Question

In the Short-Lived Isotope section, you used a metastable isotope. Define what metastable isotopes are and how Ba-137m differs from Ba-137. What applications are Ba-137 or Ba-137m used for?

Answer 1

Metastable isomers can be produced through nuclear fusion or other nuclear reactions. A nucleus thus produced generally starts its existence in an excited state that relaxes through the emission of one or more gamma rays or conversion electrons. Sometimes it happens that the de-excitation does not proceed rapidly all the way to the nuclear ground state. This usually occurs because of the formation of an intermediate excited state with a spin far different from that of the ground state. Gamma-ray emission is far slower (is "hindered") if the spin of the post-emission state is very different from that of the emitting state, particularly if the excitation energy is low. The excited state in this situation is therefore a good candidate to be metastable if there are no other states of intermediate spin with excitation energies less than that of the metastable state.

Metastable isomers of a particular isotope are usually designated with an "m"

¹³¹Ba (having half life of 11.5 days), and ^137mBa (having half life of 2.55 minutes)

Half-life is the time required for half of a radioisotope to disintegrate.

The source of the Ba-137m is a mini generator or "cow." The Ba-137m is formed by the
disintegration of Cs-137. The “m” in Ba-137m means that the nucleus of the newly
formed Barium atom is in an excited state. The excited nucleus emits energy and
becomes stable.
Cs-137 → Ba-137m + _-1e⁰ (sometimes _-1e⁰ is represented _β 0⁻¹ )
Ba-137m → Ba-137 + ₀γ⁰

meta stable barium releases gamma radiations and produce B-137.