Discovery of Neutrons: Model, Discovery, and Experiment
What are Neutrons?
Neutrons are referred to as subatomic particles that are one of the main constituents of atomic nuclei.
Neutrons are generally denoted by the symbol n or no.
Neutrons do not have any net electric charge linked to them. They do, though, have a mass that is slightly greater in magnitude as compared to a proton.
Neutrons and protons are together referred to as nucleons since they usually behave similarly.
The mass of a neutron can be nearly approximated to one atomic mass unit or amu.
Nuclear physics is the branch of science that deals with the study of the properties of neutrons and the relations of these subatomic particles with other substances.
The complete nuclear and chemical properties of an element are generally determined by the total number of protons present in its atomic nucleus (atomic number) and the total number of neutrons present in its respective atomic nucleus or it is also referred to as the neutron number.
The sum of the total number of protons present in a nucleus of a given atom and the total number of neutrons in the atomic nucleus gives the mass number of that atomic nucleus.
The protons and the neutrons present inside the nucleus of an atom are bound together through nuclear forces.
For the stability of atomic nuclei, the existence of neutrons is essential. The only exception to the above-mentioned rule is the nucleus of protium or hydrogen-1.
Discovery of Neutrons
Neutrons were initially hypothesized by the New Zealand-born British physicist named Ernest Rutherford in the year 1920.
But, the discovery of neutrons is credited to the British physicist named James Chadwick in the year 1932. He was also awarded the Nobel prize in physics for this finding in the year 1935.
During the year the 1920s, the common hypothesis on the nature of atoms was that they comprised of protons and also nuclear particles called electrons. Though, this failed to obey the Heisenberg uncertainty principle in quantum mechanics.
Consequently, in the year 1931, two German nuclear physicists noticed that when the alpha particle radiation that is emitted by polonium is made incident on beryllium, lithium, or boron, it then resulted in the production of a strangely penetrating form of radiation.
Further, it was confirmed by James Chadwick through a series of trials that these particles that constituted the strangely penetrating radiation were called neutrons.
James Chadwick fired alpha radiation at the beryllium sheet from a polonium source which led to the creation of uncharged, penetrating radiation.
This uncharged, penetrating radiation was thus made incident on paraffin wax, a hydrocarbon having a fairly high hydrogen content.
The protons that were ejected from the paraffin wax were noticed with the help of an ionization chamber.
This range of the liberated protons was measured and the contact between this uncharged radiation and the atoms of numerous gases was studied by James Chadwick.
He, at last, concluded that the oddly penetrating radiation thus comprised of uncharged particles having (roughly) the same mass as that of a proton.
These particles were later called ‘neutrons’. The total number of protons and neutrons present in the nucleus of an atom indicates the mass number of that particular atom.
Mathematically,
Mass Number = (Number of Protons) + (Number of Neutrons)
Charge and Mass of Neutrons
The electric charge thus associated with a neutron is equal to 0. Hence, neutrons are neutrally charged subatomic particles.
The mass of a neutron is nearly equal to 1.008 atomic mass units.
Subsequently, the subatomic particles named as neutrons lack an electric charge, so their mass cannot be directly determined through the analytical technique of mass spectrometry.
Properties of Neutrons
Even though the neutron is considered to be a neutral particle, the magnetic moment of these particles (neutrons) is not equal to zero.
Even though electric fields have majorly no effect on neutrons, these subatomic particles are still affected by the presence of magnetic fields.
The magnetic moment related to the neutron can be considered as a sign of its quark organization or structure and the distribution of its internal charges.
The mass of neutrons is always equal to that of protons present inside the nucleus of an atom (Mass of the neutron is 1.675 x 10-24g).
The density of neutron is equal to 1.5 x 1014 g/cc.
Applications of Neutrons
In various nuclear reactions, the subatomic particle named as the neutron plays an important role.
Information about neutrons and their activity has been especially vital in the past for the expansion of many nuclear reactors and numerous nuclear weapons.
The nuclear fissioning of some elements such as uranium-235 and plutonium-239 is almost always triggered by their neutron absorption.
Warm, cold, and hot neutron radiation plays a very significant application in neutron scattering facilities where the radiation is often used in condensed matter research with the support of X-rays.
One of the most important applications of neutrons includes the excitation of delayed and triggered gamma rays from material components. This also forms the basis for the study of neutron activation analysis, frequently abbreviated to NAA.
NAA is most commonly used to examine the small samples of materials present inside a nuclear reactor.
Neutrons Citations
- Neutrons from high-energy x-ray medical accelerators: an estimate of risk to the radiotherapy patient. Med Phys . May-Jun 1984;11(3):231-41.Â
- Neutrons in active proton therapy: Parameterization of dose and dose equivalent. Z Med Phys . 2017 Jun;27(2):113-123.
- The potential and limitations of neutrons, electrons and X-rays for atomic resolution microscopy of unstained biological molecules. Q Rev Biophys . 1995 May;28(2):171-93.
- Neutrons are forever! Historical perspectives. Int J Radiat Biol . 2019 Jul;95(7):957-984.
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