Natural Science Forum / Physics / Particle Physics / September 2004

repeat after me... google is our friend.  got a random topic like this, try
there first.
mostly when talking about shielding you use 'half thicknesses', which is the
thickness of material needed to reduce the given radiation by one half.  for
alpha and beta that is very thin as they are charged particles and can be
stopped by a sheet of paper.  for xray and gamma it is much more complicated
as it depends on the energy of them.  neutrons are even stranger to shield.
see more info at: http://hps.org/publicinformation/ate/cat47.html
http://www.globalsecurity.org/wmd/library/policy/army/fm/3-3-1_2/Appb.htm
http://www.nrc.gov/reading-rm/basic-ref/teachers/unit1.html
http://www.ehs.ucsf.edu/Manuals/RSTM/RSTM%20glossary.htm
etc, etc, etc

The way I am familiar with this is by the use of the term *mass absorption
cross-section*. Look up an offical definition. It is a description of how
much blockage a (small) unit mass of material presents to radiation. It is
as if that much totally blocking area were placed in the beam.

This description method was developed for x-rays but is applicablle to other
types of radiation. For x-rays, this cross-section is strongly dependent
upon atomic order and photon energy.

Bill

Particle physicists typically use language "radiation length" for
charged particles (beta and alpha), "attenuation length" for photons
(gamma). The measurement unit is typically g/cm^2, because it is a
convolution of density and distance. If you want to look at it in
detail, you can read to your heart's content at
http://pdg.lbl.gov/2004/reviews/passagerpp.pdf

PD