Re: stepwise procedure in wipe test,, ISO standards , if any

["Tom O'Dou" <tom_dixie@email.msn.com>]

Wipe Tests of Radioactive Sources

>1. no. of wipes needed for a radiation source at one time

Usually one wipe of a sealed source will provide sufficient information
regarding the status of radioactive material sealed within the source
encapsulation.

>2. solvent which should be used, distilled water or alcohol or acetone ,
>etc. I know that some beta source or alpha source may have very thin
>metallic film as outer coatings which corrosive solvent should not be
>applied, but how about the other solvent, are there really any guidelines

I have never seen anybody use a solvent to determine whether a source is
leaking or not and I do not recommend that anyone ever try a solvent.  Use
de-ionized water to wet the smear (which should be a cloth smear) and
provide a remote means for the smear to contact the source.  For radiography
sources or other sources of high activity, I have used a small cylindical
smear holder and passed the source through the smear remotely.  You should
not get any measurable dose when doing a leak test.

Sources with a thin metallic coating or film should never be wiped.  If you
are concerned that the source may be a source of contamination, then take a
smear on it's container or directly adjacent to the active surface.  As a
general rule, electroplated sources do not leak unless you have done
something like apply a solvent.

For alpha or beta sources that have quantifiable activity traceable to the
NIST, you should never contact the source surface with a smear of any other
device.  You have a certified activity (and maybe a certified thickness of
absorber) present at the surface of the source.  If you remove some of the
absorber or source - it is no longer certified.

>3. what size of swap paper should be used
>4. material of the swap, cotton , filter paper, tissue paper if any.

The size and type of swipe or smear paper to be used should be dictated by
the size of the smear you can count in your counting system.  For LSC
analysis or for gamma analysis, this is kinda irrelevent.  I recommend cloth
smears for any leak test - they are durable and tend not to get caught up in
source transfer mechanisms such as those used in industrial radiography.

>5. If liquid scintillation counter is not available  for beta source
>measurement, what instrument can be used for beta, ionization type chamber
>may not be appropriate all the time, particularly for very low energy beta
>source like H3 or C14 which usual ionization, geiger counter or
>contamination monitor may have very low sensitivity in the measurement thus
>making the result the same as a background counting.

If you don't have a liquid scintillation counter for your low energy beta
analysis, then you can use an open window gas flow proportional counter or
send the smear off to a laboratory that can provide LSC.

>6. In trying to measure those beta or alpha source with an electronic
>contamination monitor like LB122, LB123 (EG$G) or NE Selectra surface
>contamination monitor (IGP type) those equipment can only give count rate
>instead of counts. There seems to be no way to access the actual counts
>registered by those devices and count rate as seen by the device may not
>necessarily be the same as the count rate as shown on the device, some
>calibration factor/ count rate paralysis time may even unavailable too. So
>are there any well-recognized way to calculate the uncertainty error or
>even the MDA in the measurements.

The leak test limits for sources are 0.005 microcuries this activity is
easily quantified with ratemeters and thin window detectors for moderate to
high energy beta or alpha radiations.  Uncertainty calculations in the
measurement is pretty standard, NRC provides a method in 10 CFR.

Tom O'Dou
tom_dixie@msn.com




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