Many atomic nuclei are radioactive.
The above expression is an approximation valid when the time interval is much shorter than , as is true in this experiment. You should remove the plastic cap from the GM counter for the students studying the absorption of radiation. Co whose half life is 5.3 years and which emits rays of energy about 1.3 MeV, and T whose half life is 3.8 years and which emits particles of maximum energy about . The particles have a continuous energy spectrum from zero to the maximum. You will find that rays and particle are partially absorbed as they traverse a thickness of material, and that the absorption depends mostly in the number of electrons per square centimeter in the absorber.