Lanthanum gamma spectrum

[lodovico]

Hi,
Naturally occurring lanthanum is composed of one stable (La139) and one radioactive (La138) isotope, with La139 being the most abundant (99.91% natural abundance).
As a sample I have used 100g of lanthanum oxide (see the picture). Mixed with lanthanum there are some impurities of thorium and actinium 227 that leave their trace in the gamma spectrum, together with the two gamma emissions of the La138 isotope. I think that the emissions of Pb212 and Tl208 (from thorium decay) are so weak because the substance has been purified and there has not been enough time to reach secular equilibrium.
I used NaI 63x63, I calibrated the detector with accuracy with thorium and lutetium source, I used a lead shielded well (see the picture).

What do you think about this spectrum and my interpretation ?

Lodovico

lanthanum.png (126.9 KiB) Viewed 7240 times

lanthanum.JPG (18.06 KiB) Viewed 7240 times

DSC_0295.jpg (57.66 KiB) Viewed 7240 times

[Steve Dubyk]

Lodovico, that is really a nice spectrum and set up. How long did it take you to acquire it? I used a 40x40 mm probe with 100g of the metal, and it took about 5 hours! I was originally under the impression that the only impurity in lanthanum was Ac-227 and it's daughters, but it does look like the Tl-208 peak shows up both in your and my spectra. That would be from thorium decay. There is a paper in the Resources section on lanthanum detectors you may be interested in.

Great job!

Steve

[lodovico]

Thank you, Steve,
I run the acquiring process for about 12 hours : all night long ..
I read something about lanthanum in literature and I found that thorium and actinium often are found together lanthanum and the purification process is rather difficult because all the rare earth are chemically similar one to another. I will check in the resources section.
Lodovico