What is the value of impact parameter for a head on collision ?

Explanation

To find the value of the impact parameter for a head-on collision, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Impact Parameter**:
The impact parameter (b) is defined as the perpendicular distance from the line of action of the velocity vector of the incoming particle (like an alpha particle) to the center of the target nucleus.

2. **Defining Head-On Collision**:
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