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Re: Removable Contamination Surveys



Title: Removable Contamination Surveys
Jack,
    You're right of course that we don't swab/smear clothing or skin in these circumstances.  We use hand held frisking probes.  What I was attempting to suggest was that whatever statement was made in ICRP 26 may simply have been adopted as the default value for contamination measurements.  As with many of the values we use today is difficult if not impossible to find the source (and reasoning behind) many of the widely adopted (if not accepted) values in currently in use.
 
Regards
    Julian Ginniver
----- Original Message -----
Sent: Monday, February 04, 2002 3:41 PM
Subject: RE: Removable Contamination Surveys

Julian Ginniver writes:
 
<<areas for removable contamination measurements.  These are: 100 cm2 for skin and clothing.>>
 
 
I assume that you're not really taking swipes on their skin and clothing.

Jack Earley
Radiological Engineer

-----Original Message-----
From: julian ginniver [mailto:julian.ginniver@lineone.net]
Sent: Sunday, February 03, 2002 3:26 PM
To: Jenkins, Peter
Cc: Radsafe
Subject: Re: Removable Contamination Surveys

Peter,
    I'm not sure if this helps, but I hope so.  In the UK we have three different sized areas for removable contamination measurements.  These are:
 
100 cm2 for skin and clothing.
300 cm2 for inanimate objects e.g items of  plant an equipment (pumps, valves, pipework etc.)
and 1000 cm2 for floors and walls.
 
These area and the associated derived limits for contamination (i.e. 3.7 Bq/cm2 for most betas [corresponding to approx. 200 dpm/cm2] and 037 Bq/cm2 for most alphas) were first published in the UK in 1979.  The National Radiological Protection Board (similar to the NCRP) published a document entitled Derived limits for surface contamination, ref. NRPB-DL 2.  This documents summarised how the above values were calculated and how they related to possible doses/ uptakes by workers in the nuclear industry.  In the document it states that "advice on monitoring of skin contamination is given by the ICRP [ICRP publication 26 1977], which recommends the averaging of measurements over an area of 100cm2."  This may seem to be the origin of the area of 100 cm2, but it would seem that it was not intended to apply to anything other than skin contamination, although without a copy of ICRP 26 I cannot confirm this.  (is there anyone out there who can?)  Unfortunately the values of 300cm2 and 1000cm2 were already custom and practice within the UK nuclear industry in 1979 and there is no explanation included on how these values were derived.
 
It is interesting to not however that the clearance level in the UK for most beta emitting isotopes is 3.7Bq/cm2 which is very close to the value of 200dpm/cm2 used in the US and that the value of 100cm2 is also common to both countries.
 
What about other countries? (e.g. Europe, Canada etc.)
----- Original Message -----
Sent: Friday, February 01, 2002 7:50 PM
Subject: Removable Contamination Surveys

Can anyone give me some insight (and possible source documents) into the reasons for the 100cm^2 standard (or suggestion?) used for removable contamination surveys?  Why is it 100cm^2 and not 1,000cm^2, or something smaller or larger?  Is there anything wrong with increasing the swiped area to increasing the likelihood of detection? 

Specifically, assume a removable contamination limit is set at 200 dpm/100cm^2 for a laboratory and a researcher wishes to use a survey meter to count the swipes.  According to the manufacturer's formula and values (for efficiency of the radionuclide, etc), the meter has an MDA of 400 dpm.  Is there anything wrong with performing the survey over 200 cm^2 so that the detection limit would meet the removable contamination limit?

Thanks,

Pete Jenkins






















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