In the Classroom

Exploring Nuclear – A History of Pioneers in Nuclear Science

There have been many famous scientists and discoverers in nuclear history. Below is a brief history of those who have paved the way. How many do you know?

Henri Becquerel ? (1852 – 1908)
Discovered radioactivity

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Henri Becquerel was born into a family of scientists. His grandfather had made important contributions in the field of electrochemistry while his father had investigated the phenomena of fluorescence and phosphorescence. Becquerel not only inherited their interest in science, he also inherited the minerals and compounds studied by his father. Upon learning how Wilhelm R?ntgen discovered X rays by observing the fluorescence they produced, Becquerel had a ready source of fluorescent materials with which to pursue his own investigations of these mysterious rays. The material Becquerel chose to work with was a double sulfate of uranium and potassium, which he exposed to sunlight and placed on photographic plates wrapped in black paper. When developed, the plates revealed an image of the uranium crystals. Becquerel concluded “that the phosphorescent substance in question emits radiation which penetrates paper opaque to light.” Initially he believed that the sun’s energy was being absorbed by the uranium which then emitted X rays. Further investigation, on the 26th and 27th of February, was delayed because the skies over Paris were overcast and the uranium-covered plates Becquerel intended to expose to the sun were returned to a drawer. On the first of March, he developed the photographic plates expecting only faint images to appear. To his surprise, the images were clear and strong. This meant that the uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity, the spontaneous emission of radiation by a material. Later, Becquerel demonstrated that the radiation emitted by uranium shared certain characteristics with X rays but, unlike X rays, could be deflected by a magnetic field and therefore must consist of charged particles. For his discovery of radioactivity, Becquerel was awarded the1903 Nobel Prize for physics.

Niels Bohr (1885 – 1962)
Provided the theory explaining Rutherford’s model of atom

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Bohr was a Danish physicist and Nobel laureate, who made basic contributions to nuclear physics and the understanding of atomic structure. Bohr was born in Copenhagen on October 7, 1885, the son of a physiology professor, and was educated at the University of Copenhagen, where he earned his doctorate in 1911. That same year he went to Cambridge, England, to study nuclear physics under the British physicist Sir Joseph John Thomson, but he soon moved to Manchester to work with Ernest Rutherford. Bohr’s theory of atomic structure, for which he received the Nobel Prize in physics in 1922, was published in papers between 1913 and 1915. His work drew on Rutherford’s nuclear model of the atom, in which the atom is seen as a compact nucleus surrounded by a swarm of much lighter electrons. Bohr’s atomic model made use of quantum theory and the Planck constant (the ratio between quantum size and radiation frequency). The model proposes the explanation that an atom emits electromagnetic radiation only when an electron in the atom jumps from one quantum level to another. This model contributed enormously to future developments of theoretical atomic physics. In 1916 Bohr returned to the University of Copenhagen as a professor of physics, and in 1920 he was made director of the university’s newly formed Institute for Theoretical Physics. There Bohr developed a theory relating quantum numbers to large systems that follow classical laws, and made other major contributions to theoretical physics. His work helped lead to the concept that electrons exist in shells and that the electrons in the outermost shell determine an atom’s chemical properties. He also served as a visiting professor at many universities. In 1939, recognizing the significance of the fission experiments of the German scientists Otto Hahn and Fritz Strassmann, Bohr convinced physicists at a scientific conference in the U.S. of the importance of those experiments. He later demonstrated that uranium-235 is the particular isotope of uranium that undergoes nuclear fission. Bohr then returned to Denmark, where he was forced to remain after the German occupation of the country in 1940. Eventually, however, he was persuaded to escape to Sweden, under peril of his life and that of his family. From Sweden the Bohrs traveled to England and eventually to the United States, where Bohr joined in the effort to develop the first atomic bomb, working at Los Alamos, New Mexico, until the first bomb’s detonation in 1945. He opposed complete secrecy of the project, however, and feared the consequences of this ominous new development. He desired international control. In 1945 Bohr returned to the University of Copenhagen, where he immediately began working to develop peaceful uses for atomic energy. He organized the first Atoms for Peace Conference in Geneva, held in 1955, and two years later he received the first Atoms for Peace Award. Bohr died in Copenhagen on November 18, 1962.

James Chadwick (1891 – 1974)
Proved the existence of the neutron

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In 1913 he received his master’s degree from the University of Manchester and left for Germany to work with Hans Geiger. There, Chadwick was the first to show that beta particles possess a range of energies up to some maximum value. After WWI, Chadwick returned to England and joined forces with Ernest Rutherford. Intrigued by Rutherford’s speculation about a subatomic particle with no charge, Chadwick began a series of experiments to demonstrate the existence of such a particle. Initially, none of the experiments succeeded. Then, in 1930, Walther Bothe and Herbert Becker described an unusual type of gamma ray produced by bombarding the metal beryllium with alpha particles. Chadwick recognized that the properties of this radiation were more consistent with what would be expected from Rutherford’s neutral particle. When Frédéric and Irène Joliot-Curie subsequently claimed that Bothe and Becker’s “gamma rays” could eject high energy protons from paraffin, Chadwick knew these were not gamma rays. The subsequent experiments by which Chadwick proved the existence of the neutron earned him the 1935 Nobel Prize in physics. Not only did this singular particle provide physicists with a superlative tool for investigating the atom, it was also used to produce a wide variety of new radioisotopes and permitted the initiation of nuclear chain reactions. Hans Bethe has referred to Chadwick’s discovery as the historical beginning of nuclear physics.

