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Calliban

Member

From: Northern England, UK

Registered: 2019-08-18

Posts: 3,446

Re: Space Radiation + counter measures

Rather scary to think of a single subatomic particle with as much energy as a small bullet.  If that hits a human being it is going to do substantial damage.  I wonder if the unlikely person would actually feel the hit?  If it hits a nerve fibre they probably would.  In fact, if a particle like that hits tissue directly above a nerve, the damage to motor neurons from the secondary particle shower might be enough to impair the function of the nerve.  Not nice.

Last edited by Calliban (2024-02-22 19:09:20)

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"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,936

Re: Space Radiation + counter measures

The natural average Earthly background is about equal to the US average background of about 300-330 milli-REM.  Sorry,  I do not know how to convert that.  It's 0.3 to 0.33 REM/year,  which is not a very large number.  (Supposedly,  about a third of that background traces to coal burned in power plants.  Coal is slightly radioactive,  as is frack water backflow.)  It is very important to note that natural background varies strongly with location.  In the mountains where ore-bearing rocks are near the surface,  and there is significant radon gas coming from underground,  it is supposedly as much as 10 times higher (3-3.3 REM/year).  REM is "Roentgen Equivalent Man",  meaning radiation intensity multiplied by a human vulnerability factor.

For comparison,  the space radiation environment outside the Earth's Van Allen belts is mostly a drizzle of cosmic rays plus some solar wind,  peaking at 60 REM/year at solar minimum,  and only about 24 REM/year at solar maximum.  These were predicated on an expected 3% increase in the rates of cancer late in life.  Apparently,  the solar wind slows the cosmic rays down a lot,  and the solar wind is stronger during solar max.   That's a pretty good estimate for Venus/Earth/Mars space.  Not so sure about Jupiter and beyond.  Even with the heliopause way beyond Pluto.

Before they were recently changed (lowered slightly),  the astronaut exposure criteria were no more than 50 REM accumulated in any one year,  no more than 25 REM accumulated in any one month,  and a career exposure limit that varied with age and gender,  but which usually falls in the 300-400 accumulated REM ballpark.  50 REM accumulated over only an hour or two is fatal to 50% of those exposed,  and 100 REM in an hour or two is fatal to 100% of those so exposed.   Time makes an enormous difference. 

Those larger doses are well known since not long after Nagasaki and Hiroshima.  I saw them documented in AEC's report "Effects of Nuclear Weapons,  1957".  It's the lower doses around 1-10 REM/year and less,  that are not well known from any data,  which is where the linear-with-dose-rate scaling is used.  The assumptions underlying that dose rate scaling,  are still only assumptions.  There is no recognized data.

The fallout from a nuclear surface burst close by can be as high as 5000 REM/hour,  based on the explosions in Japan,  and after the war in the Nevada desert!  It can be lower,  even a lot lower.  But you cannot count on it being lower,  because sometimes it's just high!  Air bursts at significant altitude are a lot lower in fallout radiation intensity.  (500-5000 m is not significant altitude!)  Lots lower if the fireball does not come close to touching the surface.  Most of the fallout is surface dust brought up through the incredibly-radioactive fireball materials by the columnar suction that creates the mushroom cloud.

The lethal space radiation threat is NOT cosmic rays!  Never was,  never will be!  There are many who tell you it is,  but they are lying to you!  It is instead radiation released in a burst by explosions on the sun.  In a word,  solar flare events,  which occur erratically,  and are very,  very directional.   These are quite comparable to nearby nuclear weapon explosions.  Incredibly intense radiation intensity rates,  and over in a few hours.

The only other thing to understand is that not all radiation is the same.  Cosmic rays are mostly hydrogen nuclei moving at near lightspeed.  These are very difficult to shield.  Solar flare particles are mostly hydrogen and helium nuclei,  moving very much slower at solar wind speeds.  Those are much,  much easier to shield against,  which is what the 25 g/cm^2 figure of merit for shielding is all about.  Van Allen belt radiation is mostly solar flare and wind particles caught in Earth's magnetic field,  but still moving in circles about the field lines at something like solar wind speeds.  Intensity resembles solar flare events and nearby nuclear explosions.

GW

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,936

Re: Space Radiation + counter measures

Scientists build breakthrough nuclear fusion device with household magnets]