Uranium and Thorium along with Potassium are the most common, naturally occurring radioactive isotopes but there are also many other, lesser-known ones. One of them is Lutetium, which will be today’s main topic.
Lutetium is the last element in the Lanthanide series and it has been discovered in 1907 by French scientist Georges Urbain. Today Lutetium has very little commercial use due to its difficult production and high price but one of the uses is in the production of scintillation crystals which are used in positron emission tomography.
In nature, there are two isotopes of lutetium, 175Lu and 176Lu. Lutetium 176 is radioactive and it decays by a Beta emission into Hafnium 176 with a half-life of 37.8 billion (3.78×1010) years. Since Lutetium has a very long half-life, it is used in Lutetium-Hafnium dating of meteorites.
Lutetium has small, but detectible activity. My sample, which an LYSO crystal, measures 16 CPS above background on my RAYSID which has a [5cm3 (CsI(Tl) crystal]. Such activity is more than enough for gamma spectroscopy but it is not for measuring with a Geiger counter.
Lutetium has a very interesting gamma spectrum, it emits two gamma rays (202 keV and 307 keV) but since they are emitted at the exact same time, they sum up and form a peak at 509 keV.
Another use of lutecium is in the treatment of prostate cancer where a synthetic isotope of lutetium, 177Lu, is injected into patient’s body where it irradiates and kills cancer cells. Lutetium 177 emits two gamma rays at 113 keV and 208 keV.