james chadwick experiment atomic theory

• History & Society
• Science & Tech
• Biographies
• Animals & Nature
• Geography & Travel
• Arts & Culture
• Games & Quizzes
• On This Day
• One Good Fact
• New Articles
• Lifestyles & Social Issues
• Philosophy & Religion
• Politics, Law & Government
• World History
• Health & Medicine
• Browse Biographies
• Birds, Reptiles & Other Vertebrates
• Bugs, Mollusks & Other Invertebrates
• Environment
• Fossils & Geologic Time
• Entertainment & Pop Culture
• Sports & Recreation
• Visual Arts
• Demystified
• Image Galleries
• Infographics
• Top Questions
• Britannica Kids
• Saving Earth
• Space Next 50
• Student Center

• Is mathematics a physical science?
• Why does physics work in SI units?

James Chadwick

Our editors will review what you’ve submitted and determine whether to revise the article.

• Famous Scientists - Biography of James Chadwick
• The Nobel Prize - James Chadwick
• Atomic Heritage Foundation - Biography of James Chadwick
• James Chadwick - Student Encyclopedia (Ages 11 and up)

James Chadwick (born October 20, 1891, Manchester , England—died July 24, 1974, Cambridge , Cambridgeshire) was an English physicist who received the Nobel Prize for Physics in 1935 for the discovery of the neutron .

Chadwick was educated at the University of Manchester , where he worked under Ernest Rutherford and earned a master’s degree in 1913. He then studied under Hans Geiger at the Technische Hochschule, Berlin. When World War I broke out, he was imprisoned in a camp for civilians at Ruhleben. He spent the entire war there but nevertheless was able to accomplish some scientific work.

After the war ended, Chadwick returned to England to study under Rutherford at the University of Cambridge . He received a doctorate in 1921, and in 1923 he was appointed assistant director of research at the Cavendish Laboratory , Cambridge. There he and Rutherford studied the transmutation of elements by bombarding them with alpha particles and investigated the nature of the atomic nucleus, identifying the proton , the nucleus of the hydrogen atom , as a constituent of the nuclei of other atoms.

After the discovery of the proton, physicists had surmised that there were likely additional particles in the atomic nucleus. Elements heavier than hydrogen had a greater atomic mass than their atomic number (the number of protons). Theories for the additional particles included additional protons whose charge was shielded by electrons in the nucleus or an unknown neutral particle. In 1932 French physicists Frédéric and Irène Joliot-Curie bombarded beryllium with alpha particles and observed that an unknown radiation was released that in turn ejected protons from the nuclei of various substances. The Joliot-Curies hypothesized that this radiation was gamma-rays . Chadwick was convinced that alpha particles did not have enough energy to produce such powerful gamma-rays. He performed the beryllium bombardment experiments himself and interpreted that radiation as being composed of particles of mass approximately equal to that of the proton but without electrical charge—neutrons. That discovery provided a new tool for inducing atomic disintegration , since neutrons, being electrically uncharged, could penetrate undeflected into the atomic nucleus and led to a new model of the atomic nucleus being composed of protons and neutrons.

In 1935 Chadwick was appointed to a chair in physics at the University of Liverpool. In 1940 he was part of the MAUD Committee , which was to assess the feasibility of the atomic bomb . The committee concluded in 1941 that the 1940 memorandum of Otto Frisch and Rudolf Peierls was correct and that a critical mass of only about 10 kilograms (22 pounds) of uranium -235 was needed. Chadwick later said he realized “that a nuclear bomb was not only possible, it was inevitable. I had then to take sleeping pills. It was the only remedy.” The MAUD Committee’s results were influential in giving an impetus to the American atomic bomb program. He became head of the British delegation to the Manhattan Project in Los Alamos , New Mexico , U.S., in 1943 and formed a close rapport with its head, Gen. Leslie Groves .

Chadwick was knighted in 1945. He returned to Britain in 1946 and became the British scientific adviser to the United Nations Atomic Energy Commission . He became master of Gonville and Caius College, Cambridge, in 1946, and he received the Copley Medal of the Royal Society in 1950. He retired in 1958.

Sciencing_Icons_Science SCIENCE

Sciencing_icons_biology biology, sciencing_icons_cells cells, sciencing_icons_molecular molecular, sciencing_icons_microorganisms microorganisms, sciencing_icons_genetics genetics, sciencing_icons_human body human body, sciencing_icons_ecology ecology, sciencing_icons_chemistry chemistry, sciencing_icons_atomic & molecular structure atomic & molecular structure, sciencing_icons_bonds bonds, sciencing_icons_reactions reactions, sciencing_icons_stoichiometry stoichiometry, sciencing_icons_solutions solutions, sciencing_icons_acids & bases acids & bases, sciencing_icons_thermodynamics thermodynamics, sciencing_icons_organic chemistry organic chemistry, sciencing_icons_physics physics, sciencing_icons_fundamentals-physics fundamentals, sciencing_icons_electronics electronics, sciencing_icons_waves waves, sciencing_icons_energy energy, sciencing_icons_fluid fluid, sciencing_icons_astronomy astronomy, sciencing_icons_geology geology, sciencing_icons_fundamentals-geology fundamentals, sciencing_icons_minerals & rocks minerals & rocks, sciencing_icons_earth scructure earth structure, sciencing_icons_fossils fossils, sciencing_icons_natural disasters natural disasters, sciencing_icons_nature nature, sciencing_icons_ecosystems ecosystems, sciencing_icons_environment environment, sciencing_icons_insects insects, sciencing_icons_plants & mushrooms plants & mushrooms, sciencing_icons_animals animals, sciencing_icons_math math, sciencing_icons_arithmetic arithmetic, sciencing_icons_addition & subtraction addition & subtraction, sciencing_icons_multiplication & division multiplication & division, sciencing_icons_decimals decimals, sciencing_icons_fractions fractions, sciencing_icons_conversions conversions, sciencing_icons_algebra algebra, sciencing_icons_working with units working with units, sciencing_icons_equations & expressions equations & expressions, sciencing_icons_ratios & proportions ratios & proportions, sciencing_icons_inequalities inequalities, sciencing_icons_exponents & logarithms exponents & logarithms, sciencing_icons_factorization factorization, sciencing_icons_functions functions, sciencing_icons_linear equations linear equations, sciencing_icons_graphs graphs, sciencing_icons_quadratics quadratics, sciencing_icons_polynomials polynomials, sciencing_icons_geometry geometry, sciencing_icons_fundamentals-geometry fundamentals, sciencing_icons_cartesian cartesian, sciencing_icons_circles circles, sciencing_icons_solids solids, sciencing_icons_trigonometry trigonometry, sciencing_icons_probability-statistics probability & statistics, sciencing_icons_mean-median-mode mean/median/mode, sciencing_icons_independent-dependent variables independent/dependent variables, sciencing_icons_deviation deviation, sciencing_icons_correlation correlation, sciencing_icons_sampling sampling, sciencing_icons_distributions distributions, sciencing_icons_probability probability, sciencing_icons_calculus calculus, sciencing_icons_differentiation-integration differentiation/integration, sciencing_icons_application application, sciencing_icons_projects projects, sciencing_icons_news news.