Arthur Holly Compton (1892 – 1962)
Provided characteristics of electromagnetic radiation

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In 1919, shortly after receiving his doctorate in physics from Princeton, Compton spent a year in Cambridge working under Ernest Rutherford investigating the properties of scattered gamma rays. In the early 1920’s, at Washington University in St. Louis, he continued this line of research using X rays instead of gamma rays. He discovered that the scattering of the X-rays by graphite lowered their energy. Compton hypothesized that the X-rays must be behaving like particles (i.e., photons) that transferred their energy to the electrons of the graphite in a “collision”. This would not happen if X-rays behaved exclusively as waves. For example, the wavelength (i.e., pitch) of sound does not change as it is reflected off a surface. This provided experimental proof that electromagnetic radiation could exhibit the characteristics of particles as well as waves. In acknowledgement of the importance of this work, Compton was awarded the 1927 Nobel Prize in physics. His research then shifted to investigations of cosmic rays. Measurements at thousands of locations around the world showed that the intensity of cosmic rays was affected by the earth’s magnetic field. This provided conclusive evidence that cosmic rays must consist of charged particles. At the outbreak of WW II, Compton’s reputation was such that he was asked to direct the Metallurgical Laboratory. The “Met Lab”, as it was called, was the organization at the University of Chicago that helped guide the nation’s scientific efforts devoted to the development of the atomic bomb.

William David Coolidge (1873 – 1975)
Invented the Coolidge X-ray tube

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coolidgeIn 1913, William David Coolidge revolutionized the field of radiology by inventing what is now referred to as the Coolidge X-ray tube. No new scientific principles or discoveries were involved, and to Coolidge’s employer, the General Electric Company, the invention simply represented a new product. Nevertheless, this new product became a watershed in the field of medicine. The story of its development began in 1905 when Coolidge joined the General Electric Research Laboratory and was given the task of replacing the fragile carbon filaments in electric light bulbs with tungsten filaments. The available tungsten was difficult to work metallurgically, but Coolidge succeeded and his improved light bulb was brought to market in 1911. General Electric also manufactured X-ray tubes and Coolidge recognized that his tungsten filament together with additional modifications could significantly improve the performance of the tube. Coolidge’s improved X-ray tube employed a heated tungsten filament as its source of electrons (i.e., the cathode). Since residual gas molecules in the tube were no longer necessary as the electron source, the Coolidge (or hot cathode) tube could be completely evacuated which permitted higher operating voltages. These higher voltages produced higher energy X rays which were more effective in the treatment of deep-seated tumors. In addition, the intensity of the X rays didn’t show the tremendous fluctuations characteristic of earlier tubes and the operator had much greater control over the quality (i.e., energy) of the X rays. Coolidge later became Director of the laboratory and eventually Vice-President and Director of Research for General Electric. At the beginning of WW II, he was appointed to a small committee established to evaluate the military importance of research on uranium. This committee’s report led to the establishment of the Manhattan District for nuclear weapons development. In 1975, with 83 patents to his credit, William David Coolidge was elected to the National Inventor’s Hall of Fame, the only person to receive this honor in his lifetime.

Marie and Pierre Curie (1867 – 1934 and 1859 – 1906, respectively)
Discovered Radium and Polonium

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The Curies were French physicists and Nobel laureates, who were wife and husband. Together, they discovered the chemical elements radium and polonium. The Curies’ study of radioactive elements contributed to the understanding of atoms on which modern nuclear physics is based. However, it was Marie Curie and her daughter, Joliot-Curie who caught the public imagination. Pierre Curie was born in Paris on May 15, 1859, and studied science at the Sorbonne. Originally named Marja Sklodowska, Marie Curie was born in Warsaw on November 7, 1867. In 1891 she went to Paris (where she changed her name to Marie) and enrolled in the Sorbonne, where she obtained a physics degree. She met Pierre Curie in 1894, and they married in 1895. Marie Curie was interested in the recent discoveries of radiation. Wilhelm Roentgen had discovered X-rays in 1895, and in 1896 Antoine Henri Becquerel had discovered that the element uranium gives off similar invisible radiations. Curie thus began studying uranium radiations, and, using piezoelectric techniques devised by her husband, carefully measured the radiations in pitchblende, an ore containing uranium. When she found that the radiations from the ore were more intense than those from uranium itself, she realized that unknown elements, even more radioactive than uranium, must be present. Marie Curie was the first to use the term ‘radioactive’ to describe elements that give off radiations as their nuclei break down. Pierre Curie ended his own work on magnetism to join his wife’s research, and in 1898 the Curies announced their discovery of two new elements: polonium (named by Marie in honor of Poland) and radium. During the next four years the Curies, working in a leaky wooden shed, processed a ton of pitchblende, laboriously isolating from it, a fraction of a gram of radium. They shared the 1903 Nobel Prize in physics with Becquerel for the discovery of radioactive elements. Marie Curie was the first female recipient of a Nobel Prize. When Pierre Curie died on April 16, 1906, Marie Curie continued her own research. In 1911 she received an unprecedented second Nobel Prize, this time in chemistry, for her work on radium and radium compounds. She became head of the Paris Institute of Radium in 1914 and helped found the Curie Institute. Marie Curie’s final illness was diagnosed as pernicious anemia, which had probably no connection to overexposure to radiation. She died in Haute Savoie on July 4, 1934 — aged 66. The Curies had two daughters, one of whom was also a Nobel Prize winner. Iréne Joliot-Curie and her husband, Frédéric, received the 1935 Nobel Prize in chemistry for the synthesis of new radioactive elements.

