The distance of closest approach of `alpha` particle to the nucleus was taken as a measure of

Options

A. Atomic radius
B. Diameter of the nucleus
C. Nuclear radius
D. Size of atom

Answer

To solve the question regarding the distance of closest approach of an alpha particle to the nucleus, we can follow these steps:

### Step-by-Step Solution

1. **Understanding the Alpha Particle**:
- An alpha particle consists of 2 protons and 2 neutrons, which means it has a net positive charge of +2e (where e is the elementary charge).

2. **Understanding the Nucleus**:
- The nucleus of an atom contains protons (which are positively charged) and neutrons (which are neutral). For our purposes, we focus on the positive charge of the nucleus.

3. **Distance of Closest Approach**:
- The distance of closest approach refers to the minimum distance between the alpha particle and the nucleus when the alpha particle approaches the nucleus. At this distance, the kinetic energy of the alpha particle is converted into potential energy due to the electrostatic repulsion between the positively charged alpha particle and the positively charged nucleus.

4. **Condition for Closest Approach**:
- At the distance of closest approach, the alpha particle comes to a stop momentarily before being repelled back. This means that at this point, all the kinetic energy of the alpha particle has been converted into potential energy.

5. **Relation to Nuclear Radius**:
- The distance of closest approach is often taken as a measure of the nuclear radius. This is because, at this distance, the alpha particle is effectively interacting with the nucleus, and it gives us an estimate of how large the nucleus is.

6. **Conclusion**:
- Therefore, the distance of closest approach of an alpha particle to the nucleus is taken as a measure of the nuclear radius.

### Final Answer
The distance of closest approach of an alpha particle to the nucleus is taken as a measure of the nuclear radius.

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