Energy & Power

Nier Mass Spectrograph

Description

Background on Nier Mass Spectrograph; object id no. 1990.0446.01; catalog no. N-09567

This object consists of the following three components: ion source with oven and acceleration electrode; semicircular glass vacuum chamber; ion collector with two plates. The original device included an electromagnet, which is not part of this accession.

In 1939, as political tensions in Europe increased, American physicists learned of an astonishing discovery: the nucleus of the uranium atom can be split, causing the release of an immense amount of energy. Given the prospects of war, the discovery was just as worrying as it was intellectually exciting. Could the Germans use it to develop an atomic bomb?

The Americans realized that they had to determine whether a bomb was physically possible. Uranium consists mostly of the isotope U-238, with less than 1% of U-235. Theoreticians predicted that it was the nuclei of the rare U-235 isotope that undergo fission, the U-238 being inactive. To test this prediction, it was necessary to separate the two isotopes, but it would be difficult to do this since they are chemically identical.

Alfred Nier, a young physicist at the University of Minnesota, was one of the few people in the world with the expertise to carry out the separation. He used a physical technique that took advantage of the small difference in mass of the two isotopes. To separate and collect small quantities of them, he employed a mass spectrometer technique that he first developed starting in about 1937 for measurement of relative abundance of isotopes throughout the periodic table. (The basic principles of the mass spectrometer are described below.)

As a measure of the great importance of his work, in October 1939, Nier received a letter from eminent physicist Enrico Fermi, then at Columbia University, expressing great interest in whether, and how, the separation was progressing. Motivated by such urging, by late February 1940, Nier was able to produce two tiny samples of separated U-235 and U-238, which he provided to his collaborators at Columbia University, a team headed by John R. Dunning of Columbia. The Dunning team was using the cyclotron at the University in numerous studies to follow up on the news from Europe the year before on the fission of the uranium atom. In March 1940, with the samples provided by Nier, the team used neutrons produced by a proton beam from 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 fission prediction was verified. The Nier-Dunning group remarked, "These experiments emphasize the importance of uranium isotope separation on a larger scale for the investigation of chain reaction possibilities in uranium" (reference: A.O. Nier et. al., Phys. Rev. 57, 546 (1940)). 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. (For details, see Nier’s reminiscences of mass spectrometry and The Manhattan Project at: http://pubs.acs.org/doi/pdf/10.1021/ed066p385).

The Dunning cyclotron is also in the Modern Physics Collection (object id no. 1978.1074.01; catalog no. N-09130), and it will be presented on the SI collections website in 2015. (Search for “Dunning Cyclotron” at http://collections.si.edu/search/)

The Nier mass spectrometer used to collect samples of U-235 and U-238 (object id no. 1990.0446.01)

Nier designed an apparatus based on the principle of the mass spectrometer, an instrument that he had been using to measure isotopic abundance ratios throughout the entire periodic table. As in most mass spectrometers of the time, his apparatus produced positive ions by the controlled bombardment of a gas (UBr˅4, generated in a tiny oven) by an electron beam. The ions were drawn from the ionizing region and moved into an analyzer, which used an electromagnet for the separation of the various masses. Usually, the ion currents of the separated masses were measured by means of an electrometer tube amplifier, but in this case the ions simply accumulated on two small metal plates set at the appropriate positions. Nier’s mass spectrometer required that the ions move in a semicircular path in a uniform magnetic field. The mass analyzer tube was accordingly mounted between the poles of an electromagnet that weighed two tons, and required a 5 kW generator with a stabilized output voltage to power it. (The magnet and generator were not collected by the Smithsonian.) The ion source oven, 180-degree analyzer tube, and isotope collection plates are seen in the photos of the Nier apparatus (see accompanying media file images for this object).

Basic principles of the mass spectrometer

When a charged particle, such as an ion, moves in a plane perpendicular to a magnetic field, it follows a circular path. The radius of the particle’s path is proportional to the product of its mass and velocity, and is inversely proportional to the product of its electrical charge and the magnetic field strength. A mass spectrometer consists of three components: an ion source, a mass analyzer, and a detector. The ion source converts a portion of the sample into ions. There is a wide variety of ionization techniques, depending on the phase (solid, liquid, gas) of the sample and the efficiency of various ionization mechanisms for the unknown species. An extraction system removes ions from the sample and gives them a selected velocity. They then pass through the magnetic field (created by an electromagnet) of the mass analyzer. For a given magnetic field strength, the differences in mass-to-charge ratio of the ions result in corresponding differences in the curvature of their circular paths through the mass analyzer. This results in a spatial sorting of the ions exiting the analyzer. The detector records either the charge induced or the current produced when an ion passes by or hits a surface, thus providing data for calculating the abundance and mass of each isotope present in the sample. For a full description with a schematic diagram of a typical mass spectrometer, go to: http://www.chemguide.co.uk/analysis/masspec/howitworks.html

The Nier sector magnet mass spectrometer (not in Smithsonian Modern Physics Collection)

In 1940, during the time that Nier separated the uranium isotopes, he developed a mass spectrometer for routine isotope and gas analysis. An instrument was needed that did not use a 2-ton magnet, or required a 5 kW voltage-stabilized generator for providing the current in the magnet coils. Nier therefore developed the sector magnet spectrometer, in which a 60-degree sector magnet took the place of the much larger one needed to give a 180-degree deflection. The result was that a magnet weighing a few hundred pounds, and powered by several automobile storage batteries, took the place of the significantly larger and heavier magnet which required a multi-kW generator. Quoting Nier, “The analyzer makes use of the well-known theorem that if ions are sent into a homogeneous magnetic field between two V-shaped poles there is a focusing action, provided the source, apex of the V, and the collector lie along a straight line” (reference: A.O. Nier, Rev. Sci. Instr., 11, 212, (1940)). This design was to become the prototype for all subsequent magnetic deflection instruments, including hundreds used in the Manhattan Project.

Location

Currently not on view

Date made

ca 1940-02

associated person

Nier, Alfred O.

maker

Nier, Alfred O.

