Re: Radionuclide ID Help

[mwilliam@mailbox.uq.oz.au (Michael Williamson)]

>We have recently been asked to identify two samples containing RAM.   One is
>sand and after 15 hours of accumulating a spectrum containing 11 million
>counts(NaI[Tl]) the following major peaks are evident in order of decreasing
>abundance: 250, 366,308,198.

Here's my 2 cents worth:

Even allowing for the poor resolution of NaI detectors,the reported peaks
don't seem to align with any of the Th232 series gamma rays (the major
peaks are at 239, 338, 583, 860, 911, 969 and 2614  keV). Confusion of the
lower energy peaks is possible with a NaI spectrum but the 2614 peak from
Tl208 is the clincher, if you've got this one, you've got Th232.

Similarly with the U238 series, the big peak at 1764 keV from Bi214 will
provide positive ID because it's found well away from the jumble of peaks
below 1 Mev in a NaI spectrum.

It also occurred to me that you might have got hold of some Ir192 doped
sand (used in the oil well business for tracing induced fractures of
oil/gas bearing rocks).  One peak (308) is spot-on but the others seem to
be way out. If it was Ir192 there'd be a big one at 316 keV and another at
468.

I would suggest checking the calibration of the MCA and re-scaling to allow
viewing of the high end of the spectrum.

The watch is more problematic: an "old" watch might reasonably be supposed
to contain Ra226 and progeny (i.e. big peaks at 292, 295, 352, 609, 800 and
1764 keV).  Your numbers (154, 198, 250, 306, 364) are suggestive of
multiple emitters but don't seem to correspond to the familiar series.
Again, recalibrate and view the upper end.







Michael Williamson                              ph +61 7 365 4504
Radiation Protection Adviser                    fax +61 7 365 1577
Occupational Health and Safety Unit
University of Queensland
Brisbane 4072
Australia