chadwick experiment name

James Chadwick: The Man Behind the Neutron

Maya kuppermann may 15, 2018, submitted as coursework for ph241 , stanford university, winter 2018.

James Chadwick was born in Cheshire, England, on 20th October, 1891. He graduated from Manchester University in 1908 and went on to graduate from the Honours School of Physics in 1911. After graduation he spent two years working in Physical Laboratory in Manchester, where he worked on various radioactivity problems, gaining his M.Sc. degree in 1913. After being interned in the Zivilgefangenenlager, Ruhleben during World War I, Chadwick returned to England to continue his research. Chadwick continued to move up the ladder in the world of science when he was elected Fellow of Gonville and Caius College (1921-1935) and became Assistant Director of Research in the Cavendish Laboratory (1923). In 1927 he was elected a Fellow of the Royal Society. [1]

Discovery of the Neutron

In 1932, Chadwick made a fundamental discovery in the domain of nuclear science. Chadwick was fascinated by an experiment done by Frdric and Irne Joliot-Curie that studied the then-unidentified radiation from beryllium as it hit a paraffin wax target. The Curies found that this radiation knocked loose protons from hydrogen atoms in that target, and those protons recoiled with very high velocity. In 1932, Chadwick tried similar experiments himself and hypothesized that the radiation ejected by the beryllium was, in fact, a neutral particle with approximately the same mass as a proton. Fig. 1 depicts a schematic diagram of the experiment done by Chadwick, following on experiments done by the Curies. He later tried other targets including helium, nitrogen, and lithium, which led him to determine that the mass of the new particle was in fact just slightly greater than the mass of the proton. [1] This is reflected in the current understanding of the mass of a neutron as 1.008701 amu or 1.6750 × 10 -24 g and the mass of a proton as 1.007316 amu or 1.6727 × 10 -24 g. [2]

After only about two weeks of experimentation, Chadwick wrote a paper in which he proposed that the evidence favored the neutron rather than the gamma ray photons as the correct interpretation of the radiation. Only a few months later, in May 1932, Chadwick submitted a paper announcing the discovery of the Neutron. The existence of a neutron as a new fundamental particle was firmly established by 1934. Chadwick was awarded the Nobel Prize in 1935 for its discovery. [3]

Chadwick's discovery of the neutron was the final piece in understanding the atomic puzzle and sparked a revolution leading to the nuclear age and the creation of nuclear weapons. [4]

© Maya Kuppermann. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

[1] A. Brown, The Neutron and the Bomb: A Biography of Sir James Chadwick (Oxford University Press, 1997).

[2] D. W. Oxtoby and H. P. Gillis, Principles of Modern Chemistry, 5th Ed. (Brooks Cole, 2002).

[3] M. Oliphant, "The Beginning: Chadwick and the Neutron," Bull. Atom. Sci. 38 , 14 (1982).

[4] K. Fischer, A Brief History of Pulsed Neutron Generation ," Physics 241, Stanford University, Winter 2015.

Discovery of Neutron: Chadwick’s Experiment

Updated by Scienly
On September 16, 2024

In this chapter, we will understand the discovery of neutron discovered by James Chadwick in 1932. Up to 1932, it was considered that an atom is composed of only electrons and protons. Since electrons have negligible mass, scientists considered that the entire mass of the atom was due to the number of protons present in the nucleus.

Each proton has a mass equal to 1.676 * 10 -24 grams. This mass was taken as a basic unit of mass for measuring atomic and molecular masses.

However, Ernest Rutherford in 1920 found that, except for the hydrogen atom, the atomic masses of other atoms could not be explained in the terms of the numbers of electrons and protons only. For example, he observed that there were two protons inside the nucleus of a helium atom because the atomic number of helium is 2.

But, the actual mass of the helium atom was found to be twice the mass of two protons. In order to account for the remaining mass in the helium atoms, Rutherford in 1920 predicted that there must be the presence of two electrically neutral particles, each having the mass nearly equal to that of a proton inside the nucleus of an atom.

This prediction paved the way for the later discovery of the neutron by James Chadwick in 1932. Neutrons, as Rutherford suggested, are neutral particles with a mass nearly equal to that of protons. They exist along with protons in the nucleus, contributing to the overall mass of atoms.

