Energy & Power

• First Van de Graaff generator, 1931

  Location

  Currently not on view

  ID Number

  1979.0564.01.04

  accession number

  1979.0564

  catalog number

  1979.0564.01.04

  Data Source

  National Museum of American History

• Resistance coil for Edison dynamo

  Location

  Currently not on view

  Date made

  1881

  maker

  Edison Electric Co.

  ID Number

  EM.180941

  catalog number

  180941

  accession number

  24315

  Data Source

  National Museum of American History

• Environmental Button

  Description (Brief)

  This button demonstrates two different forms of solar power. Most people associate solar power with capturing the heat of the sun (solar thermal) or its light (photovoltaics) for use. Wind power is also a form of solar energy since the sun heats the atmosphere and causes air to circulate. For many people, the 1970s energy crisis was a call to action to change how electricity was generated and used. Making the choice to “go solar”—and encouraging others to do the same—reflected growing optimism about the potential of clean, accessible solar energy.

  Location

  Currently not on view

  date made

  1970s

  ID Number

  2003.0014.0402

  accession number

  2003.0014

  catalog number

  2003.0014.0402

  Data Source

  National Museum of American History

• 

  Experimental Incandescent Lamp

  Description (Brief)

  Experimental incandescent lamp, U.S. Patent # 247380. A ribbon radiator will glow but short-circuit before melting.

  Location

  Currently not on view

  date made

  1881

  associated person

  Maxim, Hiram S.

  maker

  Maxim, Hiram S.

  ID Number

  EM.308595

  catalog number

  308595

  accession number

  89797

  patent number

  247380

  Data Source

  National Museum of American History

• 

  Display of Edison experimental light bulb filament

  Location

  Currently not on view

  Date made

  1881

  maker

  Hammer, William J.

  Edison, Thomas Alva

  ID Number

  EM.320526

  catalog number

  320526

  accession number

  241402

  Data Source

  National Museum of American History

• 

  Nernst Incandescent Lamp

  Description (Brief)

  Invented by Walther Nernst, this incandescent lamp could operate in open air and did not violate Edison’s patents. The housing is sectioned for study of the internal ballast resistance mechanism. The glower consists of six iron rods coated with rare-earth elements. The coating gives off light when heated and protects the rod from oxidation.

  Location

  Currently not on view

  date made

  ca 1902

  associated person

  Nernst, Walther

  maker

  Westinghouse Electric & Manufacturing Co.

  ID Number

  EM.214330

  catalog number

  214330

  accession number

  38852

  Data Source

  National Museum of American History

• 

  Nernst Incandescent Lamp

  Description (Brief)

  Invented by Walther Nernst, this incandescent lamp could operate in open air and did not violate Edison’s patents. The housing is sectioned for study of the internal ballast resistance mechanism. The glower consists of three iron rods coated with rare-earth elements. The coating gives off light when heated and protects the rod from oxidation.

  Location

  Currently not on view

  date made

  ca 1904

  maker

  Nernst

  ID Number

  EM.318298

  catalog number

  318298

  accession number

  232729

  Data Source

  National Museum of American History

• 

  Nernst Incandescent Lamp

  Description (Brief)

  Invented by Walther Nernst, this incandescent lamp could operate in open air and did not violate Edison’s patents. The housing is sectioned for study of the internal ballast resistance mechanism. The glower consists of an iron rod coated with rare-earth elements. The coating gives off light when heated and protects the rod from oxidation.

  Location

  Currently not on view

  date made

  ca 1904

  maker

  Nernst

  ID Number

  EM.318299

  catalog number

  318299

  accession number

  232729

  Data Source

  National Museum of American History

• 

  Tungsten Filament Lamp

  Description (Brief)

  Heanysintered tungsten lamp, c1908. This tungsten lamp was at the heart of a Patent Office scandal that saw two men jailed and Heany’s patents disallowed. See Arthur Bright "The Electric Lamp Industry," for the Heany patent fraud case. There are also contemporary articles in Electrical World.

