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Re: gas proportional counters?
On Thu, 9 Mar 1995, Karin Gordon wrote:
>
> 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
> >
We also have LB122s at the Cross Cancer Institute. We used to use them in
our Nuclear Medicine Dept., but have found that there are two very
significant limitations.
1 The presence of an elevated background will result in an inability
to detect down to the licence requirements (in Canada) of 0.5 Bq
per square centimetre (beta-gamma).
2 Low, but technically significant levels of contamination (i.e.
above the licence condition criteria) over small areas will result
in misleadingly small readings, as this instrument averages the
contamination over 100 square centimetres. This is especially
significant in iodine therapy, where contamination is frequently
very localized.
We now use a 'pancake probe' (G-M tube), specifically: the Victoreen 190
with RP-1 probe. It is less affected by the elevated radiation fields
which we experience, has a 15 square centimetre detector face (as opposed
to the 220 square centimetre one on the LB122), so does not give falsely
low Bq per square centimetre readings (actually, it only gives
contamination in cpms, cps, etc, without any assumptions as to the area
which is contaminated), and, as a plus, costs much less,
weighs much less, gives a plainly discernable changing audible signal as
increasing areas of contamination are scanned, and also doubles as a dose
rate meter (specially designed to be so calibrated by Victoreen).
Suffice it to say, we prefer the 190!
regards, and my appologies for the conflicting nature of this response.
Chris Davey, RSO
Cross Cancer Institute
11560 University Avenue
Edmonton, Alberta, Canada
T6G 1Z2
(403) 492-7477
email: cdavey@med.phys.ualberta.ca