• Share Tweet Email Print
• Home ⋅
• Science ⋅
• Chemistry ⋅
• Atomic & Molecular Structure

James Chadwick Atomic Theory

Five Types of Atomic Models

Scientists today envision atoms as being composed of tiny, heavy, positively charged nuclei surrounded by clouds of extremely lightweight, negatively charged electrons. This model dates back to the 1920s, but it has its origin in ancient Greece. The philosopher Democritus proposed the existence of atoms around 400 B.C. No one really took up the idea with any fervor until English physicist John Dalton introduced his atomic theory in the early 1800s. Dalton's model was incomplete, but it persisted basically unchanged throughout most of the 19th century.

A flurry of research into the atomic model occurred at the end of the 19th and well into the 20th century, culminating in the Schrodinger model of the atom, which is known as the cloud model. Soon after physicist Erwin Schrodinger introduced it in 1926, James Chadwick – another English physicist – added a crucial piece to the picture. Chadwick is responsible for discovering the existence of the neutron, the neutral particle that shares the nucleus with the positively charged proton.

Chadwick's discovery forced a revision of the cloud model, and scientists sometimes refer to the revised version as the James Chadwick atomic model. The discovery earned Chadwick the 1935 Nobel Prize in physics, and it made possible the development of the atomic bomb. Chadwick participated in the super-secret Manhattan project, which culminated in the deployment of nuclear bombs on Hiroshima and Nagasaki. The bomb contributed to the surrender of Japan (many historians believe Japan would have surrendered anyway) and the end of World War II. Chadwick died in 1974.

How Did Chadwick Discover the Neutron?

J.J. Thompson discovered the electron using cathode ray tubes in the 1890s, and British physicist Ernest Rutherford, the so-called father of nuclear physics, discovered the proton in 1919. Rutherford speculated that electrons and protons could combine to produce a neutral particle with roughly the same mass as a proton, and scientists believed that such a particle existed for several reasons. For example, it was known that the helium nucleus has an atomic number of 2 but a mass number of 4, which meant that it contained some kind of neutral mystery mass. No one had ever observed a neutron or proven that it existed, though.

Chadwick was particularly interested in an experiment conducted by Frédéric and Irène Joliot-Curie, who had bombarded a sample of beryllium with alpha radiation. They noted that the bombardment produced an unknown radiation, and when they allowed it to strike a sample of paraffin wax, they observed high-energy protons being flung from the material.

Unsatisfied with the explanation that the radiation was made of high-energy photons, Chadwick duplicated the experiment and concluded that the radiation had to be composed of heavy particles with no charge. By bombarding other materials, including helium, nitrogen and lithium, Chadwick was able to determine that the mass of each particle was a little more than that of a proton.

Chadwick published his paper “The Existence of a Neutron” in May 1932. By 1934, other researchers had determined that the neutron was in fact an elementary particle and not a combination of protons and electrons.

The Importance of the Chadwick Atomic Theory

The modern conception of the atom retains most of the characteristics of the planetary model established by Rutherford, but with important modifications introduced by Chadwick and Danish physicist Neils Bohr.

It was Bohr who incorporated the concept of discrete orbits to which electrons were confined. He based this on quantum principles that were new at the time but which have become established as scientific realities. According to the Bohr model, electrons occupy discrete orbits, and when they move to another orbit, they emit or absorb not in continuous amounts, but in bundles of energy, called quanta.

Incorporating the work of Bohr and Chadwick, the modern picture of the atom looks like this: Most of the atom is empty space. Negatively charged electrons orbit a small but heavy nucleus composed of protons and neutrons. Because quantum theory, which is based on the uncertainty principle, regards electrons as both waves and particles, they can't be definitively located. You can only talk about the likelihood of an electron being in a particular position, so the electrons form a probability cloud around the nucleus.

The number of neutrons in the nucleus is usually the same as the number of protons, but it can be different. Atoms of an element that have a different number of neutrons are called isotopes of that element. Most elements have one or more isotope, and some have several. Tin, for example, has 10 stable isotopes and at least twice as many unstable ones, giving it an average atomic mass significantly different than twice its atomic number. If James Chadwick's discovery of the neutron had never occurred, it would be impossible to explain the existence of isotopes.

James Chadwick's Contribution to the Atomic Bomb

Chadwick's discovery of the neutron led directly to the development of the atomic bomb. Because neutrons have no charge, they can penetrate more deeply into the nuclei of target atoms than protons. Neutron bombardment of atomic nuclei became an important method to gain information about the characteristics of nuclei.

