John Cockcroft

John Cockcroft

English physicist, Nobel Prize winner in physics
Date of Birth: 27.05.1897
Country: Great Britain

  1. Biography of John Cockcroft
  2. Early Career and Contributions
  3. Director of the Cavendish Laboratory
  4. Later Career and Achievements
  5. Personal Life and Honors

Biography of John Cockcroft

John Douglas Cockcroft, an English physicist and Nobel Prize laureate in Physics, was born in Todmorden, Yorkshire. He was the eldest of five sons of John Arthur Cockcroft and Mod (Fielden) Cockcroft. His father owned a small cotton spinning mill, and three of his brothers followed in his footsteps, as their family had been in the business for five generations. However, John, a brilliant student and athlete, received a scholarship to study at the University of Manchester in 1914. In Manchester, Cockcroft began studying mathematics and attending lectures by physicist Ernest Rutherford.

Early Career and Contributions

Rutherford, renowned for his work on radioactivity and the structure of the atom, was able to prove that alpha particles are the nuclei of helium atoms. Furthermore, he showed that atoms consist of a positively charged nucleus, around which negatively charged electrons orbit. This was a time when mathematicians and physicists faced numerous significant challenges. Radioactivity had been discovered by Henri Becquerel less than 20 years earlier, in 1896, and Albert Einstein's theory of relativity, published in 1905, was just beginning to be understood by scientists.

However, World War I broke out, and in 1915, after a year of studies at the university, Cockcroft joined the Young Men's Christian Association volunteer unit. He was called up for military service the same year. Until his discharge in 1918, he fought on the Western Front and rose through the ranks from signaller to officer in the Royal Field Artillery.

Upon his return to Manchester, Cockcroft began working in electrical engineering and earned a Master's degree in 1922. He then became a mathematics fellow at St. John's College, Cambridge, earning a Bachelor's degree with honors in 1924, and joined the Cavendish Laboratory in Cambridge as a junior research assistant. Four years later, he obtained his doctorate. In Cambridge, Cockcroft lectured on physics and engaged in mathematical and technical developments. Together with Russian physicist Pyotr Kapitsa, he developed transformer windings for producing intense magnetic fields. He also researched surface films obtained using atomic beams.

Director of the Cavendish Laboratory

Rutherford was the director of the Cavendish Laboratory since 1919, having come here as a renowned scientist who had proved that atomic nuclei could be broken apart by bombarding them with subatomic particles. The nuclear fission that Rutherford performed, using natural alpha particle radiation (helium nuclei) and converting nitrogen atoms into oxygen atoms, opened up a new field of experimental research. The next primary goal was to learn how to carry out transmutation of atoms on a much larger scale than could be done with Rutherford's methods. Some researchers believed that this could be achieved by accelerating atomic particles in large quantities. Since positively charged particles experience strong repulsion from atomic nuclei, which are also positively charged, extremely high accelerations are required.

Many scientists in both Europe and the United States raced to achieve higher particle acceleration using two different approaches. In the so-called direct method, energy was obtained by a single high-voltage electrical pulse. In the other method, particles were accelerated cyclically through a low-voltage field multiple times. Of the two methods, the cyclic one seemed more promising to most researchers: although it required more complex equipment, it used readily available voltage, whereas the direct method required a high voltage that was difficult to obtain with the equipment of that time.

Inspired by the theories of Russian-born physicist George Gamow, Cockcroft decided to develop the direct method. Gamow, using quantum mechanics, calculated that, since subatomic particles have wave properties, they would occasionally be able to penetrate nuclear barriers, even when their energies were insufficient to overcome them. Gamow's equations explained how alpha particles could escape the nuclei of radioactive elements, but Cockcroft realized that the same principles allowed other particles to penetrate the nucleus with significantly less energy than previously thought.

