HVL-TVL OPINION

[Slaback@micf.nist.gov]

Other than as a convenient concept for the
classroom I THINK HVLs and TVLs are
misleading at best for high energy gamma
emitters.  The numerical value changes
so drastically over the shield thicknesses
normally encountered that use of some single
standard value, even with the convention of
adding an HVL for buildup, With the ready 
availability of handheld or desktop computing
shielding should simply be done directly.
For example, for Co-60 and concrete ....
  first TVL = 28+ cm2/g
  second    = 19.7
  third     = 17+
  fourth    = 16+
  seventh   = 15.6
It takes a lot of TVLs to get to a 'constant'
value.

Admittedly, this is a somewhat extreme opinion,
but any time I use a HVL or a TVL I find
myself immediately doing a proper calculation.
The only purpose the TVL serves is to reassure
myself that I am not out in left field.

P.S. That should stir up some hornets.  Send
your stingers to me and I will compile a
summary opinion.

A little risk adds spice to life.
slaback@MICF.NIST.gov