It didn't take scientists long to discover, however, that bombarding super-heavy Uranium-235 with neutrons was a way to break the nuclei apart and release an enormous amount of energy. The fission of uranium produces more high-energy neutrons that break apart other uranium atoms, and the result is an uncontrollable chain reaction. Once this was known, it was only a matter of developing a way to initiate the fission reaction on demand in a deliverable casing. Fat Man and Little Boy, the bombs that destroyed Hiroshima and Nagasaki, were the result of the secret war effort known as the Manhattan Project that was conducted to do just that.

Neutrons, Radioactivity and Beyond

The Chadwick Atomic Theory also makes it possible to understand radioactivity. Some naturally occurring minerals – as well as manmade ones – spontaneously emit radiation, and the reason has to do with the relative number of protons and neutrons in the nucleus. A nucleus is most stable when it has an equal number, and it becomes unstable when it has more of one than another. In an effort to regain stability, an unstable nucleus throws off energy in the form of alpha, beta or gamma radiation. Alpha radiation is composed of heavy particles, each consisting of two protons and two neutrons. Beta radiation consists of electrons and gamma radiation of photons.

As part of the study of nuclei and radioactivity, scientists have further dissected protons and neutrons to find that they are themselves composed of smaller particles called quarks. The force that holds protons and neutrons together in the nucleus is called the strong force, and the one that holds quarks together is known as the color force. The strong force is a byproduct of the color force, which itself depends on the exchange of gluons, which are yet another type of elementary particle.

The understanding made possible by the James Chadwick atomic model has brought the world into the nuclear age, but the door to a far more mysterious and intricate world is wide open. For example, scientists may one day prove that the entire universe, including atomic nuclei and the quarks from which they are made, is composed of infinitesimal strings of vibrating energy. Whatever they discover, they'll do it standing on the shoulders of pioneers like Chadwick.

Related Articles

Who discovered the particle theory, what does e=mc squared stand for, cern plans to search for mysterious fifth force particle, what are the 4 atomic models, what contributions did j.j. thomson make to the atom, what are the different kinds of models of atoms, about rutherford's gold foil experiment, list of the atomic theories, uses for hydrogen-3, which nuclear decay emission consists of energy only, what are the properties of protons, what is an isotope, who discovered iodine 131, different kinds of atoms, what is the difference between quarks & leptons.

• American Physical Society: This Month in Physics History
• Wired: Feb. 27, 1932: Neutron Discovered; A-Bomb on the Way
• Science ABC: Why Are Certain Elements Radioactive?
• Georgia State University: HyperPhysics: Color Force

About the Author

Chris Deziel holds a Bachelor's degree in physics and a Master's degree in Humanities, He has taught science, math and English at the university level, both in his native Canada and in Japan. He began writing online in 2010, offering information in scientific, cultural and practical topics. His writing covers science, math and home improvement and design, as well as religion and the oriental healing arts.

Find Your Next Great Science Fair Project! GO

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.

• Skip to primary navigation
• Skip to main content
• Skip to footer

Science Struck

James Chadwick’s Atomic Theory and Its Lasting Impact Explained

Today, the concept of neutron and its function is common knowledge. Its existence was first hypothesized by Rutherford in 1920, and later proved by James Chadwick in 1932. This ScienceStruck post explains how the discovery came about and the revolutionary impact it had on the understanding of the atomic structure.

Like it? Share it!

Missed Opportunity!

In 1932, James Chadwick’s experiment, which led to the discovery of neutrons, was inspired by the work of Irène and Frédéric Joliot-Curie. Had they interpreted their findings accurately, they would have been the first to discover neutrons!

Sir James Chadwick (20 October 1891 – 24 July 1974) was an English physicist, most noted for his discovery of neutrons in 1932. He received a Nobel Prize in the field of physics in 1935 for this significant discovery. In his lifetime, he worked closely with outstanding scientists like Ernest Rutherford and Johannes “Hans” Wilhelm Geiger, both of whom have made various substantial and vital contributions to the field of radiation physics.

With the accidental discovery of radiation and radioactive materials in 1896 by Henri Becquerel, a new path emerged in the study of materials and their compositions. Experimentation led scientists to discover that a radioactive substance when subjected to a magnetic field, emits three types of energy rays (radiations). These rays were identified and named as alpha (α), beta (β), and gamma (γ) rays by Rutherford, based on their charge and mass. Further experiments conducted by Rutherford in collaboration with Ernest Marsden and Hans Geiger, led them to the discovery of the atomic nucleus in 1911. This discovery was instrumental in realizing that the atom was not a solid spherical structure.

Rutherford’s Atomic Model

Based on his findings about the atomic nucleus, from his famous gold-foil experiment, Rutherford put forth an atomic model that postulated:

◈ The atom is a hollow structure with its mass and positive charge concentrated into a tiny and dense core at the center, and the negatively charged lighter electrons orbiting the core like the planetary structure. Hence, this model is also called the planetary model.

◈ The electrons do not affect the pattern and trajectory of alpha particles.

◈ The atomic mass correlates with the charge of the atomic core or the atomic nucleus.

This model, however, had a very obvious limitation. Since the electron was a constantly accelerating particle of a negative charge, it would be attracted to the positive charge of the nucleus, thus causing the atom to become unstable and implode. To overcome this, in 1921, Rutherford with the help of Niels Bohr put forth a theory, hypothesizing the existence of a neutral-charged particle that had the same mass of a proton. The particle would be a composite of an electron and a proton and would be called a “neutron”. This theory, however, was not readily accepted by the scientific community due to lack of proof.

James Chadwick’s Contribution to the Atomic Theory

In 1930, Walther Bothe and Herbert Becker conducted experiments involving bombarding the element Beryllium with alpha particles emitted from radioactive polonium. They observed that the bombardment led to the emission of a neutral radiation from the Polonium, which was highly penetrative. They mistakenly believed this radiation to be a high energy form of gamma radiations. Hence, when Irène and Frédéric Joliot-Curie performed similar experiments in 1932, involving the emission of photons from paraffin and other such hydrogen-containing compounds when bombarded with this neutral radiation, they too believed that the radiation was a high-energy gamma radiation, and published results to that effect.

