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Post by PhantomWolf on Feb 18, 2010 20:47:27 GMT -4
Captain Swoop, I'm thinking specifically about the cosmic rays. Wikipedia says: en.wikipedia.org/wiki/Cosmic_rayCosmic rays are energetic particles originating from outer space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are simple protons, with nearly 10% being helium nuclei (alpha particles), and slightly under 1% are heavier elements, electrons (beta particles), or gamma ray photons.[1] The term ray is a misnomer, as cosmic particles arrive individually, not in the form of a ray or beam of particles. However, when they were first discovered, cosmic rays were thought to be rays. When their particle nature needs to be emphasized, "cosmic ray particle" is written. The variety of particle energies reflects the wide variety of sources. The origins of these particles range from energetic processes on the Sun all the way to as yet unknown events in the farthest reaches of the visible universe. Cosmic rays can have energies of over 10^20 eV, far higher than the 10^12 to 10^13 eV that man-made particle accelerators can produce. (See Ultra-high-energy cosmic rays for a description of the detection of a single particle with an energy of about 50 J, the same as a well-hit tennis ball at 42 m/s [about 94 mph].) There has been interest in investigating cosmic rays of even greater energies.[2]
There's another optimistic little article in Wikipedia about the health effects of these rays. They say that the more energetic rays are less damaging than the lower energy ones, but that wouldn't make me feel confident about standing in the path of a single particle with 50J energy. That article also notes that shielding is difficult because of a cascading effect, high energy cosmic rays striking the shielding and throwing off more radiation. Again it comes back to that magical word, flux. Cosmic Particles are very rare, they have very low flux, and getting hit by one of them isn't going to kill you. The secondary radiation issues are well known, and occur when you use the heavier metals to "brake" the particles. It has a sexy German name, bremsstrahlung, which literally means "braking radiation." Lighter metals like Aluminium produce a lot less of it, and non-metallic shielding sources such as water and polymers don't produce it at all. As you noted, Cosmic Particles actually enter our atmosphere, so Space Shuttle, ISS (and previously MIR) crews have all been exposed to them for a long period of time with no ill effects. Even in 1969 it was known that they were rare. There was more of a worry about solar activity than cosmic particles causing damage.
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Post by porphyry on Feb 18, 2010 20:54:23 GMT -4
Phantomwolf, isn't it also true that the vast majority of cosmic rays are blocked by the Van Allen belts?
It seems to me that what we're saying here is that deep space is permeated by high energy cosmic rays which are at least 7 orders of magnitude more energetic than anything that can be created on Earth, and everyone agrees that this is hazardous in the long run to space crews -- yet NASA has had no interest in any follow-up studies with biological specimens, or to test shielding designs in real conditions, over the last 40 years.
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Post by scooter on Feb 18, 2010 21:19:53 GMT -4
It appears that "rays" and "particles" are getting intermixed here...
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Post by Obviousman on Feb 18, 2010 21:24:11 GMT -4
Don't forget that our knowledge has increased because we know have further results from the Hiroshima / Nagasaki survivors. We are now able to see resulting condition from exposure without having to expose further persons to various radiations.
Sorry, but that is false. They still do experiments with biological sample here on Earth - and on the ISS / Shuttle - and shielding is a constant source of discussion.
You should do some more research on the subject:
Bragg Curve, Biological Bragg Curve and Biological Issues in Space Radiation Protection with Shielding
Author(s): Honglu, Wu; Cucinotta, F.A.; Durante, M.; Lin, Z.; Rusek, A. Abstract: The space environment consists of a varying field of radiation particles including high-energy ions, with spacecraft shielding material providing the major protection to astronauts from harmful exposure. NASA Center: Johnson Space Center Publication Year: 2006 Added to NTRS: 2009-11-25 Document ID: 20080029277; Report Number: JSC-CN-9980
Analytic Shielding Optimization to Reduce Crew Exposure to Ionizing Radiation Inside Space Vehicles
Author(s): Gaza, Razvan; Cooper, Tim P.; Hanzo, Arthur; Hussein, Hesham; Jarvis, Kandy S.; Kimble, Ryan; Lee, Kerry T.; Patel, Chirag; Reddell, Brandon D.; Stoffle, Nicholas; Zapp, E. Neal; Shelfer, Tad D. Abstract: A sustainable lunar architecture provides capabilities for leveraging out-of-service components for alternate uses. Discarded architecture elements may be used to provide ionizing radiation shielding to the ... NASA Center: Johnson Space Center Publication Year: 2009 Added to NTRS: 2009-10-14 Document ID: 20090035371; Report Number: JSC-CN-18881
Statistical Prediction of Solar Particle Event Frequency Based on the Measurements of Recent Solar Cycles for Acute Radiation Risk Analysis
Author(s): Myung-Hee, Y. Kim; Shaowen, Hu; Cucinotta, Francis A. Abstract: Large solar particle events (SPEs) present significant acute radiation risks to the crew members during extra-vehicular activities (EVAs) or in lightly shielded space vehicles for space missions beyond the protection ... NASA Center: Johnson Space Center Publication Year: 2009 Added to NTRS: 2009-09-30 Document ID: 20090033667; Report Number: JSC-CN-18746
