Question

What is the composition of alpha particles?
(A) A positive charged
(B) Doubly ionised helium nuclei
(C) A stream of neutron
(D) Helium atoms

Answer 1

Hint: Nucleus of alpha ray is very similar to the Helium-4 nucleus. Its mass is due to the presence of two protons and two neutrons tightly bound together with no electron. It is a radiation emitted from the decay of various radioactive substances.

Complete step-by-step solution:
Alpha particles are produced during standard radioactive decay of radioactive elements. These are emitted in the form of radiation, having an average kinetic energy of 5MeV and velocity \[5\% \] as compared to the speed of light. They are also produced in accelerators of high energy particles. They are highly ionised and have low penetration power. That is why, they generally stop by a few centimetres of air or nearby the skin or can be stopped by a sheet of paper.
Mass of an alpha particle is 4.00 amu, which is the mass of a doubly ionised helium atom. Thus, they are also known as doubly ionised helium atoms i.e., helium atoms with both the electrons removed.
Alpha decay can be written as:
\[_{92}^{238}U \to _{90}^{234}Th + _2^4He\]
Where, \[_2^4He\]is the alpha particle, denoted by Greek alphabet \[\alpha \].

Hence, the correct option is (B).

Note: Due to presence of protons in alpha particle nucleus, it always possesses a charge of +2 on it and so, it is positively charged. Therefore option (A) is also correct along with option (B).