Mrs. Coronado Modern Physics Notes

1. Mrs. CoronadoModern Physics Notes TMHS

2. The Atom • Nucleus contains protons and neutrons. • Electrons orbit nucleus in energy levels.

3. Atomic Mass • Combination of protons and neutrons (nucleus). • What atom is this?

4. Atomic Number • Protons indicate the type of element. The atomic number is the number of protons.

5. Isotopes • Elements that have different numbers of neutrons.

6. 4 Major Forces in our Universe • Strong • Weak • Gravity • Electromagnetic

7. Gravity Force • Responsible for matter conglomerating into planets, stars, etc.

8. Electromagnetic Force • When you get down to it, this is the force responsible for all contact forces and forces you learned that bond atoms to make compounds. • We used to think magnetic and electric were separate forces, but now we know better. • Causes repulsion/attraction due to charges.

9. Strong Force • Binds protons and neutrons together in the nucleus of the atom. • Holds quarks together to make protons, neutrons, and other particles. • P+= 2 ups and a down. • N0= 2 downs and an up. Whimsical names-- called "flavors"—for the quarks. Quarks and Anti-Quarks

10. Weak Force • It is responsible for the radioactive decay of subatomic particles. • The weak force: • helps generate sunlight, (fusion in stars) • enable advanced medical diagnosis and treatment, • help determine the age of organic materials from carbon isotope abundances, • help determine the age of the earth from uranium isotope abundances • provide heating for the Earth and an energy source for plate tectonics, through the decays of Uranium, Thorium and Potassium.

11. There is an idea we can put the electroweak and strong in one big formula- called the Grand Unified Theory (GUT). The idea of also getting gravity in the same formula is called the Theory of Everything (TOE)!

12. Nuclear Fusion • Happens in stars, like the Sun. Nuclear energy can also be released by fusion of two light elements (elements with low atomic numbers). The power that fuels the sun and the stars is nuclear fusion. In a hydrogen bomb, two isotopes of hydrogen, deuterium and tritium are fused to form a nucleus of helium and a neutron. This fusion releases 17.6 MeV of energy. Unlike nuclear fission, there is no limit on the amount of the fusion that can occur. Happens at temperatures of 40 million Kelvin to ignite.

13. Fusion: Not ready for us yet. • The largest experiment by means of magnetic confinement has been the Joint European Torus (JET). In 1997, JET produced a peak of 16.1 megawatts (21,600hp) of fusion power (65% of input power), with fusion power of over 10 MW (13,000hp) sustained for over 0.5 sec. Its successor, the International Thermonuclear Experimental Reactor (ITER), was officially announced as part of a seven-party consortium (six countries and the EU). ITER is designed to produce ten times more fusion power than the power put into the plasma. ITER is currently under construction in France.

14. Nuclear Fission The sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's equation, E =mc2 The process of capturing the neutron and splitting happens very quickly, on the order of picoseconds (0.000000000001 seconds). Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen spontaneously.

15. Critical Mass • Although two to three neutrons are produced for every fission, not all of these neutrons are available for continuing the fission reaction. If the conditions are such that the neutrons are lost at a faster rate than they are formed by fission, the chain reaction will not be self-sustaining. • At the point where the chain reaction can become self-sustaining, this is referred to as critical mass.

16. Uranium Fuel • Natural uranium is composed of 0.72% U-235 (the fissionable isotope), 99.27% U-238, and a trace quantity 0.0055% U-234 . The 0.72% U-235 is not sufficient to produce a self-sustaining critical chain reaction in U.S. style light-water reactors, although it is used in Canadian CANDU reactors. For light-water reactors, the fuel must be enriched to 2.5-3.5% U-235. • Uranium is found as uranium oxide which when purified has a rich yellow color and is called "yellowcake". After reduction, the uranium must go through an isotope enrichment process. Even with the necessity of enrichment, it still takes only about 3 kg of natural uranium to supply the energy needs of one American for a year. • In order for these properties of U-235 to work in a bomb, a sample of uranium must be enriched; that is the amount of U-235 in a sample must be increased beyond naturally occurring levels. Weapons-grade uranium is composed of at least 90 percent U-235.

17. Power Plants and Nuclear Reactors • Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provided about 5.7% of the world's energy and 13% of the world's electricity, in 2012. (Wikipedia).

18. Radiation Therapy • Radiation therapy uses high-energy radiation to kill cancer cells by damaging their DNA. • Radiation therapy can damage normal cells as well as cancer cells. Therefore, treatment must be carefully planned to minimize side effects. • The radiation used for cancer treatment may come from a machine outside the body, or it may come from radioactive material placed in the body near tumor cells or injected into the bloodstream.

