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A Biography Of Sir James Chadwick History Essay

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Published: Mon, 5 Dec 2016

James Chadwick, a remarkable man, may rank among the greatest of all experimental nuclear physicists and he may have played a pivotal role in the development of the atom bomb. James Chadwick had many achievements – Nobel Prize, wartime knighthood, Master of Gonville and Caius, Companion of Honor — but was a troubled, hyper-tense human being, capable of love and anger as well as restraint.

Chadwick was born in Bollington, not far from Manchester, England, on October 20, 1891, to John Joseph Chadwick and Ann Mary Knowles. Chadwick senior owned a laundry business in Manchester. At the age of sixteen, Chadwick won a scholarship to the University of Manchester, where he had intended to study mathematics. However, because he was mistakenly interviewed for admittance to the physics program and was too shy to explain the error, he decided to stay in physics.

Initially Chadwick was disappointed in the physics classes, finding them too large and noisy. But in his second year, he heard a lecture by experimental physicist Ernest Rutherford about his early New Zealand experiments. Chadwick established a close working relationship with Rutherford and graduated in 1911 with first honors. Chadwick stayed at Manchester to work on his master’s degree. During this time he made the acquaintance of others in the physics department, including Hans Geiger and Niels Bohr. Chadwick completed his M.S. in 1913 and won a scholarship that required him to do his research away from the institution that granted his degree. At this time Geiger returned to Germany, and Chadwick decided to follow him.

Chadwick had not been in Germany long when World War I broke out. Soon he was arrested and sat in a Berlin jail for ten days until Geiger’s laboratory interceded for his release. Eventually Chadwick was interned for the duration of the war, as were all other Englishmen in Germany. Chadwick spent the war years confined at a race track, where he shared with five other men a stable intended for two horses. His four years there were quiet, cold, and hungry. He managed to maintain correspondence with Geiger. Although the work he did under such harsh conditions was not very fruitful, Chadwick felt that the experience of internment contributed to his maturity. Moreover, when Chadwick returned to England, he found that no one else had made much progress in nuclear physics during his time away.

His careful self-humbleness, though, kept him from the limelight, and his primary role over the next 20 years was as Rutherford’s assistant. They had a complex relationship where Chadwick was confidant, critic and counselor as well as general factotum (laborer) for the great man, particularly during their long association at the Cavendish Laboratory in Cambridge.

One of Chadwick’s first tasks was to help Rutherford establish a unit of measurement for radioactivity, to aid in experiments with the radiation of atomic nuclei. Chadwick then developed a method to measure radioactivity that required the observation of flashes, called scintillations, in zinc sulfide crystals under a microscope and in complete darkness. Chadwick and Rutherford spent much time experimenting with the transmutation of elements, attempting to break up the nucleus of one element so that different elements would be formed. This work eventually led to other experiments to gauge the size and map the structure of the atomic nucleus.

Throughout the years of work on the transmutation of elements, Chadwick and Rutherford struggled with an inconsistency. They saw that almost every element had an atomic number that was less than its atomic mass. In other words, an atom of any given element seemed to have more mass than could be accounted for by the number of protons in its nucleus. Rutherford then suggested the possibility of a particle with the mass of a proton and a neutral charge, but for a long time his and Chadwick’s attempts to find such a particle were in vain.

For twelve years, Chadwick looked intermittently and unsuccessfully for the neutrally-charged particle that Rutherford proposed. In 1930 two German physicists, Walther Bothe and Hans Becker, found an unexpectedly penetrating radiation, thought to be gamma rays, when some elements were bombarded with alpha-particles. However, the element beryllium showed an emission pattern that the gamma-ray hypothesis could not account for. Chadwick suspected that neutral particles were responsible for the emissions. Work done in France in 1922 by physicists Frederic Joliot-Curie and Irene Joliot-Curie supplied the answer. Studying the hypothetical gamma-ray emissions from beryllium, they found that radiation increased when the emissions passed through the absorbing material paraffin. Although the Joliot-Curie team concluded that gamma rays emitted by beryllium knocked hydrogen protons out of the paraffin, Chadwick immediately saw that their experiments would confirm the presence of the neutron, since it would take a neutral particle of such mass to move a proton. He first set to work demonstrating that the gamma-ray hypothesis could not account for the observed phenomena, because gamma rays would not have enough energy to eject protons so rapidly. Then he showed that the beryllium nucleus, when combined with an alpha-particle, could be transmuted to a carbon nucleus, releasing a particle with a mass comparable to that of a proton but with a neutral charge. The neutron had finally been tracked down. Other experiments showed that a boron nucleus plus an alpha-particle results in a nitrogen nucleus plus a neutron. Chadwick’s first public announcement of the discovery was in an article in the journal Nature with a title characteristic of his unassuming personality, “Possible Existence of a Neutron.”

