[ RadSafe ] Silly things to know about detection systems and HP ops.

Fri Oct 1 05:48:05 CDT 2010

I think the classical case involved the discovery of radon. According  
the the story I heard, when Rutherford worked in McGill University in  
Montreal, he and his colleagues were studying the nature of radium  
decay. But they were plagued with variable non-reproducible  counting  
results. This was until someone noticed that the abnormal results  
coincided with the passage of a secretary through the laboratory. In  
those days, women wore long voluminous skirts, and when they moved  
swiftly through the room, there was a breeze. Th lads realized that  
there was a radioactive gas that dissipated with the breeze. Would  
anyone like to debunk or correct this story?
Mike

On Oct 1, 2010, at 8:04 AM, blreider at aol.com wrote:

>
> Dr. Parthasarathy,
>
> I do hope you and others add to this, I think it will be fun and  
> useful to some.  I liked the story you posted, it is so true that  
> some dumb thing overlooked can cost time and money.  So I thought  
> it would be useful to start a string where people can post dumb  
> things they have seen other people do.  Of course none of us have  
> done any of these so there is no shame in posting!    Here are some  
> obvious time eaters I observed:
>
>>  Make sure the instrument is plugged in.  I was in an MRI machine  
>> years ago in NY and the tech couldn't get the machine going.  I  
>> finally said "did you plug it in?" and it turned out the power  
>> cord was frayed.  Eaten by rats per the tech - not a warm fuzzy  
>> for me in a medical facility.  But he got the machine going, I had  
>> shoulder surgery and lived to windsurf again!
>
>>  Noble gasses can cling to people and clothing and can move around  
>> a plant that way.  One hears of power plants that spend a lot of  
>> money because the staff didn't plan on radon from homes and  
>> containment maintenance work being detected one minute and not  
>> being around later on.  Plastics and synthetic cloth are big  
>> culprits for attracting noble gasses.
>
>>  If your lab has efficiency problems with gamma emitter that are  
>> commonly all over the place at the plant check to find out what  
>> processes are going on around you that you might not see.
>
> One nuclear plant I visited years ago had periodic larger than  
> expected Cs-137 peaks on their NaI Whole Bdy Counter (WBC).  These  
> showed up during times when they were counting people so they were  
> thought to be + counts.  It turned out the facility had a sludge  
> tank behind a half wall in the next building and when the sludge  
> was stirred occasionally the cesium would rise above the wall level  
> (I know it is a salt but there apparently was some precipitate) and  
> shine into the building next door.
> People doing other tests at the detector nearby can have sources  
> nearby that alter your detection system's background.
> Gamma spec background data can be impacted by interferences by  
> Compton edges, tail ends of other peaks, etc.  This can result in a  
> false lowering of the actual dose you are trying to evaluate
>
>
>>  Bioassay requires observation.
>
> Los Alamos HPs gave a talk years ago about a worker whose urine  
> levels of Pu-239 were elevated and didn't reduce over time.  They  
> couldn't figure out why for a while, then during an interview the  
> worker couldn't stop picking his tooth with his finger.  He had not  
> inhaled or ingested the radio nuclide, he had contaminated his  
> tooth and was slowly entering his GI tract.
> If the worker in your WBC at a nuclear plant has Cs-137 and Co-60  
> levels about a tenth of the amounts in your check source, check to  
> see that the check source has been removed from the detector.
> Radon from well-water can cling to clothing, this is especially a  
> problem for portal monitors in the morning in areas of course with  
> high uranium or radium in the environment.
> Mouth pipetting is not the best of all methods.
> Doing things you shouldn't be doing on the job in a contaminated  
> area is not a good idea.  The investigation can be embarrassing.
> The partner of someone who has a medical test such as a heart  
> stress test can transfer detectable amounts of material to the  
> plant worker through fluids.
> If an area air sampler on one side of the room has highly elevated  
> levels, and the area sampler on the other side of the room does as  
> well, perhaps it is time to check the intakes of all the people  
> working between the two samplers.
>
>>  Old media can lose data with temperature changes.  Old computers  
>> were notorious for problems with data storage as disks expanded  
>> and contracted with high summer temperatures.  I think this is  
>> less of a problem now that storage is more compacted and on  
>> different types of materials.
>
>>  Of course you all know that NaI detectors have peak energy shifts  
>> with temperature change.  If your lab has changes during the day,  
>> morning and evening checks might not catch all the shifts.  Ge  
>> detection systems also can have temp. shifts however for larger  
>> changes in temperatures.  Always a good practice to identify all  
>> peaks in the spectrum. K-40 is a good check peak we all carry with  
>> us.
>
>> Iodine plates out on long cold collection tubes so what is seen at  
>> the far detection end may be under detected.
>
>> Plutonium and other radio nuclides can plate out on container  
>> walls, which can reduce the amount in solution and alter results  
>> of a test.
>
>> Tritium moves.  Leaves.  Plastic and rubber O-rings help this along.
>
>> Mixing Am-241 and beryllium can increase neutron levels.
>
>> Very high levels of alpha emitters can break down plastic bags and  
>> floor covers faster than expected, of course the creep of material  
>> could also be contamination the usual way.
>
>> It is not good to have the exhaust from one lab placed right at  
>> the intake to another lab.
>
>> Cool old stuff like scotch tape dispensers used depleted U as a  
