Modern Physics

This set of flashcards reviews key vocabulary and concepts from the Modern Physics lecture, covering topics from nuclear weapons and reactors to medical imaging and radiation.

Quantum Theory and Theory of Relativity

Important tools for scientists to understand the atom, space, matter, and motion in modern physics.

Ultraviolet Light

Energetic enough to damage chemical bonds and rearrange molecules, providing a glimpse of the effects of X-rays and beyond.

Optical Bleaching

The fading of colors in items displayed in shop windows and on outdoor furniture due to sun exposure.

Radiation Damage

Ultraviolet light also damages your skin when you sit in the sun—a sunburn isn’t thermal damage; it’s radiation damage.

Atomic Bomb

Invention of the twentieth century that followed close on the heels of various developments in the understanding of nature.

Nuclear Energy

Energy stored in the atoms, concern that Germany would choose to follow the military path of nuclear energy.

Classical Physics

Rules of motion and gravitation identifi ed by such people as Galileo, Newton, and Kepler, and the rules of electricity and magnetism developed by others, including Ampère, Coulomb, Faraday, and Maxwell.

Quantum Physics and Relativity

Two main developments essential to the making of the atomic bomb, confirmed countless times since they were developed and have been shown to have enormous predictive power.

Nuclear Bomb

The items that are responsible for the energy released by nuclear weapons are not atoms but tiny pieces of atoms— their nuclei (plural of nucleus).

Electrons

Dominate the chemistry of atoms and molecules. Sodium is a reactive metal because of its electrons, and chlorine is a reactive gas because of its electrons.

Einstein’s equation, E = mc2

Matter and energy are in some respects equivalent. In certain circumstances, mass can become energy or energy can become mass.

Nucleus

Fantastically small—only a little more than 1015 m in diameter. The remaining 99.9999999999999% of the ion is occupied only by its 10 electrons in their orbitals.

Nucleons

Nuclear particles has about 2000 times as much mass as an electron, so 99.975% of the sodium ion’s mass is in this nucleus.

Nuclear Force

Attractive and holds the nucleus together. This new force is called the nuclear force, and at short distances it dominates the weaker electrostatic repulsion. However, the nuclear force attracts the nucleons toward one another only when they’re touching.

Radioactive Decay

The quantum process that allows the nucleons to escape from the nuclear force without fi rst obtaining the energy needed to surmount the energy barrier is called tunneling because the nucleons effectively tunnel through the bar- rier.

Half-life

The time required for half of the nuclei to decay. After one half-life, only half the original nuclei will remain intact.

Electrostatic Potential Energy

Assembling a giant nucleus out of positively charged parti-cles requires a considerable amount of work against electrostatic forces, and it is that stored work that’s released when the nucleus decays.

Nuclear Fusion

For a small nucleus to grow, something must push more nucleons toward it. Electro-static repulsion will initially oppose this growth, but once everything touches, the nuclear force will bind the particles together and release a large amount of potential energy. This coalescence process is called nuclear fusion.

Nuclear Fission

For a large nucleus to shrink, something must separate its pieces beyond the reach of the nuclear force. Electrostatic repulsion will then push the fragments apart and release a large amount of potential energy. This fragmentation process is called nuclear fi ssion.

Radioactive Decay

Discovered accidentally by French physicist Antoine-Henri Becquerel (1852–1908) in 1896. Intrigued by the recent discovery of X-rays.

Neutron

Discovered a fragment of the nucleus, the neutron, that has no electric charge and can thus approach a nucleus without any electrostatic repulsion.

Isotopes

Nuclei that differ only in the numbers of neutrons they contain the 235U nucleus contains 92 protons and 143 neutrons, for a total of 235 nucleons. In contrast, the 238U nucleus con-tains 238 nucleons: 92 protons and 146 neutrons.

Chain reaction

The fi ssion of one uranium nucleus would induce fi ssion in two nearby uranium nuclei, which would in turn induce fi ssion in four other uranium nuclei, and so on (Fig. 15.1.6).

