James Chadwick: Biography, Chadwick's Atomic Model and Experiments

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

Prior to this check, Chadwick conducted several experiments that proved 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 researching the use of nuclear fission for the creation of war weapons.

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 in the railway system and his mother was a domestic worker.

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

Academic training

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

He had a distinguished career in the academy, and in the last year of his career he was in charge of Nobel Prize Ernest Rutheford's research on the disintegration of elements and the chemistry of radioactive substances.

After obtaining his degree in Physics in 1911, he enrolled in the Master's in Physics, which culminated successfully in 1913. During that time he continued working hand in hand with Rutheford in his laboratory.

Later, he was benefited by a professional scholarship that allowed his transfer to Berlin, Germany, to further research on beta radiation with the German physicist Hans Geiger at the Technische Hochschule.

During his stay in Berlin he began the First World War, 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. In the meantime, he rejoined the research work of Rutheford, who was then leading the Cavendish Laboratory of the renowned institution.

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

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

Career

Thanks to his scientific contributions he became worthy of the Hughes medal in 1932. This recognition, awarded 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 electric charge located in the atomic nucleus.

During the Second World War 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 neuralgic part of the Tube Alloys Project, an authorized research program funded by the United Kingdom with support from Canada, to develop nuclear weapons during World War II.

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

Manhattan Project

Towards the end of the Second World War, Chadwick took 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, budgets, etc., despite being a civilian and not being American; it is worth noting that both conditions were exclusive to participate in the project.

Later he was named English gentleman in 1945, and one year later EE. UU He was awarded the Medal of Merit for his contribution of value in the Manhattan Project.

Nuclear arsenal for England

At the end of the Second World War Chadwick promoted with great impetus the initiative of the United Kingdom to develop its own nuclear arsenal.

In pursuit of that objective, Chadwick was elected as a member of the British Atomic Energy Advisory Committee, and also participated as the representative of the United Kingdom before the United Nations Commission on Atomic Energy.

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

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

Scientific contribution

The discovery of the neutron

During their investigations at the Cavendish Laboratory in Cambridge, Rutherford and Chadwick conducted experiments with alpha particles to investigate 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 before seen emanating from beryllium, when this material was exposed to the bombardment of alpha particles.

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

Chadwick made this discovery in mid-1932, and with that he defined the premises of Chadwick's atomic model, the details of which are detailed in the following section of this article.

Nuclear research

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

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

From there, Chadwick announced the inevitable nature of this type of technology for the development of weapons of war, and became directly involved in the diplomatic issues related to this process in the USA. UU and England.

Atomic model of Chadwick

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

Chadwick's eagerness to demonstrate the existence of neutral particles was generated in the 1920s. However, at that time the leading scientist made multiple attempts in vain. A decade later Chadwick replicated the experiments of Irène Joliot-Curie (daughter of Marie Curie and Pierre Curie) and Frédéric Joliot (husband of Irène) in France.

This pair of scientists had achieved the expulsion of protons from a sample of paraffin wax using gamma rays.

Chadwick thought that the emission of gamma rays contained neutral particles, and that these particles were the ones that had hit the wax sample, subsequently inducing the release of protons from the wax.

Therefore, he tried to replicate these experiments in 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.

Then, this radiation hit a similar sample of paraffin wax, and the protons of that sample were violently expelled from the material.

The behavior of the protons was observed through 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 hit 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 conceived the model initially considering that the neutron was an arrangement consisting of a proton and an electron, which generated the neutral charge. Later, the German physicist Werner Heisenberg showed that the neutron was a unique and elementary particle.

Experiments and contributions

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

The discovery of the neutron and the atomic model of Chadwick revolutionized the traditional view of science, given the collisions of neutrons with atomic nuclei and the expulsion of protons outside 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, many experiments were carried out worldwide, motivated by the discovery of Chadwick, to induce the conversion of some neutrons into protons.

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

Nuclear fision

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

It is named in this way because 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 stay in Liverpool, and for this he used a portion of the funds obtained by winning the Nobel Prize in 1935.

References

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2. James Chadwick (s.f.). Retrieved from: atomicheritage.org
3. James Chadwick (s.f.). Retrieved from: famousscientists.org
4. James Chadwick - Biographical (2014). Nobel Media AB. Retrieved from: nobelprize.org
5. James Chadwick: Biography & Atomic Theory (s.f.). Retrieved from: study.com
6. Principles of physical science (1998). Encyclopædia Britannica, Inc. Retrieved from: britannica.com
7. Wikipedia, The free Encyclopedia (2018). Discovery of the neutron. Retrieved from: en.wikipedia.org