Thomas Alva Edison (1847 – 1931)
Improved screens used to see X-rays

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Thomas Alva Edison’s reputation was well established by the time X rays were discovered in November, 1895. He had received patents for hundreds of inventions, including those for the motion picture camera and the first practical incandescent light. Upon learning of R?ntgen’s discovery, Edison set about assembling the necessary equipment to investigate this new phenomenon. Because X-ray tubes were difficult to obtain, Edison manufactured his own, something he was well equipped to do owing to his work with incandescent lights. In fact, some of his original X-ray tubes were little more than modified electric light bulbs. Edison’s investigations into X rays were wide ranging but most of his initial research was devoted to improving upon the barium platinocyanide fluorescent screens used to view X ray images (R?ntgen had discovered X rays by the fluorescence they created from a screen of barium platinocyanide). After investigating several thousand materials, Edison concluded that calcium tungstate was far more effective than barium platinocyanide. By March of 1896, Edison had incorporated this material into a device he called the Vitascope (later called a fluoroscope), that consisted of a tapered box with a calcium tungstate screen and a viewing port. Similar devices already had been developed, but Edison’s version quickly became the standard tool by which physicians viewed X-ray images. During the course of these investigations, Clarence Dally, one of Edison’s most dependable assistants, developed a degenerative skin disorder which progressed into a carcinoma. In 1904, Dally succumbed to his injuries – the first radiation related death in the United States. Immediately, Edison halted all his X-ray research noting “the X rays had affected poisonously my assistant, Mr. Dally…”

Albert Einstein (1879 – 1955)
Developed theory about relationship of mass and energy

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Einstein studied math and physics at the Polytechnic Institute in Zurich, Switzerland. He graduated in 1900. From 1902 to 1909, Albert worked as an examiner at the Swiss Patent Office in Bern. This job as patent examiner allowed him much free time, which he spent in scientific investigations. Einstein became a Swiss citizen in 1905.

The year 1905 was an epoch-making one in the history of physics, because Einstein contributed three papers to Annalen der Physik (Annals of Physics), a German scientific periodical. Each of them became the basis of a new branch of physics.

In one of the papers, Einstein suggested that light could be thought of as a stream of tiny particles. This idea forms an important part of the quantum theory. In 1900, the German physicist Max K. E. L. Planck had proposed that the radiation of light occurred in packets of energy, called quanta. Einstein extended this idea by arguing that light itself consisted of quanta, which were later called photons. Scientists before Einstein had discovered that a bright beam of light striking a metal caused the metal to release electrons, which could form an electric current. They called this phenomenon the photoelectric effect. But scientists could not explain the phenomenon as long as they assumed that light traveled only in waves. Using his theory of quanta, Einstein explained the photoelectric effect. He showed that when quanta of light energy strike atoms in a metal, the quanta force the atoms to release electrons. Einstein’s paper established the theoretical basis for the photoelectric cell, or “electric eye.” This device made possible sound motion pictures, television, and many other inventions. Einstein received the 1921 Nobel Prize in physics for this paper on quanta.

In a second paper, titled “The Electrodynamics of Moving Bodies,” Einstein presented the special theory of relativity. In this paper, he showed how the theory demonstrated the relativity of time, a previously unimaginable idea. Einstein’s name is most widely known for this theory. In a study published in 1905, Einstein showed the equivalence of mass and energy, expressed in the famous equation E=mc2.

The third major paper of 1905 concerned Brownian motion, an irregular motion of microscopic particles suspended in a liquid or gas. It confirmed the atomic theory of matter.

In 1933, while Einstein was visiting England and the United States, Nazi Germany took his property and deprived him of his positions and his citizenship. Even before this misfortune occurred, however, Einstein had been invited to become a member of the staff of the newly created Institute for Advanced Study in Princeton, N.J. Einstein accepted this position for life, and settled down in Princeton. He lived there until his death.

In 1939, Einstein writes a famous letter to President Franklin D. Roosevelt warning of the possibility of Germany’s building an atomic bomb and urging nuclear research.

In 1940, Einstein became an American citizen (but retained his Swiss citizenship). He died on April 18, 1955.

