Welcome back fellow radiation nerds, today we will learn about the radioactivity of Terbium 161!

Element Terbium

Terbium (Tb) is a rare earth element with an atomic number of 65. It has only one naturally occurring isotope, Tb-159 and it is stable. It has been discovered in 1843 by a Swedish chemist, Carl Gustav Mosander who also the chemist behind the discovery of Lanthanum, which radioactivity and uses, I already covered in an earlier video. Since Terbium is part of the Lanthanide series, it shares many of their chemical and physical properties.

Terbium 161 and its radioactivity

Terbium 161 is a short lived radioactive isotope of Terbium and it is produced by the irradiation of stable Gadolinium 160 in the PRISMAP network of research nuclear reactors which include Maria at NCBJ (Poland), RHF at ILL (France), BR2 at SCK CEN (Belgium) and SINQ spallation neutron source at PSI (Switzerland).

Terbium 161 gamma spectrum, RAYSID Gamma Spectrometer (FWHM <7%)

It has a half-life of just under 7 days and it decays through a beta emission into stable Dysprosium 161 and in the process it also releases a gamma ray at 25.7, 48.9 and 74.6 keV which my RAYSID had no problem in detecting.

My sample of Terbium is in a form of TbCl3 solution and it has activity of around 100-150 Bq. On my RAYSID Gamma Spectrometer I got only 16 CPS when measured inside of my lead castle, with the sample placed as close as possible to the detector. The soft beta radiation coming from the Terbium 161 is being shielded by the plastic container and I only got marginally higher activity compared to background with my Ludlum Model 3 Meter with 44-9 probe at 1cm distance.

Uses

Terbium 161 is currently being tested for use in nuclear medicine to treat prostate cancer and in imaging techniques such as SPECT (Single Photon Emission Computed Tomography).

Summary

While I don’t have much time left with this sample before it decays, it was a great fun measuring its radioactivity and learning about it. I’m curious to hear your thoughts on Terbium 161 and what did you find most interesting about it, let me know in the comments below!


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