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Science is wonderful thing if one does not have to earn one's living at it.
(A. Einstein)
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NUCLEAR SCIENCE TRAIL
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NUCLEAR PHYSICS HISTORY
The tremendous success of the atomic hypothesis (Dalton, 1803), in explaining both qualitatively and quantitatively the innumerable facts of chemistry, the construction of tables of atomic weights, the discovery of Avogadro's law(1811) and of Faraday's law of electrolisys(1833) all are major achievements of the first part of the nineteenth century. They made the atomic hypothesis highly plausible, and it is surprising, perhaps, that the very existence of atoms should have remained the subject of a deep skepticism lasting into the early years of the twentieth century.
One usually thinks fo atomic energy as a very recent development, yet some of the discoveries that paved the way for modern physics were made as long ago as the 1890s. For example, the German scientist, Wilhelm Roentgen, discovered X rays in 1895 and Henri Becquerel, a French physicist, discovered radioactivity in a sample of pitchblende in 1896.
The importance of these new discoveries was recognized almost immediately, and talented, dedicated scientists began to search for additional radioactive substances and to study the radiation emitted by them. Their interest was aroused because there was nothing in older physical theories that explained the energy involved in radioactivity. Two of the scientists who became interested were Pierre and Marie Curie of France. They managed to separate radium from pitchblende. This gave them a fairly intense source of radioactivity.
These were soon followed by the introduction into physics of the idea of quanta of energy, a concept that developed in a rather roundabout way, by M. Planck, 1900. Quantum concepts, which originated in thermodynamics, were destined to dominate the entire field of the physics of small objects. Together with Einstein's special theory fo relativity, in 1905, they form the foundation on which modern physics rest.
In the process of studying radioactive materials, scientists discovered that there were at least three different forms of radiation emanating from them. They were named alpha, beta and gamma rays. All the rays were found to be capable of darkening photographic plates inside a closed film holder. They differed, howevere, in their abilities to penetrate matter.
In experiments performed in 1899 it was shown that alpha and beta rays, but not gamma rays, were deflected form a straight course when subjected to magnetic forces. This proved that alpha and beta rays were electrically charged particles. Alphas were subsequently found to be positively charged and betas to be negatively charged. The beta particles were finally identified as electrons.
In 1909, Ernest Rutherford and other scientists showed that alpha particles were doubly charged nuclei of helium atoms, that is, helium atoms minus two electrons. Between 1908 and 1913 Rutherford and his associates carried out a classically beatiful series of experiments on the scattering of alpha particles by thin foils of different materials. He found that he could account for the experimental results by a planetary model of the atom. The atomic number Z was then interpreted as the charge of the nucleus in units of the same magnitude as the charge of the electron. Applying to this simple model the idea of the quantum, Niels Bohr, in 1913, accounted for the hydrogen spectrum with admirable precision. This discovery was the starting point for the tumultuos development of atomic physics that culminated in the late 1920s in the establishement of quantum mechanics (W. Heisenberg, M. Born, Louis de Broglie, E. Schrörendinger, Wolfgang Pauli, P.M.A. Dirac, and others).
The neutron discovered, in 1932, in a dramatic succession of events in which W. Bothe, F. Joliot, and J. Chadwick played a vital part, is neutral and has a mass approximately equal to that of the proton.
In 1912 cosmic rays were discovered. These are ionizing particles that impinge upon the earth's surface from high in the atmosphere. "Primary" cosmic rays are those that come into the atmosphere from outer space. They interact with gas molecules in the atmosphere to produce other particles called "secondary" cosmic rays. What finally reaches the earth's surface is a mixture of the primary and secondary rays.
In 1934 Irene Curie (daughter of Marie and Pierre Curie) and her husband Frederic Joliot discovered thar many stable elements under the bombardment of alpha particles became radioactive isotopes of other commomly stable elements (artificial radioactivity). Soon thereafter E. Fermi, E. Amaldi, B. Pontecorvo, F. Rasetti, and E. Segrè showed that neutrons could be slowed down to thermal energies and that at low velocities they were particularly effective in disitegrating other nuclei. This discovery was followed by the fission of uranium by Otto Hahn and F. Strassmann, in 1938, a particular reaction in which neutrons split the uranium nucleus into two large fragments, with the emision of several additional neutrons. This opened the way to the liberation of nuclear energy on a large scale (Fermi, 1942) and to its practical application.
The phenomenology of beta decay presented great puzzles, which were in part overcome by Fermi, in 1933, with the help of the neutrino hypothesis of Pauli(1930). This proved to be a great theoretical importance. It furnished the model that inspired Yukawa's theory of nuclear forces (1935). In his theory H. Yukawa postulated the existence of a particle (the meson or pion) having a mass intermediate between the mass of the electron and that of the proton.