Robley Evans (1907 – 1995)
Built the first whole body counter to measure radium uptake

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The defining moment in Robley Evans’ career came during his graduate studies at Caltech when his supervisor, Robert Millikan, introduced him to the Los Angeles County Health Officer, Frank Crandall. Crandall was concerned about the hazard to the public from radium-containing patent medicines, many of which were being produced in the Los Angeles area. After graduation, Evans accepted a position at the Massachusetts Institute of Technology where he continued to investigate the subject of radium poisoning. Here, Evans built the first whole body counter to measure radium uptake by the radium dial painters and carried out the first quantitative in-vivo measurements of a radionuclide in the human body. Indeed, the scintillation cameras so common in today’s hospitals are direct descendants of his original counter. Evans’ studies went well beyond measuring radium in the body: he pioneered investigations into its metabolism, its hazards, and methods for mitigating these hazards. He was primarily responsible for promulgating the first limit on radioactive material in the body, 0.1 uCi of radium-226, a value that served for more than four decades as the benchmark for bone-seeking radionuclides. Not the least of his contributions was the first use, (ca. 1930s) of radioiodine to evaluate thyroid function in humans, which is a technique that stood the test of time and remained, well into the 1980s, one of the most potent diagnostic tools available to physicians. It is no wonder Robley Evans is recognized as one of the founders of the field of Nuclear Medicine.

Gioacchino Failla (1891 – 1961)
Improved medical applications of radiation

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Gioacchino Failla, one of the greatest pioneers in the fields of biophysics and radiobiology, began his career at New York’s Memorial Hospital in 1915. Within a few years of joining the staff, he had established the first research program devoted to improving the medical applications of radiation. One of the initial products of this research was the construction of a radon generator, the first in the United States. In 1921, Failla was the first to suggest that radiation doses be expressed as the amount of radiation energy absorbed and made the first dose estimates in radium therapy in terms of microcalories per cc of tissue. With the arrival of an X-ray unit at his laboratory the following year, Failla constructed the first human phantom in the U.S. so that he could determine the effects of filtration and distance on X-ray fields in the body. In 1925, upon returning from a one-year sabbatical with Marie Curie in Paris, Failla published protocols and described equipment permitting radiotherapists to deliver the desired doses to their patients accurately. Not the least of his contributions were his roles in founding the International Commission on Radiation Units and Measurements (ICRU), and the Radiation Research Society. Later in his career, Failla left Memorial Hospital for Columbia University where he made important contributions to our understanding of radiation mutagenesis and the induction of cancer by radiation.

Enrico Fermi (1901 – 1954)
Performed first controlled self-sustaining nuclear chain reaction

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Fermi was an Italian-American physicist and Nobel laureate. He is known for achieving the first controlled nuclear reaction. Born in Rome on September 29, 1901, Fermi was educated at the University of Pisa and in some of the leading centers for theoretical physics in Europe. In 1926 he became professor of theoretical physics at the University of Rome. There he developed a new kind of statistics for explaining the behavior of electrons. He also developed a theory of beta decay and, from 1934 on, investigated the production of artificial radioactivity by bombarding elements with neutrons. For the latter work he was awarded the 1938 Nobel Prize in physics. Rather than return to the political harassment of Fascist Italy (Fermi’s wife was Jewish), Fermi and his family immigrated to the United States, where he became professor of physics at Columbia University. By this time Fermi was keenly aware of the significance of his experimental work in the effort to produce atomic energy. He created the first controlled nuclear fission chain reaction in December 1942 at the University of Chicago and worked for the rest of World War II (1939-1945) at Los Alamos, New Mexico, on the atomic bomb. Later, he opposed the development of the hydrogen bomb on ethical grounds. After the war, in 1946, Fermi became a professor of physics and the director of the new Institute of Nuclear Studies at the University of Chicago. As in his days at Rome, students from all over the world came to Chicago to study with him. His career was cut short by his untimely death from cancer on November 28, 1954, in Chicago. The Enrico Fermi Award honoring his memory is given annually to the individual who has contributed most to the development, use, or control of atomic energy.

Otto Hahn (1879 – 1968)
Discovered nuclear fission

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Hahn was a German physical chemist and Nobel laureate, whose greatest contributions were in the field of radioactivity. Hahn was born in Frankfort-am-Main and educated at the universities of Marburg and Munich. In 1911 he became a member of the Kaiser Wilhelm Institute for Physical Chemistry in Berlin and served as director of the institute from 1928 to 1945, when it was taken into Allied custody after World War II. In 1918 he discovered, with the Austrian physicist Lise Meitner, the element protactinium. Hahn, with his coworkers, Meitner and the German chemist Fritz Strassmann, continued the research started by the Italian physicist Enrico Fermi in bombarding uranium with neutrons. Until 1939 scientists believed that elements with atomic numbers higher than 92 (known as transuranic elements) were formed when uranium was bombarded with neutrons. In 1938, however, Hahn and Strassmann, while looking for transuranic elements in a sample of uranium that had been irradiated with neutrons, found traces of the element barium. This discovery, announced in 1939, was irrefutable evidence, confirmed by calculations of the energies involved in the reaction, that the uranium had undergone fission, splitting into smaller fragments consisting of lighter elements. Hahn was awarded the 1944 Nobel Prize in chemistry for his work in nuclear fission. It was proposed in 1970 that the newly synthesized element number 105 be named hahnium in his honor, but another naming system was adopted for transuranium elements beyond 104.