Supercritical mass

Additional 235U is needed—a supercritical mass. About 60 kg (132 lbm) will do it.

Little Boy Bomb

The supercritical mass was assembled when a cannon fi red a cylinder of 235U through a hole in a sphere of 235U, exploded over Hiroshima, Japan, on August 6, 1945.

The Fat Man Bomb

Used plutonium that had been synthesized from 238U in nuclear reactors,dropped over Nagasaki, Japan, on August 9, 1945.

Fusion Bomb

Exploding fi ssion bomb heats a quantity of hydrogen to about 100 million degrees Celsius initiates fusion.

Fallout

The creation and release of radioactive nuclei converts uranium and plutonium nuclei into smaller nuclei.

Dirty bombs

Nuclear weapons with poor explosive yields, so-called dirty bombs, can litter the surrounding landscape with radioactive debris.

Nuclear Fission Reactors

Developments for ways to unleash phenomenal destructive energy, they could also provide virtually limitless sources of useful energy.

Nuclear Fusion Power

Remains an elusive goal, but efforts continue to harness this form of nuclear energy as well.

Control rods

Neutron-absorbing rods, determine whether it’s above or below critical mass.

Thermal Neutrons

Slow-moving neutrons that have only the kinetic energy associated with the local temperature.

Moderator

Reactor contains something else besides uranium that slows the neu-trons down so that 235U nuclei can grab them.

Thermal Fission Reactors

Reactors that carry out their chain reactions with slow-moving, or thermal, neutrons are called thermal fi ssion reactors.

Fast Fission Reactors

Contain no moderator carry out chain reactions with fast-moving neutrons.

Emergency cooling systems

And pressure-relief valves, and many ways to shut down the reactor to reactors.

Tokai-mura disaster

Accident, did involve a critical mass and a resulting chain reaction on September 30, 1999, in Japan.

Fukushima Daiichi Nuclear Accident

The fi fth reactor accident, began on March 11, 2011, following the 9.0-magnitude Tohoku earthquake and the resulting tsunami.

Inertial Confinement Fusion

Uses intense pulses of laser light to heat and compress a tiny sphere containing deuterium and tritium.

Magnetic Confinement

Makes it possible to heat a plasma of deuterium and tritium to fantastic temperatures with electromagnetic waves.

Medical Imaging and Radiation

Two of the most signifi cant examples of medical physics: the imaging techniques that are used to detect problems and the radiation therapies that are used to treat them.

X-Rays

Played an important role in medical treatment because of the shadow images it creates.

Bremsstrahlung

Occurs whenever a charged particle accelerates. In X-ray tube bremsstrahlung, a fast-moving electron arcs around a massive nucleus and acceler-ates so abruptly that it emits an X-ray photon.

Synchrotron radiation

A rapidly accelerating charged particle will emit an X-ray, whether it’s accelerating around the nucleus of a heavy atom or around the ring of a particle accelerator.

Elastic scattering

An atom acts as an antenna for the passing electromagnetic wave, absorbing and reemitting it without keeping any of its energy.

Photoelectric effect

A passing photon induces a radiative transition in an atom; one of the atom’s electrons absorbs the photon and is tossed completely out of the atom.

Compton scattering

An X-ray photon collides with a single electron so that the two particles bounce off one another.

Electron-positron pair production

X-rays with slightly more than 1,022,000 eV can do something remarkable when they pass through an atom; they can cause electron-positron pair production.

Beta Decay

Neutrons that are by themselves or in nuclei with too many neutrons are radioactive and experience beta decay.

Neutrino

Subatomic particle with no charge and little mass.

Linear accelerator

Electric fi elds in a series of resonant cavities push charged particles forward in a straight line (Fig. 15.3.10).

Magnetic Resonance Imaging (MRI)

Locates hydrogen atoms by interacting with their magnetic nuclei since hydrogen atoms are common in both water and organic molecules, fi nding hydrogen atoms is a good way to study biological tissue.