Re: Promethium 147 in laboratories

[Keith Varnado <kvarnado@premier1.premier.net>]

At 06:30 PM 7/10/96 -0500, you wrote:
>When I used to be with our Services Department, providing routine surveys
in laboratories, one of the 'less-than-infrequent' events was the
contamination arising from mis-use of beta back-scatter thickness gauges.
The sources - usually a range for different thicknesses of eg paint paper
etc, hence promethium, thallium, strontium - consisted of beads(~1/2 mm
size) of active material mounted on very fine wire. It did not take too much
violence when inserting a test sample for the bead to be "removed" and being
in ceramic (I think) form, it was readily crushed without being noticed,
until the next survey!
The result was usually a write-off for the back-scatter gauge - try costing
several hours of fine engineering decontamination against the cost of the
equipment - OUCH! The bench was usually simple but the rest was expensive. 
>I suggest a check for such apparatus and it's recent use in the cold lab.
>Roger Gelder, NRPB, UK
>
>

Pm-147 has been and still is a common source for beta thickness gauging of
thin materials (ie, paper, plastics,etc.)and backscatter thickness gauging
of coatings on materials. It could easily be missed in routine surveys in a
cold lab due to a low
gamma efficiency (.121 Mev, 0.0029%) until you have a leaking source. Since
Pm-147 is such a low energy beta emitter, it's protective cover would be
very thin and thus subject to damage relatively easily. I also would suggest
a check for these types of gauges and, if possible, where they might have
been before. 



	Keith Varnado, CHP
	kvarnado@premier1.premier.net