Modern Physics

Atom Nucleons – subatomic particles in the atom’s nucleus (protons and neutrons). Ion – An atom with a net electric charge which is due to the loss or gain of electrons. Strong nuclear force – Nucleons attractive binding force.

Photoelectric Effect - LinkLink The energy of a photon is directly proportional to the photon’s frequency. Planck’ constant (h) – A fundamental constant of quantum theory that determines the scale of the micro world. E = h f E = photon energy h = Planck’s constant f = frequency

Einstein found support for his quantum theory of light in the photoelectric effect. The photoelectric effect is the ejection of electrons from certain metals when light falls upon them. These metals are said to be photosensitive. PHET SIMULATION LINK 38.3 The Photoelectric Effect

Physicists became convinced that the Newtonian laws that work so well for large objects do not apply to the microworld of the atom. The study of the motion of particles in the microworld of atoms and nuclei is called quantum mechanics. The branch of physics that is the general study of the microworld of photons, atoms, and nuclei is simply called quantum physics Quantum Physics

Alpha Decay alpha particle: a “doubly alpha particle: a “doubly ionized helium atom” or simply a “helium nucleus” ionized helium atom” or simply a “helium nucleus” written , ,or He written , ,or He Z > 82 for alpha decay possible Z > 82 for alpha decay possible have relatively slow speeds (0.1 c) have relatively slow speeds (0.1 c) can be stopped by a few cm of air or can be stopped by a few cm of air or an ordinary sheet of paper natural  ’s have energy between 4 and 10 MeV natural  ’s have energy between 4 and 10 MeV half-lives from s to yr half-lives from s to yr (link)link

Beta Decay electron, written e or  electron, written e or  or positron, written e or  or positron, written e or  occurs primarily in light nuclei occurs primarily in light nuclei penetrates many meters of air penetrates many meters of air or thin sheets of metal or thin sheets of metal high speed (approach speed of light) high speed (approach speed of light) or (link)link

Gamma Decay high energy photons high energy photons (electromagnetic radiation) (electromagnetic radiation) written  written  penetrates 2 km air or 30 cm lead penetrates 2 km air or 30 cm lead short lifetimes short lifetimes energy range of keV to MeV energy range of keV to MeV have short wavelength (high frequency) have short wavelength (high frequency) (link) link

Alpha particles penetrate least and can be stopped by a few sheets of paper; beta particles by a sheet of aluminum; gamma rays by a thick layer of lead Radiation Penetrating Power

N(t) = # radioactive nuclei present at time t present at time t N 0 = number initially present = the disintegration constant, = the disintegration constant, which is equal to (ln 2)/T 1/2, which is equal to (ln 2)/T 1/2, where T 1/2 is the half-life where T 1/2 is the half-lifehalf-life of the decaying nucleus of the decaying nucleus

The radioactive carbon isotopes in the skeleton diminish by one half every 5730 years. The red arrows symbolize relative amounts of carbon Carbon Dating

In a typical example of nuclear fission, one neutron starts the fission of the uranium atom and three more neutrons are produced when the uranium fissions Nuclear Fission

Critical Mass The critical mass is the amount of mass for which each fission event produces, on the average, one additional fission event. A subcritical mass is one in which the chain reaction dies out. A supercritical mass is one in which the chain reaction builds up explosively Nuclear Fission

Components of a Fission Reactor A reactor contains three main components: the nuclear fuel combined with a moderator, the control rods, and water The Nuclear Fission Reactor

In the fusion reactions of hydrogen isotopes, most of the energy released is carried by the lighter-weight particles, protons and neutrons, which fly off at high speeds Controlling Nuclear Fusion