However, when Chadwick read the paper, he realized that a photon could not possibly be dislodged by a mere alpha particle. He, henceforth, conducted similar experiments of his own utilizing a linear amplifier, a refined polonium source, and an ionization chamber. He treated a number of substances and elements to this radiation and measured the recoil atom’s energy. He finally concluded that the radiation was, in fact, composed of neutral particles that had the same mass as protons. He called these neutral particles as neutrons. A paper to this effect was published by him in 1932, and shortly thereafter, other papers replicating the find were published by scientists like Norman Feather and Philip Dee.

Modified Atomic Theory

The existence and discovery of neutrons revolutionized the understanding of the atomic structure. It proved the validity of Rutherford’s atomic model and explained its stability. The postulates added to the atomic theory were:

◈ The nucleus of an atom consists of subatomic particles called nucleons.

◈ These nucleons are of two types: protons and neutrons.

◈ The neutrons are neutrally charged particles with the mass equal to that of a proton.

◈ A neutron is composed of an electron and proton couple.

◈ The collective mass of the protons and neutrons provides the atomic mass of an element.

German physicist Werner Heisenberg later, through his own experiments, proved that the neutrons were, in fact, a new particle and not a electron-proton composite.

This theory along with the discovery of neutrons was later instrumental in the invention of the atomic bomb. The atomic theory was later improved on by Niels Bohr to account for emission and absorption energy spectra observed in atoms, and a new model called the Niels Bohr model was hypothesized. This model is the presently accepted model to explain the atomic structure.

Get Updates Right to Your Inbox

Privacy overview.

May 1932: Chadwick Reports the Discovery of the Neutron

By 1920, physicists knew that most of the mass of the atom was located in a nucleus at its center, and that this central core contained protons. In May 1932 James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron.

Chadwick was born in1891 in Manchester, England. He was a shy child from a working class family, but his talents caught his teachers’ attention, and he was sent to study physics at the University of Manchester, where he worked with Ernest Rutherford on various radioactivity studies.

In 1914, Chadwick decided to travel to Germany to study with Hans Geiger. Unfortunately, not long after he arrived, WWI broke out and Chadwick ended up spending the next four years in a prison camp there. This did not entirely stop his scientific studies. To keep from being bored, he and some fellow prisoners formed a science club, lectured to each other, and managed to convince the guards to let them set up a small lab. Though many chemicals were hard to get hold of, Chadwick even found a type of radioactive toothpaste that was on the market in Germany at the time, and managed to persuade the guards to supply him with it. Using some tin foil and wood he built an electroscope and did some simple experiments.

After the war, Chadwick returned to England, where he finished his PhD in Cambridge in 1921 with Rutherford, who was then Director of Cambridge University’s Cavendish laboratory. Chadwick was able to continue to work on radioactivity, now with more sophisticated apparatus than tin foil and toothpaste. In 1923, Chadwick was appointed assistant director of Cavendish Laboratory.

Photo: AIP Emilio Segre Visual Archives

James Chadwick

Rutherford had discovered the atomic nucleus in 1911, and had observed the proton in 1919. However, it seemed there must be something in the nucleus in addition to protons. For instance, helium was known to have an atomic number of 2 but a mass number of 4. Some scientists thought there were additional protons in the nucleus, along with an equal number of electrons to cancel out the additional charge. In 1920, Rutherford proposed that an electron and a proton could actually combine to form a new, neutral particle, but there was no real evidence for this, and the proposed neutral particle would be difficult to detect.

Chadwick went on to work on other projects, but kept thinking about the problem. Around 1930, several researchers, including German physicist Walter Bothe and his student Becker had begun bombarding beryllium with alpha particles from a polonium source and studying the radiation emitted by the beryllium as a result. Some scientists thought this highly penetrating radiation emitted by the beryllium consisted of high energy photons. Chadwick had noticed some odd features of this radiation, and began to think it might instead consist of neutral particles such as those Rutherford had proposed.

One experiment in particular caught his attention: Frédéric and Irène Joliot-Curie had studied the then-unidentified radiation from beryllium as it hit a paraffin wax target. They found that this radiation knocked loose protons from hydrogen atoms in that target, and those protons recoiled with very high velocity.

Joliot-Curie believed the radiation hitting the paraffin target must be high energy gamma photons, but Chadwick thought that explanation didn’t fit. Photons, having no mass, wouldn’t knock loose particles as heavy as protons from the target, he reasoned. In 1932, he tried similar experiments himself, and became convinced that the radiation ejected by the beryllium was in fact a neutral particle about the mass of a proton. He also tried other targets in addition to the paraffin wax, including helium, nitrogen, and lithium, which helped him determine that the mass of the new particle was just slightly more than the mass of the proton.

Chadwick also noted that because the neutrons had no charge, they penetrated much further into a target than protons would.

In February 1932, after experimenting for only about two weeks, Chadwick published a paper titled “The Possible Existence of a Neutron,” in which he proposed that the evidence favored the neutron rather than the gamma ray photons as the correct interpretation of the mysterious radiation. Then a few months later, in May 1932, Chadwick submitted the more definite paper titled “The Existence of a Neutron.”

By 1934 it had been established that the newly discovered neutron was in fact a new fundamental particle, not a proton and an electron bound together as Rutherford had originally suggested.

The discovery of neutron quickly changed scientists’ view of the atom, and Chadwick was awarded the Nobel Prize in 1935 for the discovery. Scientists soon realized that the newly discovered neutron, as an uncharged but fairly massive particle, could be used to probe other nuclei. It didn’t take long for scientists to find that hitting uranium with neutrons resulted in the fission of the uranium nucleus and the release of incredible amounts of energy, making possible nuclear weapons. Chadwick, whose discovery of the neutron had paved the way for the atomic bomb, worked on the Manhattan Project during WWII. He died in 1974.