Victor F. Hess (1883 – 1964)
Discovered cosmic rays

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Today, Victor F. Hess is best known for his discovery of cosmic rays in 1911. Originally, however, there was considerable uncertainty about the exact nature of the radiation he had detected. It wasn’t until 1936, when further research by Hess and others (e.g. Robert Millikan who coined the term cosmic rays) had confirmed the extraterrestrial origins of the radiation, that Hess was awarded the Nobel Prize in physics. Other cosmic ray studies by Hess involved their biological effects, their seasonal variation and the influence of magnetic disturbances on their intensity. However, for most of his career, Hess studied the medical uses of radium and the nature and diagnosis of radium poisoning. Between the years 1945 to 1965, Hess measured the radium body burdens of thousands of radium workers. Many of these measurements utilized extremely sensitive techniques developed by Hess at Fordham University. As a footnote, it was during WW I that Hess was the first to utilize Geiger counters for the detection of gamma rays.

Saul Hertz (1905- 1950)
An American physician who discovered the use of radioactive iodine for the treatment of thyroid disease.

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In collaboration with the physicist Arthur Roberts of MIT, Saul Hertz began studies in rabbits to evaluate the effects of I-128 produced in very small quantities by neutron bombardment on the thyroid. The experiments demonstrated the tracer capabilities of radioactive iodine and its effects on the thyroid gland. In 941, Hertz produced a I-130 – I-131 mixture as a therapeutic dose to the first human patient, and administered it to a patient with Graves’ hyperthyroidism, or Graves’ disease. This was the first successful treatment of humans with an artificially produced radioactive material.

As the interest in atomic energy for peaceful purposes was heightened, Hertz established the Radioactive Isotope Research Institute in Boston, Massachusetts, in 1946. Its purpose was to apply fission products to the treatment of thyroid cancer, goiter, and other malignant growths. He worked with the government to centralize an agency to handle the distribution of radioactive isotopes for use by private enterprises working on approved projects. He made extensive studies of radioactive iodine in the treatment of thyroid cancer as well as in the production of total thyroidectomy in the treatment of certain cases of heart disease. Hertz studied the application of radioactive phosphorus and the influences of hormones on cancer as displayed by isotope studies.

Hertz wrote over 50 scientific publications dealing mainly with topics in thyroid physiology, its disease and treatment. He influenced the development of nuclear medicine through his research and instruction at both Harvard and MIT. The development of radioactive iodine in the treatment of thyroid disease is the cornerstone on which nuclear medicine was built.

Jean Frédéric Joliot and Irène Curie (1900 – 1958 and 1897 – 1956, respectively)
Discovered artificial radioactivity

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In 1925, Frédéric Joliot accepted the position of special assistant to Marie Curie. The next year, he married Marie’s daughter, Irène, forming one of the most remarkable scientific partnerships of all time: Frédéric served the role of chemist, Irène that of physicist. Unfortunately, the early stage of their careers was defined by failure rather than success. Not only did they fail to discover the neutron, misidentifying it as a gamma ray, they also just missed discovering the positron. Later on, however, it was their observations of these very particles that led to their discovery of artificial radioactivity, which is considered to be their greatest triumph. Irène and Frédéric had noted that the bombardment of aluminum with alpha particles resulted in the emission of neutrons and positrons. As expected, the neutrons were emitted only as long as the aluminum was being bombarded by alpha particles. What astonished Frédéric and Irène was the continued emission of positrons long after the alpha source had been removed from the target. Immediately, Frédéric and Irène performed careful analyses, which showed that the alpha bombardment had produced a positron-emitting radionuclide of phosphorous from the aluminum. Not only had they produced the first artificial radionuclide, they were the first to experimentally confirm transmutation, the conversion of one element into another element! Up to this point, the only radioactive materials available for medical and scientific research were those that occurred naturally. Now a method was available for creating a wide new variety of radioisotopes. The impact was immense, and for this discovery the Joliot-Curies won the 1935 Nobel Prize for chemistry. Later, during WW II, they helped hamper German efforts to develop an atomic bomb by ensuring that the entire stock of heavy water from the Norsk Hydro Plant was secured and shipped to Britain before France and Norway came under German control. After the war, they made major contributions to the construction of France’s first nuclear reactor.

Ernest O. Lawrence (1901 – 1958)
Invented the cyclotron

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During the 1920s, the only available method for probing nuclei was that developed by Ernest Rutherford, which consisted of bombarding the nuclei with alpha particles. A major problem with this technique was overcoming the repulsive forces between the positively charged alpha particle and the target’s positively charged nucleus. The relatively low energies possessed by alpha particles compounded the problem. Rutherford’s method worked reasonably well with light elements, whose nuclear charges were small, but failed with elements of high atomic numbers. To overcome this problem, a number of machines were developed for accelerating charged particles to higher energies, but the cyclotron of Ernest Lawrence would prove the most important tool in high-energy physics. Lawrence conceived the idea for the cyclotron in 1929 after coming across an article by Rolf Wider?e. The article described an accelerator that employed a pair of linearly arranged cylinders and an alternating electric field. Lawrence’s inspiration was to reconfigure Wider?e’s cylinders as D-shaped chambers and position them between the poles of a magnet. Within the “dees”, ions (e.g., protons) were accelerated in a series of steps over a spiral path. As such, the cyclotron could be small yet capable of generating very high energy ions. Even Lawrence’s first machine, only 4.5″ in diameter, accelerated protons to 80,000 eV. Later, Lawrence used improved versions of the cyclotron to investigate nuclear processes and to produce a variety of new and medically important isotopes (e.g., the phosphorus-32 used in early attempts to treat leukemia). For this work, Lawrence received the 1939 Nobel Prize in physics. Today, descendants of this first cyclotron continue to play an important role in the treatment of cancer and have proven to be the physicist’s most useful tool for exploring the nature of matter.

