[ RadSafe ] Are these gamma spec ID's valid?

Fri Apr 18 15:59:51 CDT 2014

Thanks very much Jim.

A friend did some gamma spec of Japanese samples a while back (see http://carlwillis.wordpress.com/tag/gamma-spectrometry/ ).

His comment was that the so-called “Co60” peak is actually due to the “Compton edge for K-40.”

Have you seen this before ?

Seems legit to me, but an illustration would be appreciated.

Jaro

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From: Jim Hardeman [mailto:jim.hardeman at gmail.com] 
Sent: April-18-14 3:57 PM
To: jaro_10kbq at videotron.ca
Subject: Re: [ RadSafe ] Are these gamma spec ID's valid?

Jaro --

The ID of Co-60 in the air sample is bogus -- you wouldn't see the 1173 keV peak w/o the 1332 keV peak, since BOTH are emitted at 100%. What's more likely is that the edge at ~1332 is the sum of the annihilation peak (511 keV) and the Cs-137 gamma peak (662 keV) -- which just happens to come up to 1173 keV. With as much Cs-137 as is present, there's probably a lot of scattering going on, which would give you a continuum to sum with the 511 peak.

The identification of K-40 at 1460 keV is good, as is Ra-226 (and daughters) at 185 keV, etc.

I would expect to see Cs-134 and Cs-137 based on what's on the ground. I don't see Y-88 in the air sample.

What I would EXPECT to see in a Japanese air sample today is natural background (i.e., U and Th daughters) + K-40 + Cs-134 + Cs-137 -- and that's pretty much what I see in that sample.

Note that proper interpretation of gamma spectra is as much art as science ... just reading the nuclides off an "identified lines" list isn't going to get you to the right answer. It's entirely possible, for example, that the peak search "found" a Y-88 peak, but it's also likely that the counting statistics give an error (at either 2 or 3 standard deviations) of greater than 100%.

My $0.02 worth ...

Jim Hardeman

jim.hardeman at gmail.com

On Fri, Apr 18, 2014 at 2:01 PM, Jaro Franta <jaro_10kbq at videotron.ca> wrote:

Put two similar gamma spec graphs next to each other, on same scale, to see
how the ID's match up:  Seems some species are only ID'd when it suits the
purpose, others seem speculative.
(I added the red vertical lines to aid in matching up peaks)

https://dl.dropboxusercontent.com/u/11686324/MKaltofen_gamma_spec_compare.jp <https://dl.dropboxusercontent.com/u/11686324/MKaltofen_gamma_spec_compare.jpg> 
g

Overall impression?

Thnx

Jaro
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