What are Neutrons?

It is a neutral subatomic particle and is present in the nucleus of the atom. They are usually denoted by N and net charge associated with it is zero. It is present in the nucleus and proton and neutron together are called nucleons. Total number of protons and neutrons gives the atomic mass of an element. 

It also stated that neutrons present in the nucleus differ in isotopes as isotopes have the same atomic number but different atomic mass.

For the stability of the atom, the neutron is a must but there is an exception in protium-1.

Nuclear physics is the branch of science in which the study of neutron and other electromagnetic induction is done. Neutrons and protons are together and have the same physical quantity in the nucleons.

Physical properties and chemical properties of an atom is decided by the number of proton and neutron present in the atom - 

  • Neutrons are slightly heavier than protons and balance the electron and hold the electron in the atom.

  • The number of the proton is equal to the number of neutrons in the nucleus or number of a nucleus is greater than one from the number of protons

  • If the number of neutrons gets more than the number of proton in excess in the nucleus then the particle becomes radioactive and breaks up to release alpha or beta rays

  • Neutron has penetrating power greater than gamma rays 

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Discovery of Neutrons

Its existence was noted by the Rutherford Nuclear Model of Atom (Alpha particle scattering experiment. It also gives us remarkable information of the arrangement of the constituent particles) in this experiment where most of the alpha particle passes undeviated, some through smaller angles and some with an angle larger than 180 degrees. Thus it indicated the presence of a particle in the middle part of the atom (nucleus); it marked the presence of a mass particle and the neutron was discovered later in 1932 by James Chadwick.

As electrons have negligible mass and thus the mass of an atom is due to proton only it would create problems in the model thus it was indicated the presence of the neutral particle with an equal mass of the proton must be present in the atom.

Rutherford realized that atomic mass of different elements cannot be explained unless there is the presence of another particle thus,

Rutherford in 1920 stated that a kind of neutral particle with a mass equal to the mass proton

In 1932 during the study of the artificial transmutation of atoms, James Chadwick discovered a particle indicated by Rutherford in 1920. When a thin foil of beryllium is bombarded with fast-moving alpha particles and beryllium changes into carbon and emits a neutral particle of the same mass as the proton.

The particle was also found in many other reactions and this new fundamental particle was named neutrons because of its neutral nature.

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Properties of Neutrons

  • There are electrically neutral particles. The mass of the neutron is 1.675 x \[10^{-24}\] which is slightly greater than the mass of a proton.

  • The weight cannot be analytically measured using this technique as they have no electric charge.

  • They are highly penetrating but not much when compared to cosmic rays.

  • They are unable to ionize a gas. Therefore, they do not produce a track in Wilson's cloud chamber.

  • The total sum of the neutron and proton present in an atom and it accounts for the approximate mass of an atom in a.m.u(atomic mass unit).

  • That the neutron is not an elementary particle, as it has a magnetic field.

  • These subatomic particles are affected by the magnetic field but have no effect of an electric field

  • Its magnetic field can be related with the quarks substructure and internal distribution of the charge

  • Its mass can be measured by subtracting the mass of the proton from the atomic mass 

  • Neutron is composed of three quarks and these elementary particles gave neutron its magnetic particle( quarks model was discovered in the 1960s)

  • Thus the magnetic field of the neutron ( neutral particle) is not zero 

Application of Neutrons

  • Neutrons are highly ionized and penetrating particle and can be used in boron capture therapy and medical uses  but it actives the matter when absorbed and leaves it to be radioactive

  • It plays an important role in nuclear reaction( in particular knowledge and behaviour of the neutron has helped in the development of the nuclear weapon and nuclear reactor 

  • In the development of the neutron lenses

  • Neutron is used in the method of NAA( neutron activation analysis) it is used to analyze a simple sample of materials in a nuclear reactor and neutron emitter is used in finding light nuclei in the environment 

  • It is used in neutron tomography that is used in medical uses but it can have unfortunate side effects that leave the affected area radioactive thus it is not used widely

  • It is used in boron capture therapy in which a small beam of neutron is used to cure cancer

  • Neutron radiation can deliver energy to cancerous regions orders of magnitude greater than gamma-ray.

  • The uranium-235 and plutonium-239 are used in the nuclear fission reactor by almost every time by absorption of the nucleus

  • In nuclear scattering facilities where the radiation is used to condensed matter in research using X rays the warm, hot, and cold neutron application is used.

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FAQ (Frequently Asked Questions)

1. How to find the number of Neutrons in an atom of an element?

The first step is to find the atomic number and atomic weight of the element using the Periodic Table. 

Ideally, the atomic weight is the measurement of the total number of particles present in the atom’s nucleus. But, the mass number denotes the number of particles in an atom’s nucleus. To find the mass number, the atomic weight is rounded off to the nearest whole number.

 Mass number= Number of Protons + Number of Neutrons

Number of Neutrons= Mass number- Number of Protons

For every element,

Number of Protons= Atomic number


Number of Neutrons= Mass number- Atomic Number