Lise Meitner (1878 – 1968)
Assisted Hahn in discovering fission

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Meitner was an Austrian-Swedish physicist, who first identified nuclear fission. She was born in Vienna and educated at the universities of Vienna and Berlin. In association with the German physical chemist Otto Hahn, providing the theoretical basis for fission, she helped discover the element protactinium in 1918, and was a professor of physics at the University of Berlin from 1926 to 1933. When Nazi Germany annexed Austria in 1938, Meitner, a Jew, fled to Sweden. In her absence, Hahn and Fritz Strassmann continued experiments they had begun earlier with Meitner and demonstrated that barium was produced when a uranium nucleus was struck by neutrons. This was absolutely startling because barium is so much smaller than uranium! Hahn wrote to Meitner, “it [uranium] can’t really break up into barium . . . try to think of some other possible explanation.” While visiting her nephew Otto Frisch for the Christmas holidays in Denmark, she and Frisch proved that a splitting of the uranium atom was energetically feasible. They employed Niels Bohr’s model of the nucleus to envision the neutron inducing oscillations in the uranium nucleus. Occasionally the oscillating nucleus would stretch out into the shape of a dumbbell. Sometimes, the repulsive forces between the protons in the two bulbous ends would cause the narrow waist joining them to pinch off and leave two nuclei where before there had been one. Meitner and Frisch described the process in a landmark letter to the journal Nature with a term borrowed from biology: fission. In 1939 Meitner published the first paper concerning nuclear fission. She is also known for her research on atomic theory and radioactivity. In her work she predicted the existence of chain reaction, which contributed to the development of the atomic bomb.

Hermann Joseph Muller (1890 – 1967)
Father of radiation genetics

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Hermann Muller, the father of radiation genetics, began his career with T.H. Morgan studying mutations in fruit flies (Drosophila). Muller grew impatient with the mutation rate in Drosophila and was the first to increase the mutation rate using heat. Still not satisfied, he irradiated the flies with 50 kilovolt X-rays that resulted in an even greater incidence of mutations. In doing so, he was the first to demonstrate radiation-induced genetic alterations! Moreover, he did so in a quantitative manner that determined the mutation frequency. Nevertheless, it took nearly two decades for this work to be recognized with the Nobel Prize. The delay was in large part due to his left-wing politics, his controversial views on eugenics and his often unpopular opinions about the hazards of radiation. In 1931, the severe criticism and pressure to which these views exposed Muller caused him to leave the United States. A year later he ended up in Leningrad directing the genetics laboratory at the Institute of Applied Botany. Eventually, Stalin’s reign of terror and disagreements with Trofim Lysenko led Muller to leave for Scotland, where he and S.P. Ray-Chaudhuri studied mutation frequency and dose rate dependence. About this time, he began warning about needless exposures to radiation and their associated risks of cancer and heritable genetic effects. By the late 1940s, the nuclear weapons testing program had begun and Muller was back in the United States, a vocal critic of the Atomic Energy Commission’s views on the hazards of worldwide fallout. As a result, the AEC did not choose Muller as an official US delegate at the 1955 United Nations International Conference on the Peaceful Uses of Atomic Energy. Nonetheless, Muller attended and after virtually every presenter referenced his work, he was given an extended standing ovation!

Herbert Parker (1910 – 1984)
Developed the Manchester System for radium therapy

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Herbert M. Parker began his remarkable career in 1932 by developing, along with James R. Paterson, what ultimately became known as the Manchester System for radium therapy. Their techniques enabled physicians to arrange radium needles or tubes in configurations that would maximize the radiation dose to a tumor while minimizing that to healthy tissue. Other techniques had been developed but the Parker and Paterson system was the most comprehensive and widely used, and is considered a milestone in the field of radiology. In 1938, Parker left England for the Swedish Hospital in Seattle where he conducted research in supervoltage therapy. At the start of WW II, he joined the “Metallurgical Laboratory” at the University of Chicago. Soon afterwards, Parker left Chicago for Oak Ridge where he established the health physics program at what eventually became Oak Ridge National Laboratory. In 1944 he returned to the state of Washington and established the health physics program at the Hanford Engineer Works, a program that he directed until 1956 when he became overall manager for the Hanford Laboratories. Among his many other accomplishments, he was instrumental in the development of the roentgen equivalent physical (“rep”) sometimes called the roentgen equivalent parker, and roentgen equivalent biological (“reb”) units, predecessors to the rad and rem. He also established the first maximum permissible concentration for a radionuclide in air: 3.1 x 10-11 microCurie per cubic centimeter for Plutonium-23.

