Trinitite – The Quest for Europium and More: A 17 Day Gamma Spectrum

[Go-Figure]

You are the king of the long measurements (and patience), Massimo!
Maybe you can this way determine the optimal test period for these samples in your conditions, a good balance between time and result quality ;)

One thing I learned, initially my focus was mainly in the accumulation time with the sample, so in my first multiday measurement I started with a single day background followed by a very long accumulation with the sample.
That was the wrong appproach, because the final spectrum is a subtraction:
(shielded background+sample spectrum) - (shielded background spectrum) = result sample spectrum.

it's really pointless to have a supersmooth first term if the second is not, the result will not look good, particularly when the result spectrum is small (in terms of counts) compared with the two terms of the subtraction.
That is less of a problem if the sample is more active, and as the shielding gets more and more performing, so if you are able to decrease background by 95%+ you can probably pay less attention to it.
In my case my current shielding can only get rid of about 75% of background so I learned first hand that extending the acquisition time of the background that you are later going to subtract, making it comparable (or equal) to the acquisition time with the sample, is much more effective than extending the acquisition time with the sample indefinitely while having an "insufficient" background.

It takes time, yeah, luckily I am a patient man :)

Massimo

[Sparky]

Massimo,

We may never know for sure, but I believe the broad peak you identified at 80 keV, is most probably the various isotopes identified in the Pittauerova paper, including Ba133. I’m no expert, but in my limited experience, lead florescence is a lopsided, elevated region between 75 keV (K alpha 1) and 85 (k beta2), with the 75 keV end dominating.

When I first built my shield, I used Trinitite as my subject and I had considerable lead florescence. I added more and more material in the inner core, and that area leveled out and disappeared. In the end, I had a broad peak, centered at 80, much like yours. The first two spectrums below are of Trinitite , first and last, as I improved my shield.

The last spectrum is of a Cs137 source in my shield, with and without the copper disk that serves as a floor to the shield. I did this to intentional create a Florescence peak for reference. Note the shape.

[Go-Figure]

Hi Sparky,

I just bought some more pewter which will allow me to double its thickness in my graded shield, so my next attempt will be with about 9 mm of pewter instead of 4-5 mm, that should further reduce fluorescence and it'll be interesting to compare results between spectra recorded with the two versions of the shield.

I'll update on the results.

Massimo