Chadwick’s Experiment – Discovery of Neutron

Now it had predicted that the nucleus contains not only protons but also another type of particle named neutron. James Chadwick in 1932 discovered the third fundamental particles called neutrons inside the nuclei of atoms.

Discovery of Neutron by Chadwick's Experiment.

Sir Chadwick bombarded a thin foil of beryllium or boron with a stream of alpha particles. He observed that highly penetrating rays were produced, which were not affected by electric and magnetic fields. These rays, or say radiations, consisted of electrically neutral particles, which were called neutrons. The nuclear reaction is as follows:

4 Be 9 + 2 He 4 – – – – – – – – > 6 C 12 + 0 n 1

Here, n is neutron. 4 Be 9 represents beryllium atom, while 2 He 4 represents an alpha particle.

Important Characteristics of Neutrons

There are the following characteristics of neutrons. They are as:

Neutron is the third fundamental subatomic particle present in the nucleus of an atom.
This subatomic particle carries no charge or zero electric charge, meaning it is an electrically neutral particle.
The mass of the neutron is determined to be 1.675 x 10 -24 g, 1.675 x 10 -27 kg, or 1 amu, which is nearly equal to the mass of the proton or hydrogen atom.
The e / m value of a neutron is zero.

Note : Except for hydrogen atom ( 1 H 1 ), neutrons are present in all atoms of other elements along with the fundamental particles called electrons and protons.

Subatomic Particles

In this section, we have listed the important properties of the three principal fundamental particles of the atom, namely the electron, proton, and neutron in a table.

Structure of Atom

The atom consists of three most important fundamental subatomic particles called electrons, protons, and neutrons. The protons and neutrons are found in the central part, named the nucleus of an atom. Electrons revolve around the nucleus in an imaginary circular path called orbit.

Almost all the ordinary chemical properties of matter are examined in terms of atoms composed of electrons, protons and neutrons. Therefore, we will assume that atom contains only these three principal subatomic particles.

Other Subatomic Particles

In addition to electrons, protons and neutrons, many other subatomic particles such as mesons , positrons , neutrinos and antiprotons have been discovered. A great deal of recent research has discovered more subatomic particles, such as quarks , pions , and gluons , which play important roles in the deeper understanding of atomic structure. These discoveries have made the picture of the atom more complex, especially in fields like particle physics.

However, the three fundamental subatomic particles of the atom (electron, proton, and neutron) remain sufficient for most of the needs of chemistry. Chemists primarily focus on how atoms interact and bond with each other. This basic model still effectively explains chemical reactions and properties.

FAQs on Discovery of Neutron

1. what is a neutron.

A neutron is a subatomic particle found in the nucleus of an atom. It has no electric charge, meaning that it is an electrically neutral. Its mass is slightly heavier than the mass of a proton.

2. Who was known for the discovery of the neutron?

British physicist James Chadwick was known for the discovery of the neutron. He discovered it in 1932. He and Niels Henrik David Bohr were the students of Sir Ernest Rutherford. Chadwick was born on 20 Oct 1891 at the place of Bollington, Cheshire, England. He died at Cambridge, England.

3. What was awards given to James Chadwick for the discovery of neutron?

For the discovery of neutron, James Chadwick was awarded the Hughes Medal of the Royal Society in the year 1932 as well as the Nobel prize for physics in the year 1935.

4. What role do neutrons play in an atom?

Neutrons, along with protons, make up the nucleus of an atom. They contribute atomic mass as well as play a crucial role in the stability of the nucleus.

5. How is the mass of a neutron compared to a proton?

The mass of a neutron is nearly the same as that of a proton, but it is slightly heavier. Both have a mass approximate to 1 atomic mass unit (amu).

6. Do all atoms have neutrons?

Except for the hydrogen atom, all atoms of other elements have neutrons. Hydrogen atom contains only one proton and one electron.

7. What is the difference between a neutron and a proton?

The main difference between them is that neutrons have no electric charge, while protons carry a positive charge. Both have nearly similar masses and are located in the nucleus of an atom.

Drawbacks of bohr’s atomic model.