Join your Society

If you embrace scientific discovery, truth and integrity, partnership, inclusion, and lifelong curiosity, this is your professional home.

James Chadwick: Unveiling the Neutron’s Secrets

February 13, 2024

James Chadwick was a noteworthy figure in the scientific community, remembered most prominently for his groundbreaking work in physics. Born on October 20, 1891, in Manchester, Chadwick’s early education set the stage for his future achievements. At the University of Manchester, he was mentored by Ernest Rutherford, a relationship that would profoundly shape his career. Chadwick’s academic journey led him to the discovery that secured his place in history.

In 1932, Chadwick made a significant scientific breakthrough by discovering the neutron, a particle in the nucleus of an atom that carries no electrical charge. This discovery not only earned him the Nobel Prize in Physics in 1935 but also played a crucial role in the development of atomic research, particularly in the creation of nuclear reactors and weapons. His contribution to science extended far beyond his neutron discovery, influencing atomic theory and nuclear physics for years to come.

Chadwick’s personal life was as remarkable as his professional one. Despite the challenges of his time, including the impact of World Wars, he continued to contribute to important research. His work had a lasting effect not just in academia, but also on the political stage, shaping the path of international nuclear policy. Chadwick passed away on July 24, 1974, leaving behind a legacy of scientific inquiry and achievement.

Key Takeaways

• James Chadwick was an English physicist who discovered the neutron in 1932, revolutionizing the field of nuclear science.
• His discovery led to the Nobel Prize in Physics in 1935 and had significant implications in the development of nuclear reactors and atomic weapons.
• Chadwick’s enduring legacy is marked by his contributions to scientific knowledge, his role in nuclear research during historical events, and his distinguished honors and recognitions.

Early Life and Education

Born into a modest family in a small town near Manchester, England, James Chadwick exhibited a remarkable aptitude for physics from a young age. His tireless curiosity and academic prowess paved the way for a distinguished education that would later define his profound contributions to science.

University Studies and Influences

Chadwick’s journey into the world of physics accelerated when he enrolled at the University of Manchester . There, he was not just a student of the subject; he became part of a lineage of scientists that would change the world. In 1911, he graduated from the Honours School of Physics and two years later, he completed his master’s degree. The time he spent at the university wasn’t just about acquiring knowledge; it was also about establishing connections and absorbing the influences around him, including the tutelage of Ernest Rutherford, a pioneer in the field of nuclear physics.

Key Academic Collaborations

After Manchester, Chadwick’s academic pursuits led him to Gonville and Caius College, Cambridge , arguably one of England’s finest cradles of learning. It was here, surrounded by the intellectual fervor of Cambridge, that Chadwick’s work started to intersect with the significant scientific developments of his time. Collaborating with esteemed physicists, he was at the forefront of exploring the intricacies of atomic structure. However, his academic endeavors were interrupted by World War I. During the conflict, Chadwick found himself at the Ruhleben internment camp for civilians in Germany, where even under difficult circumstances, he continued to engage with physics, demonstrating his resilience and dedication to his field.

Discovery of the Neutron

In 1932, James Chadwick’s groundbreaking work at the Cavendish Laboratory shed light on the atomic structure, revealing the neutron and profoundly influencing the field of particle physics.

Experiments with Beryllium

The path to Chadwick’s discovery began with experiments involving beryllium . When alpha particles, which are helium nuclei, were fired at a beryllium sample, an unknown radiation was produced. Unlike alpha and beta particles , this radiation had no charge and was therefore not deflected by magnetic or electric fields. Chadwick soon realized that these particles must be neutrally charged, and given their ability to penetrate and knock protons out of paraffin wax, he figured they must possess mass. This revelation led him to conclude that the mysterious radiation consisted of particles that were similar to protons in mass but without the charge. He had discovered the neutron .

Impact on Particle Physics

The identification of the neutron was monumental for particle physics. Prior to Chadwick’s work, the atom was thought to be composed of a nucleus containing protons with electrons around it. The discovery of the neutron provided a clearer picture of the atomic nucleus, which now was understood to contain neutrons in addition to protons. This added knowledge was key to furthering the understanding of atomic structure and the strong force holding the nucleus together. It also played a crucial role in the development of nuclear reactors and weapons, reshaping the landscape of modern science and international politics.

Contribution to Nuclear Science

James Chadwick’s work laid the cornerstone for nuclear science as we understand it. He unravelled mysteries of the atomic nucleus, which has ripple effects in both scientific research and practical applications.

The Manhattan Project

In the high-stakes arena of World War II, Chadwick’s expertise was pivotal. After drafting the critical MAUD Report, which galvanized U.S. leaders to invest in nuclear research, he became a leading figure in the Manhattan Project . His insights helped in harnessing nuclear fission , pivotal to the development of the atomic bomb.

Work on Fission

Chadwick not only discovered the neutron but also contributed to the understanding of nuclear fission. Fission is the process where an atomic nucleus splits, releasing a substantial amount of energy. His engagement with this phenomenon was critical in unlocking the potential of nuclear energy , particularly with elements like uranium .

Advancements in Physics

He blazed trails in the study of the atomic nucleus, earning the Nobel Prize in Physics in 1935. Chadwick’s proof of the neutron’s existence was a turning point, it advanced the comprehension of the nucleus profoundly and had major implications for both theoretical and applied physics.

Honors and Legacy

James Chadwick, a notable physicist, earned significant honors throughout his career, making substantial contributions to our understanding of atomic structure. His legacy extends into modern physics, influencing research and technology far beyond his lifetime.

Awards and Recognition

Chadwick’s groundbreaking work on discovering the neutron in 1932 catapulted him to international recognition. This monumental achievement earned him the Nobel Prize in Physics in 1935 , solidifying his reputation as a pioneering scientist.

