A Level Physics Practice Exam

Why is an alpha particle unaffected by the strong nuclear force once it leaves the nucleus?

1. It is repelled by electromagnetic forces

2. Strong nuclear force acts over short ranges only

3. Alpha particles are neutral

4. They become unstable outside the nucleus

The correct answer is: Strong nuclear force acts over short ranges only

An alpha particle is primarily a cluster of two protons and two neutrons, which is tightly bound within the nucleus by the strong nuclear force. This force is responsible for holding the particles together in the nucleus, but it operates effectively only at very short distances, typically on the order of about 1 femtometer (10^-15 meters). Once an alpha particle is emitted from the nucleus, it moves away from the nuclear environment, where the strong nuclear force no longer has a significant influence due to its limited range. As the alpha particle travels outside of the nucleus, the separation distance exceeds the effective range of the strong nuclear force, leading to its ineffectiveness in keeping the alpha particle bound. This critical factor is what allows alpha particles to behave differently once they are no longer confined within the nucleus, allowing them to travel away freely. In contrast, while the alpha particle does experience electromagnetic forces due to its positive charge, this is not the primary reason why it is unaffected by the strong nuclear force. The neutral nature of the alpha particle is also irrelevant in this context, as it still retains its positive charge and is part of a nuclear interaction when within the nucleus. Additionally, an alpha particle becoming unstable outside of the nucleus relates to its decay process