Re: gas proportional counters?

[Karin Gordon <kgordon@cc.UManitoba.CA>]

Hi Melissa

I have been using the Berthold sealed Xenon-filled proportional counters
for many years for beta/gamma contamination monitoring in our
radiopharmacy and nuclear medicine departments.  The first unit we bought
about 15 years ago was the model LB1210 - line operated, wall mounted for
hand and clothing monitoring, with a simple CPS output. We have three of
those units in use- they seem to last forever, with the following caveat. 
The detector has a very thin titanium foil window which will not stand up
to a whole lot of physical abuse, like frisking over your lab coat pocket
with pointy objects poking out. Once you puncture that window, the
detector is dead (unlike the refillable butane detectors) and youre
looking for mucho bucks to replace it. In the RPharm/ Nuc. Med  
environment, we don't work with low energy betas, so we taped a stronger  
skin material (either heavy mylar or old x-ray film - whatever was 
available) over the detector face to toughen it up. The cover material 
certainly didn't attenuate any gammas, but we had to re-measure detection 
efficiency for betas using calibrated sources.

About 6 years ago, I evaluated the Berthold LB122 and a similar instrument
from a second W. German manufacturer.  The Berthold LB122 is a portable
battery operated proportional detector instrument - can be purchased with
the sealed Xenon detector or a refillable butane detector. The big feature
of the Berthold LB122 and more recently, the model LB123, is the on-board
microprocessor, which makes this a very "SMART"instrument. The
microprocessor's memory contains detector efficiency data for about 32
radionuclides. In operation, you take a 20 second background reading,
which is stored in memory and then dial in the radionuclide of interest. 
The microprocessor subtracts background, corrects for detector efficiency
for the selected radionuclide, corrects for the detector surface area and
gives an output in becquerels per square centimetre. This output is 
renewed every second or so - one heck of a lot faster than I could 
calculate it.  It also reads out in straight CPS, if you dont want to use 
all the fancy features.  For each radionuclide, you can set an audible 
alarm threshold (Bq/cm-2). I purchased my instrument with two 
identical detectors.  I use the unit (with one detector) either in a 
wall mount with a line power supply or as a hand-held portable survey 
instrument.  I also purchased a custom floor monitoring trolley which 
holds the 2 detectors side by side, and with cabling that enables the 
input of both detectors simultaneously to the electronics. The floor 
trolley was a Godsend for my middle-aged back, and the increased comfort 
level ensures more thorough monitoring of spills hitting the floor.

I even took my unit to monitor a crematorium work area and the inside 
of the oven after the removal of HOT ashes from a deceased patient  
who a few days earlier had  been injected with Sr-89 - but that's another 
story! 

I'm very happy with this instrument; even though it is quite expensive, 
it makes quantification of contamination a breeze! In NM depts, I would 
still mount a tough skin over the fragile detector face. For my own kit 
and in research labs using low energy betas like S-35, we dont cover the 
face- just are a lot more careful!
 
I have recommended that the 8 nuclear medicine departments I consult to 
in our area acquire a Berthold LB-122 or  LB123  or another 
instrument with comparable features to meet their contamination 
monitoring requirements - so I guess that's a substantial endorsement.
Some of our richer researchers are also considering purchasing them.

AECB inspectors visiting our facilities are also using these instruments.

Hope this is helpful!

Karin Gordon



On Thu, 9 Mar 1995, M. Woo wrote:

> I'm looking for recommendations on gas proportional counters.  We're
> looking for something reliable from a company with good support -- and, of
> course, the budget isn't infinite.
> 
> I don't want to sound rude (but I will anyway), but I'd like to hear from
> users, not from sales reps, please.  :-)  Sales brochures that I receive
> often go straight from my mail slot into the nearest waste container.
> 
> Thanks in advance, everyone!
> 
> -- 
> Melissa Woo                       | University of Illinois at Urbana-Champaign
> Health Physicist                  | Environmental Health & Safety Bldg., MC225
> office phone: 1.217.244.7233      | 101 S. Gregory St., Urbana, IL  61801
> m-woo@uiuc.edu                    | http://www.cso.uiuc.edu/ph/www/m-woo
>