The honors bestowed upon him include:

• Knighted in 1945, becoming Sir James Chadwick.
• Elected as a member of the Royal Society , a fellowship of many of the world’s most eminent scientists.
• Recipient of the Copley Medal (1950), the Hughes Medal (1932), and the Franklin Medal .

Chadwick’s peers recognized his contributions with several medals and awards, not just in the UK but worldwide, attesting to the impact of his scientific endeavors.

Influence on Modern Physics

James Chadwick’s discovery didn’t just earn him awards; it fundamentally shifted the course of physics. He gave the world a peek at the atom’s inner workings, which led to significant advancements in both physics and chemistry.

He played a vital role in developing atomic energy applications, his discoveries leading to:

• Nuclear power production and its use in medicine and industry.
• Nuclear weapon development, although the moral implications of such applications would remain a point of contention.

Chadwick’s contributions to the war effort through his expertise in nuclear physics were also notable. His neutron discovery was indeed a cornerstone that helped usher in the nuclear age, underscoring his lasting influence on modern science.

Personal Life and Death

James Chadwick led a life that was as remarkable in its personal dimensions as it was in his professional achievements. Born in Cheshire, England, Chadwick’s home life began humbly. He found companionship when he married Aileen Stewart-Brown, a woman who shared his passion for science and supported his research.

Together, they had twin daughters, who brought a new dimension of joy and warmth into Chadwick’s life filled with scientific inquiries.

Chadwick’s final years were spent in the town of Cambridge, where he passed away on July 24, 1974. His biography, which details both his personal life and scientific contributions, paints a picture of a man devoted to his family and his work.

Though Chadwick has long since passed, his legacy lives on—not just in the neutron’s discovery, but also in the memories shared by those who knew him and the family that loved him.

• Place of Death: Cambridge
• Spouse: Aileen Stewart-Brown
• Children: Twin Daughters
• Birthplace: Bollington, Cheshire, England

His story is not just one of scientific endeavor but also a narrative showcasing the balance between personal commitments and professional pursuits.

Leave a Comment Cancel reply

Save my name, email, and website in this browser for the next time I comment.

most recent

Physicists , Biographies

Max born: the remarkable life of the quantum pioneer.

Max Planck: Unveiling the Father of Quantum Theory

Niels Bohr: Unveiling Quantum Mysteries for the Everyday Genius

Werner Heisenberg and the Uncertainty Principle: A Revolutionary Concept Simplified

Alexandru Proca: Unveiling the Legacy of the Romanian Physicist

Bernard d’Espagnat: Unveiling the Philosopher of Quantum Mysteries

© 2024 INFO

James Chadwick

Claimed by Natalie Payne (npayne7)

Sir James Chadwick (1891-1974) was an English physicist and diplomat, best known for winning the 1935 Nobel Prize in Physics for discovering the neutron. He also wrote the Military Applications of Uranium Detonation (MAUD) report, which led the US government to realize the potential of nuclear weapons and to begin serious research into the subject. He was the head of the British group that worked on the Manhattan Project, which resulted in the production of the first atomic bombs. He was knighted in 1945 by King George VI for his contributions to science. In 1946, he was appointed the British advisor to the United Nations Atomic Energy Commission. Later in life, he continued to work in academia as the Master of of Gonville and Caius College, Cambridge. During his tenure, the academic reputation of the college increased dramatically, and he retired from this position in 1959. He passed away in his sleep on July 24, 1974 at the age of 82.

• 1 Early Life and Education
• 2.1 Germany
• 2.2 Cambridge
• 2.3 Liverpool
• 3 Later Life
• 5 Further Reading

Early Life and Education

James Chadwick was born on October 20th, 1891 in Bollington, Cheshire, England. He was the eldest child of Joseph Chadwick and Mary Knowles. His parents moved to Manchester, England in 1894 while he remained in Bollington with his grandmother. He joined his parents in Manchester at age 11 while attending the Central Grammar School for Boys. After graduation from secondary school in 1908, he matriculated at the Victoria University of Manchester. He intended to study mathematics, but he enrolled in the physics program by mistake, and he graduated from the university's Honours School of Physics in 1911. His next two years were spent at the Physical Laboratory in Manchester working on various radioactivity problems under Ernest Rutherford , and he earned a M.Sc in 1913.

In 1913, he was awarded the 1851 Exhibition Scholarship to be able to move to Berlin and study at the Physikalisch Technische Reichsanstalt under Hans Geiger. There he studied beta radiation, and with the help of the newly invented Geiger counter, Chadwick was able to demonstrate that beta radiation produces a complete (continuous) spectrum and not just spectral lines as previously thought. He was still in Berlin at the time of the outbreak of World War I, and was interned at the Ruhleben internment camp for the duration of the war. After his release, he accepted the Wollaston Studentship at Gonville and Caius College, Cambridge, and moved back to England in 1919

While at Cambridge, Chadwick continued to work under Rutherford who was the newly appointed head of the Cavendish Laboratory. In 1919, Rutherford succeeded in disintegrating atoms by bombarding nitrogen with alpha particles, with the emission of a proton, which was the first artificial nuclear transformation. Together, Chadwick and Rutherford continued this work by accomplishing the transmutation of other light elements by bombardment with alpha particles, and by studying the properties and structure of atomic nuclei. At the time, it was believed that the nucleus of an atom contained protons and electrons, but the concept of spin created anomalies in the model. Atoms had the right atomic number but the wrong spin. This led Chadwick and Rutherford to hypothesize the existence of another subatomic particle. In 1932, Walter Bothe and his student Herbert Becker used polonium to bombard beryllium with alpha particles, and this produced a new, unusual form of radiation. It was initially believed that this was to be gamma radiation, because the rays were neutral, because they did not deflect when passed through a magnetic field and extremely penetrating. Frédéric and Irène Joliot-Curie discovered that when a beam of the radiation hit a proton-rich substance like paraffin, protons were knocked off. The Joliot-Curies believed that this was gamma radiation, but Chadwick and Rutherford disagreed because they believed that protons were too heavy for this to occur. Chadwick then designed an experiment to test for the presence of neutrons. The apparatus consisted of a cylinder of polonium aimed at a piece of beryllium. The resulting radiation was then directed towards a piece of paraffin, and the displaced protons from the paraffin were measured with a Geiger counter.