Edith Quimby (1891 – 1982)
Determined distribution of radiation doses in tissue from various arrangements of radium needles

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Edith Hinkley Quimby began her career in 1919 at the Memorial Hospital in New York City where Gioacchino Failla had established the first research laboratory devoted to the medical uses of radiation. Although no standard techniques were available at the time, radium was widely used to treat cancer. Radium-containing needles were applied to tumors in a makeshift fashion, with no certainty that the tumors received the required exposures. Quimby was the first to determine the distribution of the radiation doses in tissue from various arrangements of radium needles. The techniques she described in 1932 for choosing the most effective grouping of radium needles were widely adopted in the United States and served as the forerunner of Parker and Paterson’s Manchester system. During the same period, she quantified the different doses from beta and gamma radiation required to produce the same biological effect such as skin erythema (i.e., reddening of the skin). In doing so, she pioneered the concept of the relative biological effectiveness of radiation (RBE). This important concept is still employed by radiobiologists and served as the basis for the quality factor used to convert an absorbed dose measured in rad (or gray) to a dose equivalent in rem (or sievert). Although radiologists had previously used X-ray film to estimate radiation exposures, Quimby was the first (ca. 1923) to institute a full scale “film badge” program, which consisted of cutting X-ray film into strips, covered them with black paper and distributed them among the laboratory personnel. In the 1940s, Quimby and Failla moved to Columbia University and began working with the newly available artificial radioisotopes being produced by accelerators and reactors. The early clinical trials with radioactive sodium and iodine to diagnose and treat various medical disorders established her as one of the pioneers of nuclear medicine. Quimby finished her career at Columbia University by teaching a new generation about radiation physics and the clinical use of radioisotopes.

Wilhelm Conrad R?ntgen (1845 – 1923)
Discovered X-rays

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On November 8, 1895, at the University of Würzburg, Wilhelm R?ntgen’s attention was drawn to a glowing fluorescent screen on a nearby table. R?ntgen immediately determined that the fluorescence was caused by invisible rays originating from the partially evacuated glass Hittorf-Crookes tube he was using to study cathode rays (i.e., electrons). Surprisingly, these mysterious rays penetrated the opaque black paper wrapped around the tube. R?ntgen had discovered X-rays, a momentous event that instantly revolutionized the fields of physics and medicine. However, prior to his first formal correspondence to the University Physical-Medical Society, R?ntgen spent two months thoroughly investigating the properties of X-rays. For his discovery, R?ntgen received the first Nobel Prize in physics in 1901. When later asked what his thoughts were at the moment of his discovery, he replied “I didn’t think, I investigated.” It was the crowning achievement in a career beset by more than its share of difficulties. As a student in Holland, R?ntgen was expelled from the Utrecht Technical School for a prank committed by another student. Even after receiving a doctorate, his lack of a diploma initially prevented him from obtaining a position at the University of Würzburg. He even was accused of having stolen the discovery of X-rays by those who failed to observe them. Nevertheless, R?ntgen was a brilliant experimentalist who never sought honors or financial profit for his research. He rejected a title (i.e., von R?ntgen) that would have provided entry into the German nobility, and donated the money he received from the Nobel Prize to his University. R?ntgen did accept the honorary degree of Doctor of Medicine offered to him by the medical faculty of his own University of Würzburg. However, he refused to take out any patents in order that the world could freely benefit from his work. At the time of his death, R?ntgen was nearly bankrupt from the inflation that followed WW I.

Ernest Rutherford (1871 – 1937)
Father of nuclear physics: named and characterized alpha, beta and gamma particle

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Ernest Rutherford is considered the father of nuclear physics. Indeed, it could be said that Rutherford invented the very language to describe the theoretical concepts of the atom and the phenomenon of radioactivity. Particles named and characterized by him include the alpha particle, beta particle and proton. Even the neutron, discovered by James Chadwick, owes its name to Rutherford. The exponential equation used to calculate the decay of radioactive substances was first employed for that purpose by Rutherford and he was the first to elucidate the related concepts of the half-life and decay constant. With Frederick Soddy at McGill University, Rutherford showed that elements such as uranium and thorium became different elements (i.e. transmuted) through the process of radioactive decay. At the time, such an incredible idea was not to be mentioned in polite company: it belonged to the realm of alchemy, not science. For this work, Rutherford won the 1908 Nobel Prize in chemistry. In 1909, now at the University of Manchester, Rutherford was bombarding a thin gold foil with alpha particles when he noticed that although almost all of them went through the gold, one in eight thousand would “bounce” (i.e. scatter) back. The amazed Rutherford commented that it was “as if you fired a 15-inch naval shell at a piece of tissue paper and the shell came right back and hit you.” From this simple observation, Rutherford concluded that the atom’s mass must be concentrated in a small positively-charged nucleus while the electrons inhabit the farthest reaches of the atom. Although this planetary model of the atom has been greatly refined over the years, it remains as valid today as when it was originally formulated by Rutherford. In 1919, Rutherford returned to Cambridge to become director of the Cavendish Laboratory where he had previously done his graduate work under J.J. Thomson. It was here that he made his final major achievement, the artificial alteration of nuclear and atomic structure. By bombarding nitrogen with alpha particles, Rutherford demonstrated the production of a different element, oxygen. “Playing with marbles” is what he called it; the newspapers reported that Rutherford had “split the atom.” After his death in 1937, Rutherford’s remains were buried in Westminster Abbey near those of Sir Isaac Newton.