  Brass medium-screw base with skirt, one glass insulator and one ceramic insulator. Seven single-arch non-ductile (sintered) tungsten filaments in series, 7 upper & 6 lower supports (note eyes on upper supports - insulators?), carbon-paste connectors, Siemens seal, asbestos(?) insulator. Tipped S-shaped envelope with taper at neck, 1/2 frost. Mazda A type. “Pat Oct. 15, 1907” stamped on base, “329458”(?) printed on base. “9” inked on one side of press, “H” molded on other side. Label reads: “Heany V Tungsten Pat Dec. 25. 06 Pat Dec. 03. 07 Other Patents Pending”. “Heany” on label in stem. Partial “H” on envelope appears to be remnant of a William Hammer Collection marking.

  Location

  Currently not on view

  date made

  ca 1908

  maker

  Heany, John Allen

  Heany Lamp Co.

  ID Number

  EM.320466

  catalog number

  320466

  accession number

  241402

  Data Source

  National Museum of American History

• 

  Nernst Incandescent Lamp Component

  Description (Brief)

  This glower assembly was the active element in a Nernst incandescent lamp. When it burned out it could be quickly replaced. The glower consists of iron rods coated with rare-earth elements. The coating gives off light when heated and protects the rod from oxidation.

  Location

  Currently not on view

  date made

  ca 1900

  maker

  Westinghouse Electric & Manufacturing Co.

  ID Number

  EM.334501

  catalog number

  334501

  accession number

  271855

  Data Source

  National Museum of American History

• 

  First betatron of Donald Kerst, 1940

  Description

  Object N-08216 is the assembly of the first Kerst Betatron as it appeared in the Atom Smashers exhibition at the NMAH. mounted horizontally, a toroidal vacuum chamber made of white ceramic with two cylindrical ports, each joined to fused-on glass extensions; circular magnet coils mounted above and below plane of vacuum chamber; rectangular laminated iron yoke surrounding the coils on top, bottom and two sides; enclosing the yoke, a rectangular metal frame of four horizontal angle strips joined by four welded vertical straps, two on each side, and by four bolts, two on each end. Between the yoke laminations and each coil is a thin sheet of slightly flexible, warped, black material, like plastic or impregnated cardboard; each is in two pieces to fit around the central axis. Two circular gray plates are positioned at the top and bottom of the vacuum chamber, separating it from the upper and lower coils, respectively.

  It is presumed that the left-hand cylindrical port contains the electron source, and the right-hand port contains the beam of x-rays from the internal target. Wires protrude from both cylindrical ports.

  History and basic principles

  Among the many investigators who attempted to accelerate electrons by magnetic induction, none were successful until Donald Kerst produced 2.3-MeV electrons in a betatron at the University of Illinois in 1940. He later constructed a number of betatrons of successively higher energies, culminating in the 300-MeV betatron at the University of Illinois. Kerst’s success was due to a very careful theoretical analysis of the orbit dynamics in accelerators (including a study of the requirements for injection); to a preliminary analysis of all conceivable effects relevant to the operation of a betatron; and to a careful and detailed design of the magnet structure, vacuum system, and power supply. This was the first new accelerator to be constructed on the basis of a careful scientific analysis and a completely engineered design. Its success represented a turning point in the technology of particle accelerators from cut and try methods to scientifically engineered designs. All later accelerators, including the newest high energy synchrotrons, have been influenced by this early work of Kerst. It is only in the light of these later developments that we see the importance of the betatron not merely as a valuable instrument in itself but as a milestone in the development of particle accelerators generally. For example, the radial and vertical oscillations of the beam in all particle accelerators are now universally called betatron oscillations after the pioneering work of Kerst and Robert Serber, who together in 1941 published the first theoretical analysis of such oscillations as they occur in the betatron.

  The betatron was quickly put to use in industry, medicine, and nuclear physics research. It was the first accelerator to provide gamma rays for photo-nuclear studies. In the late 1940s and early 1950s the betatron was used for much of the experimental research on photo disintegration of the deuteron, on photo-nuclear reactions (including the discovery of the giant dipole resonances), and important early work on nuclear structure from electron scattering. Of great importance was the pioneering use of megavolt electron beams for the production of energetic X rays for the therapeutic treatment of cancer. His fascinating depiction of this treatment included a description of the first use of phantoms and the intense activity precipitated by a student afflicted with brain tumor, heroic efforts that achieved much, but were unable to save the student. Kerst took a one-year leave of absence from the University of Illinois (1940-41), designed a 20-MeV betatron and a 100-MeV betatron working with the engineering staff at General Electric. He oversaw the construction and operation of the 20-MeV betatron, which he brought back to Urbana. During World War II days, Kerst built a 4-MeV portable betatron for inspecting bomb duds in situ and, most importantly, built a 20-MeV betatron at Los Alamos for study of bomb assembly implosions. His work was described in the official history of Los Alamos as: “The technical achievements are amongst the most impressive at Los Alamos.” After World War II Kerst built a 300-MeV betatron at the University of Illinois that was brought into operation in 1950 and provided a facility for studying high energy physics until it was superseded by synchrotrons and then by electron linacs.

