JAMES CHADWICK: BIOGRAPHY, ATOMIC MODEL, EXPERIMENTS - SCIENCE - 2025

James Chadwick (1891-1974) was a leading English physicist recognized for the discovery of the neutron in 1932. Shortly after, in 1935, he was awarded the Nobel Prize in Physics for his contribution to the scientific community. Chadwick's concern with neutral charges arose about 10 years before he was able to prove their existence.

Prior to this check, Chadwick performed several experiments that were unsuccessful. It was successful in 1932, when it was based on the experiments of the French Irène Joliot-Curie and Frédéric Joliot. Later, Chadwick devoted himself to research on the use of nuclear fission for the creation of weapons of war.

Biography

origins

Chadwick was born in the town of Bollington, in the northeast of England, on October 20, 1891. He was the son of two humble workers: his father worked on the railway system and his mother was a domestic worker.

From a very young age, Chadwick stood out as an introverted and extremely intelligent child. He began secondary school in Manchester, and at the age of 16 he won a scholarship to study pure physics at the defunct Victoria University of Manchester.

Academic training

The young promise of physics formally began his university studies in 1908, at the age of 17.

He had an outstanding passage through the academy, and in the last year of his career he attended the investigations of the Nobel Prize winner Ernest Rutheford on the disintegration of the elements and the chemistry of radioactive substances.

After obtaining his degree in Physics in 1911, he enrolled in a master's degree in Physics, which he successfully completed in 1913. During that time, he continued to work hand in hand with Rutheford in his laboratory.

Later, he was awarded a professional scholarship that allowed him to move to Berlin, Germany, to further research on beta radiation together with the German physicist Hans Geiger at the Technische Hochschule.

During his stay in Berlin, World War I began in July 1914. Due to an accusation of espionage, he was interned in a concentration camp for civilians in Ruhleben until 1918.

In 1919 Chadwick returned to England and began his doctorate at the University of Cambridge. Meanwhile, he rejoined the research work of Rutheford, who by then led the Cavendish Laboratory of the renowned institution.

In 1921, at the age of 21, he obtained his Ph.D. degree (Philosophie Doctor), presenting a special research paper on nuclear forces and atomic numbers.

In 1923 he was appointed as assistant director of research at Cambridge Cavendish Laboratory. Chadwick served in this role until 1935, when he decided to move to the University of Liverpool.

Career

Thanks to his scientific contributions, he was awarded the Hughes medal in 1932. This recognition, granted by the Royal Society of London, rewards those who make discoveries about the physical sciences and / or their practical applications.

In 1935 he was awarded the Nobel Prize in Physics for the discovery of the neutron as an elementary particle with no electrical charge located in the atomic nucleus.

During World War II Chadwick had an active participation in the British Committee of the MAUD, a commission created to analyze the feasibility of using nuclear technology in the manufacture of a bomb.

James Chadwick was also a central part of the Tube Alloys Project, a research program authorized and funded by the United Kingdom with support from Canada, to develop nuclear weapons during World War II.

Chadwick was noted for his wit and political poise during this period, as his proposals served as a bridge for investigative collaboration negotiations between the United Kingdom, Canada, and the United States.

Manhattan Project

Towards the end of World War II, Chadwick took over the baton of the British mission in the Manhattan Project. The latter was a joint research project between the United States, the United Kingdom, and Canada, with the aim of developing the first atomic bomb.

Chadwick had free access to all the confidential information of the project: designs, plans, data, estimates, etc., despite being a civilian and not an American; It is worth noting that both conditions were exclusive to participate in the project.

He was later made an English knight in 1945, and a year later the US awarded him the Medal of Merit for his contribution of courage to the Manhattan Project.

Nuclear arsenal for England

At the end of the Second World War, Chadwick strongly promoted the initiative for the United Kingdom to develop its own nuclear arsenal.

In pursuit of that goal, Chadwick was elected as a member of the British Atomic Energy Advisory Committee, and also served as the UK's representative to the United Nations Atomic Energy Commission.

Around 1948 James Chadwick served as a professor at Gonville & Caius College, University of Cambridge. Then, in 1950, he was honored again by the Royal Society of London by receiving the Copley Medal.

8 years later he decides to voluntarily retire to North Wales. James Chadwick passed away on July 24, 1974, in the city of Cambridge.

Chadwick Atomic Model

Chadwick's atomic model focuses on the modeling of the atomic nucleus made up not only of protons (positive charges), but also of neutrons (neutral charges).

Chadwick's efforts to demonstrate the existence of neutral particles began in the 1920s. However, at that time the prominent scientist made multiple attempts to no avail. A decade later Chadwick replicated the experiments of Irène Joliot-Curie (daughter of Marie Curie and Pierre Curie) and Frédéric Joliot (Irène's husband) in France.

This pair of scientists had succeeded in expelling protons from a paraffin wax sample using gamma rays.

Chadwick believed that the gamma ray emission contained neutral particles, and that these particles were the ones that had collided with the wax sample, subsequently inducing the release of protons from the wax.

Therefore, he tried to replicate these experiments at the Cavendish Laboratory and used polonium - which had been used by the Curies as a source of gamma rays - to irradiate beryllium with alpha particles.

This radiation then impacted on a similar paraffin wax sample, and the protons in that sample were violently expelled from the material.

The behavior of the protons was observed using a small ionization chamber, adapted to the experiment by Chadwick himself.

