NORM: the lead I used to build my shield with. :)

[stamasd]

I have built my lead castle using 4 large bricks of lead, 50lbs/23kg each, plus a number of smaller lead slabs of 10 pounds/4.5kg each. After building it in the shape I wanted, I was left with a few of the smaller 10lbs slabs.
I was curious what the lead itself may contain in terms of radioactive impurities. So I took a 12h background reading with the empty castle (including an inner layer of copper) and then put inside 2 of the leftover lead slabs, because that's all I could fit - so around 20lbs/9kg of lead inside the castle (inside the copper lining, next to the detector) and took another 12h reading.

Here is the result below. There's the K-40 peak at 1460keV, and a 511keV peak where it's expected to be. Apart from that, I can see a little evidence of a peak at 194keV which may be Ra-226, and one at 609keV likely from Bi-212. But they are very small above the continuous background spectrum. So I may be able to say that there is a little uranium contamination of the lead, but not much. The number of counts in the peaks is less than 500-600 over 12h above the subtracted background.

The origin of the lead is mostly recycled bullets, plus some other sources such as recycled car tire wheel weights and so, according to the seller I got it from. There's probably a small percentage of antimony in the lead, 5-6% as it's commonly added to harden the bullet alloy.
Not very exciting I know, but here it is.

Pb-20lbs-12h-2inCsI-1300V-130vol-pbcu-43200s.png

[stamasd]

FWIW, I also tested today a block of 500g industrial graphite. That showed surprisingly little activity. Seems quite clean and free of intrinsic radioisotopes. There is a little peak at 609keV for Bi-214, but only 60 counts over 6h which is actually the same as the excess counts from K-40 that it registered.

[Peter-1]

A block of tungsten, which served as shielding in a radiation laboratory, produced a clear spectrum of thorium. The block weighs 2.7 kg. I was able to measure similar spectra in other pieces; these are likely impurities introduced during the tungsten manufacturing process. Unfortunately, it is not suitable for effectively shielding the NaI crystal.

Peter