  (Above text excerpted from Donald William Kerst, 1911—1993, a Biographical Memoir by Andrew M. Sessler and Keith R. Symon, Copyright 1997, National Academies Press, Washington DC.)

  It is no accident that the magnetic induction accelerator was so late to be realized. The concept had been advanced repeatedly in the preceding twenty years, but the problems of establishing and maintaining a particle beam were far greater than those encountered with several other accelerator types that were reduced to practice in the 1930’s.

  Electrons, due to their relatively small mass, are much more “skittish” than the much more massive protons, and in the betatron must make a thousand times more circuits to reach the same energy as protons accelerated in a cyclotron. Where the cyclotron runs continuously, allowing the protons to find their own orbit, the betatron is pulsed: electrons must be injected at the right velocity to be captured into stable orbits, and held in them by a balance between the magnetic fields responsible for their acceleration and their orbit guidance, respectively. Kerst’s success depended decisively upon close mathematical analysis of these orbits, especially those immediately after injection into the vacuum chamber. This analysis was performed in collaboration with theoretical physicist, Robert Serber.

  The principle of operation of the betatron is similar to that of a high voltage transformer. Alternating currents in the upper coils produce an increasing magnetic field, thus inducing an electromotive force around the electron’s circular orbit. This force, which Kerst calculated to be only 17 volts maximum acts on the electrons during each of their 200,000 circuits of the vacuum chamber, imparting a total energy of over two million electron volts (MeV).

  The electrons are introduced into the vacuum chamber by an injector; they are not brought out of the vacuum chamber, but strike an internal target, converting their energy into x-rays which emerge through a second port.

  Kerst, like E.O. Lawrence at the University of California, Berkeley, saw no intrinsic limits to his device. From the moment Kerst’s first device operated successfully in July 1940, he and his University looked forward to one more powerful (300 MeV) even than the cyclotrons being developed at Berkeley. Begun in 1945, immediately after World War II, with a special appropriation from the Illinois State Legislature, it was soon to be outmoded by newer methods of particle acceleration (e.g., the synchrotron).

  Location

  Currently not on view

  date made

  early 1940's

  maker

  Kerst, Donald

  ID Number

  EM.N-08216

  accession number

  233629

  Data Source

  National Museum of American History

• 

  Radon-beryllium neutron source used by E. Fermi & associates, 1933-34

  Description

  Object EM*N-08430 consists of radon gas and a beryllium rod, enclosed in a glass tube, all enclosed in an exterior brass cylinder. This apparatus was used in 1934-35 by Enrico Fermi and coworkers in producing slow neutrons in investigations on induced radioactivity.

  The brass rod pulls apart; inside is a glass tube sealed at both ends. Inside one end of the glass tube is a small sealed glass pod, prevented from sliding by wads of cotton. Inside the pod is a mass of black granules; the tube glass is discolored purple in this pod region. The outer brass rod/tube has internal pads at each end.

  History

  In their attempts to excite and transform atomic nuclei, physicists were limited throughout the 1920’s to bombarding atoms with particles, chiefly alpha particles, spontaneously emitted by sources consisting of naturally radioactive substances, for example radium. (Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus.) Disadvantages of using alpha particles included the limited supply and great expense of radium and similar substances, as well as the limited energy and uncontrollability of these spontaneous radiations. The situation was overcome by the use of neutrons, first discovered by James Chadwick in 1932. (See Chadwick ionization chamber replica; object ID no. - - - -) Chadwick recognized evidence of the particle in I. and F. Joliot Curie’s description of phenomena resulting from the bombardment of beryllium by alpha particles. Although the husband and wife team missed the neutron discovery, their continuing investigations of the bombardment of light elements by alpha particles led them in 1934 to recognize that in this process radioactivity was being induced artificially in the target nuclei. (See Joliot-Curie apparatus replica; object ID no. EM*N-09624.2)

  Based on the above discoveries, Enrico Fermi at the University of Rome immediately inferred that if alpha particles could induce artificial radioactivity, neutrons should do so - - and far more readily. He quickly gathered his group of young coworkers to help him exploit the field thus opened.

