Question

Which of the following statements is/are correct about alpha, beta and gamma rays?
A. The alpha particles are positively charged, high energy particles emitted from the nucleus of any radioactive atom. These are highly ionizing.
B. Beta particles contain both negatively and positively charged particles, negatron and positron respectively. These are emitted when a radioactive atom is undergoing spontaneous disintegration. These are moderately ionizing.
C. Gamma particles have no charge as they contain high frequency electromagnetic radiation and have very high ionizing power.
D. All of the above.

Answer 1

Recall that ionization is the process by which electrically neutral atoms are converted into electrically charged atoms (or ions) by either gaining or losing electrons. The ionization power depends on the magnitude of charge of the ionizing particle. Given that alpha particles are synonymous to the Helium nuclei, beta particles to electrons and positrons, and gamma rays to photons, determine the ionizing power relative to each of the processes, which should lead you to the appropriate option.

Complete step by step answer:
We know that radioactivity can be described as the process by which an unstable nucleus spontaneously breaks down resulting in the release of energy and matter from the nucleus. This happens when the binding energy of the nucleus isn’t sufficient to hold its nucleons together.
We also know that ionization is the process by which an atom acquires a positive or negative charge by losing or gaining electrons, resulting in the formation of an electrically charged atom called an ion.
The three main radioactive processes are alpha decay (helium nucleus production), beta decay (electron or positron production) and gamma decay (photon production).
Alpha decay results in the production of a stream of $\alpha$ particles, or two closely bound protons and neutrons similar to that of a Helium atom that has been stripped of its two electrons. The decay process is given as follows:
${}_Z X^{A} \rightarrow {}_{Z-2} Y^{A-4} + {}_2 He^4 +\;Energy$
Where Z is the atomic number and A is the mass number. The Helium particles $He^{2+}$ thus produced have a charge of +2 , and hence are positively charged particles and are emitted via the above radioactive decay of the nucleus of the parent atom X. Since the alpha particles are ionic with a $+2$ charge they are capable of stealing electrons via a Coulombic force (ionic bond) to satisfy their valency of $+2$, leaving the atom that they are stealing from with a $+2$ charge which means that this atom is now ionized by the alpha particles. Thus, alpha particles are highly ionizing. This means that statement A is true.
Let us now look at beta decay.
Beta decay results in the production of a stream of beta particles of either type: negatron or positron. A negatron is nothing but a negatively charged particle such as an electron, whereas a positron is an antielectron, or a positively charged electron. This process is also a result of spontaneous radioactive nuclear disintegration. The beta decay processes are given as follows:
For $\beta^{-}$ decay: ${}_Z X^{A} \rightarrow {}_{Z+1} Y^{A} + {}_{-1}e^{0} + \bar{\nu} +\;Energy$
For $\beta^{+}$ decay: ${}_Z X^{A} \rightarrow {}_{Z-1} Y^{A} + {}_{+1}e^{0} + \nu +\;Energy$
Where ${}_{-1}e^{0}$ is the negatron and ${}_{+1}e^{0}$ is the positron. $\bar{\nu}$ is an antineutrino and $\nu$ is a neutrino, both of which have zero electrical charge and are emitted to only conserve spin and angular momentum in the reaction. Both the electron and the positron are charged particles which means that they are capable of ionizing other atoms by combining with them. This means that the combining atom can either gain or lose a beta particle, leaving it with a $-1$ or $+1$ charge accordingly. Thus, beta particles are ionizing but since they only impart a charge of $+1$ or $-1$ in comparison to $+2$ that alpha particles impart, beta particles are moderately ionizing. This means that statement B is also true.
Finally, let us check the claims of statement C by looking at gamma decay.
Gamma decay results in the production of gamma rays or electromagnetic radiation of short wavelengths (less than $10^{-10}\;m$). Since gamma rays do not possess any electric charge, the emission of gamma rays does not alter the atomic or mass number of the emitting atom, and results only in a change in the energy state of the nucleus from an excited state to the ground state. This is given as:
${}^{*}_Z X^{A} \rightarrow {}_{Z} X^{A} + \gamma$
Now, gamma rays or photons are uncharged particles, and though they do directly ionize other atoms, they may cause atoms to emit other particles which will ionize them. This happens via processes like the photoelectric effect and Compton scattering which are beyond the scope of this question, and this form of indirect ionization is less efficient than the ionization carried out by alpha and beta particles owing to its multi-process dependence. Thus, gamma rays have a low ionizing power. This means that statement C is incorrect.

Therefore, the correct statements are A and B.

Note: Do not get confused between ionization power and penetration power.
Ionization power is the efficiency with which a particle is able to carry out ionization of a neutral atom. The ionization power of alpha particles is 100 times that of beta particles and 10000 times that of gamma rays.
Penetration power is the extent to which a particle is capable of traversing through a material medium unimpeded. The penetration power of alpha particles is ${\dfrac{1}{100}}^{th}$ of beta particles and ${\dfrac{1}{10000}}^{th}$ of gamma rays.
Therefore, Ionization power and Penetration power are inversely related.