[ RadSafe ] FW: Reporter's question about lower limits ofdetection

Busby, Chris C.Busby at ulster.ac.uk
Mon Aug 8 06:23:25 CDT 2011

The laboratory is in Wales. It is owned by Green Audit. We have a number of instruments and detectors which are made for us in Germany and the Ukraine: the filters were shielded with 2 inches of lead and for this we used a 2" wall lead tube of 3" internal diameter with Netherlands made  2" Scionix Nai(Tl) detector counting for 24 hours and captured by an MCA as usual. The system was calibrated using a Cs source of known activity and AR Potassium Chloride (1460keV). Control was the background. Spectra were examined using "Identify" and "Fitzpeaks" software. Overall activity of the filter was calculated by the metod of relative areas. The Cs 134 peak at 796keV was employed. To check on the results the filter was sent to the ESG laboratory at Harwell  which used to be the UK Atomic Energy laboratory. They used a N cooled Ge detector. The results were the same. 

-----Original Message-----
From: radsafe-bounces at agni.phys.iit.edu on behalf of Steven Dapra
Sent: Mon 08/08/2011 03:11
To: The International Radiation Protection (Health Physics) Mailing List
Subject: Re: [ RadSafe ] FW: Reporter's question about lower limits ofdetection
Aug. 7

         This depends on how one chooses to define the word 
"trivial."  Who measured the levels of radiation, where they were 
measured, distance driven after exposure, etc., etc., are irrelevant 
and immaterial.

         Where is your "laboratory," Chris, and what kind of 
instruments are (presumably) you using to conduct these 
measurements?  Describe your methods of testing, including your controls.

Steven Dapra

At 06:39 AM 8/7/2011, you wrote:

>Dear Radsafers,
>It was my intention to show that the levels in Japan in air were not 
>trivial. I do know this because I have measured it in several car 
>filters for which the engine size is known and the number of km 
>driven after the incident is known. The efficiency of the filters is 
>assumed to be 50% but this is not known for sure although I have 
>asked the manufacturers. The filters showed between 1.2 and 3Bq per 
>cu metre of Cs-137. This can be compared with the attached data from 
>Harwell. The results were from my lab and also from Harwell who we 
>paid to do the analysis.
>I am interested to learn that the levels were higher in the USA 
>during the atmospheric tests than in the UK: Stewart Farber says 
>100mBq/m3. Probably because the US is where many of the tests were done.
>But my argument was about Japan, not levels in the USA. I am quite 
>aware that the levels in the USA were far smaller, as we would 
>expect. But i see a maximum of 0.116pCi is 4.29mBq/m3 The average is 
>0.7mBq/m3. Compare with the graph attached. But I think it depends 
>on where you live, doesnt it? And what other stuff comes along as a passenger.


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