Can the Equivalent Sphere Model Approximate Organ Doses in Space
Author(s): Lin, Zi-Wei Abstract: For space radiation protection it is often useful to calculate dose or dose,equivalent in blood forming organs (BFO). It has been customary to use a 5cm equivalent sphere to. simulate the BFO dose. However, many ... NASA Center: Marshall Space Flight Center Publication Year: 2007 Added to NTRS: 2009-08-24 Document ID: 20090028812; Report Number: MSFC-309, MSFC-319
Effects of Nuclear Cross Sections at Different Energies on Space Radiation Exposure from Galactic Cosmic Rays
Author(s): Li, Zi-Wei; Adams, James H., Jr. Abstract: Space radiation from galactic cosmic rays (GCR) is a major hazard to space crews, especially in long duration human space explorations. For this reason, they will be protected by radiation shielding that ... NASA Center: Marshall Space Flight Center Publication Year: 2007 Added to NTRS: 2009-08-20 Document ID: 20090028663; Report Number: MSFC-378
Radiation Protection Effectiveness of Polymeric Based Shielding Materials at Low Earth Orbit
Author(s): Badavi, Francis F.; Stewart-Sloan, Charlotte R.; Wilson, John W.; Adams, Daniel O. Abstract: Correlations of limited ionizing radiation measurements onboard the Space Transportation System (STS; shuttle) and the International Space Station (ISS) with numerical simulations of charged particle transport through ... NASA Center: Langley Research Center Publication Year: 2008 Added to NTRS: 2009-08-11 Document ID: 20090026971; Report Number: LF99-5666
Validity of the Aluminum Equivalent Approximation in Space Radiation Shielding
Author(s): Badavi, Francis F.; Adams, Daniel O.; Wilson, John W. Abstract: The origin of the aluminum equivalent shield approximation in space radiation analysis can be traced back to its roots in the early years of the NASA space programs (Mercury, Gemini and Apollo) wherein the primary ... NASA Center: Langley Research Center Publication Year: 2009 Added to NTRS: 2009-08-06 Document ID: 20090026532; Report Number: L-19705, LF99-9078, NASA/TP-2009-215779
Radiation Protection for Lunar Mission Scenarios
Author(s): Clowdsley, Martha S.; Nealy, John E.; Wilson, John W.; Anderson, Brooke M.; Anderson, Mark S.; Krizan, Shawn A. Abstract: Preliminary analyses of shielding requirements to protect astronauts from the harmful effects of radiation on both short-term and long-term lunar missions have been performed. Shielding needs for both ... NASA Center: Langley Research Center Publication Year: 2005 Added to NTRS: 2009-07-29 Document ID: 20050215115
etc
etc
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Post by PhantomWolf on Feb 18, 2010 21:24:21 GMT -4
Phantomwolf, isn't it also true that the vast majority of cosmic rays are blocked by the Van Allen belts? It seems to me that what we're saying here is that deep space is permeated by high energy cosmic rays which are at least 7 orders of magnitude more energetic than anything that can be created on Earth, and everyone agrees that this is hazardous in the long run to space crews -- yet NASA has had no interest in any follow-up studies with biological specimens, or to test shielding designs in real conditions, over the last 40 years. From my reading on the matter, no. (Though I am willing to be corrected here.) If we just talk the main two (Inner and Outer) and ignore the weak third belt. The Outer belt is created by negitively charged electrons in the solar wind hitting the magnetic field of the Earth and becoming trapped. The Inner belt is created by positively charged protrons that have come from decayed neutrons that are created when a cosmic ray hits our atmosphere. The strength of the inner belt would indicate that they have no issues getting through the belts, most likely because of their speed. To become trapped in the magnetic field the particles have to be travelling at just the right speed and angle, or else they will curve out of the belt or into the Earth's atmosphere. Of course Gamma Cosmic Rays will go through both belts without any deflection at all. What does stop a lot of cosmic radiation is the strength of the solar wind. In years where it is weak, we get a lot more cosmic radiation than in years where the solar activity and thus solar winds are stronger. You also seem to be concentrating entirely on the energy of the partickle, and not the more important value of flux. 1 particle at 50J hitting an 85kg person is nothing. 100,000 particles at 0.5J hitting the same person is likely to hurt. In the first case you'd get an average of 58 rads. Since it is only a single particle, the energy absorbsion is likely to be low, but even if you absorbed the lot, and it was spread out over your body you'd be in the low area of mild radiation poisoning (50-100 rem.) Note: this isn't what would happen IRL as it wouldn't be spread out of your body. In the second case, you'd have an average of 588 rad. This time that would be spread over your entire body. If we say that again the Q (yield into the tissue) is 1, that's 588 rem, or acute radiation poisoning, meaning a 60% chance of fatality after 30 days. So as you can see, in the first case, 50J and you live and probably never notice it, second case, you're dead, even though the energy levels of the particles are lower. So as to NASA doing no deep space radiation research for 40 years... why would they need to? They weren't planning any long term missions until the last 5-6 years, at which point they started working on radiation issues again. It comes down to the fact that they have a limited money supply, so why spend money on things you have no need of there and then when you have plenty to spend it on already? There have been numerous papers published on the matter in the past 40 years though.
