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Neutron – Discovery, Definition, Characteristics, Applications

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  • Last Updated : 03 Sep, 2021
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James Chadwick, an English physicist, discovered the neutron in 1932. Many researchers throughout the world were examining the particle’s properties and interactions just a few years after its discovery. When hit with neutrons, many elements undergo fission, a sort of nuclear process in which the nucleus of heavy material is split into two almost equal smaller fragments. Each fissioned nucleus emits extra free neutrons, as well as those bound to the fission pieces, throughout this reaction. 

Under the direction of scientist Enrico Fermi, a group of American researchers demonstrated in 1942 that enough free neutrons are created during the fission process to sustain a chain reaction. This breakthrough paved the way for the development of the atomic bomb. Following technological developments, nuclear energy was used to produce enormous amounts of electric power on a vast scale. The ability to manufacture huge quantities of radioactive isotopes useful for a number of purposes has been made possible by the absorption of neutrons by nuclei subjected to the high neutron intensities available in nuclear reactors. In addition, the neutron has emerged as a crucial instrument in pure research. 

Understanding the structure of matter requires knowledge of its properties and structure. Neutron-induced nuclear reactions provide crucial information on the atomic nucleus and the force that holds it together.

What is a Neutron?

Neutrons are subatomic particles that are one of the primary constituents of atomic nuclei within Electrons and Protons. Neutron, neutral subatomic particle that is a constituent of every atomic nucleus except ordinary hydrogen.

Neutrons and protons are together termed as nucleons since they behave in a very similar manner within the nuclei of atoms. The mass of a nucleon may be roughly approximated to at least one mass unit (often abbreviated to a.m.u.). The branch of science that deals with the study of the properties of neutrons and also the interactions of those subatomic particles with different matter and nonparticulate radiation is named atomic physics.

A neutron is present inside the nucleus of an atom, Hydrogen atom does not contain a nucleus. As protons and neutrons, both are present inside the nucleus, they are combinedly known as nucleons.

Discovery of Neutron

The existence of neutrons was noted with the help of the Rutherford Nuclear Model of Atom. there are a few points noted in the discovery of neutrons. (It also gives us remarkable information of the arrangement of the constituent particles)

  • In this experiment where most of the alpha particle passes unreflected.
  • some of them deviate through smaller angles and some with an angle greater than 180 degrees.
  • Thus it indicated the presence of a particle in the middle part of the atom i.e nucleus; it marked the presence of a mass particle and the neutron was discovered later in 1932 by James Chadwick.

Discovery of neutron

As electrons have negligible mass and this means the mass of an atom is only due to proton only but it would create problems in the model thus it was indicated the presence of some neutral particle with a proton that has equal mass to that of a proton must be present in the atom. Rutherford realized that the atomic mass of different species cannot be determined unless there is the presence of another particle thus, Rutherford in 1920 stated that there is a kind of neutral particle with a mass equal to the mass proton is present. James Chadwick, in 1932 during the study of the artificial transmutation of atoms, discovered a particle indicated by Rutherford in 1920. When a  fast-moving alpha particle is bombarded with a thin foil of beryllium and beryllium changes into carbon and emit a neutral particle of the same mass as the proton. This new fundamental particle was named neutron because of its neutral nature and The particle was also found in many other reactions.

Charge and Mass of Neutron

  • A neutron has no electric charge linked with it. Neutrons are neutrally charged subatomic particles as a result.
  • A neutron’s mass is approximately 1.008 atomic mass units. The mass of a neutron is approximately 1.674 × 10-27 kg when measured in kilogrammes.
  • Because neutrons do not have an electric charge, mass spectrometry cannot be used to estimate their mass directly.
  • By subtracting the mass of a proton from the mass of a deuterium nucleus (deuterium is a hydrogen isotope with one proton, one electron, and one neutron in its atomic structure), the mass of the neutron may be computed. 
    Because the mass of the electron is so little in comparison to the proton and neutron, the mass of the neutron may be estimated by subtracting the proton’s mass from the mass of the deuterium atom.

Characteristics of Neutron

  1. The magnetic moment of neutrons is not equal to zero, despite the fact that they are considered neutral particles. Despite the fact that electric fields have no effect on neutrons, magnetic fields have an influence on these subatomic particles. 
  2. Neutrons have a lot of penetration, although not as much as cosmic rays. They haven’t been able to ionise a gas yet. 
  3. The approximate mass of an atom in a.m.u is equal to the entire sum of the neutron and proton present in an atom (atomic mass unit). Its mass is calculated by subtracting the proton’s mass from the atomic mass.
  4. The magnetic field affects these subatomic particles, whereas an electric field has no influence on them. Its magnetic field is linked to the substructure of quarks and the charge’s internal distribution.
  5. Neutron is made up of three quarks, which are the fundamental particles that give neutron its magnetic properties.

The table below shows the important other characteristics related to Neutrons as:





Relative mass 

Equal to H atom         

Actual mass

1.6 × 10-27 kg

The representation of atoms in terms of their atomic mass and atomic number can be done as:

Applications of Neutrons

  1. Neutrons are highly ionised and penetrating particles that can be employed in boron capture therapy and medical applications. However, when absorbed, they activate the substance and make it radioactive.
  2. It is significant in nuclear reactions (understanding of the neutron’s behaviour, in particular, has aided in the creation of nuclear weapons and reactors).
  3. The neutron activation analysis (NAA) method is used to study a simple sample of materials in a nuclear reactor, and the neutron emitter is used to locate light nuclei in the environment.
  4. It is utilised in medical neutron tomography, but it has unfavourable side effects that leave the afflicted area radioactive, hence it is not frequently employed. The neutron lens was being developed at the time.
  5. It’s utilised in boron capture treatment, which uses a tiny neutron beam to treat cancer. The energy delivered to malignant regions by neutron radiation is orders of magnitude larger than that delivered by gamma radiation.
  6. Uranium-235 and plutonium-239 are virtually always utilised in nuclear fission reactors due to nucleus absorption.
  7. Warm, hot, and cold neutron applications are employed in nuclear scattering facilities where radiation is utilised to condensate matter in X-ray studies.

Sample Problems

Problem 1: Define the term Nucleon.


Protons and neutrons both are present inside the nucleus, they are combinedly known as nucleons.

Problem 2: Calculate the number of neutrons in the sodium atom.


The atomic number of sodium (Na) is 11.

The mass number of sodium is 23

Therefore, using the formula:

No. of neutrons =  Atomic mass − atomic number

                          = 23-11

                          = 12

Problem 3: What is the atomic mass of Nitrogen? 


Let the atomic mass of Nitrogen be a.

Then by the formula:

No. of neutrons =  Atomic mass − atomic number

                       7 =  a – 7

                       a = 14

Hence, the atomic mass of nitrogen is 14.

Problem 4: If atoms contain charged particles, why do they not have a charge?


They contain the same number of protons as electrons, which make them neutral.

Problem 5: How many neutrons do carbon have?


The atomic number of Carbon (C) is 6.

The mass number of Carbon is 12.

Then by the formula:

No. of neutrons =  Atomic mass − atomic number

                          = 12 – 6

                          = 6

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