Gamma Spectrometry Forum

Hi All,

I was testing a new 2" NaI(Tl) detector today, I recorded a 30 minute background spectrum with the detector sitting on my desk (see spectrum below in red). Represented in linear form it comes out as predicted with a little hump for K40 approximately in the middle and no significant stand out features. Obviously our histogram is showing the counts in each bin.

Then I was wondering how it would look if we plotted energy per bin instead of counts per bin, so I calibrated the spectrum in PRA and exported the histogram to a spreadsheet where I simply multiplied the energy by the number of counts in each bin, and plotted it (see green spectrum below).

Immediately it is possible to see more detail and structure in the spectrum. Since this is a very simple calculation to do, I don't know why the programmers have not added this feature as a third option to the usual Lin and Log options.

In the spectrum below we can see K40 stands out very prominently at 1460, we also see Ti208 at 583 and Pb212 at 238 etc...
Below I also feature a Cs137 spectrum, represented both as counts and energy, as you can see the features change and the 662 peak becomes more prominent.
It's possible that this feature is common on other software and that I haven't seen it, but thought I would share it with you guys anyway.

Steven

Here is another comparison for Thorium..

The red line is your typical counts per channel, and the green line is energy deposited per channel.
Steven

Very interesting and it could be the base for a feature.

In Theremino MCA something approching is the "scale options" parameters which allows to dose fit the log scale as you wish.

Hello Steven,

i have a problem with your thorium spec. What are the last 3 peaks?
Here my spec from thoriumoxid.

Peter

Peter,

If I am not mistaken, the last peak is Ti208 at 2614 keV, the second last peak is the Compton edge and the third last peak is the pair production escape peak (2614 - 511 = 2103 keV)

These are also visible in your spectrum, but not so obvious.

You have an extra peak at 1600 keV in your spectrum, which I think may be K40.

Be careful with Theremino because the rubbery calibration system can move peaks to wherever you want them.

Steven

Hello Steven,
I think my calibration is ok. I tested with Am241 Cs137 K40 Lu176 Ra226 Kr85 and Th
Here my last test with KCl -> K40

Peter

Peter,

That's interesting, there must be something in your Thorium oxide at 1600 keV which is not in my Thorium mantle.

Steven

Hello Steven,

I have a mantle like this here.


and as you can see, its the same spec with a peak at ~1600 keV. Ac228 ???


Peter

Peter,

Thanks, just as you were posting this I was recording a spectrum with the latest version of PRA.

On the screen clipping I have marked as many peaks as I could identify.

The peak at 1630 is now showing on my spectrum, I have identified it as Ac228, I also have a little peak at 3025 keV which can't identify.

Steven