[ RadSafe ] GM vs ion chamber for dose measurement

[WesVanPelt]

Radsafers,

I have used the Victoreen 450 for years. It has good and bad features, but
overall is a good dose rate instrument.

One "feature" that may mislead when measuring low dose rates is this. The
digital display will not show a negative dose rate. Why is this an issue? If
the instrument drifts out of calibration and reads less than zero, it shows
a positive number. In other words -0.015 mrem/h will display as +0.015
mrem/h. I have slowly moved a source closer to the instrument and watched
the display drop to zero and then go up again.  I mentioned this problem to
Victoreen many times, but they never had any interest in correcting it.

Does anyone know if the current ion chamber ratemeter models show this
"feature"?

PS. I know that Victoreen is out of business, but I forget who now owns
their ion chamber ratemeter product line.

Wes

New email: wesvanpelt at verizon.net
Wesley R. Van Pelt, PhD, CIH, CHP 
Radiation Safety & Environmental Radioactivity
Wesley R. Van Pelt Associates, Inc.
 
......
   
  This brings me to my question for radsafe: What is the best hand held ion
chamber to purchase for mainly radiology uses? The best I can find are the
450 and 451P's by Victoreen. Sometimes these meters give erratic readings
due to temperature or mechanical agitation (dropping). 
  They do have a good response rate and accurate digital readout over all
energies of interest. The plastic case is water-resistant and filters fewer
low energy photons (than a metallic encased meter). But there must be
something better in this millennia?

......