Atomic and Nuclear Physics Goals: quanta-photons-matter waves, Isotopes, Binding Energy, Nuclear Decay and Nuclear Reactions

Electricity, Magnetism, Light and the Electromagnetic Spectrum what do they have in common?  Moving electrons (electric fields) create electromagnetic radiation as exited electrons return to ground state  The moving electron quantizes the energy  Max Plank – energy absorbed and given off in multiples quanta and depends on the frequency of exited electron  Energy of quanta E = h f h=6.63 ee- 34Js  Quantum Mechanics – theory deals with energy and quantum states

Photons  Calculate energy of a photon of Red light:  E = h f c = λ f f = c/λ  = (6.63 ee -34 Js) (4.29 ee14 1/s)  = 2.84 ee -19 J  Energy of a photon of Violet light = 4.97 ee -17 J  Much more energy!!!  Einstein applied “quanta” to all electromagnetic radiation electromagnetic radiation occurs in “bundles” called photons particles of light  Explained the photoelectric effect where even the brightest red light can’t produce, violet does!  so, when the frequency is increased then the number of photons produced increases

 Compton Shift confirms that photons are particle- like because they have momentum p = m v  Collisions of photons and electrons produced a wavelength shift hence transferring energy  The Low energy frequencies of the electromagnetic spectrum act more wave-like and are sent in continuous waves that are easily diffracted AM vs Fm  Light photons are wave-like and particle-like reflected, refracted, diffracted, interfere and exhibit the photoelectric effect  Higher frequency electromagnetic waves exhibit more photon-like character less interference

Wave Model  deBroglie – matter-waves  Heisenberg – uncertainty  Wave Model of the atom – 4 quantum numbers  Energy Level (period), Sublevel (spdf), Orbital and Spin (+ o -)  Why is the electron cloud studied?  Because that is one way photons are produced  What about another way that photons are produced  Electromagnetic energy can also be released from the Nucleus of atoms

Nuclear Physics  Elemental Keys show atomic number, symbol and average atomic mass  Atomic number Z number of protons identifies the element  N number of neutrons varies  Isotopes – elements with differing number of neutrons  Average atomic mass – averaged mass of all isotopes of an element (beanium lab)  Mass Number – total amu umu P + N  1/12 of a C-12 atom 6 P and 6 N

 Energy of the nucleus is associated with the Strong Force what is a force?  Transfer or conversion of energy…what energy?  Binding Energy – opposes the repulsive P – P electromagnetic force (coulomb force) default mass  energy is released when nuclei fuse or split matter is not conserved and is converted to ENERGY  Energy and mass, however, are conserved in nuclear reactions

Calculating Binding Energy  E = m c²  = (Z)( µ) + (N)( µ) - mass bound x MeV / µ  (problems)

Nuclear Decay  Nuclear Decay – an unstable nucleus emits alpha, beta particles and gamma photons to become stable  Alpha He-4 nucleus 2 P 2 N (paper)  Beta electron or positron N becomes P (Al foil)  Gamma is energy does not affect identity (penetrate Pb)  Decay Series (U-235 series)  Half-Life – time for ½ of a radioisotope to decay steady T ½ (1/2)² ex= H-Ls

Fission and Fusion reactions  Fission (radioactivity) – natural or initiated by energetic particles like neutrons  Heavy nuclei split into smaller nuclei called daughter products  daughter nuclei are more tightly bound and have less mass so energy is emitted  U n -> Be Kr-93 +3n + gamma  nuclear chain reaction but can be controlled by Cd rods that absorb neutrons  U-235 only.7% enriched to sustain reactions  Ce has the most binding energy Z = 58

 Fusion – lighter nuclei slam together to release positrons, neutrinos and gamma  Thermonuclear reaction  Stars fuse 4 H to He then He to C  Proton – Proton cycles  Fusion reactors use deuterium H-2 extreme high temperatures plasma contained by magnetic fields  Massive stars fuse nuclei to elements as big as Fe then Supernova to produce all otter elements

 The End  Wait……………..There is more………….  Think of a branch of Physics that considers all forms of energy  What is this fascinating subject?  Astronomy!  A Great way to shine  Shine on Physicists!