(meteorobs) Meteorite pix

[mexicodoug at aim.com]

Matt Mundorf schreef:

"Hmmm.  Is the radioactivity generally because of the obsorbed radiation
that is emitted from a number of sources in space or that the material
in the meteor itself is radioactive?"

Marco explained:
It are shortlived isotopes formed in the meteorite by cosmic radiation 
while it
was in space.

Hello,

Right, Marco.  Keeping in mind that "cosmic radiation" is a misnomer or 
confusing term at best.  More conventionally the so-called cosmic RAYS 
are ions and particles, mostly protons, accelerated to 'a non-trivial 
fraction of, to nearly the speed of, light". It is their collision with 
the meteorite that has enough energy to alter certain atomic nuclei and 
leaving them unstable enough to decay which is the source of 
radioactivity.

However, Cosmic RAYS is also a misnomer, since it is a relatively 
random background of solar and extrasolar PARTICLES AND not a ray, 
radiation or from a radiant.  So you could call them femto-meteors 
(micro-meteorites is already spoken for) when they collide with Earth 
or meteoroids, even though the former are not orbiting the Sun.

The high energy of the particle collision with meteoroids in space 
generates new isotopes in the rinds of the meteoriods, some of which 
are rather short lived - easier to meaure ages with precision.  
Meteoriticists like to study the isotope ratios for in fresh meteorites 
as this provides at least two types of information.  Once on Earth, 
they are mostly shielded by cosmic ray particles by the earth's 
magnetic field and atmospheric collisions.

1) How long the meteoroid has been circulating in space - cosmic rays 
typially don't make it more than a meter or so through mass, so, 
assuming the meteoroid was ejected from a deep crater somewhere, rather 
than being a primordil bolder, the cosmic ray exposure by comparing 
isotope ratios can indicate how long ago the ejection event(s) did (or 
didn't) originate.
2) Similar information by putting together a puzzle to form a gradient 
and estimate the size of the original meteoriod before it ablated.  But 
this is a softer science requiring many assumptions.

My two centavos as I understand it,
Best wishes and Good Health,
Doug



-----
Dr Marco (183294) Langbroek
Dutch Meteor Society (DMS)

e-mail: marco at langbroek.org
http://www.dmsweb.org
http://www.marcolangbroek.nl
-----
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