>> weight in the dispenser.
>
>>  If you have a lot of material, 10 half lives may not be the  
>> amount of time you need to reduce the material to below regulatory  
>> levels.
>
>> Large area detectors need to be efficiency calibrated for a  
>> geometry that makes sense and is repeatable.  If you are using a  
>> large area detector to look for small particles you need to know  
>> what the bounds of the results will be with position, size and  
>> density of the subject radio nuclides.
>
>> Sky shine can affect boundaries of facilities with appreciable  
>> amounts of penetrating radiations.  Even more in warm climates  
>> with no ceiling shielding.
>
>> Release of uncontaminated feral cats and other wild animals caught  
>> at a highly contaminated site to a nearby location will only cause  
>> further contamination spread.  Get the local Heath Dept involved  
>> or at least decon the animals before release.
>
>> Some oil, gas and water facilities can have plate out of thorium  
>> isotopes in addition to radium.  Thorium can be  more of a problem  
>> than radium for internal dose.
>
>> Set points often need to be set considering the hardest to detect  
>> radio nuclides rather than the easy to detect ones.
>
>> QA should be done at the final part of the process after all  
>> processes are finished bu before products are released.  An  
>> analyzed in time to recall a product before it is released.   
>> Especially if that product is a medical isotope to be injected  
>> into a patient.
>
>
> It is kind of fun to think of the "gotchas" and this might make a  
> nice little list if you all put your observations in.  I should  
> have started earlier, it is now so late!
>
> Thanks
> Barbara Reider, CHP
>
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: parthasarathy k s <ksparth at yahoo.co.uk>
> To: The International Radiation Protection (Health Physics) Mailing  
> List <radsafe at health.phys.iit.edu>
> Sent: Thu, Sep 30, 2010 10:44 pm
> Subject: Re: [ RadSafe ] low energy gamma-spikes pranks done with  
> photomultiplier tubes! Blocked air flow causes problem
>
>
> Dear Dr Dixon,
> In our counting laboratory in Leeds we found an inexplicable shift  
> of a few
> hannels in the case of a sensitive gamma spectrometer. The  
> multichannel
> nalyser and associated instrumentation belonged to one company  
> (Nuclear
> iodes??) whereas the detector was from Nuclear Enterprises. Both  
> companies
> efended their turf.
> We recorded room temperature continuously. The ambient temperature  
> in the sub
> asement laboratory was strictly controlled within plus or minus a  
> few degrees.
> e spent better part of a month trying to figure out the cause of  
> shift. The
> eason was pretty simple. Some one has inadvertently kept a folder  
> (the typical
> unctional one distributed in conferences) over the electronic  
> instruments
> hereby blocking the air flow.
> here was another instance in which an instrument behaved  
> quixotically because
> he fibrous filter which removes dust got clogged over the years. We  
> may not get
> such experience from text books
> Regards
> Parthasarathy
>
> _______________________________
> rom: "Dixon, John E. (CDC/ONDIEH/NCEH)" <gyf7 at cdc.gov>
> o: The International Radiation Protection (Health Physics) Mailing  
> List
> radsafe at health.phys.iit.edu>
> ent: Thu, 30 September, 2010 23:05:54
> ubject: Re: [ RadSafe ] low energy gamma-spikes pranks done with
> hotomultiplier tubes!
> With regard to the energy spectrum shift, I have experienced such a  
> shift in
> olid state detectors due to extreme variances in environmental  
> temperature (the
> temperature of the area being surveyed). I haven't heard of the  
> 'whisker'
> henomenon.
> John E. Dixon
> ________________________________
> From: radsafe-bounces at health.phys.iit.edu on behalf of  
> parthasarathy k s
> ent: Thu 9/30/2010 12:34 PM
> o: The International Radiation Protection (Health Physics) Mailing  
> List
> ubject: Re: [ RadSafe ] low energy gamma-spikes pranks done with
> hotomultiplier tubes!
>
> I recall that in our formative years in the Bhabha Atomic Research  
> Centre, we
> sed to all sort of crazy things with photomultiplier tubes. In our  
> enthusiasm
> ne of my colleagues used a magnet of considerable strength and  
> virtually
> isplaced the electrode of a PM tube with disastrous consequences!
>
> ndeed we studied the response  by removing the electrostatic  
> shields. We also
> tudied influence of earth's magnetic field; if I recall correctly  
> it was
> ignificant for large area photomultiplier tubes.
>
> hile on this, let me describe a very interesting experience we had  
> while using
> arge area photomultipliers.
> The Department of Medical Physics, University of Leeds had an  
> understanding with
> he Nuclear Enterprises by which the company used to pass on low  
> background
> hotomultipliers with sodium iodide (Tl) crystals as integral line  
> assemblies
> or studies. While working with one such units our routine was to  
> record Cs-137
> 0.66 MeV) gamma line and TL-208 (2.61 MeV) gamma line at the  
> beginning. One day
> e found that both these lines have shifted considerably down. It  
> appeared that
> here was some change in the internal electrode structure which led  
> to this.
> A well experienced member of the technical staff told us that he  
> had found such
> n event earlier; he went through his old records and located a  
> remedy.We found
> hat in large area PM tubes small whisker like structures can  
> develop and work
> s a short circuit lowering the voltages between electrodes. The  
> impact of this
> ill be considerable if it happens at the initial stages. The remedy  
> was to send
>  very low voltage high current pulse between the suspected  
> electrodes and burn
> ff the whisker.  Once this was done the gamma lines appeared in the  
> same
> hannels of the multichannel analyser.
>
> Regards
> arthasarathy
>
>
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