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Post by porphyry on Feb 18, 2010 21:35:17 GMT -4
Obviousman, your list of references does show that NASA is very interested in this issue, but the fact remains, there has been no deep space experimentation with biological specimens.
Phantomwolf, you say there's no danger from a single 50J particle, but how do you know? Not that I'm saying flux isn't important, but the single particle energy might also be important. Terrestrial studies can't address this issue because it's impossible to make such high energy particles in the lab.
It's pretty much gotten to the point where I can't reply without repeating myself.
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Post by PhantomWolf on Feb 18, 2010 22:07:50 GMT -4
Phantomwolf, you say there's no danger from a single 50J particle, but how do you know? Not that I'm saying flux isn't important, but the single particle energy might also be important. Terrestrial studies can't address this issue because it's impossible to make such high energy particles in the lab. Because we know how and why radiation is damaging. A single particle simply isn't able to do a lot of damage because it is just far too small. Imagine shooting a 100m x 100m cube of jelly (jello for USA) with a .22 rifle. How much damage does it do? Now shoot it with 1,000 small rocks from a bungee slingshot. How much damage would that do? Radiation does its most harm by shear number of hits over time, not the enegry of any single particle.
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vq
Earth
What time is it again?
Posts: 129
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Post by vq on Feb 18, 2010 22:44:26 GMT -4
Obviousman, your list of references does show that NASA is very interested in this issue, but the fact remains, there has been no deep space experimentation with biological specimens. Phantomwolf, you say there's no danger from a single 50J particle, but how do you know? Not that I'm saying flux isn't important, but the single particle energy might also be important. Terrestrial studies can't address this issue because it's impossible to make such high energy particles in the lab. It's pretty much gotten to the point where I can't reply without repeating myself. Suppose you are a researcher interested in the effects of deep space radiation on an animal. You can design a massive and complex spacecraft to travel into deep space and return to the earth's surface so you can examine the animals (hopefully preventing their death from other causes during their long trip), or you can design a small and relatively cheap probe that carefully measures the radiation environment and then expose specimens to the same environment here on earth.
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Post by Obviousman on Feb 19, 2010 1:10:19 GMT -4
Obviousman, your list of references does show that NASA is very interested in this issue, but the fact remains, there has been no deep space experimentation with biological specimens. Did you read any of the references? Perhaps you could explain what benefit there is in launching an expensive deep space probe to investigate matters that can be investigated - more cheaply and efficiently - on Earth?
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Feb 19, 2010 1:43:29 GMT -4
but the fact remains, there has been no deep space experimentation with biological specimens. Unless you can demonstrate such experimentation is necessary, there is no reason to find the lack of it odd or unusual.
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Post by BertL on Feb 19, 2010 2:22:41 GMT -4
Obviousman, your list of references does show that NASA is very interested in this issue, but the fact remains, there has been no deep space experimentation with biological specimens. Don't humans count as a biological species? (I edited the astronauts' mouths so that they would look saddened because of a lack of recognition of them as a biological species.)
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Post by gillianren on Feb 19, 2010 2:52:26 GMT -4
Wow. Astronauts boldly traveling into the Uncanny Valley!
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Post by trebor on Feb 19, 2010 3:10:02 GMT -4
I'm thinking specifically about the cosmic rays. Wikipedia says: You don't need to go into deep space to test exposure to those. Cosmic rays are at such high energies that they pass right through the earth's magnetic field and into the atmosphere. As such the effects of them can be examined in low earth orbit easily enough. isn't it also true that the vast majority of cosmic rays are blocked by the Van Allen belts? Not really. The higher energy cosmic rays pass right through the Earth's magnetic field, the lower energy particles get trapped and become the VABs.
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Post by Tanalia on Feb 19, 2010 6:59:56 GMT -4
One other component of flux is the time factor -- it's not a matter so much of how much radiation you might absorb from a 50J particle, as the fact that a human-sized target might get hit by such a particle an average of maybe once every few decades.
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Post by Obviousman on Feb 19, 2010 8:17:36 GMT -4
Some more reading material for you:
SPACE RADIATION CANCER RISK PROJECTIONS FOR EXPLORATION MISSIONS: UNCERTAINTY REDUCTION AND MITIGATION (JSC-29295) Francis A. Cucinotta, Walter Schimmerling, John W. Wilson, Leif E. Peterson, Gautam D. Badhwar, Premkumar B. Saganti, and John F. Dicello (2001)
SPACE RADIATION CANCER RISKS AND UNCERTAINTIES FOR MARS MISSIONS Francis A. Cucinotta, Walter Schimmerling, John W. Wilson, Leif E. Peterson, Gautam D. Badhwar, Premkumar B. Saganti, and John F. Dicello RADIATION RESEARCH 156, 682-688 (2001)
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