With his colleague Ernest Walton at the Cavendish Laboratory, Cockcroft developed an installation based on the direct method, capable of delivering a voltage of just 600 kilovolts to a tube containing hydrogen. (Millions of volts would be required to overcome the nuclear barrier.) Using this setup, Cockcroft and Walton bombarded lithium with hydrogen nuclei, or protons, in April 1932. "Almost immediately," Cockcroft recalled, "at an energy of 125 kilovolts, Dr. Walton saw nuclear scintillation, characteristic of alpha particles." They transformed lithium and hydrogen into helium, thereby becoming the first scientists to artificially split an atom. Their achievement also experimentally confirmed Gamow's theory and showed that the amount of energy released during atomic transformations precisely corresponded to the fundamental equation of Einstein's theory of relativity: E = mc².

In the 1930s, Cockcroft continued his experiments using various bombarding particles and atomic nuclei, such as boron and fluorine. After the discovery of artificial radioactive elements by Frederic Joliot and Irene Joliot-Curie, Cockcroft and Walton demonstrated that they could also produce such elements by irradiating boron and carbon with hydrogen nuclei. In 1934, Cockcroft, an able administrator, was appointed director of the Mond Laboratory of the Royal Society in Cambridge. A year later, he worked with Rutherford to redevelop the Cavendish Laboratory, installing a cyclotron – an accelerator invented by Ernest O. Lawrence. Cyclotrons were soon improved and became widely accepted, although the Cockcroft-Walton generator continues to be used as a source of protons in several powerful installations.

Later Career and Achievements

In 1939, World War II broke out, and Cockcroft once again participated in British military developments. He was primarily responsible for the development and deployment of radar, a decisive factor that ensured Britain's success in the air war against Germany. In 1940, he was sent to the United States as Vice President of the Tizard Committee, which negotiated the exchange of technical military information with American scientists before the United States entered the war. After returning from the US, Cockcroft headed the Department of Scientific Research of the British Royal Air Force. In 1944, he traveled to Canada to lead the Atomic Energy Division under the National Research Council of Canada; this group participated in the Manhattan Project to develop and produce the first atomic bomb. Cockcroft returned to England in 1946 to head the newly formed Atomic Energy Research Establishment, which resulted in the creation of the world's first atomic power station at Calder Hall in northern England. He was actively involved in various fields, serving as a member of the British Atomic Energy Authority and CERN (European Organization for Nuclear Research) in Geneva, Switzerland. He founded what is now known as the Rutherford High Energy Laboratory, whose state-of-the-art facilities are open to the entire scientific community of British universities.

Cockcroft and Walton shared the Nobel Prize in Physics in 1951 "for their work on the transmutation of atomic nuclei by artificially accelerated atomic particles." In his speech, Ivar Waller of the Swedish Royal Academy of Sciences said, "Cockcroft and Walton's work confirmed the validity of Einstein's law regarding the equivalence of mass and energy. During the transmutation of lithium, energy is released because the total kinetic energy of the resulting helium nuclei exceeds the energy of the initial nuclei. According to Einstein's law," Waller continued, "this increase in energy is caused by a corresponding loss of mass of the atomic nuclei." In 1959, Cockcroft became the Master of Churchill College, Cambridge. At the time of his death in 1967, Cockcroft was President of the Pugwash Conference and was one of the leaders of the Liberal Party.

Personal Life and Honors

Cockcroft married Una Elizabeth Crabtree in 1925, and they had four daughters and a son. In addition to the Nobel Prize, Cockcroft received the Royal Medal of the Royal Society (1954), the International Gold Medal of the Danish Society of Engineers, Electricians, and Mechanics (1958), and the "Atoms for Peace" Award established by the Ford Foundation (1961). He was a Fellow of the Royal Society and an honorary member of the American Academy of Arts and Sciences and the Swedish Royal Academy of Sciences. Cockcroft was knighted in 1948. He held honorary degrees from the University of Oxford, the University of London, the University of Toronto, and the University of Glasgow.