ID Number

1990.0446.01

accession number

1990.0446

catalog number

1990.0446.01

Data Source

National Museum of American History

Survey boat GRAND

Description

Grand is one of four boats used to survey the "ruggedest" 300 miles of the Colorado River's Grand Canyon during the 1923 expedition by the U.S. Geological Survey. Led by Col. Claude Birdseye, the expedition's primary purpose was to survey potential dam sites for the development of hydroelectric power. Indeed, the survey party mapped twenty-one new sites.

Grand is eighteen feet long, with a beam of four feet, eleven inches. Heavily built of oak, spruce, and cedar, the boat weighs about 900 pounds. Grand is one of three boats ordered in 1921 by the survey's sponsors, the Edison Electric Company, and built at the Fellows and Stewart Shipbuilding Works in San Pedro. The vessels were patterned after those designed by the Kolb brothers, who had based their boats on vessels used by trappers in the upper Colorado River canyons.

Location

Currently not on view

date made

1921

associated date

1923

associated institution

US Geological Survey

maker

Fellows and Stewart Shipbuilding Works

ID Number

TR.034381

catalog number

034381

34381

accession number

71541

Data Source

National Museum of American History

Multiwire proportional chamber from J-particle experiment of S. Ting at Brookhaven

Description

This object consists of a rectangular frame (steel, copper) holding signal wires (gold plated wires) separated by planes of high voltage wires (Cu-Be wire). Three planes of signal wires oriented at 60 degree increments; at +80, +20 and at -40. In operation, the entire chamber was filled with gas: 80% argon to provide an ionization medium for creating a detectable electrical signal; and 20% methylal, both as a spark extinguishing and as a cleaning agent (to prevent ageing of the wires due to carbon deposits). This chamber is one of four from left arm of the spectrometer setup at the Brookhaven Alternating Gradient Synchrotron (AGS), which measured electrons and positrons resulting from decay of a hypothesized massive "J" particle.

Basic Principles and History

A multiwire proportional chamber (MWPC) is constructed with alternating planes of high voltage wires (cathode) and sense wires (anode), which are at ground. All the wires are placed in a special gas environment. Spacing between planes is usually on the order of millimeters and voltage differences are typically in the kilovolt range. When a charged particle passes through the gas in the chamber, it will ionize gas molecules. The freed electrons are accelerated towards the sense wire (anode) by the electric field, ionizing more of the gas. In this way a cascade of charge develops and is deposited on the sense wires. The smaller the diameter of the sense wires, the higher the field gradient near the wire becomes. This in turn causes a larger cascade, increasing the efficiency of the chamber.

Georges Charpak built the first MWPC in 1968. Unlike earlier particle detectors, such as the bubble chamber and the first generation of spark chambers, which can record the tracks left by particles at the rate of only one or two per second, the multiwire chamber records up to one million tracks per second and sends the data directly to a computer for analysis. In 1992 Charpak received the Nobel Prize for Physics in acknowledgment of his invention of the MWPC, an electronic particle detector that revolutionized high-energy physics experiments and has had applications in medical physics.

The MWPC in the J-particle experiment of S.C.C. Ting at Brookhaven

The 1976 Nobel Prize in physics was shared by a Massachusetts Institute of Technology physicist who used Brookhaven's Alternating Gradient Synchrotron (AGS) to discover a new particle and confirm the existence of the charmed quark. Samuel C.C. Ting was credited for finding what he called the "J" particle, the same particle as the "psi" found at nearly the same time at the Stanford Linear Accelerator Center by a group led by Burton Richter. The particle is now known as the J/psi.

Ting's experiment took advantage of the AGS's high-intensity, 30 GeV proton beams, which bombarded a stationary beryllium target to produce showers of particles. The decay modes of these particles were identified using a two-arm spectrometer detection system. J particles decay into various combinations of lighter particles; one of these combinations is an electron and a positron. A small fraction of these enter the detection system, one particle in each arm of the spectrometer. Then dipole magnets deflect them out of the plane of the intense beam and measure their momentum; Cerenkov counters measure their velocity; multi-wire proportional chambers their position; scintillator hodoscopes their moment of passage; lead-glass and lead-lucite shower counters their total energy.

In each spectrometer arm there are 4 MWPCs (Ao, A, B, C) with 2 mm wire spacing and a total of 4,000 wires on each arm. There are eleven planes of proportional wires (2 in Ao, 3 each in A, B, & C), and in A, B, & C the planes are rotated 20 degrees with respect to each other to reduce multitrack ambiguities. To ensure the chambers have 100% uniform efficiency at low voltage and a long live time in the highly radioactive environment, a special argon-methylal gas mixture at 2 deg. C was used.

The identification of the J-particle and its significance

A strong peak in electron and positron production at an energy of 3.1 billion electron volts (GeV) led Ting to suspect the presence of a new particle, the same one found by Richter. Their discoveries not only won the Nobel Prize; they also helped confirm the existence of the charmed quark -- the J/psi is composed of a charmed quark bound to its antiquark.

The J/ψ (or J/psi) is a very special particle. Its discovery was announced in 1974 independently by two groups: one lead by Samuel Ting at Brookhaven National Laboratory (BNL) in New York and the second lead by Burton Richter at Stanford Linear Accelerator Center (SLAC) in California. J/ψ is special because it established the quark model as a credible description of nature. Having been invented by Gell-Man and Zweig as a bookkeeping tool, it was not until Glashow, Iliopoulos and Maiani (GIM) that the concept of quarks as real particles was taken seriously. GIM predicted that if quarks were real, then they should come in pairs, like the up and down quarks. Candidates for the up, down, and strange were identified, but there was no partner for the strange quark. J/ψ was the key.

Like the proton or an atom, the J/ψ is a composite particle. This means that J/ψ is made of smaller, more elementary particles. Specifically, it is a bound state of one charm quark and one anti-charm quark. Since it is made of quarks, it is a “hadron“. But since it is made of exactly one quark and one antiquark, it is specifically a “meson.”

For further details, see

http://hitoshi.berkeley.edu/129A/Cahn-Goldhaber/chapter9.pdf

http://www.nobelprize.org/nobel_prizes/physics/laureates/1976/ting-lecture.pdf

Location

Currently not on view

Date made

1972-1973

designer

Becker, Ulrich

ID Number

1989.0050.01.1

accession number

1989.0050

catalog number

1989.0050.01.1

Data Source

National Museum of American History

Preampliier for multiwire proportional chamber from J-particle experiment of S. Ting at Brookhaven

Description

One signal amplifier on rectangular plastic circuit board. Apparently one of these preamplifiers would have been plugged into one corresponding socket of Mulitwire Proportional Chamber 1989.0050.01.1. A sticker accompanying this object reads "8 wire signals [from associated socket on chamber] get amplified .0002V to .8V" (to output to the computer). Similarly for all sockets of all four chambers in each of the two arms of the spectrometer setup at the Brookhaven Alternating Gradient Synchrotron, which was used to measure electrons and positrons resulting from decay of a hypothesized massive "J" particle.

Rectangular green plastic circuit board, with electronic components soldered on upper surface. As viewed from front of board: at left end of bottom edge are 12 contact strips, only 8 of which are connected to the circuits. Near the right end of the bottom edge are 10 such contact strips. Protruding from right edge are 10 pairs of short wires, which are inserted into a green plastic connector fitting, which has 9 contact sockets on the other side.

For background on the multiwire proportional chamber from J-particle experiment of S. Ting at Brookhaven see description for object ID no. 1989.0050.01.1

Location

Currently not on view

date made

1972-1973

designer

Becker, Ulrich

ID Number

1989.0050.01.2

accession number

1989.0050

catalog number

1989.0050.01.2

Data Source

National Museum of American History

Telegdi digital wire spark chamber spectrometer

Description

Three disjoint parts comprise the spectrometer assembly, 1977.0532.01, as follows: 01.1, the spectrometer proper - a rectangular aluminum base on which are mounted four sets of wire spark chambers (7 total), each ca. 0.4 x 0.4 x 0.03 m; 01.2, an individual core memory plane; 01.3, three light aluminum tanks that in the spectrometer assembly are placed between the 4 sets of spark chambers. The whole object includes a fraction of the associated assembly wiring.

The spectrometer proper (.01.1) consists of seven spark chambers, square planes mounted on edge on the surface of a rectangular metal base. Both the pulsed and read planes are made of 4 mil aluminum wires spaced 1 mm apart and enclosed in 1/2 mil Mylar windows. Four of the spark chambers have vertical wires and three have horizontal wires. The individual chambers are positioned on the base in order to measure the coordinates of charged particles as they trace helical orbits in a uniform perpendicular magnetic field. This data allows the energy and momentum of each particle to be determined.

Basic Principles and History

The complete Telegdi spectrometer system consists of a homogeneous magnet containing wire spark chambers with magnetic core readout. The spark chambers were covered with 0.5 mil Mylar, and a 9 to 1 neon-helium mixture flowed through them during operation. Within the spectrometer assembly, each wire chamber is connected to a corresponding memory plane containing ferrite cores. The ferrite core memory planes are located outside the spectrometer magnet in order to avoid interference from the magnetic field. Three aluminum tanks, with 5x10E-4 in. Mylar windows, serve as "helium boxes" placed between the 4 sets of spark chambers to reduce multiple scattering of charged particles (electrons) orbiting through the spectrometer.

Wire spark chambers with magnetic-core readout differ from ordinary visual spark chambers in that one of the plane electrodes (the “write plane”) is divided into wires, each of which is grounded through a ferrite core. Plug-in cables make the connection between the wire chamber and a memory plane. When a spark strikes a write wire, current flows through the core and “sets” it, thus digitizing the spark location. This information may then be transmitted conveniently to an online computer or stored on magnetic tape. For technical details see B. A. Sherwood, Phys. Rev. 156, 1475 (1967).

Between 1958 and 1965 bubble chambers dominated among particle detectors used in particle physics experiments. Bubble chambers enabled allowed photographs to be taken of the particle tracks in a three-dimensional volume and later analyzed exactly as to energy and momentum of each particle. However, accelerators soon provided such copious streams of particles that human scanning of bubble chamber photographs in search of events of interest became the most time-consuming part of the experiment.

The wire spark chamber provided electronic information of the path of a charge particle and was immediately mated with a digital computer programmed to analyze each track for distinct characteristics of interest. The Telegdi wire spark chamber spectrometer, one of the earliest applications of electronic readout spark chambers and on-line computer analysis, was developed in 1964 by V. L. Telegdi and his students at the University of Chicago to measure the energy distribution of positrons in the decay of muons. For detailed information on this experiment, see B. A. Sherwood, ibid.

Location

Currently not on view

date made

1963-1964

maker

Telegdi, V. L.

Sherwood, B. A.

Fryberger, D.

ID Number

1977.0532.01.1

catalog number

1977.0532.01.1

accession number

1977.0532

Data Source

National Museum of American History

Core memory plane for Telegdi wire spark chamber spectrometer

Description

A rectangular circuit board bearing on each side a grid of fine wires with solder joints and pin connections. From one end extend 32 black insulated wires formed into two tied bundles of 16 each, 90 inches long. The bundles are wrapped at intervals with black tape and with masking tape near the ends. The ends of the wires in each bundle emerge from their black sheaths, pass through short translucent plastic tubes, and enter a socket connector fitting. The fine wires running parallel to the length of the board have yellow insulation; the wires perpendicular to these are in eight sets on each side of the board. One set on each side has brown insulation; another, red insulation, and the remaining twelve appear as bare copper.

The wires of all 16 sets terminate in connector strips along one edge of the board. On the opposite edge is a green plastic pin socket fitting . At two corners are wide copper strips folded around on each side of the board; these are soldered to strips of different metal.

A complete spark chamber spectrometer system consists of a homogeneous magnet containing wire spark chambers with magnetic core readout. Within a spectrometer assembly, each wire chamber is connected to its corresponding core memory plane. The core planes must be located outside the spectrometer magnet. For technical details see B. A. Sherwood, Phys. Rev. 156, 1475 (1967).

For background on the Telegdi spark chamber spectrometer assembly, see description for object ID no. 1977.0532.01.1

Location

Currently not on view

date made

1963-1964

maker

Telegdi, V. L.

Sherwood, B. A.

Fryberger, D.

ID Number

1977.0532.01.2

catalog number

1977.0532.01.2

accession number

1977.0532

Data Source

National Museum of American History

Phrenological bust of Thomas Alva Edison

Description

In 1878 Thomas Edison had achieved international renown due to his invention of a machine that could talk: the phonograph. His inventive activities in the field of telegraphy were well known in that important industry. Although his most prolific days as an inventor lay ahead, people understood that "the Wizard of Menlo Park" was someone to be taken seriously.

This bust of Edison was made in 1878 for the Phrenological Institute of New York. Phrenology (today dismissed as false science) involved the study of the shape and size of people's heads. Phrenologists believed that one could measure and rank factors like intellegence, honesty and creativity through a close study of the external features of the head. An accurate record of Edison's head would preserve a record of someone perceived as quite creative and intellegent, allowing comparisions to be made to a known standard.

The bust was made by J. Beer, Jr.

Date made

1878

1878

associated person

Edison, Thomas Alva

maker

S. R. Wells & Co.

ID Number

EM.310582

catalog number

310582

accession number

123470

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

Bose-Einstein Condensation Apparatus

Description

The apparatus that was used to produce the first Bose-Einstein Condensate (BEC) observed in a gas of atoms

In 1995, a group of physicists led by Eric A. Cornell and Carl E. Wieman produced the first BEC in a gas of 2000 rubidium atoms at the NIST–JILA laboratory at the University of Colorado at Boulder. Just about four months later, a group led by Wolfgang Ketterle independently produced a BEC with about 200,000 sodium atoms. Cornell, Wieman and Ketterle were awarded the 2001 Nobel Prize in Physics for their accomplishments.

The Cornell and Wieman BEC apparatus consisted of an atomic trap that cooled atoms by means of two different mechanisms. First, six laser beams cooled the atoms, initially at room temperature, while confining them near the center of an evacuated glass box. Next, the laser beams were turned off, and magnetic coils were energized. Current flowing in through the coils generated a magnetic field that further confined most of the atoms while allowing the more energetic ones to escape. Thus, the average energy of the remaining atoms decreases, making the sample colder and even more closely confined to the center of then trap. Ultimately, many of the atoms attain the lowest possible energy state allowed by quantum mechanics, and become a single entity – a BEC. Other research groups are now using BEC principles for investigations in the field of atom quantum optics, including quantum information processing and development of the atomic analogue of the laser.

The core components of the Cornell-Wieman BEC apparatus are in the Modern Physics Collection at the Smithsonian Institution’s National Museum of American History, in accession no. 1998.0213.

Background on the Bose-Einstein Condensate (BEC) phenomenon

[Adapted from “The Bose-Einstein Condensate,” E.A. Cornell and C.E. Wieman in Scientific American, March, 1998, pp 40-45; and from “Very Cold Indeed: The Nanokelvin Physics of Bose-Einstein Condensation,” Journal of Research of the National Institute of Standards and Technology, V. 101, Jul.–Aug. 1996, p. 419]

In June 1995, a team of scientists succeeded in cooling a gas of 2,000 rubidium atoms to a temperature less than 100 billionths of a degree above absolute zero, causing the atoms to lose for a full ten seconds their individual identities and behave as though they were a single “superatom.” That is, the atoms’ physical properties, such as their motions, became identical to one another. This Bose-Einstein Condensate (BEC), the first observed in a gas, can be thought of as the matter counterpart of the laser – except that in the BEC it is atoms, rather than photons of light, that behave in perfect unison (all going in the same direction with the same energy).

The BEC offers a macroscopic window into the strange world of quantum mechanics, the theory of matter based on the observation that elementary particles, such as electrons, have wave properties. Quantum mechanics uses these wavelike properties to describe the structure and interactions of matter. In ordinary macroscopic matter, the incoherent contributions of the large number of constituent atoms obscure the wave nature of quantum mechanics. But as atoms get colder, they start to behave more like waves and less like particles. Cool a cloud of identical atoms so cold that the wave of each atom starts to overlap with the wave of its neighbor atom, and all of a sudden one creates a BEC. In a BEC, the wave nature of each atom is precisely in phase with that of every other. Quantum mechanical waves extend across the collection of atoms, an image of which can be observed with the naked eye.

Some five decades earlier, physicists had realized that the BEC concept could explain superfluidity in liquid helium, which occurs at much higher temperatures than gaseous Bose-Einstein condensation. (Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity.) When it passes below a critical temperature, liquid helium makes the transition from an ordinary liquid to a superfluid and starts to behave like a quantum fluid. But the helium atoms in the liquid state interact quite strongly, and the system is difficult to understand on an elementary level. Thus, physicists had been pushing for many years to observe Bose-Einstein condensation in a system closer to the gaseous state.

Brief description of fermions and bosons, and Bose-Einstein statistics

All elementary particles, and even composite particles such as atoms, can be divided into bosons and fermions. [The spin of an elementary particle is a truly intrinsic physical property, akin to the particle's electric charge and rest mass, and is expressed as a spin quantum number.] Bosons are particles that have integer spin; 0, 1, 2, 3, and so on (in units of reduced Plank constant, h/(2π)). Fermions are particles that have half-integer spin: 1/2, 3/2, 5/2, and so on, in the same units. Examples of bosons are particles that transmit interactions (i.e., force carriers), such as photons (electromagnetic force), and a large portion of the atoms of individual chemical elements. Examples of fermions are particles that are the elementary building blocks of matter: electrons, protons, neutrons, and the quarks inside protons and neutrons. All atoms are composed of fermions, but if the atom consists of an even number of fermions, it will be a composite particle with integer spin, which is a boson. The new statistics (see below) was first studied in 1924 by Satyendra Nath Bose, so physicists call particles for which only symmetrical states occur in nature bosons. [According to the Oxford English Dictionary, the term “boson” was introduced by physicist Paul Dirac in 1947; P.A.M. Dirac Princ. Quantum Mech, (ed. 3) ix. 210.]

Fermions, the particles with half-integer spin obey Fermi-Dirac statistics. Accordingly, they occupy anti-symmetric quantum states; this property forbids fermions from sharing quantum states – a restriction known as the Pauli Exclusion Principle. Bosons, the particles with integer spin, on the other hand, obey Bose-Einstein statistics (see below). Accordingly, they occupy symmetric quantum states; this property allows bosons to share quantum states. Thus, the latter property allows a collection of identical atoms that are bosons to be cooled to the same quantum state, which is termed a BEC.

Satyendra Nath Bose (1 January 1894 - 4 February 1974) was an Indian mathematician and physicist, best known for his work on quantum mechanics in the early 1920s, which provided the foundation for Bose–Einstein statistics and the theory of the BEC. Specifically, Bose developed a statistical model, based on a counting method that assumed that light could be understood as a gas of indistinguishable quanta or particles. Bose is honored as the namesake of such a particle, a boson

Albert Einstein (14 March 1879 - 18 April 1955) was a renowned, German-born theoretical physicist who developed the theories of special and general relativity, effecting a revolution in physics. In 1924, Einstein received a paper from Bose describing his statistical model. Einstein noted that Bose's statistics also applied to some types of atoms, as well as to the proposed indistinguishable light particles, and submitted his translation of Bose's paper for publication in the Zeitschrift für Physik. Einstein also published his own articles describing the Bose statistical model and its implications, among them the condensate phenomenon that derives from the fact that the number of quantum states available for a collection of bosons at very low energy becomes exceedingly small. With less and less room for all of the particles when the temperature is decreased, they accumulate (condense) in the lowest possible (ground) energy state, as a BEC. [According to the Oxford English Dictionary, the term “Bose-Einstein Condensation” was first used in a 1938 scientific publication; Physical Review, 54 947.] Bose-Einstein statistics are now used to describe the behaviors of any assembly of bosons.

Location

Currently not on view

ID Number

1998.0213.01.01

catalog number

1998.0213.01.01

accession number

1998.0213

Data Source

National Museum of American History

Sections of Magnets for Superconducting Super Collider

Description

The principal objects in accession no. 2012.0186 in the NMAH Modern Physics Collection are representations for public display of key magnet components of the Superconducting Super Collider (SSC), a large U.S. Department of Energy particle accelerator facility that was under construction from 1990 to 1993 in Ellis County, Texas, approx. 25 miles south of Dallas. The SSC was designed to produce collisions of opposing beams of protons at energies of 20 trillion electron-Volts (TeV) for experiments to advance the fundamental understanding of matter and energy. The main accelerator ring was to be located in an underground concrete tunnel with a 54-mile oval path that would encircle the City of Waxahachie. The SSC project was terminated by the U.S. Congress in October 1993, largely due to budgetary issues. The object shown in the image is a display model of a short section of a parallel pair of superconducting dipole magnets in their vacuum vessels, cut-through to show in cross-section the cold mass sub assembly (beam pipe, magnet coils, collar, yoke) and the cryogenic system conduits and insulation.

Background on SSC magnet technology

The SSC main ring design contains the two parallel proton beam pipes, each under high vacuum and encased in powerful electromagnets, in order to confine the protons to travel in their respective, opposing, paths around the ring. The two proton beams are accelerated in opposite directions over many million transits around the ring using precisely-timed energy bursts from radiofrequency cavities. When the beams achieve the desired energy, they can be brought into collision in several experimental halls located around the ring, where highly sensitive detectors capture data on the resulting showers of subatomic particles.

A sequence of electromagnets produces the necessary magnetic fields to both guide and focus the proton beams. Dipole magnets produce the field configurations that bend the beams of electrically-charged particles (protons) on their track in the beam pipe around the oval ring, and quadrupole magnets produce the field configurations that narrowly focus the beams along the central axis of the beam pipes. As designed, the SSC main ring was to use 4,326 15.8 meter long dipole magnets and 1,012 5.9 meter quadrupole magnets.

High electrical currents are required in the electromagnet coils in order to produce the strong magnetic fields that are, in turn, required to guide the proton beams in their transits at such high energies. The SSC employs superconducting technology to enable essentially unhindered current flow in the magnet coils. The coils are wound with cables that contain superconducting wire. A strand of the wire contains filaments of niobium-titanium alloy embedded in a copper matrix. For superconductivity to occur in nobium-titanium, the coils must be cooled to extremely low temperatures. Thus, a cryogenic cooling system with liquid helium and liquid nitrogen blankets the coils and iron cores of the magnets.

A similar accelerator technology is used at the Large Hadron Collider (LHC) now operating at CERN, the European Laboratory for High Energy Physics, in Geneva, Switzerland.

Location

Currently not on view

ID Number

2012.0186.01

accession number

2012.0186

catalog number

2012.0186.01

Data Source

National Museum of American History

Charpak drift chamber connected to electronics box

Description

This object consists of two drift chamber assemblies attached to an electronic box. The two drift chamber assemblies have green plastic walls and transparent plastic windows, in metallic frames with parallel wires running horizontally in the first window and vertically in the second. They are attached to a single perforated metallic covered preamp. The latter assembly is attached on one side to rectangular, metal-enclosed, box for electronics. Wires connect the drift chamber assembly to one side of electronics box. Two high voltage cable receptacles protrude on opposite side of electronics box near top edge.

Basic Principles and History

A wire chamber is a chamber with many parallel wires, arranged as a grid and put on high voltage, with the metal casing being on ground potential. As in the Geiger counter, a particle leaves a trace of ions and electrons, which drift toward the case or the nearest wire, respectively. By marking off the wires which had a pulse of current, one can see the particle's path. If one also precisely measures the timing of the current pulses of the wires and takes into account that the ions need some time to drift to the nearest wire, one can infer the distance at which the particle passed the wire. This greatly increases the accuracy of the path reconstruction and is known as a drift chamber.

While testing their newly developed multiwire proportional chamber (see Object ID no. 1977.0708.02), Charpak and his collaborators found that the difference in arrival times of electrons at adjacent wires, they could quickly estimate just where between the two wires an ionizing particle had passed. They showed that this principle of location - - measuring the time for electrons to drift from the point where produced to a sensing wire - - could be extended from one or two millimeters to many centimeters. The essential refinement was the addition of “field shaping” wires which, by producing a uniform electric field, ensured a constant drift velocity of the electrons. In practice, the drift chamber must be preceded or followed by a counter to mark the starting time of the drifting electrons.

In 1992 Charpak received the Nobel Prize for Physics in acknowledgment of his invention of the MWPC, an electronic particle detector that revolutionized high-energy physics experiments and has had applications in medical physics.

For additional technical information, see:

http://www.nobelprize.org/nobel_prizes/physics/laureates/1992/charpak-lecture.pdf and,

http://cds.cern.ch/record/117989/files/CERN-77-09.pdf?bcsi_scan_2687365ababd2c82=b3SiuvtOAg0NfXwMHl9pO/npSm4KAAAArlNvLw==&bcsi_scan_filename=CERN-77-09.pdf

Location

Currently not on view

Date made

1969

maker

Charpak, G.

ID Number

1977.0708.01

catalog number

1977.0708.01

accession number

1977.0708

Data Source

National Museum of American History

Standard Tungsten Lamp

Description

Irving Langmuir received a Ph.D. in physical chemistry in 1906 from the University of Göttingen. He studied under Walther Nernst, who had invented a new type of incandescent lamp only a few years before. In 1909 Langmuir accepted a position at the General Electric Research Laboratory in Schenectady, New York. Ironically, he soon invented a lamp that made Nernst's lamp (and others) obsolete.

Langmuir experimented with the bendable tungsten wire developed by his colleague William Coolidge. He wanted to find a way to keep tungsten lamps from "blackening" or growing dim as the inside of the bulb became coated with tungsten evaporated from the filament. Though he did not solve this problem, he did create a coiled-tungsten filament mounted in a gas-filled lamp—a design still used today.

Up to that time all the air and other gasses were removed from lamps so the filaments could operate in a vacuum. Langmuir found that by putting nitrogen into a lamp, he could slow the evaporation of tungsten from the filament. He then found that thin filaments radiated heat faster than thick filaments, but the same thin filament–wound into a coil–radiated heat as if it were a solid rod the diameter of the coil. By 1913 Langmuir had gas–filled lamps that gave 12 to 20 lumens per watt (lpw), while Coolidge's vacuum lamps gave about 10 lpw.

During the 1910s GE began phasing-in Langmuir's third generation tungsten lamps, calling them "Mazda C" lamps. Although today's lamps are different in detail (for example, argon is used rather than nitrogen), the basic concept is still the same. The lamp seen here was sent to the National Bureau of Standards in the mid 1920s for use as a standard lamp.

Lamp characteristics: Brass medium-screw base with skirt and glass insulator. Two tungsten filaments (both are C9 configuration, mounted in parallel) with 6 support hooks and a support attaching each lead to the stem. The stem assembly includes welded connectors, angled-dumet leads, and a mica heat-shield attached to the leads above the press. The shield clips are welded to the press. Lamp is filled with nitrogen gas. Tipless, G-shaped envelope with neck.

Date made

ca 1925

date made

ca. 1925

ID Number

1992.0342.23

accession number

1992.0342

catalog number

1992.0342.23

Data Source

National Museum of American History

Non-ductile Tungsten Lamp

Description

Thomas Edison and others considered element number 6, carbon, ideal for lamp filaments in part because it has the highest melting point of any element. Element number 74, tungsten, has the next highest melting point but it then existed only as a powder. Attempts to make it into a workable form failed until early in the 1900s when a burst of invention occurred in Europe. A pressing technique called "sintering" (squeezing a material into a dense mass) was adopted by several inventors.

The most commercially successful design proved to be that of Dr. Alexander Just and Franz Hanaman of Austria. Their work on sintering tungsten was based on a prior sintering process developed by Carl Auer von Welsbach for his filament made of osmium. Just and Hanaman made a tungsten and organic paste, squirted it through a die, baked out the organic material, then sintered the tungsten in a mix of gasses. The resulting filament gave about 8 lumens per watt and lasted 800 hours.

Another Austrian, Dr. Hans Kutzel, used an electric arc to make a tungsten and water paste. He then pressed, baked, and sintered the tungsten in a manner similar to Just and Hanaman's procedure. Yet another pair of Austrians, Fritz Blau and Hermann Remane, adapted the osmium lamp process (they worked for Welsbach) by making a filament from an osmium and tungsten mix. They soon changed their "Osram" lamp filament to tungsten only. (The German word for tungsten is wolfram.)

All three filaments were brittle and collectively known as "non-ductile" filaments. Individual filaments could not be made long enough to give the proper electrical resistance, so lamps needed several filaments connected end-to-end. U.S. companies quickly licensed rights to all of the non-ductile patents. This particular lamp was made under license by General Electric and sent to the National Bureau of Standards for use as a standard lamp.

Lamp characteristics: Medium-screw base with glass insulator. Five single-arch tungsten filaments (in series) with 5 upper and 8 lower support hooks. The stem assembly features soldered connectors, Siemens-type press seal, and a cotton insulator. Tipped, straight-sided envelope with taper at neck.

Date made

ca 1908

date made

ca. 1908

maker

General Electric

ID Number

1992.0342.16

catalog number

1992.0342.16

accession number

1992.0342

Data Source

National Museum of American History

Metal Disintegration Machining System for Three Mile Island Nuclear Reactor Vessel

Description

The metal disintegration machining (MDM) system consists of a box enclosing a cutting head assembly and an attached articulating arm assembly. The lower end of the arm is attached to the top of the cutting head assembly. The MDM system is the principal object of accession no. 2012.0171 in the NMAH Modern Physics Collection.

Background on Metal Disintegration Machining (MDM) System

Edited excerpts from "Phase 4 Status Report, Removal of Test Specimens from the TMI-2 Reactor Vessel Bottom Head, Project Summary, MPR-1195", October 1, 1990, prepared for U.S. Nuclear Regulatory Commission (NRC) Office of Nuclear Regulatory Research (RES). [Copy of Report in NMAH Curator's file for this accession.]

Introduction

Following the accident in March of 1979, the Three Mile Island Unit 2 (TMI-2) [nuclear] reactor vessel sustained significant internal damage. The resulting damage to the lower head and the margin to failure have been of interest to the nuclear industry. In early 1988, GPU Nuclear, the owner/operator of the TMI facility, had completed a large portion of the disassembly and defueling work inside the reactor and was preparing to remove the lower structural internals and defuel the lower head. At that point, NRC-RES initiated a project with MPR Associates to remove metallurgical specimens of the lower head and adjacent areas to determine the extent of damage to the vessel and to gain insight into the events that took place inside the vessel during the accident. The project was set up such that sampling work in the vessel would be performed by MPR after GPU Nuclear had completed defueling. Defueling ended on Jan. 30, 1990, at which time GPU Nuclear turned control of the reactor vessel over to MPR.

Techniques and Special Tooling

[In order to satisfy NRC-RES, GPUN and MPR project objectives], electrical discharge machining was selected for vessel sampling. The cutting technique used is referred to as metal disintegration machining (MDM). Both the MDM process and the more commonly used electric discharge machining (EDM) remove conductive material by melting away small bits of material using an electric arc between an electrode and the work piece. EDM makes and breaks electrical arcs by switching the electrical current on and off using transistors. MDM makes and breaks electrical arcs by moving the electrode into and away from the work material. MDM was used in the project due to the high conductivity of the reactor vessel water. The MDM cutting head has two U-shaped graphite electrodes to cut the triangular [boat-shaped] samples. The electrodes are attached to hydraulic cylinders and slide on tracks mounted at angles to provide a sample with an included angle of about 60 degrees. The electrodes are consumable and were designed to be replaced after each sample cut. PCI Energy Services, under contract to MPR, developed and tested the MDM cutting equipment. The MDM head was positioned at the vessel sample locations with a delivery system consisting of several long pipe sections and a hinged arm which articulated the MDM cutting head to the desired angle for sampling the vessel head. The MDM cutting system was used to cut samples both in open areas of the vessel and at incore penetrations.

For details on the MDM cutting system and associated equipment, and for a full description of the development and qualification program, refer to the above Report document in the Curator's file for this acquisition.

Location

Currently not on view

date made

1988-1989

maker

PCI Energy Services, Inc.

ID Number

2012.0171.01

accession number

2012.0171

catalog number

2012.0171.01

Data Source

National Museum of American History

Edison ammeter

Date made

c1882

ca 1882

associated person

Edison, Thomas Alva

maker

Bergmann & Co.

ID Number

EM.331146

accession number

294351

catalog number

331146

collector/donor number

20-03

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

Replica of apparatus used by Joliot-Curie in the discovery of artificially induced radioactivity

Description

Object EM*N-09624.2 is a replica of the apparatus used by Joliot-Curie in the discovery of artificial radioactivity. The apparatus consists of batteries, a geiger counter tube, and electronics

Component parts have been given index numbers under N-09624.2 as follows:

.2.1.1 Amplifying and counting apparatus

.2.1.2 Vatea vacuum tube

.2.1.3 Mazda metal vacuum tube

.2.1.4 Visseaux vacuum tube (lost)

.2.1.5 Small brass nut for binding post, found loose in crate in which object parts were returned from loan to Oak Ridge, Sept. 2, 1997

.2.1.6 Small brass hexagonal nut , found loose in same crate.

.2.1.7 Very small bras round-head screw, found loose in same crate

.2.2 Geiger counter tube with tripod and base

.2.2.1 Jack plug detached from wire connected to Geiger counter tube

.2.3.1 Tray with 15 batteries

.2.3.2 Short wire with white jack fittings (original location unclear)

.2.4.1 Large battery, Mazda Type R.5910

.2.4.2 Red wire for positive terminal

.2.4.3 Gray wire for negative terminal

See folder in curator's files "Loan to Oak Ridge 1991.9100 for details of the loan of the replica Becquerel and Joliot-Curie apparatus to the American Museum of Science and Energy in Oak Ridge, TN, and for information on the damage the objects sustained while on loan.

History and basic principles:

James Chadwick in his experiments at the Cavendish Laboratory in 1932 demonstrated the existence of the neutron, the uncharged particle of about the mass of a proton long anticipated by Ernest Rutherford and members of his Cambridge research group. Chadwick recognized evidence of the neutron in I. and F. Joliot-Curie's description of phenomena resulting from the bombardment of beryllium by alpha particles.

Irene Curie, daughter of Marie, and Irene's husband, Frederick Joliot, had pointed out the phenomena in which Chadwick had recognized evidence of the neutron. Although they missed that discovery, continued investigation of the bombardment of light elements by alpha particles led them to in 1934 to recognize that in the process radioactivity was being induced artificially in the target nuclei. Their Nobel prize followed immediately.

Object EM*N-09624.2 is a replica of the apparatus used in their discovery. The aluminum cylinder is a Geiger counter tube to measure counts of radioactive disintegrations. The batteries provide the Geiger counter with high voltage, while the chassis contains the electronic equipment to amplify and add its counts.

Date made

1934

maker

Joliot-Curie, F and I

ID Number

EM.N-09624.2

catalog number

EM*N-09624.2

accession number

277564

Data Source

National Museum of American History

Charpak multiwire proportional chamber

Description

This object consists of an aluminum housing with two planes of stainless steel wires, rotated by 90 degrees, in a single window with four preamp units attached, one on each side. The wires are stretched between two planes of stainless steel mesh. See G. Charpak, et. al., Nucl. Instr. Meth. 62, 262 (1968) for details.

Basic Principles and History

A multiwire proportional chamber (MWPC) is constructed with alternating planes of high voltage wires (cathode) and sense wires (anode), which are at ground. All the wires are placed in a special gas environment. Spacing between planes is usually on the order of millimeters and voltage differences are typically in the kilovolt range. When a charged particle passes through the gas in the chamber, it will ionize gas molecules. The freed electrons are accelerated towards the sense wire (anode) by the electric field, ionizing more of the gas. In this way a cascade of charge develops and is deposited on the sense wires. The smaller the diameter of the sense wires, the higher the field gradient near the wire becomes. This in turn causes a larger cascade, increasing the efficiency of the chamber.

Georges Charpak built the first MWPC in 1968. Unlike earlier particle detectors, such as the bubble chamber and the first generation of spark chambers, which can record the tracks left by particles at the rate of only one or two per second, the multiwire chamber records up to one million tracks per second and sends the data directly to a computer for analysis. The price was that each wire, accumulating ions in its immediate neighborhood, must have its own electronic amplifier to record the signal; this was only practical due to the development during the previous decade of compact and inexpensive solid-state amplifiers.

In 1992 Charpak received the Nobel Prize for Physics in acknowledgment of his invention of the MWPC, an electronic particle detector that revolutionized high-energy physics experiments and has had applications in medical physics.

With the invention of the MWPC, high-energy physics entered a new era. The speed and precision of the MWPC and its subsequent generations of detectors – the drift chamber (see Charpak drift chamber, object ID no. 1977.0708.01) and the time-projection chamber – revolutionized the field of experimental particle physics. The MPWC allowed experiments to collect data at much higher collision rates and to test theories predicting the production of rare events and new massive particles. Notable examples include the discoveries of the charm quark at SLAC and Brookhaven in 1974 (Nobel Prize awarded in 1976), the W and Z bosons at CERN in 1983 (Nobel Prize awarded in 1984), and the top quark at Fermilab in 1995. For additional technical information see:

http://www.nobelprize.org/nobel_prizes/physics/laureates/1992/charpak-lecture.pdf and,

http://cds.cern.ch/record/117989/files/CERN-77-09.pdf?bcsi_scan_2687365ababd2c82=b3SiuvtOAg0NfXwMHl9pO/npSm4KAAAArlNvLw==&bcsi_scan_filename=CERN-77-09.pdf

The Modern Physics Collection also contains one of the MPWCs used in the discovery of the charm quark at Brookhaven; see Multiwire proportional chamber from J-particle experiment of S.C.C. Ting at BNL; object ID no. 1989.0050.01.1.

Location

Currently not on view

Date made

1968

maker

Charpak, G.

ID Number

1977.0708.02

catalog number

1977.0708.02

accession number

1977.0708

Data Source

National Museum of American History

Argonne superconducting solenoid

Description

This object consists of a set of two or three nested solenoids housed within stainless steel cylindrical frames The solenoids are wound from niobium-zirconium (25%) copper coated cable. The frames have holes and slots for circulation of liquid helium within. The solenoid was designed to be used as a high-field magnet for the Argonne 10-inch liquid helium bubble chamber.

Disjoint part 1978.0469.01.2 is a retaining ring (or flange) with notches and bolt holes that was originally mounted with 2 studs inside the outer rim of one face of the cylindrical housing of the solenoid magnet (disjoint part 1978.0469.01.1). Originally, three curved strips, each covering one third of the ring circle, were attached over the ring. These strips, the screws, that presumably held them, and the two studs are not now with the ring. The three arc strips comprise disjoint part 1978.0469.01.3.

When acquired, the Argonne superconducting solenoid consisted of its 3 disjoint parts joined together as the original single object in the acquisition. For display in the "Atom Smashers" exhibit at the National Museum of American History, the ring .01.2 and its 3 associated strips .01.3 were removed to expose the coils of the solenoid assembly .01.1.

In addition, three among the set of nine spacers (irregularly shaped, thin, flat non-metallic pieces) that were mounted with an adhesive on the annular face of the solenoid frame have become separated. The three separated spacers (not numbered) have been retained in storage with the disjoint parts.

Basic Principles and History

A magnetic field is an essential feature in a bubble chamber in order to distinguish the sign of charged particles and to measure their momenta from the curvature of their bubble tracks. Charged particles moving through a magnet field are deflected in a circular path in a direction that is perpendicular to both the magnetic field lines and their direction of motion. In a chamber of a given size, higher momentum particles require correspondingly stronger magnetic fields in order to produce particle tracks of sufficiently small radius of curvature for measurement purposes.

To analyze the tracks from high-energy collisions, it is necessary to maintain the entire chamber in a strong uniform magnetic field (in excess of 20 kilogauss). Conventional (copper-coil) electromagnets that carry the high currents necessary to produce these magnetic fields can be prohibitively massive and can have attendant high cooling requirements. The discovery of superconductivity over a century ago raised the prospect of producing extremely intense electric currents – and thereby, the ability to generate correspondingly high magnetic fields using coils carrying those currents. Niobium was used in the various superconducting materials from which these coils were fabricated. Such niobium-based alloys must be cooled to cryogenic temperatures with liquid helium to become superconductive. In 1955 coils made with drawn niobium wire produced 5.3 kilogauss at a temperature of 1.2 degrees Kelvin. By the 1960’s, coils made of a compound of niobium and tin reached 40 kilogauss at 4 deg. K. The further development and application of these coils was subsequently carried out almost entirely at high-energy accelerator laboratories.

In 1963, a group at Argonne National Laboratory (ANL), together with physicists from Carnegie-Mellon University, began fabricating the first “large” superconducting solenoid magnet. Although built for use with a 10-inch diameter liquid helium bubble chamber, the Argonne superconducting solenoid was intended to test materials and fabrication techniques for building much larger superconducting magnets. The solenoid was originally composed of three concentric nested coils; in that form it produced 67 kilogauss. When used with the 10-inch bubble chamber, the innermost coil was removed. The coils are wound with several types of cable, with multiple strands in case any individual one should prove faulty. Holes and slots in the stainless steel casing, and stainless steel mesh between layers of winding, allow liquid helium to circulate through the magnet.

Success with this first large solenoid led the ANL group to use superconducting coils to provide the magnetic field for a 12-foot diameter liquid hydrogen bubble chamber. Completed in 1969, they were larger by an order of magnitude than any previous superconducting coils. Thereafter, superconducting magnets were use in other bubble chambers of the same size around the world. Among other attributes, superconducting magnets had the benefit of reducing total consumption of electrical power by more than 97%.

Location

Currently not on view

Date made

1964

designer

Fields, T.H.

manufacturer

Argonne National Laboratory

AVCO Corporation

ID Number

1978.0469.01.1

accession number

1978.0469

catalog number

1978.0469.01

Data Source

National Museum of American History