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PART XIII – NEW PARTICLES AND ATOMIC ACCELERATORS

THE WORLD OF ATOM by Boorse

Chapter 72: The positive Electron – The First Particle of Antimatter (Carl D. Anderson 1905 – 1991)

The Positive Electron. Dirac’s theory implies negative-energy states and the possibility of electrons emerging from these states along with anti-electrons (positrons). Dirac suggested that the chance of such pair being created would be small because it would require energy equivalent to at least twice the mass of electron. However enough energy is present in cosmic radiation to create such a pair as it passes through a sheet of matter. Carl Anderson’s discovery of such pair of particles in his cosmic ray photographs established the Dirac theory as one of the most reliable in physics. This has led to the concept of antimatter.

Chapter 73: The discovery of the Deuteron (Harold Clayton Urey 1893 – 1981)

A Hydrogen Isotope of Mass 2 and its concentration. Fractional distillation of hydrogen to obtain a concentration of deuteron was accomplished by Harold Urey in 1932. This allowed the experimental investigation which resulted in the discovery of neutron soon afterwards.

Chapter 74: Discovery of the Neutron (James Chadwick 1891 – 1974)

The Existence of a Neutron. Scientists faced great difficulty in accounting for the mass and charge of a nucleus in terms of the electron and proton only. Chadwick pictured the beryllium radiation as being not electromagnetic but rather as consisting of neutral particles with masses equal to the mass of the proton. He proved that these particles are highly penetrating because they have no charge and are thus not repelled by the electric fields surrounding nuclei. Neutron and proton are now considered as two different energy states of the same fundamental particle, the nucleon. 

Chapter 75: Fermi’s Contributions (Enrico Fermi 1901 – 1954)

Quanta of a Field as Particles. Fermi-Dirac statistics add the restriction that electrons influence one another in such a way as to pre-empt or exclude identical motion in the same volume element (Pauli’s exclusion principle). Fermi did this to account for degeneracy. This was soon used to explain the properties of metals and to solve all kinds of solid-state problems. Fermi showed how various atomic problems can be treated statistically, to give results that are fairly accurate. Fermi demonstrated the existence of new radioactive elements produced by neutron irradiation. He developed a complete theory of β-decay and β-emission from the nucleus. His neutron research finally culminated in the first self-sustaining nuclear chain reaction on Dec 2, 1942.

Chapter 76: Artificial Nuclear Disintegration (John Cockcroft 1897 – 1967, Ernest Walton 1903 – 1995)

Experiments with High Velocity Positive Ions. Cockcroft and Walton were the first to construct an ion accelerator of sufficient energy to produce nuclear disintegrations.Gamow showed that α-particles, because of their wave nature, do indeed penetrate the Coulomb potential barrier at relatively low energies. Cockcroft became convinced that the wave properties of protons would allow them to enter light nuclei at low energies. Ernest Walton was then developing one of the first linear accelerators. Their collaboration in 1932 resulted in the first proton-induced artificial nuclear disintegration. The results showed that nuclei could be disrupted by particles of lower energy than previously supposed.

Chapter 77: The Electrostatic Generator (Robert Jemison Van De Graaff 1901 – 1967)

The Electrostatic Production of High Voltage for Nuclear Investigations. The Van de Graaff generator was developed as a particle accelerator for physics research; its high potential is used to accelerate subatomic particles to great speeds in an evacuated tube. It was the most powerful type of accelerator of the 1930s until the cyclotron was developed.

Chapter 78: The Cyclotron (Ernest O. Lawrence 1901 – 1958), Milton S. Livingston 1905 – 1986)

Production of High-Speed Ions. Lawrence introduced a new procedure: to accelerate ions to very high speeds in a series of steps, each of which would involve only a relatively small voltage. In a cyclotron, one must first have a magnetic field at right angles to the plane of the path of the ion and then an alternating electric field that changes its direction periodically in phase with motion of the ion.

Chapter 79: The Discovery of Induced Radioactivity (Jean F. Joliot 1900 – 1958, Irene Curie Joliot 1897 – 1956)

A New Type of Radioactivity. The Joliot-Curies showed in 1934 that when lighter elements, such as boron and aluminum, were bombarded with α-particles, the lighter elements continued to emit radiation even after the α−source was removed. They showed that this radiation consisted of positrons. The induced radioactivity appeared because an unstable nucleus had been created. This discovery set off similar research in physics laboratories around the world. 

Chapter 80: Prediction of the Meson (Hideki Yukawa 1907 – 1981)

On the Interaction of Elementary Particles. Hideki Yukawa developed a quantum field theory of the nuclear forces. He quantized the nuclear force field in complete analogy with the electromagnetic radiation field. The interaction between two charged particles is described as arising from the mutual emission and absorption of photons. Yukawa postulated that a much heavier particle is emitted by the neutron and then absorbed by the proton that generates strong interactions between them and thus account for nuclear forces. Later pi mesons (pions) were discovered that have the property predicted by Yukawa.

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MAIN POINTS

1. Discovery of positron confirm the negative energy levels of Dirac’s theory.
2. At the fundamental level matter and antimatter are created together.
3. Discovery of Deuteron helped with the discovery of neutron.
4. Neutron and proton are two different energy states of the same fundamental particle.
5. Development of particle accelerators for research of the nucleus.
6. Creation of unstable nucleus and induced radioactivity.
7. A quantum field theory of the nuclear forces.

THEORY
The inside of the nucleus has no charge. It mainly consists of “neutrons.” As the energy levels decrease in the direction of increasing radius the neutron becomes a positively charged proton. Therefore, “protons” seem to exist on the surface of the nucleus. As energy level decreases further with increasing radius, the charge switches polarity, and we have negatively charged electrons. A sharp gradient of decrease in mass exists from proton to electron. Beyond electrons we have the fluid energy of electromagnetic radiation. The charged layer made up of protons and electrons is like a softening solid becoming partially fluid. Therefore, in nature, solid mass is separated from fluid energy by a semi-fluid layer of charge. The solid mass, the electrifying charge, and the fluid energy exist in perfect balance.

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