RE: path length vs. distance traveled

["Fulmer, Philip" <philip.fulmer@cplc.com>]

Gary,

It does get confusing at times.  Here's my recollection and
understanding.

1.  "path length" is defined in NCRP 51 as the total length of the path
of a particle moving through a medium, measured along the actual path,
whether or not rectilinear.  I've also heard this referred to as "track
length," the total distance traveled by the particle (not the crow's
flight distance).

2.  "depth of penetration" usually refers to the farthest linear
distance into the absorber that a particle travels.  For instance, if an
electron in its tortuous windings penetrates to a depth of 2 cm (linear
thickness) into a fictitious absorber, rebounds and travels backwards
for some distance before stopping, the depth of penetration is 2 cm,
even though the electron may actually be at a shallower depth at its
terminal point.

3.  The "range" of the particle is the average of the path lengths of
particles of a given energy, while the "projected range" is the average
of the farthest depths of penetration of particles of a given energy.

If I've muddied the waters further (or farther), my apologies.  

Philip
__________________________
Philip C. Fulmer, PhD, CHP 
Carolina Power & Light Company
Harris Energy and Environmental Center
3932 New Hill-Holleman Road
P. O. Box 327
New Hill, NC 27562-0327
philip.fulmer@cplc.com
(919) 362-3363      

>----------
>From: 	DamschenGA[SMTP:damschenga@mkf.ornl.gov]
>Sent: 	Wednesday, January 07, 1998 11:14 AM
>To: 	Multiple recipients of list
>Subject: 	path length vs. distance traveled
>
>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).
>
>Are these correct? If not, where can I find a clear explanation of the
>terms?
>
>Thanks,
>Gary Damschen
>damschenga@mkf.ornl.gov
>
>