Glenn Seaborg (1912 – 1998)
Discovered (or co-discovered) the elements plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium and nobelium, as well as a wide variety of radionuclides including iodine-131, technetium-99m, cobalt-60, cesium-137, and iron-55

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Glenn Seaborg made major contributions to science as a discoverer, administrator and educator. During the 1930s, 1940s and 1950s at E.O. Lawrence’s lab in Berkeley and the University of Chicago, Seaborg discovered (or co-discovered) the elements plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium and nobelium, as well as a wide variety of radionuclides including iodine-131, technetium-99m, cobalt-60, cesium-137, and iron-55. Indeed, he helped configure the periodic table as we now know it by placing the actinide series under the lanthanide series. For his discoveries of the transuranic elements and his determination of their chemistry, Seaborg was awarded the 1951 Nobel Prize in chemistry. As an administrator, Seaborg guided the nation’s nuclear programs for ten years while Chairman of the Atomic Energy Commission. As an educator, he was tireless in his efforts to inform the public about the benefits of nuclear power and the use of radionuclides in medicine, industry and the biological and physical sciences. Recently, the element 106 has been named Seaborgium, in honor of Seaborg’s life-long achievements in radiochemistry.

Frederick Soddy (1877 – 1956)
Establishes theory of nuclear reactions (with Rutherford)

Joseph John Thomson (1856 – 1940)
Discovered the electron

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In 1884, at age 28, J.J. Thomson became Director of the Cavendish Laboratory at Cambridge University. He turned what he described as a “string and sealing wax laboratory” into the world’s preeminent center for experimental nuclear physics. Thomson and his student Ernest Rutherford were the first to demonstrate the ionization of air by X rays. So fundamental is this phenomenon that the phrase “ionizing radiation” remains the most concise way to characterize the wide range of electromagnetic and particulate radiation emitted by atoms. Nevertheless, Thomson is best known for his investigations into the nature of “cathode rays”, (i.e., electrons). By deflecting these “rays” with an electric field, something that had been done previously with a magnetic field, Thomson provided conclusive proof that they were negatively charged particles. He determined their mass to be one two-thousandth that of the hydrogen atom, the smallest object known at that time. Thomson was thus the first to identify the existence of subatomic particles. This opened the door to a new world that his student, Ernest Rutherford, would later master, as well as provide his own significant contributions to nuclear physics. Later, Thomson demonstrated that the interaction between electrons and matter produced X-rays and that X-rays interacting with matter produced electrons. Although it would fail the test of time, Thomson is usually credited with the first “modern” model of the atom, the so-called “plum pudding” model. In it, he pictured a sphere of positive charges mixed together with an equal number of electrons (i.e., negative charges). For his theoretical and experimental investigations into the electron and the conduction of electricity by gases, Thomson was awarded the 1906 Nobel Prize in physics. Ironically, Thomson, who had characterized the material properties of electrons, would live to see his son George P. Thomson receive the Nobel Prize for experimentally confirming the wavelike properties of electrons.

George von Hevesy (1885 – 1966)
Conceived the idea of using radioactive tracers

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The discoveries of George von Hevesy have done as much as those of any other individual to influence science in the 20th century. Ironically, it was his inability to accomplish a task assigned by Ernest Rutherford in 1911 that led to his greatest discovery: radiotracers. Hevesy had just joined the research group at the University of Manchester headed up by Rutherford who was investigating the radioactive properties of radium-D (Pb-210). Much to Rutherford’s annoyance, the lead with which the radium-D was associated interfered with his analyses. Not realizing that radium-D was a radioactive form of lead, Rutherford erroneously thought it could be chemically isolated and told Hevesy “My boy, if you are worth your salt, you try to separate radium-D from all that lead”. Out of his failure to complete that impossible task, Hevesy conceived the radiotracer technique by which radioisotopes could be used to investigate the behavior of stable atoms. It is a technique second to none in its analytical power. Hevesy not only performed the first radiotracer studies on plants and animals, using both natural and artificial radionuclides, he also performed the first tracer studies employing stable nuclides by using deuterated water to measure the turnover of hydrogen in the body. In addition to these studies, which earned him the 1943 Nobel Prize in chemistry, Hevesy developed the technique of neutron activation analysis, perhaps the most powerful non-destructive technique for the elemental analysis of solid samples. Despite the importance of the radiotracer technique and neutron activation analysis, Hevesy took the greatest pride in his discovery of the element hafnium. In part, this was because of the magnitude of the effort involved and in part because of the important role hafnium played in the organization of the periodic table.

ANS Darlene Schmidt Science News Award

The ANS Darlene Schmidt Science News Award recognizes journalists and science writers who demonstrate a keen effort on reporting accurate and well-researched science-related media stories to draw the…

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For Students

Know Nukes

There have been many famous scientists and discoverers in nuclear history. Here is a brief history of those who have paved the way.

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Know Nuclear

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