Trinitite Small Sample - Though he be but little, he is fierce!

[Go-Figure]

Hello there.
Last month something unexpected happened to me. I so some science popularization on social media and on a few websites which sometimes share the contents. Just some science in the basement for fun.
A guy got in touch with me saying he had just bought a Trinitite sample and he would like me to test it in order to find out if it’s a genuine one.
I said ok, send me the sample, I’ll be glad to test it and report the result to you, free of any charge of course.

I received the sample a few days before Christmas. It’s very small and weighs just 1 gram. It’s generally sandy, but with a very distinctive glassy olive green part on one side. Visually it definitely looked genuine so I had little doubt I was dealing with an actual Trinitite sample, but you still want to know what’s inside.

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I had to admit I was initially a bit worried that I wasn’t going to be able to extract much from such a small sample, I should have known better, experience already told me size often is misleading, and as soon as I got the sample close to the Geiger counter the read went straight up to 2500 CPM, that’s as high as any other Trinitite sample I tested got.

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The more sandy side was less hot as usual, giving me roughly a third of the counts.

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Before starting recording the background with my GS 2’’x2’’ I did my usual preliminary test with the PDS 100G, first I recorded a 2 hours background, the aim was not the get an accurate background spectrum, which with this device cannot be subtracted anyway, but have something to compare the counts from the sample with.
The average from the background was 49.50 CPS and a dose rate of 0.083 μSv/h.

05-Background - Salotto - 7200 Secs - 191220 - LOG.png

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I then repeated the measurement putting the sample (inside a small plastic bag) at contact with the PDS 100G, and, over 4 hours, I recorded an average of 55 CPS and 0.096 μSv/h. That means the sample increased the count rate of the background by roughly 10%. In my experience that’s quite a lot for a Trinitite sample, particularly given the small size. Also, as you can see, the Cs137 gamma peak at 661.67 keV was well visible even without subtracting background, although the logarithmic scale makes it easier to see.

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So I went into the actual long measurement quite confident. The shielding for this measurement was 5 mm of plastic, 1 mm of copper, 8 mm of pewter and 13-15 mm of lead, or what I call my Version 2-2.

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My shielded background for this measurement was 58.83 CPS, as low as I’ve ever got (my unshielded background is 255-260 CPS), although a doubling of the lead is long overdue.

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Given the good sample activity I decided a 10 day measurement (5 day background + 5 day background++sample) was going to be enough and indeed at the end of the acquisition time the spectrum was smooth and clear, here presented in both counts per bin and energy per bin view.

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12-Trinitite - ID - 120 Hours - BG Subtraction - Energy x Bin - Shield V2-2 - 0.036 Clean - 24_29-12-20.png

The result is pretty straightforward, no real surprise. The sample is quite active for a 1 gram Trinitite specimen (13 CPS), but in terms of peaks that you can clearly spot with a 2’’x2’’ NaI(Tl) it’s not particularly rich. Cesium 137 and Americium 241 are there loud and clear, but that’s always the case, the real unknown is whether or not other radionuclides will show up and as far as that is concerned there was not much here.
Europium 152 strongest peak around 121 keV was only able to produce a small bump, that’s why I decided not to label the even smaller bump you see around 340-350 keV, which undoubtedly has some Eu152 in it, besides the natural “contributors”.
Same for the very small bump around 1100 keV, only really visible in the energy per bin view. An Eu152 peak could happen around there (1085 keV + 1112 keV), but it’d be a bit odd to have that and absolutely nothing at 964 keV, which is supposed to be roughly as strong (or as weak). So I conservatively decided not to label any of those peaks.
At high energies there’s the usual peak above 1400 keV which is a “combo” of Europium 152 and Potassium 40.

Last, the quantitative analysis.

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It’s always fun to test Trinitite, you never know what you are going to get, this sample was promising, but in the end a bit anticlimactic as far as the spectrum is concerned.
Next week I’ll pack the sample and send it back to its owner together with the results and the evidences that it’s indeed genuine Trinitite.

I don’t have new samples to test at the moment so I don’t know when the next post will be.
That’s all for today, happy new year folks.

Massimo

[Rob Tayloe]

I had always thought about Trinitite as being associated with the first atom bomb test in New Mexico in 1945. I am pretty certain that the specimens that I've measured all came from that location. But there are other locations where Trinitite has been produced. I am uploading a pdf document that briefly discusses some of the different locations where Trinitite has been found; I don't recall how or where I came by this information.

Pittauerova_trinitite.pdf

Around 11.5 years ago I was able to take a Trinitite specimen and make a measurement of the gamma spectrum using a HPGe detector. The first image was after about 18 hours of counting, the second image was from around 3 days of counting.

trinite 2.jpg

trinite 1.jpg

[kotarak]

That's pretty interesting - I've tested a few Trinitite samples obtained from completely different sources and all of them were in the 300-600 CPM range.

[Go-Figure]

I had always thought about Trinitite as being associated with the first atom bomb test in New Mexico in 1945. I am pretty certain that the specimens that I've measured all came from that location. But there are other locations where Trinitite has been produced. I am uploading a pdf document that briefly discusses some of the different locations where Trinitite has been found; I don't recall how or where I came by this information.

Hi Rob, if you check this thread about the best Trinitite sample I've ever tested you'll see I referenced that very paper, and I also got in touch with one of the authors https://www.gammaspectacular.com/phpBB3 ... 69158006cd

There's been a number of testing sites over the decades, although it must be said that not all tests produced the same result in terms of the kind of material they left on the ground, depending on many factors, like the "fuel" of the bomb and the original composition of the sand. Anyway i'd like to test some sample coming from different sites and compare the results first hand to see how they differ from Trinitite, if anyone has any please let me know!
How did you get access to a HPGe detector? Is it yours?

That's pretty interesting - I've tested a few Trinitite samples obtained from completely different sources and all of them were in the 300-600 CPM range.

That also depends on the Geiger counter itself, the Ranger is quite sensitive and also has a quite large pancake probe which can detect alphas. Different geigers would give different count rates testing the same sample or the background. With this particular geiger I've never got less than 900 CPM from any Trinitite sample, and some of them were pretty weak.

[kotarak]

That also depends on the Geiger counter itself, the Ranger is quite sensitive and also has a quite large pancake probe which can detect alphas. Different geigers would give different count rates testing the same sample or the background. With this particular geiger I've never got less than 900 CPM from any Trinitite sample, and some of them were pretty weak.

I've used GQ GMC-600+ counter with an alpha-capable pancake GM tube - LND 7317 (probably the same tube is in the Ranger) - a lower-voltage version of the LND 7311 in Ludlum 44-9 probe.

[Go-Figure]

That also depends on the Geiger counter itself, the Ranger is quite sensitive and also has a quite large pancake probe which can detect alphas. Different geigers would give different count rates testing the same sample or the background. With this particular geiger I've never got less than 900 CPM from any Trinitite sample, and some of them were pretty weak.

I've used GQ GMC-600+ counter with an alpha-capable pancake GM tube - LND 7317 (probably the same tube is in the Ranger) - a lower-voltage version of the LND 7311 in Ludlum 44-9 probe.

Well, I've never used that counter so I can't really compare the two. All I can say is that even my very first Trinitite sample, which I tested in June 2019, and in my personal experience was as close to a useless piece of rock as a Trinitite sample could get (barely 3 CPS with the 2''x2'' NaI(Tl)) gave me nearly 1000 CPM with the Ranger. https://www.gammaspectacular.com/phpBB3 ... ?f=5&t=526
So I tend to think it has something to do with the counter, but without testing them together you never know!

Massimo