It was his discovery of the neutron, in an experiment of disarming simplicity in 1932, which pulled him from Rutherford’s shadow and won him, with unusual promptness, the Nobel Prize for physics in 1935. He was now a giant in his field, and all his studious efforts to give credit to others could not conceal it. That same year, Chadwick took a position at the University of Liverpool to establish a new research center in nuclear physics and to build a particle accelerator.

Chadwick’s reputation manifested his involvement with the atomic bomb and the single-mindedness he brought to the early thinking and feasibility work in Britain, and to the subsequent development of the weapon in the US. Chadwick, among the first to see the potential for a weapon and to realize that Nazi Germany might be making it, threw himself into the task and ended up in effect in charge on the British side.

Chadwick’s discovery of the neutron made possible more precise examinations of the nucleus. It also led to speculations about uranium fission. Physicists found that bombarding uranium nuclei with neutrons caused the nuclei to split into two almost equal pieces and to release energy in the very large amounts predicted by Einstein’s formula E=mc2. This phenomenon, known as nuclear fission, was discovered and publicized on the eve of World War II, and many scientists immediately began to speculate about its application to warfare. Britain quickly assembled a group of scientists under the Ministry of Aircraft Production, called the Maud Committee, to pursue the practicality of an atomic bomb. Chadwick was put in charge of coordinating all the experimental efforts of the universities of Birmingham, Cambridge, Liverpool, London, and Oxford. Initially Chadwick’s responsibilities were limited to the very difficult and purely experimental aspects of the research project. Gradually, he became more involved with other duties in the organization, particularly as spokesperson.

Chadwick’s work in evaluating and presenting evidence convinced British government and military leaders to move ahead with the project. Chadwick’s involvement was broad and deep, forcing him to deal with scientific details of uranium supplies and radiation effects as well as broader issues of scientific organization and policy. His correspondence during this time referred to issues ranging from Britain’s relationship with the United States to the effects of cobalt on the health of sheep.

As the pressures of war became greater, the British realized that even with their theoretical advances, they did not have the practical resources to develop a working atomic bomb. In 1943 Britain and the United States signed the Quebec Agreement, which created a partnership between the two countries for the development of an atomic bomb. Chadwick became the leader of the British contingent involved in the Manhattan Project in the United States. Although he was shy and used to the isolation of the laboratory, Chadwick became known for his tireless efforts at collaboration and his keen sense of diplomacy. He maintained friendly Anglo-American relations despite a great variety of scientific challenges, political struggles, and conflicting personalities. On July 16, 1945, he witnessed the first atomic test in the New Mexico desert.

After the war, Chadwick’s work continued to focus on nuclear weapons. He was an advisor for the British representatives to the United Nations regarding the control of atomic energy around the world. Although he pushed for atomic policy issues as much as he pushed for scientific solutions, Chadwick eventually saw the uselessness of the atomic bomb. Margaret Gowing, in her article, “James Chadwick and the Atomic Bomb,” wrote that Chadwick made a remark about the bomb stating Its effect in causing suffering is out of all proportion to its military effect.

Chadwick’s postwar involvement with nuclear energy was not limited to weapons. He also was interested in medical applications of radioactive materials, and he worked to develop ways of regulating radioactive substances. Chadwick was a dedicated and tireless scientist who balanced his commitments to science with a commitment to his family. He and his wife, Aileen Stewart-Brown, whom he married in 1925, had twin daughters. Chadwick was shy and serious and had an exacting sense of discipline and a tireless attention to detail. When he was at the Cavendish laboratory, all papers that went out for publication passed under his critical gaze.

Here is a man known as psychologically fragile – so weak at times that he would plead illness to avoid an unwelcome confrontation with a mere undergraduate – who for five years drives meetings, bashes scientific heads together, bullies ministries and conducts the most delicate diplomacy with the Americans.

He went on to join the great and good in postwar Britain and was honored for his work, but what he had done in the war, constantly struggling against his own nature and instincts, left him weakened and at times almost defeated by life. Although his ability to solve problems and organize people never left him, he seems increasingly to have used illness (which mystified his doctors) to shield himself against difficulties. In 1950 he was proposed as vice-chancellor of Cambridge University, but turned it down on health grounds.

He was knighted in 1945 and in 1948 was elected master of Gonville and Caius College, a post from which he retired in 1959. Three years later he retired also from the United Kingdom Atomic Energy Authority, on which he had served as part-time member from 1957. Sir James Chadwick died in Cambridge, England, on July 24, 1974.

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