Re: Advice

[AndrewsJP@AOL.COM]

In a message dated 12/18/2001 9:16:46 AM Eastern Standard Time, interior-radiation-focal-point@pdo.co.om writes:



> John,
>
>
> Here in PDO -Sultanate of Oman we've have Identified the existence of NORM
>
> in our fields/ facilities.
>
> A comprehensive contamination survey was conducted using  a Min-monitor
>
> serial 900 Scn.  We  are currently looking at how best we can measure the
>
> Gamma exposure in our fields
>
>
> Looking forward to you prompt response and let me promise to be more
>
> explicit in my needs next time.
>
>
>
>
>
> Rashid


Rashid, for low level gamma radiation from NORM, the easy way to monitor is to use a NaI(Tl) detector and a ratemeter with and audio output.  Spectrometry is normally not required and the NaI(Tl) detector is sufficiently sensitive to find gamma radiation at and slightyly above background levels.  I would suggest a 2.5 x 2.5 cm detector (1" x 1" in the US) as a reasonable size.  Larger is better but costs more, especially if they get broken in rough usage.  We ususally pad our detectors with bubble pack or styrofoam or foam padding to reduce gain drift from temperature changes and to protect the detector from breakage.  


When calibrating this type of instrument, it is necessary to establish a constant threshold in energy terms.  To do this you should set the discriminator using a low energy source such as Am-241 or Co-57.  These detectors do not have plateau characteristics like GM detectors have.  Calibration should be to radium when monitoring for NORM.


There are a number of manufacturers of these devices.  Typically these are referred to micro-R meters in the US.  See Eberline Instruments or Ludlum Measurements for examples.  There are many others. 


Good luck.