State the laws of radioactive decay. Define the term 'decay constant' for a radioactive substance.

Explanation

### Step-by-Step Solution:

1. **Laws of Radioactive Decay**:
- **First Law**: Radioactive decay is a spontaneous process that does not depend on external factors. This means that the rate of decay is intrinsic to the radioactive substance itself and is not influenced by environmental conditions such as temperature or pressure.

- **Second Law**: During the disintegration of a radioactive atom, only one type of particle can be emitted at a time. This means that either an alpha particle or a beta particle can be emitted, but not both simultaneously.

- **Third Law**: The emission of an alpha particle results in a decrease of the atomic number by 2 and a decrease of the mass number by 4. This means that when an alpha particle is emitted, the resulting atom will have a different identity (element) due to the change in atomic number.
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