is quantified in quantum mechanics math.
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------------------------ E = h*f , Energy = Planck’s Constant * frequency
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- But, the answer is not a single number. The math conclusions from quantum mechanics requires predictions about the probabilities of different outcomes from an event. It can not predict an outcome of a single event with certainty. Probabilities quantify the amount of uncertainty in the answer.
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- (5) How much radiation do you get from ordinary sunlight? How does that compare to the radiation from a 50,000 watt TV broadcasting station?
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- Solar energy arriving on the surface of the Earth is 1000 watts / meter^2.
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- This energy arrives as an electromagnetic wave. A magnetic wave traveling perpendicular to an electric wave. The amplitude of the electric field, “Eo”, can be calculated by:
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--------------------- Eo^2 = 2 * I / c * eo
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--------------------- “c” is the speed of light = 3 * 10^8 meters / second
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------------------- “eo” is permittivity of free space = 8.854*10^-12 Coulombs^2 / Newton* meters^2.
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- ------------------ “I” = power / surface area = 1000 watts / meter^2
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--------------------- “P” = power = watts = volt * Coulomb / sec = volts*amperes = Joules / sec.
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-------------------- “ V” = volt = Joule / Coulomb = Joule / ampere*sec.
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-------------------- “E” = Energy = Joules = mass * velocity^2 = m*v^2
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-------------------- “ F” = Force = Newton = Joule * meter = mass * acceleration = energy over distance.
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---------------------- Eo^2 = 2 * 1000 / 3*10^8 * 8.854*10^-12 volts^2 / meter^2
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--------------------- Eo^2 = 75*10^4 volts^2 / meter^2
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----------------------- Eo = 868 volts per meter , radiation arriving from sunlight.
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----------------------- Amplitude of the magnetic field, Bo = Eo /c
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----------------------- Bo = 0.3*10^-5 Tesla
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----------------------- Tesla = kg / Ampere * sec^2
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- That does not tell us much until you compare the power of sunlight to the power of a 50,000 watt TV broadcast.
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---------------------- I = Power / 4 *pi*r^2
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--------------------- Eo = 0.02 volts per meter, radiation from the TV broadcast.
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- Sunlight provides 43,000 more radiation that a 50,000 watt TV broadcast station. ( 868 v/m / 0,02 v/m)
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(6) The average exposure is 360 millirems per year. If one is classified as an “occupational radiation worker“, as astronauts are, then the maximum radiation dose is limited to 5,000 millirems per year. Radiation can come in a single dose or a long exposure. If a single dose 75,000 brings on radiation sickness, nausea. If you receive 300,000 millirems over 30 days you have a 50 / 50 chance of death. Here are examples of the average radiation the average person might receive:
----------------------------- Single dose
------------ CT Scan --------------------------- 1,100 millirems
------------ X-ray ------------------------------ 80 millirems
------------ Mammogram ------------------------ 13 millirems
------------ Panoramic Dental X-ray ------------ 1 millirems
------------------------------Long Exposure
------------ Average person --------------------------- 300 millirems /year
------------ Average medical exposure ---------------- 53 millirems /year
------------ Potassium in the body --------------------- 39 millirems /year
------------ Natural gas in the home -------------------- 9 millirems /year
------------ Eyeglasses containing thorium ----------- 10 millirems /year
------------ Drinking water ------------------------------- 5 millirems /year
------------ Building materials --------------------------- 3 millirems /year
------------ Airplane trip at 39,000 feet ---------------- 0.5 millirems /year
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RSVP, with comments, suggestions, corrections. Index of reviews available ---
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