Para nut , Brazil nut

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Peter-1
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Para nut , Brazil nut

Post by Peter-1 » 19 Feb 2018, 22:49

Hello,

I tried to measure some brazil nuts / para nuts (Bolivien). Exactly 200 grams. The spectrum is very confusing, but it is clear to see an increased radiation. Does anyone have an idea? BKG was 15,5 cps , with the nuts 17,1 cps. After calculation with the geometry of my system is about 40 - 70 Bq for this 200 grams.
Paranuts.jpg
Peter

MaxGaspa
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Re: Para nut , Brazil nut

Post by MaxGaspa » 20 Feb 2018, 07:32

Please, can you increase the acquiring time of both background and spectrum? It seems to me you used 600s that at 0.12 cps (the count rate at the K40 peak) means 75 counts. The statistical fluctuation of a count (in each bin) is (at 1-sigma) the square root of the counts (sqrt(75) = 8.6).

Well, it's a little bit more complicated because the Fano's factor should be also considered but we can ignore it for the moment.

So it seems that the difference (if any difference exists) has the same magnitude of the statistical error.

To increase the number of counts in each bin you can either increase the acquiring time and/or decrease the number of bins.

Moreover, please, remove the IIR filtering. It is a cosmetic filter that decrease the actual signal to noise ratio, if you remove it we could have an idea of the actual statistical fluctuations.

Hope this helps

Max

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Peter-1
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Re: Para nut , Brazil nut

Post by Peter-1 » 22 Feb 2018, 02:39

Hello Max,

thanks for the explanation. I have now measured once again with a longer time. 10000 s = 2 3/4 hrs. that should be enough. here is the last spec.
2018_02_21-Paranüsse-3a.jpg
On 4 locations you can see a greater level of activity.

Peter

Alain
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Re: Para nut , Brazil nut

Post by Alain » 09 Jul 2018, 00:09

Hi Peter,

maybe this topic is not alive any more, but I will reply anyway, maybe someone in the future will reading it and it would help him. I've made some measurements of Brazilian nuts also a few years ago. According to literature, these nuts should have increased radium concentration because of very deep and extensive root sistem of the Brazil walnut tree. Radium content should be among the highest of any food (speaking only of natural radium, of course). But the concentration (or specific activity, to be precise), is still very, very low, so it doesn't represent a health risk (exact values can be found in the literature, I forgot them now).

From your spectra it can be seen the following:

-analysis is difficult because of IIR filter, as already MaxGaspa explained
-even on the second spectra, measuring time is too low. Such samples should be measured at least 1 day or even more (stability of the system is crucial for that - temperature, HV...)
-interesting part of the spectra is only left from K-40, but because you probably wanted to see enhanced right portion, you set Equaliser master higher than 0 (408 in your case). This makes difficult to see details on the left portion, which is more interesting for this sample. Try to make a new spectra with Equalizer master set to 0, Bins=x1, IIR filter=0, thin line
-from your first spectra you can see, that whole spectra of the sample becoming elevated over background left of the first prominent peak (in your case this is K-40). This is normal because of Compton scattering. In almost every vegetable food K-40 is elevated, that is expected and seen also in your case
-first signs of some indications to elevated peak (left from K-40) could be around 600 keV. If this is true, that could be Bi-214 at 609 keV (radon progeny)

Following remarks are on spectra No. 2:

-second elevated peak (if first is 609 keV, from spectra No.1) could be around 230 keV. Pb-214 at 242 keV could be expected in such sample as radium/radon progeny. But quality of spectra is not good enough for confirmation
-third elevated peak appears around 70-80 keV, which is Pb X-ray fluorescence region, and normaly that is a double peak (similar than yours, but that may be just coincidence because too short measurement time and related big statistical fluctuation, which can give totaly erroneous picture). This peak is present always, when radon progenies are in question (Pb is its progeny) or if stable Pb in food is elevated (can often be the case come from the elevated Pb in the soil or because of the polution).
-fourth elevated peak could be guessed around 50 keV, Pb-210 at 46,5 keV is expected as radon progeny. You can now clearly see negative influence of IIR filter on these two peaks (Pb-X and Pb-210) if you compare with the first spectra, where this filter was switched on and it smoothed these two peaks almost to vanihshing them. Try to avoid that filter everytime, especially in low-energy region under 100 keV, where peaks are becoming more and more narrow and made from less channels/bins than at higher energies. IIr filter here has devastating effect on their visibility and sharpness!

From this assumptions one could derive some hints (or guessings), that you proved the presence of radium (its progenies) in the sample, but with insufficient confidence. Good thing is, that you incinerated second sample, thus concentrated radium concentration (specific activity). I hope you endured well the awful smell, when doing this: Brazil nuts are very rich in fats and nitrogen-compounds (proteins), therefore at thermal decomposition, escaping gases are not quite pleasant smelling.

One thing is very important: radium has quite long half-life time (1600 years), compared to progenies. So its peaks will be difficult to see, most prominent is at 186 keV. It is much more easier to see its progenies (more exactly - progenies of radium daughter, Rn-222, which is alpha emmiter only and cannot be seen directly in gamma spectra). But because radon, fom which these progenies grow, is a gas (a noble one!), you have to close it in a sample cup, otherwise it escapes very soon after its creation. Simply said: close the sample (ash) in the cup hermetically (seal the lid!) and wait for ingrow of radon and its progenies to reach so called "secular equilibrium" between them. That could be expected after one month. This is probably the most important step in the whole procedure, if you want see anything! Then you put the cup with sample (without opening it!) in the detector and measure it. Please note all advices, described above for assesing quality spectra. If you wil be succesful, you should see all typical radon progenies: Pb-214, Bi-214 and Pb-210, an unmistakeable typical "five fingers" spectra signature of radium progenies.

I hope my instructions were clear enough for you or everyone, who wish to measure low activity of radium in the samples. I will try to find my Brazil-nuts spectra and post it here.

Regards,
Alain
Regards,
Alain

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