Ra226 spectra

[keuleeule]

Hi all,
I was able to measure all weekend long with different sources I have.
These are my first spectra after getting support from Steven - thanks again for that.

I have a couple of Ra226 sources from smoke detectors and I measured all of them after each other.
My calibration is not that accurate, as that was my first calibration with Cs137.

I do not get, why the resolution is different in all my examples (each one representing an own Ra226 source)

a) it may depend on the activity? ( as higher the cout rate as lower the resolution, but Spectrum 5 has counted 2017 counts but has just 4,7Res.
b) it all depends on the position of the source?
How do you deal with the position at all? Do you have centered all your probes, or do you have any geometrical recommendation?
c) source itself are different?

Where I can get some help how to calibrate correctly?
In my mind it would be the best to mix up two known Nuklides, one in the lower keV range, one in the higher keV range.
How to deal with a single source like Cs137? 662keV is known, but the K -Line at 32keV does it depend on the housing of the source itself? Do you take both of them to have a low and a higher known energy peak for calibration?
The backscatter around 200 keV will depend on the used material all around, so that seems not to be a good calibration point, or?

Thanks and regards, Kolja

[Sesselmann]

Kolja,

The resolution will only agree when you have chosen the R.O.I. correctly.

1) First you record a good spectrumwith a known source,
2) then select the R.O.I. for each peak of interest ('b' for beginning bin and 'e' for ending bin, you should now have the whole peak coloured blue or yellow.
3) select a bin inside each R.O.I. and record the standard deviation (SD) and the mean energy peak.
4) open the calibration panel and enter the Arb.U, SD and known energy in KeV.
5) save and exit.

Now you can choose to show energy instead of arbitrary units in the Control panel.

Steven

[keuleeule]

As far I know for calibrating two known peaks are mandatory... otherwise interpolation is not possible.
as Cs137 is a monoenergetic source it is difficult or not possible or is the 32keV peak used as well?
(compared to the stored example of Cs137 spectrum : http://www.gammaspectacular.com/image/catalog/137cs.png it seems you uses the 32keV peak as it is marked as a ROI...


As I´m having Cs137 source, I should need to mix that with a second known source for calibration, but all other sources are not really known (natural sources), beside Am241 59keV, is that a possible methode?

I wonder, as I´m pretty sure I had only Cs137 to calibrate the Scint in my education as Nuc-Med assistant 23years ago.

Finaly I found to hit <DEL> button to delete a previously selected ROI.


Can you check if my calibration was correctly performed?
If I look to the Cs137 Spectrum for reference it looks different... is it all about shielding?

Thanks, Kolja

[keuleeule]

With the "new" calibration I tried to figure out my D-Uranium metal stripe from a Victoreen 440 RF/C.

here my results, it is a strange looking spectrum...

[Sesselmann]

Kolja,

Thanks for posting, these are very beautiful spectra, about as good as you will ever see from NaI(Tl), the reason your spectrum looks different to the sample is the size of your 3x3" detector, peaks become more pronounced and the compton plateu looks flatter.

Of course it is normal to use the 32 keV x-ray peak as a calibration point when using Cs-137.

You also seem to have a peak to the left of the 32 keV peak, I wonder what that is?

Did you have any other sources near by when recording the spectrum, or maybe some metal that emits secondary x-rays?

Steven

[luuk]

Hi Kolja,

Nice spectra so I it looks that the 3x3"is working as expected?
What resolution can you measure with it?
The peak left of the 32KeV is maybe a lead peak from shielding?
Remember that NaI(Tl) is none linear below 100 KeV!

Have fun with your detector,
Luuk

[keuleeule]

Just for clarification,
the second marked peak is Am241 as I wanted to have a second well known peak.

If I place the marker in the 662keV peak it says 5,9 something resolution...
(visible on the screenshot I did)

Shielding is: 6x 0,65mm Copper pipes (3,9mm in total) surounded by rainwater pipe "zinc" (0,65mm) surrounded 3 turns 0,5mm lead so far.
entrance of detector is still open after approx 10cm, so detector sits 10cm inside these pipes.

thanks both of you! regards, Kolja