In February 1932, after only weeks of experimenting with neutrons, Chadwick announced his findings in the letter to the editor of Nature . He officially published his work in May 1932, with the article titled "The Existence of a Neutron". With Chadwick's discovery, Heisenberg proposed the proton-neutron model for the nucleus. Rutherford believed that a neutron was just a proton-electron pair, but Heisenberg demonstrated that there were no electrons present in the nucleus. In 1935, Chadwick won the Nobel Prize in Physics for his discovery of the neutron (read his Nobel lecture here )

In 1935, months before he was awarded his Nobel Prize, Chadwick was offered the Lyon Jones Chair of the School of Physics at the University of Liverpool. He wanted to start a nuclear physics research group at Liverpool, but the laboratories were so outdated (they still ran on direct current electricity) that this wasn't possible. He was instrumental in renovating the labs to a modern state, and he used some of his own Nobel Prize money to procure a cyclotron (particle accelerator) for the university.

In 1939, the British government asked Chadwick to begin research into nuclear weapons. Despite the difficult working conditions due to the air raids on Liverpool, by spring of 1941 his group had determined that the critical mass of uranium-235 for a nuclear detonation was about 8 kg. In the summer of 1941, Chadwick wrote a report that summarized all of the nuclear weapon research done in the UK, called the Military Applications of Uranium Detonation (MAUD) report. President Roosevelt read this report, and soon after, the US government began the Manhattan Project to develop the atomic bomb. From 1944 to 1946, Chadwick and his family lived at Los Alamos National Laboratory in New Mexico so he could oversee the British group working on the Manhattan Project. He was present at the Trinity nuclear test on July 16, 1945 when the world's first atomic bomb was detonated (watch a video of the Trinity detonation here )

He was knighted in 1945 by King George VI for his contributions to physics. After the war ended, he was appointed to the the UK Advisory Committee on Atomic Energy (ACAE) and the United Nations Atomic Energy Commission. In 1948, he accepted the position of Master of Gonville and Caius College, where he did his Ph.D. The academic reputation of the college increased dramatically during his Mastership, due to the increase in the number of research fellowships and the hiring of controversial faculty. It was during his tenure that Francis Crick and James Watson discovered the double helix structure of DNA. He remained in this position until his retirement in 1959. He passed away peacefully in his sleep on July 24, 1974 at his home in Cambridge.

The discovery of the neutron lead to the development of the model of the atom as we study it today. This transformed subatomic physics and chemistry, allowing scientists to discover new elements. It also lead to the discovery of nuclear fission, which has been used in war (for weaponry) and peace (nuclear reactors). The process of nuclear fission has had some major consequences since the first atom bombs were dropped on Hiroshima and Nagasaki during World War II, including the Chernobyl and Fukushima nuclear disasters, which have had a lasting impact on humanity. Without James Chadwick, this groundbreaking process would never have been utilized.

Further Reading

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

Chadwick, James (1932)."The Existence of a Neutron" Proceedings of the Royal Society A 136 (830): 692-708. PDF

Navigation menu

National Museum of Nuclear Science & History

James Chadwick

Physicist los alamos, nm, manhattan, ny united kingdom, manhattan project veteran nobel prize winner scientist trinity test eyewitness.

Sir James Chadwick (1891-1974) was an English physicist and winner of the 1935 Nobel Prize in Physics.

James Chadwick began his academic studies at the University of Manchester under the tutelage of Ernest Rutherford. Here, he earned his B.S. in 1911 and his MSc in 1913. Chadwick then decided to take up research under Hans Geiger in Berlin. His intention was to study beta radiation, but shortly into this endeavor, World War I broke out and the German government imprisoned Chadwick in the Ruhleben internment camp for four years.

Aided by sympathetic German soldiers, Chadwick was able construct experiments even while imprisoned during the war. When the war came to a close, Chadwick returned to England and continued research under his previous advisor Ernest Rutherford at the Cavendish Laboratory at Cambridge University. There, he received his doctorate in 1921 and remained with the laboratory until he moved to the University of Liverpool in 1935.

SCIENTIFIC CONTRIBUTIONS

Chadwick is best known for his discovery of the neutron in 1932. A neutron is a particle with no electric charge that, along with positively charged protons, makes up an atom’s nucleus. Bombarding elements with neutrons can succeed in penetrating and splitting nuclei, generating an enormous amount of energy. In this way, Chadwick’s findings were pivotal to the discovery of nuclear fission, and ultimately the development of the atomic bomb. For more on Chadwick’s scientific contributions, please visit the  Nobel Prize website .

WORLD WAR II

Chadwick was a member of the British MAUD Committee, which concluded that the creation of nuclear weapons was possible and even inevitable. This supposition contributed towards President Roosevelt’s decision to build the atomic bomb. Additionally, Chadwick was an integral figure in the Tube Alloy Project—the codename for the British program to devise and develop nuclear weapons. His overtures to government officials in the UK and US were central to UK-US cooperation.

From 1943 to 1946, Chadwick headed the British Mission to the Manhattan Project. He also served as the technical advisor to the US-Canadian-UK Combined Policy Committee, which coordinated control of the project between the three nations involved. In 1944, Chadwick moved his family to the Project’s main research facility in Los Alamos. Finding the housing conditions distasteful, his twin daughters objected to the move, and so the family relocated to Washington D.C. where he continued to contribute to the Project’s efforts.

