What's a half life of a penny

Radioactive isotopes has a characteristic half life that is ranging from less than a second to million of years.

Explanation:

One of the characteristics of radioactive material is that the radio active isotopes instantly gives off particles. This process is termed as radio active decay. For this activity pennies are used pennies headed up it means that nuclei have undergone radio active decay, or tails up it means that nuclei that haven't yet decayed.