path length vs. distance traveled

[DamschenGA <damschenga@mkf.ornl.gov>]

I am reviewing some Health Physics training materials and came across a
section that I found confusing. When discussing LET, stopping power, and
specific ionization, the text uses "path length," "distance of travel,"
"track," and "depth of penetration" interchangeably. When I went to my usual
sources to verify my recollection of the meanings of these terms, I ended up
more confused than I started out.

My recollection is as follows:

path length: the linear distance from the start point of the charged
particle's path to its end point.

distance of travel: the actual distance traveled by the particle from the
start point of the particle's path to its end point. 

track: the actual path taken by the charged particle.

depth of penetration: the linear distance from a charged particle's point of
entry into an absorber to its path's end (path length in absorber).

  ___                   ___
   |      *\             |
 p |       /             |<--depth of penetration
 a |      /<--track,     |
 t |      \   distance   |
 h |    |\ \ of travel   |
   |    | \/             |
 l | ____\_______________|__absorber
 e |     /
 n |    / /\
 g |    \/  \
 t |        /
 h |       /
  _|_     *   

(sorry if the graphic doesn't work - try a monospaced font if it gives you
problems)

Are these correct? If not, where can I find a clear explanation of the
terms?

Thanks,
Gary Damschen
damschenga@mkf.ornl.gov