Trinitite Sample 2 - From the First Nuclear Bomb Explosion

[Go-Figure]

Hi folks,
This is my second attempt with a Trinitite sample.
I got a second sample from United Nuclear, knowing that I am doing gamma spectroscopy the people from UN selected a nice glassy sample for me.
You typically have two kinds of Trinitite sample: sand-like and glass-like. The glassy ones supposedly were closer to the surface therefore should be more radioactive. They certainly look better, as you can see from the photos.

First test on the sample with the Geiger counter produced a peak read of 800 CPM. The previous sample got over 900 CPM so that wasn’t a very encouraging start, but in the end gammas are what matters and I know by now that Geiger counters can be pretty misleading in this respect, since most of what they detect at contact are alphas and betas.

The first sample was really tricky to test, I was surprised when I realised my scintillator was picking no more than 2 CPS from it, working in a background which was giving more than 250 CPS. Having no shield I wondered if I was going to be able to identify any peak at all.
In the end Cs137 and Am241 showed up pretty clearly, but the third radionuclide I was looking for, Eu152, was much harder to spot, the only peak associated with it clearly visible was the one at 1408 keV.

Things were better this time.
Not that the activity was higher, we are still at 2 CPS, but the result looks clearer.
This is the first time I used some sort of lead shielding. My proper shielding is not ready yet, but people from UN, without me asking, sent me a small sample of a shielding product they sell called RadMax, which is basically a lead sheet roughly 1mm thick.

The background of the room when I do my tests typically gives 255 CPS ad 0.107-0.108 µGy/h if no shield is used.
A single layer of that cannot be called a proper shielding, but was still enough to reduce my background from 255 CPS to 145 CPS, so we are talking about a 43% decrease. That certainly helped.
Interestingly the reduction in exposure from the background (-25%) was significantly lower than the reduction in counts, an indication that the shield mostly blocked low energy gammas, which is expected for a single sheet.

First I recorded a 12 hours background (partially shielded this time) and then I subtracted it from the sample spectrum which I recorded over a 24 hours time.
As expected the shield gave me a distinct fluorescence peak around 75-80 keV. A layer of copper and one of plastic would have helped there, but in the end the background subtraction removed it completely, so no harm was done.

Today is 27033 days (74.06 years) since the Trinity test, which means Cs137 is reduced to 18% of its original activity, that’s enough for its main gamma peak at 661.67 keV to emerge nicely. The X-ray peak at 32 keV is a bit mixed up with that of Am241 at 26 keV, but no doubt it’s there.

Americium 241 is another signature radionuclide you expect from Trinitite. The bomb used for the test was a Plutonium device and Am241 is a product of beta decay of Pu241, which in turns come from Pu239 (the fuel) via double neutron capture.
Its half-life time is 432.2 years, therefore its activity is still 88% of what originally was , so no wonder both its peak at 26 keV and 59 keV are there and tall.

Then there is Eu152. If Am241 is a signature radionuclide for a Plutonium bomb explosion, Eu152 (just like Eu154) is a signature of the Trinity site, whose sand contained Eu151, and Eu153, both stable, which were activated by the capture of slow neutrons turning them into Eu152 and Eu154, with the difference that Eu154 (half-life time 8.6 years) is now reduced to a mere 0.25% of its original activity, so you cannot expect to see it anymore, while Eu152 (half life time 13.5 years) has still a 2.25% of its original activity left “in the tank”. Not much, but it’s worth give it a try.

Unlike my first test I think I can say I identified Eu152 with a reasonable degree of certainty this time, which was the main goal of this second attempt.
The 1408 keV peak is again the more visible, being far away from anything else, but the 121.78 keV peak is also there this time. Pretty close to it there are other peaks between 160 and 200 keV which are of no easy identification. The energy is compatible with Cs137 back scatterpeak, and I wonder if that can be the explanation.
Other peaks expected from Eu152 are at 244 – 344 – 411 – 444 – 778 – 867 – 964 – 1085 – 1112 and 1408 keV.
The first two appear to be there, albeit a bit south of where they are supposed to be. This likely has to do with my calibration which appears to be 8-12 keV off across the board above 200 keV. Cs137 main peak is a good indication of that, being centred at 649 keV instead of 661.
There’s a region of activity between 400 and 480 keV, but it’s too “messy” for me to call a peak there, Cs137 Compton Edge might be in the mix as well.

I have peaks around 860 keV and 1070 which, again, given the slight calibration drift are compatible with what is expected for Eu152, but I put a question mark there since in that same region the 964 keV peak (which was supposed to be stronger of the other two) didn’t show up at all.
Finally, the 1408 keV peak is definitely there.

Other possible candidates which might have, in theory, show up was Cobalt 60 and Barium 133. The former with its half life tome of 5.27 years is now 1/17000 of what it used to be, therefore you don’t expect to see it even in your wildest dream, while the latter is reduced to 0.76% so it’s still a very long shot.
The peak around 160 keV might be compatible with Ba133 summing peak, but it doesn’t look reasonable to conclude it is, since there’s no other sign of its presence.

Again, the sample is definitely safe to handle, the gamma exposure from it almost at contact being only a small fraction of the normal background (and a small fraction of the partially shielded background as well).

When I have a proper shield I will repeat this test again, but for now I am happy I made an improvement on my first attempt and, I think, I “caught” Eu152 without ambiguity.

Spectrum is in both counts per bin and Ebergy per bin. The side tested was the glassy one, which appeared to be the more active of the two.

[pilgrim]

Nice sample!
This is the spectrum recorded with mine.

Trinitite.JPG

[Go-Figure]

Nice sample!
This is the spectrum recorded with mine.
Trinitite.JPG

How many CPS were you getting from the sample?
Judging by the spectrum your sample appears more active than mine. I was only getting 2CPS.

[Peter-1]

Hello,
Months ago I measured a sample with 4 grams of trinitite. The background was 17 CPS with the 4 grams of trinitite, then 26 CPS. Measuring time over 12 hours. In the diagram the background has already been subtracted. Unfortunately, I have no source where I could buy something else.

2018_10_25-Trinitit-2.png

Peter

[Go-Figure]

Hello,
Months ago I measured a sample with 4 grams of trinitite. The background was 17 CPS with the 4 grams of trinitite, then 26 CPS. Measuring time over 12 hours. In the diagram the background has already been subtracted. Unfortunately, I have no source where I could buy something else.
2018_10_25-Trinitit-2.png

Peter

So it's 9 CPS from the sample? That's 4.5 times what I got from mine, both of them.
I was thinking to measure them simultaneously to double the activity.

I got both of them from United Nuclear. There are several other sellers around, but I heard not all of them sell genuine samples. Another good source could be Mineresco, but they don't ship outside the US.

Massimo

[pilgrim]

How many CPS were you getting from the sample?
Judging by the spectrum your sample appears more active than mine. I was only getting 2CPS.

About 30 CPS, but I don't remember the background inside the lead, I think about 18 CPS, so 12 CPS for the sample.
If it helps I remember I got 19 ± 1.4 CPM of Alpha only.
The total mass of my samples is about 6 g.

[Go-Figure]

How many CPS were you getting from the sample?
Judging by the spectrum your sample appears more active than mine. I was only getting 2CPS.

About 30 CPS, but I don't remember the background inside the lead, I think about 18 CPS, so 12 CPS for the sample.
If it helps I remember I got 19 ± 1.4 CPM of Alpha only.
The total mass of my samples is about 6 g.

Do you remember where did you get your sample?