  Basic principles of Fermi’s neutron source

  When a radioactive element that emits alpha particles is mixed with a light element such as beryllium, neutrons are emitted because many of the alpha particles are absorbed by the nuclei of the light element. The radon-beryllium mixture in the tube of object no. EM*N-08430 was used as a source of neutrons by Fermi and his associates at the University of Rome in 1934-35 for their investigations of neutron-induced radioactivity, which showed that nuclear reactions could be produced in almost all elements by bombarding them with neutrons.

  In Fermi’s neutron source, radon gas (Rn 222) was bled from a solution of radium (Ra 226) and collected on and around the beryllium metal at one end of the tube. The radon decays with a half-life of 3.8 days to lead (Pb 210) by way of two short lived alpha-emitting isotopes. The three alpha particles resulting from the decay of the isotopes interact with the beryllium (Be 9) to produce neutrons.

  Location

  Currently not on view

  Date made

  1934-1935

  maker

  Fermi

  coworkers

  ID Number

  EM.N-08430

  catalog number

  N-08430

  accession number

  247572

  Data Source

  National Museum of American History

• 

  Sample of Plutonium-239

  Description

  The discovery of nuclear fission in uranium, announced in 1939, allowed physicists to advance with confidence in the project of creating "trans-uranic" elements - artificial ones that would lie in the periodic table beyond uranium, the last and heaviest nucleus known in nature. The technique was simply to bombard uranium with neutrons. Some of the uranium nuclei would undergo fission, newly understood phenomenon, and split violently into two pieces. In other cases, however, a uranium-238 nucleus (atomic number 92) would quietly absorb a neutron, becoming a nucleus of uranium-239, which in turn would soon give off a beta-particle and become what is now called neptunium-239 (atomic number 93). After another beta decay it would become Element 94 (now plutonium-239)

  By the end of 1940, theoretical physicists had predicted that this last substance, like uranium, would undergo fission, and therefore might be used to make a nuclear reactor or bomb. Enrico Fermi asked Emilio Segre to use the powerful new 60-inch cyclotron at the University of California at Berkeley to bombard uranium with slow neutrons and create enough plutonium-239 to test it for fission. Segre teamed up with Glenn T. Seaborg, Joseph W. Kennedy, and Arthur C. Wahl in January 1941 and set to work.

  They carried out the initial bombardment on March 3-6, then, using careful chemical techniques, isolated the tiny amount (half a microgram) of plutonium generated. They put it on a platinum disc, called "Sample A," and on March 28 bombarded it with slow neutrons to test for fission. As expected, it proved to be fissionable - even more than U-235. To allow for more accurate measurements, they purified Sample A and deposited it on another platinum disc, forming the "Sample B" here preserved. Measurements taken with it were reported in a paper submitted to the Physical Review on May 29, 1941, but kept secret until 1946. (The card in the lid of the box bears notes from a couple of months later.)

  After the summer of 1941, this particular sample was put away and almost forgotten, but the research that began with it took off in a big way. Crash programs for the production and purification of plutonium began at Berkeley and Chicago, reactors to make plutonium were built at Hanford, Washington, and by 1945 the Manhattan Project had designed and built a plutonium atomic bomb. The first one was tested on July 16, 1945 in the world's first nuclear explosion, and the next was used in earnest over Nagasaki. (The Hiroshima bomb used U-235.)

  Why is our plutonium sample in a cigar box? G.N. Lewis, a Berkeley chemist, was a great cigar smoker, and Seaborg, his assistant, made it a habit to grab his boxes as they became empty, to use for storing things. In this case, it was no doubt important to keep the plutonium undisturbed and uncontaminated, on the one hand, but also, on the other hand, to make it possible for its weak radiations to pass directly into instruments - not through the wall of some closed container. Such considerations, combined probably with an awareness of the historic importance of the sample, brought about the storage arrangement we see.

  Location

  Currently not on view

  Date made

  1941-05-21

  Associated Date

  1941-05-29

  referenced

  Segre, Emilio

  Seaborg, Glenn T.

  Kennedy, Joseph W.

  Wahl, Arthur C.

  Lewis, G. N.

  University of California, Berkeley

  maker

  Segre, Emilio

  Seaborg, Glenn

  ID Number

  EM.N-09384

  catalog number

  N-09384

  accession number

  272669

  Data Source

  National Museum of American History

• 

  Experimental Laser Crystal

  Description

  A major breakthrough marks only the beginning of a scientist's work. In November 1960 Peter Sorokin and Mirek Stevenson, at IBM's Watson Research Center, successfully demonstrated a second type of laser. They energized a crystal of calcium-fluorine treated with a variety of uranium (written in chemical symbols as CaF2:U3+) to generate a pulse of laser light.

  Sorokin and other colleagues experimented with many elements as they learned more about both pulsed and continuous-wave lasers. This crystal, from mid-1962, was the first one made of strontium, fluorine and samarium (SrF2:Sm2+) to successfully operate. Laser research was a very competitive field. Despite their efforts at IBM, Sorokin told museum staff that a team from Bell Labs, "made the first CW [continuous wave] solid-state laser using an ordinary crystal of CaF2:U3+. After that achievement we abandoned our CW efforts and went on to other topics." Those other topics included significant early work on generating laser beams using liquid dyes.

  Location

  Currently not on view

  date made

  1962

  ID Number

  1985.0268.06

  catalog number

  1985.0268.06

  accession number

  1985.0268

  Data Source

  National Museum of American History

• 

  Home-made Laser

  Description

  The term “home-made laser” almost seems a contradiction but that is not the case. This gas laser was built by high school student Stephen M. Fry in 1964, only four years after Ali Javan made the first gas laser at Bell Labs. Fry followed plans published in Scientific American's "The Amateur Scientist" column in September 1964, (page 227).

  The glass tube is filled with helium and neon and, as the magazine reported, "seems to consist merely of a gas-discharge tube that looks much like the letter 'I' in a neon sign; at the ends of the tube are flat windows that face a pair of small mirrors. Yet when power is applied, the device emits as many as six separate beams of intense light."

  The discharge tube is the only piece of this particular laser that remains. The flat windows (called "Brewster windows") are square instead of round, and the electrodes are parallel to the gas tube instead of perpendicular. Otherwise it resembles the drawings in the magazine. Fry later earned a Ph.D. in physics with a dissertation on lasers.

  Location

  Currently not on view

  Date made

  1964

  date ordered, given, or borrowed

  1985-03-15

  maker

  Fry, Stephen M.

  ID Number

  1985.0269.01

  accession number

  1985.0269

  catalog number

  1985.0269.01

  Data Source

  National Museum of American History

• 

  Carrier Centrifugal Refrigeration Compressor

  Description

  The first successful mechanical refrigeration equipment was patented soon after the Civil War, but the large size and high cost of these early machines restricted their use to industrial processes. In his effort to improve mechanical air-conditioning systems, Willis Haviland Carrier (1876-1950) introduced the first practical centrifugal refrigeration compressor in 1922 (pictured here). This machine provided the foundation for safer, smaller, and more powerful and efficient large-scale air-conditioning systems.

  Prior to the introduction of the centrifugal compressor--which compressed the refrigerant gas through the centrifugal force created by rotors spinning at high speed—reciprocating compressors compressed the refrigerant by the action of pistons inside cylinders, much like an automobile engine. The centrifugal compressor proved an extremely important advancement and paved the way for "comfort" air conditioning in theaters, department stores, hospitals, banks, offices, and hotels.

  Carrier installed this initial compressor at his company's Newark, N.J., offices, where he gave the first public demonstration of the machine on May 22, 1922. Two years later, he sold the compressor to the Onondaga Pottery Company of Syracuse, N.Y., for the air conditioning of its lithography plant. The machine remained in use there until about 1957, when the Carrier Company repurchased the compressor for donation to the Smithsonian. Earlier, in 1924, the Carrier Company had installed centrifugal refrigeration machines in the J. L. Hudson department store in Detroit and the Palace Theater in Dallas, thereby introducing the phrase "air conditioning" into the public vocabulary.

  Location

  Currently not on view

  date made

  1922

  maker

  Carrier Corporation

  ID Number

  MC.318219

  catalog number

  318219

  accession number

  232896

  Data Source

  National Museum of American History

• 

  Carbon Filament Lamp

  Description (Brief)

  Incandescent lamp with United States base and a milk-glass envelope.

  Location

  Currently not on view

  date made

  ca 1884

  maker

  Weston

  Weston Electric Light Co.

  ID Number

  EM.334460

  catalog number

  334460

  accession number

  271855

  Data Source

  National Museum of American History

• 

  experimental silicon photosensitive electromotive force cell

  Description (Brief)

  Engineer Russell Ohl worked at Bell Labs during the 1930s and made a discovery that contributed to the invention of both solar cells and transistors. While researching semiconductors—materials whose ability to conduct electricity can be manipulated—he found positive (P) and negative (N) regions created by impurities in his silicon sample. The barrier between the regions, called a P-N junction, prevented electrons from moving—until he exposed the silicon to sunlight. Then electrons crossed the junction and generated a current, converting sunlight into electrical energy. The silicon rod mounted in this reflector contains a P-N junction across the center and is drawn as figure eight on U.S. Patent 2,402,662, "Light-Sensitive Electric Device," issued to Ohl on 25 June 1946.

  Location

  Currently not on view

  Date made

  1940

  associated date

  1940

  associated user

  unknown

  associated person

  Ohl, Russell S.

  maker

  Ohl, Russell S.

  ID Number

  EM.334949

  catalog number

  334949

  accession number

  314577

  maker number

  10

  patent number

  2402662

  Data Source

  National Museum of American History

• 

  ME&M knife switch

  Location

  Currently not on view

  ID Number

  EM.336947

  catalog number

  336947

  accession number

  1979.0875

  Data Source

  National Museum of American History

• 

  Columbia University Cyclotron (John R. Dunning, 1939)

  Description

  Background on Dunning Cyclotron; object id no. 1978.1074.01

  This object consists of the core component of an early particle accelerator (“atom smasher”), based on the principle developed in 1931 by Ernest O. Lawrence at the University of California, Berkeley. Professor John R. Dunning (1907-1975) and his team constructed this example of Lawrence’s “cyclotron” starting in 1936 in the basement of the Pupin Physics Laboratories building at Columbia University in New York City. A schematic diagram and brief historical account of the Dunning system appears in “The Nuclear Chain Reaction- Forty Years Later”, Robert G. Sachs ed., 1984, p.17/fig. 5 (go to http://storage.lib.uchicago.edu/fermi/fermi-020/fermi-020.pdf). While this cyclotron was not particularly innovative, it did introduce one new feature. In order to get the highest possible voltage on the accelerating electrodes of the cyclotron (the “dees”), the Dunning cyclotron team used a system designed by team member Herbert L. Anderson to feed the dees with a pair of resonant concentric lines coupled to a high-power oscillator; their cyclotron was the first to use the resonant concentric line feeding system. During its long operational life, this cyclotron underwent modifications, and its present state (see image in associated media files) does not reflect its original design.

  When thrilling word was received in January 1939 that German scientists Otto Hann and Fritz Strassman had identified a completely unexpected effect, the splitting of the uranium nucleus when it absorbs a neutron, the cyclotron was not yet fully functioning. It therefore just missed being used as the first neutron source to verify the discovery outside Europe. In late January 1939, Dunning’s team initially used a radioactive beryllium-radon mixture as the neutron source to bombard a uranium oxide target, to verify the fission process. Subsequently, Dunning repeated the experiment many times to be sure that his findings were accurate. He used two different neutron sources: the natural beryllium radon mixture; and the cyclotron (in which an energetic beam of protons from the cyclotron struck a stationary metal target to produce a secondary neutron beam). Right away, the cyclotron was rapidly and intensively put to use in numerous experiments to follow up the news from Europe.

  In March 1940, the team used the cyclotron to show that it was the comparatively rare uranium-235 isotope that was the most readily fissile component, and not the abundant uranium-238. The samples of U-235 and U-238 were provided by Dunning’s colleague Alfred O. Nier of the University of Minnesota. Nier isolated small quantities of the isotopes by means of a device based on a mass spectrometer originally developed for measurement of relative abundance of isotopes. Nier’s device is also in the Modern Physics Collection (object id no. 1990.0446.01; catalog no. N-09567), and it is presented on the SI collections website. (Search for “Nier Mass Spectrograph” at http://collections.si.edu/search/) This proof, that U-235 was the fissile uranium isotope, opened the way to the intense U.S. efforts under the Manhattan Project to develop an atomic bomb.

  After a long and useful life, the Dunning cyclotron was retired in 1965. The core components were donated to the Smithsonian Institution in December 1965, but the carbon steel electromagnet, weighing over 30 tons, remained at the Pupin Laboratories until its removal a few years ago. Since the cyclotron was modified over its life, the images of the object now at the Smithsonian (see accompanying media files) do not necessarily represent the original object circa 1939, as noted above.

  Basic principles of the cyclotron

  The cyclotron is the simplest of circular particle accelerators. (To see a diagram of a typical cyclotron, go to https://www.physics.rutgers.edu/cyclotron/theory_of_oper.shtml.) At its center is a vacuum chamber which is placed between the pole pieces of a large electromagnet. Within the chamber is a pair “dees” - two flat D-shaped hollow metallic shells - positioned back-to-back forming a cylindrical space, with a uniform gap between the straight sides of the two dees. The plane of the dees is parallel to the faces of the magnet pole pieces. An alternating voltage is applied across the gap between the dees, creating an associated time-varying electric field in that space.

  Electrically charged particles, such as protons or alpha particles, are introduced into the chamber from an ion source at the center. The charged particles are constrained to travel in a circular path inside the dees in a plane perpendicular to the direction of the static uniform magnetic field produced by the electromagnet. The electric field accelerates the particles across the gap between the dees. The electric field is made to alternate with the “cyclotron period” of the particle (determined by magnetic field strength and the particle’s mass and charge). Thus, when the particles complete a semi-circle and arrive at the gap again, the electric field has reversed, so that the particles are again accelerated across the gap. Due to their increased speed in the constant magnetic field, the particles now move in a larger circle.

  The increasing speed of the particles causes them to move in a larger radius with each half-rotation, resulting in a spiral path outward from the center to the outer rim of the dees. When they reach the rim the particles are pulled out by a deflecting electrode, and hit a target located at the exit point at the rim of the chamber, or leave the cyclotron through an evacuated beam tube to hit a remote target. Nuclear reactions due to the collisions of the particle beam and the target atoms will create secondary particles which may be guided outside of the cyclotron and into instruments for analysis.

  Although the radius of the particle’s radius increases with its speed (energy), it can be decreased with a higher magnetic field strength. In a given cyclotron, the limit to the energy for a given type of particle is set by the strength of the magnetic field and the diameter of the dees, which is in turn determined by the diameter of the magnet pole pieces. Thus very large powerful magnets were constructed for cyclotrons. However, due to relativistic effects, as particles approach the speed of light, their relativistic mass increases. Thus, the classical cyclotron is capable of accelerating particles up to only a few percent of the speed of light. To achieve higher particle energies, later generation cyclotrons used either modifications to the frequency of the electric field (as in the “synchrocyclotron”), or modifications to the magnetic field during acceleration (as in the “isochronous cyclotron”).

  For accelerating particles to the highest energies in circular machines, the “synchrotron” was developed in the mid-1940s. In contrast to a cyclotron, particles in a synchrotron are constrained to move in a circle of constant radius by the use of a ring of electromagnets, open in the middle and so much less massive than an equivalent cyclotron magnet. The magnetic field is varied in such a way that the radius of curvature remains constant as the particles gain energy through successive accelerations by a synchronized alternating electric field. For an example of the powerful electromagnets used in modern synchrotrons for high energy physics research, see object id no. 2012.0186.01, Sections of Magnets for Superconducting Super Collider, presented on the SI collections website. (Search for “Sections of Magnets for Superconducting Super Collider” at http://collections.si.edu/search/)

  Uses of cyclotrons.

  For several decades, cyclotrons were the best source of high-energy beams for nuclear physics experiments; several cyclotrons are still in use for this type of research. They enable the determination of various properties, such as the mean spacing between atoms, and the creation of various collision products. Subsequent chemical and particle analysis of the target material may give insight into nuclear transmutation of the elements used in the target.

  In medicine, cyclotrons and synchrotrons can be used in particle therapy to treat cancer. Ion beams from these accelerators can be used, as in proton therapy, to penetrate the body and kill tumors by radiation damage, while minimizing damage to healthy tissue along their path. The particle beams can be used to bombard other atoms to produce short-lived positron-emitting isotopes suitable for PET imaging.

  Location

  Currently not on view

  ID Number

  EM.N-09130

  accession number

  1978.1074

  catalog number

  1978.1074.01

  Data Source

  National Museum of American History

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