Question

The most penetrating radiation out of the following is
(A) X-rays
(B) $\beta - rays$
(C) $\alpha - rays$
(D) $\gamma - rays$

Answer 1

Hint For massive particles, heavier and more charged particles are less penetrating compared to lighter and less charged particles. For massless particles, the frequency of the rays determines its penetrating power, and it’s a direct proportion i.e. the higher the frequency, the higher the penetrative power.

Complete step by step answer
In general, there are different types of radiation each having different energy depending on how they’re produced. One type of radiation is particle radiation.
Particle radiations are radiations whose constituents are particles which have masses, hence have a non-zero net energy even when they are at rest. For particle radiation, the speed of the constituent particle, which of course can change, affects the total energy of the radiation. The penetrating power of particle radiation is mostly determined from the charge and mass of the radiation rather than the energy. Radiation with a larger mass are easily stopped by the atoms of barriers due to head on collisions. Also, when they are charged the particle interacts electro-statically with the atoms of the barrier thus limiting their penetration power. Since alpha particles are made up of helium ions and beta particles are made of electrons, we can conclude that beta particles are more penetrating than alpha particles.
The other common types of radiation are electromagnetic radiation. This type of radiation is not contained with charged or massive particles, they are made up of pure energy called photons. For EM radiation, the energy is purely determined by the frequency of the photons of the radiation. The penetration power of EM radiation is entirely determined by the energy. Higher energy translates to higher penetration power. Gamma rays have a higher energy than X-rays thus a higher penetrating power. In fact, the gamma ray has the highest energy in the electromagnetic spectrum.
Now, due to the charge and massive nature of the beta particle, its penetrating power is limited. But the charge-less nature of the gamma ray makes it the highest penetrating radiation ever.
Hence, the correct option is D.

Note
These high penetrating radiations are considered to be very dangerous. Externally, the higher the penetrating power the more dangerous the radiation is considered. Beta particles can penetrate through the skin, for example, while the alpha rays cannot. However, internally (like when inhaled or swallowed), the alpha rays due to their larger masses, and dense nature of its radiation, they potentially damage more tissues than beta particles.