Author Topic: Just Asking A Question  (Read 5179 times)

Offline Noldi400

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Just Asking A Question
« on: July 01, 2012, 11:38:30 AM »
I'm putting this in the Hoax folder just because it's intended to address a gap in my knowledge that I've been made aware of by HB claims.

I have some basic understanding of radiation from courses taken along the way during a career in EMS/Emergency Management. I know the difference between particle and EM radiation and why there are different shielding requirements.

I've searched around quite a bit but have been unable to find a clear answer to this question: am I correct in thinking that EM radiation outside the VAB is relatively light? That is, not enough to pose a health threat? Also, I know solar flares can put out considerable particle flux, which is not all that hard to shield from, but how much EM do they produce and how much of a problem would it be for astronauts on the lunar surface?

I remember that there was a (small) solar event during one of the missions (16? 17?) and the only precaution they took was to put the cosmic ray experiment in an ETB bag to keep it from being affected - evidently no precautions were needed for the crew.

So there it is - a legit question. Anyone help me out?

 ???So now you're saying the NSA killed Kennedy?
 :)Oh, no... They shot him, but they didn't kill him. He's still alive.
 :o

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Offline Tedward

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Re: Just Asking A Question
« Reply #1 on: July 01, 2012, 01:53:43 PM »
I am no expert in radiation but I know the sun is a sphere. It is interesting watching SOHO for example and watching a CME blow off to a part of the sky we are not in.

Offline Valis

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Re: Just Asking A Question
« Reply #2 on: July 01, 2012, 03:06:53 PM »
The radiation outside the VAB poses a health risk in prolonged missions, like a trip to Mars. Solar flares are an extra risk, but the background level from cosmic rays and such is not negligible.

Offline Chew

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Re: Just Asking A Question
« Reply #3 on: July 01, 2012, 06:26:55 PM »
Each year in a spaceship outside the VAB increases the incidence of cancer across a population by ~4%. There are a butt-ton of caveats to that statement but it should give you the gist of what "they" mean when they talk about the dangers of interplanetary travel.

Offline cjameshuff

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Re: Just Asking A Question
« Reply #4 on: July 01, 2012, 07:00:16 PM »
Also, as far as EM vs. particle radiation goes, there is fairly little ionizing x-ray/gamma ray radiation in open space, but charged particles tend to produce x-rays when they hit stuff like spacecraft hulls. Using light metals and plastics tends to reduce this problem, which is a big part of why spacecraft use stuff like aluminum and polyethylene for shielding rather than lead. This also means that magnetic shielding could be a long term solution. The radiation environment on the lunar surface was somewhat harsher than the radiation environment in open space because of this and because of the occasional proton hitting a nucleus hard enough to transmute it to something less stable.

Offline Noldi400

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Re: Just Asking A Question
« Reply #5 on: July 01, 2012, 07:08:27 PM »
It may be that I phrased that badly.

The point I was after was whether the ionizing EM radiation they expected to encounter on the Apollo missions was low enough that they did not need any special precautions given the mission duration.  I know that the spacecraft and suits were constructed to provide the needed particle resistance (while keeping the walls as thin as possible to minimize bremsstrahlung); it's just that I never see any mention of ionizing EM protection and was wondering how to respond to that specific point.

I know that on long-term missions almost any increased level poses a hazard because of cumulative damage and the lack of downtime for the body to make repairs.

EDIT:

Quote
Also, as far as EM vs. particle radiation goes, there is fairly little ionizing x-ray/gamma ray radiation in open space,

Ah. THAT's what I was asking. Thanks. About as risky as eating off Fiestaware, then, huh?  ;)

And thanks to everyone who answered.
« Last Edit: July 01, 2012, 07:24:07 PM by Noldi400 »
"The sane understand that human beings are incapable of sustaining conspiracies on a grand scale, because some of our most defining qualities as a species are... a tendency to panic, and an inability to keep our mouths shut." - Dean Koontz

Offline gillianren

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Re: Just Asking A Question
« Reply #6 on: July 01, 2012, 11:06:10 PM »
Ah. THAT's what I was asking. Thanks. About as risky as eating off Fiestaware, then, huh?  ;)

Depends on the colour.  Most of mine is cobalt blue or black, and those are colours which never had uranium in the glaze!
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Offline HeadLikeARock

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Re: Just Asking A Question
« Reply #7 on: July 02, 2012, 01:52:00 PM »
The only hoax claim I've heard in respect to this is the gamma radiation emitted by the surface due to bombardments with GCRs. I htink it was precipitated by this image, showing the moon's gamma emission:-



Looks pretty hot! No scale on the image though, so impossible to draw a conclusion about actual levels.

