First, that's a pretty lame title for the thread, I know!
Today I report about another 28 day long measurement on the Trintite Type 5 sample from Mineral Research Company.
This is obvious looking at how high the Eu152 peaks are, but what really surprised me the first time around was the 81 keV peak, which I eventually labelled as Ba133, The bomb had an explosive lens system containing Baratol, which in turn contained stable Ba132. Activation due to neutron capture created Ba133, also visible in other Trinitite spectra.
There was some debate on that peak, due to its proximity to the peak expected from the lead shield fluorescence and also to the possibility of the presence of Pb212 and Pb214 in the sample.
So I decided to repeat the measurement improving my shielding with two pewter sheets of 15 x 75 cm, which allowed me to add roughly 4 mm more pewter to the shield. Pewter is pretty good at absorbing the XRF from the shielding. I didn’t expect the additional 4 mm of pewter to bring an improvement of the same magnitude as the first 4 mm of pewter did, but I expected to get better.
- 04 - OLD Background - 336 Hours - Counts x Bin - Shield V2-1 - 0.036 Gauss - 31-03_07-04+01-05_8-05-20.png (58.01 KiB) Viewed 11071 times
And this is the shielded background with 8 mm of pewter. I have to add I slightly improved the overall shielding which decreased from 61 to 59 CPS (my unshielded background in my test room is typically 255-260 CPS with this probe).
Now that doesn’t look like a dramatic improvement at first sight but you can see the XFR peak stands out less compared with the rest of the background spectrum in the picture below, so the effect of fluorescence is further reduced.
- 05 - Background - 336 Hours - Counts x Bin - Shield V2-2 - 0.036 Gauss - 03-11_06-20+25-06_2-07-20.png (60.38 KiB) Viewed 11071 times
- 7 days of background.
- 14 days with the sample in the chamber.
- Further 7 days of background.
The 14 day background spectrum was later subtracted from the sample + background spectrum,
The result is the best I had so far, it’s smoother and clearer for one thing and the 81 keV peak is loud and clear. I really don’t think fluorescence from the shield can account for such a strong peak. I tested more active Trinitite specimens with the previous version of my shielding (4mm of pewter instead of 8 mm) and nothing like that ever showed up in the XRF region, not even close.
Spectrum is presented in counts per bin and energy per bin views.
He’s also among the authors of this paper on Trinitite [broken link removed - Steven]
He had the following comments on the specimen and the spectrum:
“You were indeed lucky to get the high Eu152 specimens from MinResCo. The only specimens I’ve seen with this much Eu152 came from the shed at Trinity where the original surface was preserved. None of the usual eBay sellers has anything like it."
He added that another author of the paper (J.R) “has an excellent hpGe system. I am not sure what the 81 KeV peak is on my system because I don’t see other Ba133 peaks but he says he always sees the 81 KeV peak when there is Ba133 present and it definitely shows up on other hpGe systems.”
He also mentioned another measurement conducted by the other author of the paper (J.R), and I found this part particularly interesting:
“He mounted a large specimen of Trinitite and ground off one millimeter at a time. He measured the gamma activity in each fraction and plotted that. Fission products (Am241, Ba133, Cs137) all decreased rapidly from layer to layer while activation products and naturally occurring nuclides (Eu152,K40) stayed the same. We considered this pretty strong evidence that Ba133 comes mainly from Baratol and the low amount of Ba133 that I subsequently found in rock tends to confirm this.”
This was another reason for me to attribute that 81 keV mainly to Ba133.
I also want to show another potential piece of evidence that this is the case, in the following photo you see the spectrum both with and without background subtracted, the one in the upper half of the image includes background.
Putting all together I think Ba133 is by far the most likely candidate for that peak.
Again, there seems to be something else close to that peak around 85-86 leV but I decided to leave it unlabeled.
As for the rest, I identified a couple more Eu152 peaks, the one at 964 keV pretty clear, the other at 1213 keV much less obvious and I am not sure labelling it was the right thing to do. I mean, Eu152 is there, but if that peak is visible then the one at 1299 keV should be visible too and I see no sign of it.
The 1400-1500 keV peak drifted “north” in the final days of the acquisition due to thermal drifting. Last week weather got hotter here in Italy, as a consequence in the final days of accumulation of the background the K40 peak moved towards slightly lower energies and when subtracted that resulted in a higher energy difference peak (around 1475 keV). It’s not the first time this happens to me with Trinitite, the difference peak in that region is so weak it takes very little to make it “move” one way or another. It still comes from K40 (NORM) and Eu152 (activation).
One final point on the 13 keV peak. As you know the Trinity bomb was a Plutonium device so it wasn’t straightforward to me why I found an Uranium X-rays peak in it. In the end I thought Uranium could come from Plutonium decay so I went checking its nuclear data (http://nucleardata.nuclear.lu.se/toi/nu ... iZA=940239) which links that X-ray to Pu239, another indication of the presence of “unburned” plutonium in the specimen. Anyway, its contribution to the peak around 40 keV must be very small.
Finally, the quantitative analysis confirms the results of previous tests, the only difference is the slight improvement in terms of shielding which brought my shielded background to 59 CPS vis 255-260 CPS of my unshielded one.
Have a nice weekend.
Massimo
