### Theory:

Some of the units of radioactivity are:
• Curie
• Rutherford
• Becquerel
• Roentgen
Curie:
Curie is the quantity of a radioactive substance that undergoes $$3.7 \times 10^{10}$$ disintegrations in one second.
The value is close to the activity of $$1\ g$$ of radium $$226$$. Curie is the oldest unit of radioactivity.

$$1\ curie$$ $$=$$ $$3.7 \times 10^{10}$$ $$disintegrations\ per\ second$$

Rutherford:
Another unit of radioactivity is Rutherford.
Rutherford ($$Rd$$) is the quantity of a radioactive substance, which produces $$10^{6}$$ disintegrations in one second.
$$1\ Rd$$ $$=$$ $$10^{6}$$ $$disintegrations\ per\ second$$

Becquerel:
Becquerel ($$Bq$$) is defined as the quantity of one disintegration per second. The SI unit of radioactivity is becquerel.
Roentgen:
One roentgen ($$R$$) is the quantity of radioactive substance which produces a charge of $$2.58 \times 10^{-4}$$ $$coulomb$$ in $$1\ kg$$ of air under standard conditions of pressure, temperature and humidity.
Roentgen measures the radiation exposure of $$\gamma$$ rays and $$X\ -rays$$.