Chadwick formed a particularly congenial relationship with General Leslie Groves during the war. The two’s friendship aided British efforts to maintain strong support with the United States throughout the Manhattan Project. Chadwick was the only civilian—and non-American—allowed to access the entirety of the Manhattan Project’s research, data, and production plants.

Throughout the war, Chadwick drafted agreements to supply uranium for the Manhattan Project. Additionally, he observed the first atomic explosion, known as the Trinity test. Because of Chadwick’s insistence, British observers were allowed to be present at the bombing of Nagasaki.

Shortly after the war ended, Chadwick became an outspoken advocate for the United Kingdom to acquire a nuclear stockpile of its own. He was appointed to the British Advisory Committee on Atomic Energy (ACEA) and served as the UK delegate to the United Nations Atomic Energy Commission. Patrick Blackett , another Nobel laureate and eminent British scientist, vehemently opposed Chadwick’s argument for British atomic capability. Ultimately, though, Chadwick won out and the United Kingdom pursued its own nuclear arsenal.

Chadwick became the Master of Gonville and Caius College at Cambridge University in 1948. He resided in this administrative position for the remainder of his career. He took up retirement in North Wales beginning in 1958. He eventually moved back to Cambridge, where he passed away in 1974.

In addition to receiving the Nobel Prize in Physics, James Chadwick was knighted in 1945. He was awarded the US Medal of Merit in 1946 and the Copley Prize by the British Royal Society in 1950.

Additional Resources:

Excerpt from Great Lives from History Scientists and Science by Joseph Spradley

Chadwick’s Famous “Possible Existence of a Neutron”

Related Profiles

J. r. wallace, h. a. behling, michael olsen.

Michael Olsen was a member of the Special Engineering Detachment at Los Alamos. 

James Chadwick

James Chadwick Year 1951 Subject Physics Award Franklin Affiliation Gonville and Caius College | Cambridge, United Kingdom Citation For the identification of the neutron as part of the nucleus of the atom.

James Chadwick was born in Cheshire, England, in 1891. He studied at Manchester University, graduating from the Honours School of Physics in 1911 and obtained his M.Sc. degree in 1913. While at Manchester, he he worked on various radioactivity problems. He continued his studies in Berlin to work in the Physikalisch Technische Reichsanstalt at Charlottenburg under Professor H. Geiger. He later returned to England and was granted the Wollaston Scholarship at Gonville and Cains College in Cambridge, where he resumed working on atomic studies.

In 1932, Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge. This discovery contributed to the successful controlled fissioning of Uranium-235, and eventually to the development of the atomic bomb. Fo this discovery he was awarded the Hughes Medal of the Royal Society in 1932, and the Nobel Prize for Physics in 1935.

Chadwick remained at Cambridge until 1935 when he was elected to the Lyon Jones Chair of Physics in the University of Liverpool. From 1943 to 1946 he worked in the United States as Head of the British Mission attached to the Manhattan Project for the development of the atomic bomb. He returned to England and, in 1948, retired from active physics and his position at Liverpool on his election as Master of Gonville and Caius College, Cambridge. He retired from this Mastership in 1959.

Information as of 1951

• Buy Tickets
• TFI Transformation
• Accessibility
• Frequently Asked Questions
• Itineraries
• Daily Schedule
• Getting Here
• Where to Eat & Stay
• All Exhibits & Experiences
• The Art of the Brick
• Wondrous Space
• Science After Hours
• Heritage Days
• Science Park
• Events Calendar
• Staff Scientists
• Benjamin Franklin Resources
• Scientific Journals of The Franklin Institute
• Professional Development
• The Current: Blog
• About Awards
• Ceremony & Dinner
• Sponsorship
• The Class of 2024
• Call for Nominations
• Committee on Science & The Arts
• Next Generation Science Standards
• Title I Schools
• Neuroscience & Society Curriculum
• STEM Scholars
• GSK Science in the Summer™
• Missions2Mars Program
• Children's Vaccine Education Program
• Franklin @ Home
• The Curious Cosmos with Derrick Pitts Podcast
• So Curious! Podcast
• A Practical Guide to the Cosmos
• Archives & Oddities
• Ingenious: The Evolution of Innovation
• The Road to 2050
• Science Stories
• Spark of Science
• That's B.S. (Bad Science)
• Group Visits
• Plan an Event

• Français
• Preparatory

Question Video: Identifying the Advancement to Atomic Theory That James Chadwick Proved Chemistry • Second Year of Secondary School

Join nagwa classes.

Attend live Chemistry sessions on Nagwa Classes to learn more about this topic from an expert teacher!

• Remaining Seats: 14

James Chadwick proved the existence of ＿.

Video Transcript

James Chadwick proved the existence of blank. (A) The quantum atomic model, (B) the electron cloud model, (C) the electron, (D) the neutron, or (E) the proton.

Experiments conducted by James Chadwick helped advance the understanding of atomic structure. In his experiment, a sample of beryllium was bombarded with positively charged 𝛼 particles. This resulted in the beryllium emitting high-energy unknown radiation, which was then directed at paraffin wax. This caused the wax to emit protons, which were counted using a detector. This unknown radiation was high energy and neutral and was found to have a mass about the same as a proton. This led to the conclusion that a neutral particle is present in the atom called the neutron. This discovery was incredibly important as it explained the existence of isotopes, which are atoms of the same element with the same number of protons but a different number of neutrons.

Therefore, James Chadwick proved the existence of answer choice (D) the neutron.

Attend live sessions on Nagwa Classes to boost your learning with guidance and advice from an expert teacher!

• Interactive Sessions
• Chat & Messaging
• Realistic Exam Questions

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy

You are using an outdated browser. Please upgrade your browser to improve your experience and security.

Enhanced Page Navigation

• James Chadwick - Nobel Lecture: The Neutron and Its Properties

James Chadwick

Nobel lecture.

Nobel Lecture, December 12, 1935

The Neutron and Its Properties

Nobel prizes and laureates, nobel prizes 2023.

Explore prizes and laureates