Question

The energy of thermal neutrons is nearly
(A) $0.25eV$
(B) $0.025eV$
(C) $200MeV$
(D) $0.025\;Joule$

Answer 1

It is necessary to understand what thermal neutrons are. Thermal neutrons are free neutrons that have energy that is corresponding to the average energy of the particles in the surroundings of the neutron.

Complete step by step answer
Thermal neutrons are a term used for neutrons detection temperature, which provides information about the free neutrons energy ratings. Neutrons can be present under the influence of temperature, hence the term temperature/thermal is used. The energy values of the free neutrons are in accordance with the Maxwell-Boltzmann distribution of energy. Hence, higher the temperature, higher the energy value of free neutrons.
Free neutrons are often associated with the decaying process, which releases neutrons from a chemically radioactive component under a set of conditions. The free neutrons are unstable and have a short lifetime. Neutron emission is possible in the beta decay process. Now, the thermal status of these free neutron releases are classified based on their temperature upon release.
Some of the classification include, thermal neutron, cold neutron, epithermal neutron, slow neutrons, and resonance neutrons etc., which are varied by energy range in the Maxwell-Boltzmann energy distribution graph. The thermal neutron is said to have an energy range of $0.025eV$ during its release via a decay process. The speed of these types of neutrons are comparatively slow and have a speed up to $2.19km/s$ .
Thus, option (B) is the right answer for the given question.

Note:
You can get a free neutron during beta minus decay process and gamma decay process. Now, free neutrons are highly unstable and due to its unstable nature, it is very dangerous and should be controlled properly to prevent exposure to radiation.