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Chemistry question - re Th activity on lens
Ok. Its Friday. It is a challenge. Anything worth doing is worth being
excessive about. So.....
Some alternative methods for non-destructive Th activity assessment:
neutron activation analysis (using the Fl)
similarly, neutron prompt gamma analysis using the Th
collect the He released by the alpha decay, assess by mass
spectroscopy, and directly relate to the Th activity (is there a 2 pi
effect here?)
xray flouresence to directly assess the Th content (nice high Z
material, thin sample should eliminate self-absorption issues)
absolute alpha count using Fuji film in close contact to the lens
(should be adequately sensitive, depending on the precision and accuracy
requirements, can also assess the distribution)
Add a thin coat of ZnS and count the alphas the old fashioned way.
Some of these methods have to make an assumption about the Th daughter
equilibrium, some do not.
If the thickness is the question then neutron depth profiling may work, or
xray fluoresence off the underlying glass.
Of course there are probably less exotic (and simple) optical techniques.
>I can't understand why this has generated so much interest. Why is it
>necessary to calculate this activity with a high degree of precision?
> Bill Lipton
>Tad Blanchard wrote:
> If a glass lens is coated with 1000 Angstroms of Thorium-Fluoride,
>how do we determine the total activity (picocuries?) of the Thorium in the
>coating?
Disclaimer: Only my opinions .....
Lester Slaback, Jr. C.H.P. [Lester.Slaback@NIST.GOV]
NBSR Health Physics
Center for Neutron Research
NIST
100 Bureau Dr. STOP 3543
Gaithersburg, MD 20899-3543
301 975-5810 voice
301 921-9847 fax
"A little risk adds a bit of spice to life."
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