The Yukawa meson was ultimately found by C.M.G. Lattes, G.P.S. Occhialini, C.F. Powell, in 1947. There promply followed the discovery fo several other particles that are still only slightly understood. In 1948, C.M.G. Lattes and E. Gardner at syncro-cyclotron of California University got the production of the artificial pion.
This extremely sketchy historical outline has touched upon only the milestones in the development of nuclear physics. All parts are deeply and vitally interrelated, and the development of highly abstracts theories is as necessary to progress as the construction of gigantic accelerating machines(accelerators
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PARTICLES ACCELERATORS
In the early 1900's, radioactive particles could be obtained only from materials found in nature. The studies that physicists wanted to perform even then required both highter intensities and higher energies than were obtainable form the natural sources. The ability to vary energy and intensity to suit a particular experiment was also desirable. In addition, there was a need to know precisely the composition of the beam of particles, where the beam was hitting the target, and the spread in energy at the target. In other words, what was needed was control, which is the essence of the experimental method.
In the 1930s, scientists began to build machines with which the needed degree of control could be achieved. These machines were called accelerators.
CHRONOLOGICAL LIST OF ACCELERATORS
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Cockroft and Walton accelerator, built by John Douglas Cockroft and Ernest T. S. Walton (Nobel prizes in 1951), that accelerated protons to 700 kev.
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Van de Graaff electrostatic accelerator, proposed by Robert Van de Graaff, that accelerated protons to Mev.
Van de Graaff accelerator
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Cyclotron accelerator, invented and constructed by Ernest Orlando Lawrence.
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Betatron eletron accelerator, constructed by Donald W. Kerst at University of Illinois. It achived energies of 2.5 Mev.
University of Wisconsin Professor Donald W. Kerst, who built the first betatron, standing between his original machine (now in the Smithsonian Institution) and the University of Illinois 300 MeV betatron, the world's largest.
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Synchrocyclotron accelerator,in Berkeley.
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Proton Synchrotron, in Brookhaven.
Over the years several types of accelerators have been constructed. Each has been designed either to solve a unique set of problems or to attack well-known problems in a unique fashion.
Each machine had to be justified on two grounds: (1) the importance of the problems it was to attack, and (2) the probability of success.
When the Bevatron at the Lawrence Radiation Laboratory was being designed, one of the questions being asked by physicists was: "Do the antiproton and antineutron exist?". One of the most impressive single experiments was the identification of the antiproton with the Bevatron (6.2 BeV) at the University of California. This identification of the antiproton convincingly established the validity of a theoretical concept dating from the 1930's, which stated that for every type of particle(such as a proton) there should be a related state in nature, the antiparticle(in this case, an antiproton).
Originally developed as tools for frontier physics, machines commomly known as particles accelerators today are routinely applied in science, industry, medicine, environmental protection, ando other fields. While they come in a range of sizes and types, accelerators that produce relatively low energy beams have become some of the most powerful nuclear analytical tools. Among the practical applications of such low-energy accelerators are highly sensitive scientific analyses of trace elements in studies of air pollution, for example, or in health care and treatment.
Accelerators and their products are used in almost all branches of high technology and modern medicine. Some typical applications of low-energy acceleratores - most of them being cyclotrons, electrostatic generators, and linear accelerators - are: as analytical tools, in life science and medicine, in material science, in environmental protection and in industry.
In Japan medical applications of accelerators alone include 13 cyclotrons with PET (Positron Emission Tomography) capabilities, heavy-ion accelerators, and more than 500 linear accelerators used for therapeutic applications, mainly located at hospitals.
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RIO DE JANEIRO CYCLOTRON
In Rio de Janeiro at the Physics Department of the Instituto de Engenharia Nuclear a multiparticle, variable energy isochronous cyclotron(CV-28) was installed in 1974 with the purpose of research in nuclear reactions, nuclear data, radiation damage, radioisotope production, etc.
The CV-28 cyclotron group at the Instituto de Engenharia Nuclear soon after its completion in 1974.
Standing, left to right, Mr.Otavio, Ms. Genice, Ms. M. Lucia, Physicist Clorivaldo, Engineer Floriano, Engineer Zagronsky, Ms. Marlene, Chemist Gevaldo, Physicist Telmo, Chemist Arthur (head of the Physics Dept.), Mr. Valdezio, Engineer Furlanetto and Physicist Orlando. Botton, left Mr. Helio and Mr.Lima.
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The RDS-111 cyclotron at the Instituto de Engenharia Nuclear soon after its completion in 2002.
RDS-111 cyclotron (extractor)
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RDS-111 & CV-28 cyclotrons building
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