[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: What about radiation

Martin Horejsi wrote:
> 
> draco@bios.iuf.net wrote:
> 
> "As far as I know all meteorites should have high level of radiation due to
> the influence of UV, x-rays and other Solar and cosmic rays? Somebody knows
> anything about it? Maybe all found meteorites are the sources of different
> diseases such as cancer?" 


> For some reason, probably stemming from comic books and cartoons, many
> people believe meteorites are or should be radioactive. Fortunately,
> meteorites are not radioactive at all.
> 
> Although meteorites have been exposed to cosmic radiation, they do not
> contain materials which emit any radioactive particles. Also, "UV, x-rays
> and other Solar and cosmic rays" may have been formed through processes
> founded in radioactive decay, but they in themselves are not the same type
> of radiation, and although dangerous to humans, they are just high energy
> electromagnetic waves.
> 


Radiation & meteorites is a subject that popular entertainment seems to
have used enough to make public education necessary by all of us.  The
risk is about as serious as "The Blob" actually running amok from the
interior of a space rock.  (Maybe the latter is a bigger risk? (:-) )

Right, UV will not induce a nuclear transformation and consequently
cannot be a source of radioactivity in meteorites.  The photon energy is
too tiny compared to nuclear transition levels.  No activation that way.

No.  Cosmic rays are not just electromagnetic waves.  Protons are
plentiful, just as you expect from looking at all the hydrogen in the
universe. (Also, high energy gamma rays--electromagnetic--can change
nuclei.) They have two components, one from within the solar system and
another from the rest of the galaxy.  Energy of the charged particles is
sufficient to overcome the few million electron volt Coulomb barriers
surrounding nuclei and penetrate to enact a change.  The energy spectrum
can range from subgigaelectron volt to excess of 10^20 eV for the
particles inducing Centauro events, so named because "over a hundred"
secondary tracks can form from hitting an atomic nucleus  (think of it,
enough energy in a single subatomic particle to theoretically vaporize
drops of water).

Thus you can get induced activity in meteorites (unless your sample is
from a shielded interior).  This is useful for understanding time spent
in space by a meteorite.  Such activity tends toward equilibrium (decay
rates and new parent isotope creation) in space with time.  When they
hit the earth, the half-lives of short-lived species can cause loss to
science of information quickly.  Fresh falls have no more than low
activity, of interest to labs.  I have yet to hear of one shown to be
dangerously radioactive.  The cosmogenic nuclides created by the
interactions tell its history and will probably do more for you than
seeking miniscule activity (unless someone brings you a fresh fall like
Monahans immediately so you can measure activity as it starts to fall). 
The meteorites in your collection are just not what you can call
"radioactive." 

Curiously, uranium is not an "iron-loving" element and should be
concentrated in the outer parts of the Earth.  The "planetary"
meteorites may be more like Earth in this regard than ordinary
chondrites, but I don't have reference tables on hand.  Maybe I should
be more afraid of radiation from the (earth) rocks you throw at me for
saying this?  Be kind and throw meteorites at me instead.

----------
List Archives are located at http://www.meteoritecentral.com/list_best.html
For other help, FAQ's and subscription info and other resources,
visit  http://www.meteoritecentral.com/mailing_list.html
----------
References: