# What is the decay equation of cesium 137?

Apr 2, 2016

${\text{_ 55^137Cs -> ""_ 56^137Ba + ""_"-1}}^{0} \beta$

#### Explanation:

Cesium-137 has an atomic number of 55, so is written as

""_55^137Cs.

It is also a $\beta$-emitter, which means it undergoes $\beta$-decay by a neutron decaying into a proton, releasing an electron.

Protons and neutrons have the same mass, so the mass number doesn't change. The atomic number increases by one, because one more proton is formed.

Because the atomic number changes, this is a new element, number $56$, barium, or

""_56^137Ba

In the form of an equation, this is written as

${\text{_ 55^137Cs -> ""_ 56^137Ba + ""_"-1}}^{0} \beta$

This video shows a sample of Cs-137 being tested by a hand-held detector.