Question

Which of the following has the maximum penetrating power?

A. $\alpha $-particle
B. Proton
C. $\gamma $-particle
D. Positron

Answer 1

Hint: By the word penetration we understand that it is the proximity in which an electron approaches the nucleus. To choose the particle having maximum penetration power, we have to look at the mass of these particles.

Complete step by step solution:
i) Alpha particles are heaviest among the subatomic particles. We know, heavier the mass of particles, less the penetrating power of the particle. Due to heavy mass, movement of alpha particles is not much and is completely stopped by an ordinary paper sheet. So, A is not the correct answer.
ii) Protons also possess heavy mass and as we know larger the mass of a particle, less the penetration power of the particle. So, protons have less penetration power. So, B is not the correct answer.
iii) Positron is very unstable and decomposes quickly. So, its penetration power is considered as negligible. So, positron has negligible penetration power. Hence, option D is incorrect.
iv) The penetration of gamma rays $\left( \gamma \right)$ is more among all the given options, as it is very light as it is an electromagnetic wave and dense materials, such as lead, etc. are used to stop them. So, $\gamma $-particle has maximum penetrating power.

Hence, the correct option is C.

Note:
Students might be confused about the heavier mass of alpha particles. Alpha particles are heavier because they contain two protons and two neutrons. Beta-particles have less mass than alpha particles but more mass than gamma particles. So, among alpha, beta and gamma particles, mass of alpha particle is highest, then beta particle and then gamma particles.