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Fukushima soil

Posted: 17 Jul 2018, 05:44
by Svilen
I received today the soil sample from Luuk and here is the result. Just 2.5h measurement, great linearity of the detector in PRA - no tricks. Outstanding preparation from Luuk - thank you very much!
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Re: Fukushima soil

Posted: 17 Jul 2018, 14:42
by luuk
Hi Svilen,
Nice spectrum resolution looks good to me, thanks for posting.

Re: Fukushima soil

Posted: 19 Jul 2018, 00:19
by Alain
Wow, nice spectra Svilen!

Can you display the spectra also with logarithmic scale (y), if this is possible in PRA? For me it seems that first peak is 32 keV from Cs-137, the second one is probably Pb X, then backscatter and then three marked peaks. But there may be some other peaks between 796 and 1461 keV (Cs-134 and radon progenies), which would become visible, if you would turn on the log scale. Left side of the 662 keV peak seems broadened to me in at the bottom part (foot). Consequentialy the FWHM at 662 kev should indicate a higher value than you are used to in your detector with pure Cs-137 samples (didi you compare them?). I should guess that this left broadening is from the smaller Cs-134 peaks at 604 and 569 keV, which are "hidden" in the main Cs-137 peak. They are so small that they are "fused" with 662 keV peak, due to sample age and consequentialy 11-times lower Cs-134 activity compared to 2011 value. Sometimes this broadening in soil samples is also visible in Chernobly contaminated soil, where Cs-134 is already decayed below detection limit, but radon progeny Bi-214 at 609 kev contribute to the left side, which is almost always present in the soil. I believe PRA has some sort of Gaussian peak deconvolution, which can separate multiplets to single peaks (I'm not familiar with PRA). Can you turn it on? It would be interesting to see, what this function "sees" in the left flank of 662 keV peak.
Can you please tell any detail about weight of the sample and cps countrate with the sample and of background? Just for curiosity, that I can imagine the order of specific activity.

Re: Fukushima soil

Posted: 19 Jul 2018, 03:25
by cicastol
Nice Svilen!
Alain wrote: CUT

It would be interesting to see, what this function "sees" in the left flank of 662 keV peak.
Hi Alain,
i'ts very hard IMHO to split the left 134Cs from the main 137Cs peak in Fukushima soil sample using "normal" NaI(Tl) detector, probably need detector with 4-5% or better resolution, only Luuk could know the answer!

This was my attempt :


Re: Fukushima soil

Posted: 19 Jul 2018, 04:16
by iRad
I have a 2X2 Luuk built 6% detector that can see it nicely. I also have a couple other Scionix detectors in the 6% range that pick it out nicely. Unfortunately, 4 to 5% (or better) is out of the range of NaI(Tl) crystals, and into the range of exotically expensive detectors... Cheers, Tom

Re: Fukushima soil

Posted: 19 Jul 2018, 05:15
by luuk
I posted some time ago spectra from the Fukushima soil detected with different detectors from bad ones up till the best possible, there you can see more peaks from the Cs-134, and you can also see what spectrum you can expect with a certain resolution.
Look in: The Rad-Lab/Spectra/ “Fukushima soil tested with different detectors”.
Please keep in mind that at the time of my test (05-2015) the Cs134 was much stronger then now!

Re: Fukushima soil

Posted: 19 Jul 2018, 05:48
by pilgrim
Just received my sample, this is my spectrum.
12000 seconds, NaI 2", GS1100-PRO, 2cm Lead Pig.
In the comments you can see the energy and the resolution of each peak.
Fukushima Soil Sample, NaI2x2 + GS110 pro @ 929V. - 3h20m.JPG
I read the Alain's post before but I forget to take a screenshoot with logarithmic scale (sorry!) but at least you can see the Gaussian peak ;-).
The system was already on because I was doing another measurement, so the calibration could be not optimal.
I will take another spectrum these days.

The sample contains ≤ 5Grams of soil.

Re: Fukushima soil

Posted: 19 Jul 2018, 06:11
by luuk
Nie spectrum, thanks for posting.
I cannot read the resolution what is it?

Re: Fukushima soil

Posted: 19 Jul 2018, 09:08
by Svilen
Thanks for all the replies. Nice spectra, Daniel and Ciro! Thank you for your analysis, Alain.

I guess in all the software MCAs logarithmic scale is possible, including PRA. I checked it of course, but in this case it is not very different, except some trends in the higher energies, where it needs a longer exposition also.

Yes, the first peak is the 32 keV from Cs-137, followed by x-rays, but I marked just the more interesting ones.

The 662 keV peak is really extended to the left because of the Cs-134 peak, which as the others also mentioned, is not detectable with the resolution between 7 and 8 that this detector has. As you supposed, the resolution there is lower in compare to a pure Cs-137 peak. You can see it on the pictures below - from just a Cs-137 (1) containing sample (6.9 FWHM is too optimistic there, but lets say it is 8) and the soil sample (2), where the resolution is above 10 (well I also marked a bit wider ROI in compare to the first picture).
I also add the logarithmic scale with gaussian correlation as you requested (3).

The counts are ~95/s for the sample vs ~15/s background in the shielding.

Short description of the sample from luuk: "The sample contains ≤ 5Grams of soil, it is soil that is harvest from different places around the Fukushima power plant about 3 weeks after the incident. The soil contains sand, small stones and some plant parts".
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Re: Fukushima soil

Posted: 19 Jul 2018, 13:19
by pilgrim
luuk wrote:Nie spectrum, thanks for posting.
I cannot read the resolution what is it?
Hi Luuk,
6.4 % for Cs137 @ 660 Kev;
5.7 % for Cs134 @ 800 Kev;