Chadwick detected that the behavior of the protons released by the wax could only be explained if those particles had collided with other electrically neutral particles, and with a very similar mass.

Two weeks later, James Chadwick published an article in the scientific journal Nature about the possible existence of neutrons.

However, Chadwick initially conceived the model considering that the neutron was an arrangement made up of a proton and an electron, which generated the neutral charge. Later, the German physicist Werner Heisenberg showed that the neutron was a single, elementary particle.

Experiments

After the discovery of the neutron, Chadwick focused on going further and further with respect to the characterization of this new atomic component.

The discovery of the neutron and Chadwick's atomic model revolutionized the traditional view of science, given the collisions of neutrons with atomic nuclei and the expulsion of protons out of the atom.

Beta decomposition is a process through which beta particles (electron or positron) are emitted from the nucleus of the atom, to balance the presence of protons and neutrons in the atomic nucleus.

Due to this process, countless experiments were carried out worldwide, motivated by Chadwick's discovery, to induce the conversion of some neutrons into protons.

Because each chemical element is identified according to the number of protons it has, previous experiments opened the door for the creation and / or discovery of new chemical elements with a greater number of protons under their belt.

Nuclear fision

Chadwick emphasized his later analyzes on the use of neutrons to divide heavy nuclei atoms into several smaller nuclei, through the process of nuclear fission.

It is named this way because the division occurs in the nucleus of the atom and produces an extremely large amount of energy. This concept was used for the design of powerful nuclear weapons.

Chadwick even financed the purchase of a particle accelerator during his time in Liverpool, using a portion of the proceeds from winning the Nobel Prize in 1935 for this.

Chadwick's contributions to science

Among the contributions of James Chadwick to science, the discovery of the neutron stands out, for which he won the Nobel Prize in Physics in 1935. He also participated in the construction of the atomic bomb in the United States, wrote about radiation from radioactive substances and discovered tritium.

The discovery of the neutron

During their research at the Cavendish Laboratory in Cambridge, Rutherford and Chadwick conducted experiments with alpha particles to inquire about the nature of the atomic nucleus. It is worth noting that the atomic nucleus was discovered by Rutherford in 1911.

These investigations were carried out by analyzing a radiation never seen before emanating from beryllium, when this material was exposed to the bombardment of alpha particles.

This radiation consisted of particles of mass very similar to the mass of the proton, but without an electric charge. These particles were called neutrons, due to the neutrality of their composition.

Chadwick made this discovery in mid-1932, thereby defining the premises of Chadwick's atomic model, the details of which are broken down in the next section of this article.

Nuclear investigations

The discovery of the neutron by Chadwick set the stage for the discovery of nuclear fission and the development of weapons of war with this technology.

Chadwick found that, by bombarding an element's atom with neutrons, the nucleus of this material can be penetrated and split, generating a significant amount of energy.

From there, Chadwick announced the inevitability of this type of technology for the development of weapons of war, and became directly involved in diplomatic affairs related to this process in the US and England.

Chadwick collaborated in the construction of the atomic bomb along with other American and Canadian scientists between 1943 and 1945.

He was in charge of directing the English scientific delegation that worked in the Los Álamos laboratory, in New Mexico, United States. In 1939 the United States began researching the Manhattan Project, the code name for the atomic bomb.

President Franklin Delano Roosevelt was warned by nuclear scientists Edward Teller, Leó Szilárd and Eugene Wigner, through Albert Einstein, about the use of nuclear fission for the production of bombs by the Nazis.

Discovery of tritium

Tritium had already been identified in 1911 by the English scientist Joseph John Thomson, but he believed that it was a triatomic molecule.

Ernest Rutherford had also already announced it, but it was not until 1934 that Chadwick, working for Rutherford's team, cataloged it as a hydrogen isotope.

Tritium is a radioactive isotope of hydrogen, whose symbol is ³H. It consists of a nucleus made up of a proton and two neutrons.

Tritium is generated by bombardment with free neutrons of nitrogen, lithium, and boron targets.

Facilitation of uranium 235 fission

The discovery of the neutron by James Chadwick facilitated nuclear fission; that is, separation of uranium 235 from uranium -238, a chemical element found in nature.

The enrichment of uranium 235 is the process that natural uranium undergoes in order to obtain the isotope 235 and produce nuclear energy. Fission is a nuclear reaction; that is, it is triggered in the nucleus of the atom.

This chemical reaction occurs when a heavy nucleus is divided into two or more smaller nuclei and some by-products such as photons (gamma rays), free neutrons and other fragments of the nucleus.

Treaty on Radiation of Radioactive Substances

In 1930 James Chadwick wrote a treatise on radiation from radioactive substances.

Chadwick managed to measure the mass of the neutron and deduced that it was similar to that of the proton with one difference: that it had a neutral electrical charge.

Then, he concluded that the atomic nucleus was made up of neutrons and protons and that the number of protons was similar to that of electrons.

His research and contributions to the work of the physics laboratory at the University of Manchester and at the University of Cambridge in England, were key to the knowledge of nuclear energy and the construction of Rutherford's atomic model.

Articles of interest

Schrödinger's atomic model.

De Broglie atomic model.

Heisenberg atomic model.

Perrin's atomic model.

Thomson's atomic model.

Dalton's atomic model.

Dirac Jordan atomic model.

Atomic model of Democritus.

Bohr's atomic model.

Sommerfeld atomic model.

References

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