19. Diagnostic Imaging X-rays CT scans (use X rays but look at slice of image) MRI (uses magnets to excite hydrogens) Ultrasound

20. The Fat Man The Fat Man atom bomb was created due to the fact that plutonium 239 has such a fast spontaneous fission rate. A new design was needed to facilitate such an isotope. The Little Boy is too slow to work with such an isotope. So, Seth Neddermeyer created an idea to use explosive charges to compress a small sphere of plutonium quickly to a required density that will make the plutonium go critical and produce a nuclear explosion. Thus, the Fat Man atom bomb was born The Little Boy The "little boy" atom bomb was designed to be a gun type bomb. They call it a gun type bomb due to the fact that the bomb shoots a mass of uranium 235 into another mass of uranium 235 to create a supercritical mass. Once the supercritical mass is formed the initiator emits a burst of neutrons creating the fission chain reactions. These chain reactions continue until the energy released becomes so big that the bomb blows itself up. . http://www.123helpme.com/view.asp?id=153378

22. Decay Particles Alpha Beta Positron 4 He 2 0 0 e e -1 1

23. Alpha Decay Occurs only with very heavy elements. Nucleus too large to be stable. Atom loses 2 protons and 2 neutrons 4 He 2 226 222 Ra Rn 88 86

24. Beta Decay Occurs with elements that have too many neutrons for the nucleus to be stable. Positron or electron is emitted. 0 e n -1 40 40 K Ca 19 20 anti- neutrino

25. 1) A neutron inside the nucleus of an atom breaks down, changing into a proton. 2) It emits an electron and an anti-neutrino (more on this later) which go zooming off into space. 3) The atomic number goes UP by one and mass number remains unchanged.

26. Positron Decay Occurs with elements that have too many protons for the nucleus to be stable. 0 e n 1 2 2 He H 2 1 neutrino If a positron hits an electron, they annihilate each other, resulting in gamma rays, that are detectable.

27. 1) Something inside the nucleus of an atom breaks down, which causes a proton to become a neutron. 2) It emits a positron and a neutrino which go zooming off into space. 3) The atomic number goes DOWN by one and mass number remains unchanged.

28. Neutrino and Anti-Neutrino Proposed to make beta and positron decay obey conservation of energy. Like electrons, but No mass, No charge. Energy and ½ spin. Does not react easily with matter. Hard to detect.

29. Discovery of Neutrinos • A neutrino hit a proton in a hydrogen atom. The collision occurred at the point where three tracks emanate on the right of the photograph. • About 65 billion solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun in the region of the Earth

30. Gamma Radiation, g Released by atoms which have undergone a nuclear reaction. Results when excited nuclei return to ground state. High energy! E = hf!

31. A photon- Light as a particle • A “particle” of light- has no mass • A “quantum” of light energy • The energy of a given photon depends on the frequency (color) of the light

32. Light is also a wave! • Travels at constant speed c in a vacuum. • c = lf • c: 3 x 108m/s • l: wavelength (m) • f: frequency (Hz)

33. Duality of Light • The fact that light behaves as a particle OR a wave, gives it the title “dual natured”.

34. Energy-Mass Equivalence • E=mc2 m is matter lost, c is speed of light • Happens in Fission (lg mass) and Fusion (low mass) :

35. Calculating Photon Energy • E = hf • E: energy (J or eV) • h: Planck’s constant • 6.62510-34 J s or 4.14 10-15eV s • f: frequency of light (s-1, Hz)

36. The “electron-volt” (eV)is an energy unit • Useful on the atomic level. • If a moving electron is stopped by 1 V of electric potential, we say it has 1 electron-volt (or 1 eV) of kinetic energy!

37. Converting eV to J 1 eV = 1.60210-19J

38. Photoelectric Effect • The phenomena where photons collected can cause electrons to be emitted from a metal.

39. Photoelectric Effect • Why is this useful? Photovoltaic cells (solar cells).

40. Photoelectric Simulation • http://phet.colorado.edu/en/simulation/photoelectric • In general what wavelengths produce the most electrons? • Does intensity affect it? How?

41. Absorption Spectrum Absorption spectra always involve atoms going up in energy level. ionized 0 eV -10 eV

42. Emission Spectrum Photon is emitted and atom drops to lower quantum energy state. 0 eV DE hf Excited state -10 eV

43. Emission Spectrum Emission spectra always involve atoms going down in energy level. ionized 0 eV -10 eV

44. Comparing Absorption and Emission Spectra

45. Uses for quantum mechanics… Quantum mechanics inspired the idea of… • Transistors • Digital cameras • Quantum computers (a work in progress) • Teleportation (which does exist!)

46. Quantum Entanglement • Quantum entanglement occurs when particles such as photons, electrons, molecules as large as Bucky balls,and even small diamonds interact physically and then become separated; the type of interaction is such that each resulting member of a pair is properly described by the same quantum mechanical description (state), which is indefinite in terms of important factors such as position,momentum, spin, polarization, etc.

48. Quantum Superposition • Quantum superposition is a fundamental principle of quantum mechanics that holds that a physical system—such as an electron—exists partly in all its particular, theoretically possible states (or, configuration of its properties) simultaneously; but, when measured or observed, it gives a result corresponding to only one of the possible configurations (as described in interpretation of quantum mechanics).

49. Heisenberg’s Uncertainty Principle • In quantum mechanics, the uncertainty principlesets a limit to the precision with which certain pairs of physical properties of a particle, such as positionx and momentump, can be known simultaneously. The more precisely the position of some particle is determined, the less precisely its momentum can be known, and vice versa. • It is impossible to measure simultaneously both the position and velocity (or momentum) of a microscopic particle with absolute accuracy or certainty.

50. Schrödinger's Cat • Schrödinger's cat: a cat, a flask of poison, and a radioactive source are placed in a sealed box. If an internal monitor detects radioactivity (i.e. a single atom decaying), the flask is shattered, releasing the poison that kills the cat. The Copenhagen interpretation of quantum mechanics implies that after a while, the cat is simultaneously alive and dead. Yet, when one looks in the box, one sees the cat either alive or dead, not both alive and dead. This poses the question of when exactly quantum superposition ends and reality collapses into one possibility or the other.