Radionuclide ID Help -Reply

[FRAMEP@ORAU.GOV]

Nucpharm wrote:

>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. Also a watch with
>luminescent dial (fairly old) 14 hours of data acquisition
>approximately 9 million counts: 364,306,198,252,154. I presumed the
>364 peaks are from I-131 which is stored in an adjacent room but it
>is not present on the background spectrum.

Oh person! This is great stuff - gamma spec analyses and NaI to boot.
The software ain't been writ that do this as well as a human.

Both seem to be the same thing: radium 226. The sand probably has the
entire uranium series but its the radium and its daughters that you
pick up. Don't know why you dont see K-40s 1460 keV peak in the sand
- should be there. 

I suspect the energies are too high because the energy calibration
was done with a source hotter than the samples ie a gain shift. Also
could just be a gradual shift over the (long) count time.

The 250/252 is probably Pb-214s 242 keV gamma. The 306/308 is its 295
keV gamma and the 364/366 is its 252 keV gamma.  The 198 is Ra-226s
186 keV gamma. I'm surprised Bi-214s 609 keV wasn't picked up too.

The 154 is a bit of a mystery. I'd guess its a backscatter peak but
might conceivably (a real longshot) be an x-ray escape peak from the
186 gamma.

I wouldn't put much emphasis on the peak intensities.

Fun.

Paul Frame
Professional Training Programs
Oak Ridge Associated Universities
framep@orau.gov