More than you want about alpha

[P3D <gosfield@xxxxxxxxxxxxxxxxx>]

MORE THAN YOU WANT TO KNOW ABOUT ALPHA PARTICLES

In decay by alpha particle emission, the nucleus ejects an alpha 
particle, which consists of two neutrons and two protons (basically a 
Helium nucleus).  The alpha particle is emitted with kinetic energy 
usually between 4 and 8 million electron volts (MeV, E=mc^2 etc.)
 
The particles are quite energetic, but have _very_ short ranges in solid 
materials, e.g. about 0.03 mm in body tissues.
A typical path length in air is approx 4 cm for an alpha particle of 5.5 
MeV.  The energy required to ionize an air molecule is 33.7 electron 
volts per ionization.  So the typical alpha particle described above 
creates about 1.6 x 10E5 ionizations.  If we consider the path lengthof 
4.2 cm as the mean range in air, we get 3.9 x 10E4 ionizations in each cm 
of the path.  This is quite useful in allowing discharge of static 
through neutralization of charge.  The figures above are derived from the 
values for Americium-241, which is a medically useful isotope.  I don't 
have the figures for Polonium, which is not used medically.  The same 
Americium produces particles with mean path length of 0.0054cm in soft 
tissue.

The very short path length of alpha particles means that they create 
almost negligable hazard as an external radiation source.  A few cm of 
air, a sheet of paper, or a rubber glove would all provide almost 
complete shielding.  Even if the particles reach the skin, only the most 
superficial layers would receive any radiation dose.

If eaten or breathed in, energetic alpha particles can represent a 
hazard, due to their densely ionizing nature.  

---the above is paraphrazed and quoted from Physics in Nuclear Medicine, 
Second Edition, by Sorenson and Phelps, W.B.Saunders Company pub.1987

So as someone else pointed out, don't sniff your Staticmaster, and don't 
chew it. You might want to store it in a paper bag or paper box or plastic 
bag.  

May your room be clean and your slides be clear.

ted (a nuclear kinda guy)
gosfield@xxxxxxxxxxxxxxxxx





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