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The ionization power of $\alpha,\beta $ and $\gamma $-rays is in the decreasing order:
A) $\alpha > \beta > \gamma $
B) $\beta > \alpha > \gamma $
C) $\gamma > \alpha > \beta $
D) $\beta > \gamma > \alpha $

Answer Verified Verified
Hint: Ionisation can be defined as a process in which an electron is given sufficient energy to separate it from the atom. Hence, ionization power can be said as one’s ability to ionize the other atom. The ionization power of a particle depends on the factors such as its nucleus and size of the particle.

Complete step by step answer:
1) $\alpha - $Particles: They are particles that consist of two protons and two neutrons which are tightly bound together. They can also be called as a helium nucleus. $\alpha - $Particles are heavy and slow in speed compared to other forms of radiation. Due to their heavy mass, slow speed and double-positive charge make them highly ionizing particles.
2) $\beta - $Particles: They are high energy and high-speed particles. They have a mass which is half ${1000^{th}}$ of the mass of a proton. Due to their low mass and high energy they can reach very high speeds close to the speed of light. This means they lose energy very fast and hence, they have very less ionizing power compared to $\alpha - $particles.
3) $\gamma - $Particles: They are a packet of electromagnetic energy also known as photons. Gamma photons are the most energetic type of photons in the electromagnetic spectrum. $\gamma - $Ray photons have generally more energy than $100keV$. Due to their highly energized photons, they interact rarely with the matter and travel very far and have very little ionizing power.
4) Therefore, the correct order of the ionization power will be $\alpha > \beta > \gamma $ which shows option A is correct.

Note:
Ionization energy and ionization power are the same concepts. Here in this question, the ionization power of particles on other atoms or elements has been asked. One must not confuse it with individual particle ionization energy.