In analyzing nuclear decay reactions, we apply the **many conservation laws**. **Nuclear decay reactions** are subject to classical **conservation laws for charge, momentum, angular momentum, and energy**(including rest energies). Additional conservation laws, not anticipated by classical physics, are:

- Law of Conservation of Lepton Number
- Law of Conservation of Baryon Number
- Law of Conservation of Electric Charge

Certain of these laws are obeyed under all circumstances, others are not. We have accepted conservation of energy and momentum. In all the examples given we assume that the number of protons and the number of neutrons is separately conserved. We shall find circumstances and conditions in which this rule is not true. Where we are considering non-relativistic nuclear reactions, it is essentially true. However, where we are considering relativistic nuclear energies or those involving the weak interactions, we shall find that these principles must be extended.

Some conservation principles have arisen from theoretical considerations, others are just empirical relationships. Notwithstanding, any reaction not expressly forbidden by the conservation laws will generally occur, if perhaps at a slow rate. This expectation is based on quantum mechanics. Unless the barrier between the initial and final states is infinitely high, there is always a **non-zero probability** that a system will make the transition between them.

For purposes of analyzing non-relativistic reactions, it is sufficient to note four of the fundamental laws governing these reactions.

**Conservation of nucleons**. The total number of nucleons before and after a reaction are the same.**Conservation of charge**. The sum of the charges on all the particles before and after a reaction are the same**Conservation of momentum**. The total momentum of the interacting particles before and after a reaction are the same.**Conservation of energy**. Energy, including rest mass energy, is conserved in nuclear reactions.

Reference: Lamarsh, John R. Introduction to Nuclear engineering 2nd Edition