There was a paper published a few years ago by four Japanese scientists (you can see the whole paper here - http://www.google.co.uk/url?sa=t&rct=j&q=highland+radiation+moon+neutron&source=web&cd=1&ved=0CEwQFjAA&url=http%3A%2F%2Fjpsj.ipap.jp%2Flink%3FJPSJS%2F78SA%2F149%2Fpdf&ei=Fd7xT_faOcnG8gO4p4yIDQ&usg=AFQjCNF359n2cc8nF1xPJKmPi0o-EUwidA). From table I, you can see that the level of exposure due to gamma radiation from GCR's hitting the surface is 3.3 mSv per YEAR (and that's an upper value). This approximates to 0.03 mSv for the longest Apollo missions - less than half the typical exposure for a transatlantic flight.

Offline Luke Pemberton

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Re: Just Asking A Question
« Reply #8 on: July 02, 2012, 03:34:47 PM »
Following up from HLAR, the LRO has produced an interesting result regarding dose from secondary radiation.

Once I find time, I'll write a response to the question posed. It's not a trivial problem, but is very answerable in a few paragraphs. I'm just busy moving house at the moment as I start a new job soon.  :'(
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Offline ka9q

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Re: Just Asking A Question
« Reply #9 on: July 04, 2012, 03:03:07 AM »
EM radiation - electromagnetic radiation or photons - is generally not a serious threat to humans in space. The sun emits almost all of its EM radiation in the near infrared, visible and near UV spectrum where the photon energies are too low (i.e., the frequencies are too low or wavelengths are too long) to be ionizing. They mainly just heat whatever they hit.

A small fraction of sunlight is at shorter, ionizing UV wavelengths that could injure an unprotected astronaut by burning the skin or damaging the eyes, just as it can cause sunburn on the ground even through the ozone layer. But most structural and window materials (including ordinary glass and the Lexan in helmets) are opaque to UV, so it's easy to protect an astronaut. Solar UV is mainly a materials problem for the engineers, not a health problem for the surgeons. Along with charged particle radiation, UV slowly degrades space solar arrays.

The only real risk from solar UV to astronauts is from UV-transparent quartz windows specifically installed for UV photography. Quartz windows were installed on some of the Apollo J-mission CMs and on Skylab, so the astronauts had to protect their eyes and skin and cover the quartz windows with a shade or UV filter when not in use for UV photography. Dr. Owen Garriott, who flew on the second Skylab crew, recently told me that various alarms would go off if the UV windows on Skylab were left uncovered for any length of time.

There are almost no solar X-rays, which are shorter (more energetic and ionizing) than UV. A blackbody has to be heated to millions of kelvins to emit significant X radiation, and the sun's photosphere (the "surface" we see glowing with visible and near IR light) is less than 6000K. It's just not hot enough. (Nuclear weapons are hot enough to glow mainly in soft X rays for a few microseconds. These X rays are quickly absorbed by the surrounding air, rapidly heating it to form the fireball that re-radiates in the visible. The outer layers of the sun perform much the same function for the nuclear fusion reactions going on in the core.)

The solar corona is at several million kelvins (for reasons still not fully understood) but it is too thin to generate much X radiation. The sun emits significant X radiation only during flares when a massive chunk of solar atmosphere is suddenly heated to millions of kelvins and thrown off the surface. Again the mechanisms are not understood, but a section of a magnetic field line coming out of the sun detaches and forms a closed loop that rapidly collapses and dumps its stored energy into the plasma. A big flare can emit enough X radiation to significantly increase ionization in the D layer of the earth's ionosphere, increasing radio signal absorption so suddenly that the entire HF ("shortwave") radio band goes dead. (The D layer is what normally keeps you from hearing distant AM radio stations during the day; it dissipates at night, letting signals reach the higher F layers that act as efficient reflectors for long-distance propagation.)

This Sudden Ionosopheric Disturbance or radio blackout is often the first sign that a big solar flare is in progress. Because SIDs are caused by X rays traveling at the speed of light, they happen only 7 minutes after the event (light travel time from the sun) and affect the entire day side of the earth (radio propagation on the night side is initially unaffected). If there's a coronal mass ejection, its charged particles are much harder to shield so they can threaten astronauts. But most flares don't produce a CME. Even when they do form they often miss the earth/moon entirely.  And even when they do hit us they arrive hours or days after the flare so there's often a warning. Spacecraft now constantly watch the sun, several from the Earth-Sun L1 point 1.5 million km toward the sun. Any CME must pass L1 on its way to earth, so these satellites give us at least 30 minutes of warning.

The STEREO missions have cameras continually watching the sun in the extreme ultraviolet where the sun is ordinarily fairly dark. Flares show up spectacularly on these cameras, which have returned many stunning pictures, often in 3D as viewed from two seperated spacecraft.