1. Physics 1202: Lecture 38 Today’s Agenda Announcements: Extra creditsExtra credits –Final-like problems –Team in class –Teams 12, 13 & 14 HW 10 due this FridayHW 10 due this Friday Review session this FridayReview session this Friday –Q-center –Q-center 5:30-7 pm in Gentry 131. Nuclear & Particle Physics

2. Nuclear Physics

3. The nucleus Made of –Z protons –N neutrons –Mass number A = Z + N Z A Size and shape –Almost spherical –Not always though 1.2 X 10 -15 m =1.2 fm

4. The strong nuclear force A force must exist to compensate electric repulsion Nuclear force –Always attractive –The same between protons or neutrons –100 times stronger than electrostatic force –Short-range: about only 3 fm

5. The strong nuclear force Neutron are essential –Provide the “glue” to maintain protons together –Meed more n as A grows

6. Binding energy The mass of an atom is less than its constituents 12 C (m=12 u): used to defined the atomic mass unit u 6 protons + 6 neutrons + 6 electrons –Adding = 12.09893 u “missing” mass = negative or binding energy The binding energy E b E b is very large – 12 C: (  m)c 2 = (12.09893-12) u c 2 = 92.2 MeV – roughly 10 7-8 times chemical energy (~ 1 eV) (remember atomic levels)

7. Binding energy per nucleon E b /A – increases with A until 56 Fe: fusion –decreases after: fission

8. Radioactivity Discovered (1896) Henri Becquerel –Uranium salt near photographic plates Three types of radiation –Alpha: alpha particle ( 4 He nucleus) –Beta: 2 types of beta particles »Electron (  - ) and positron (  + ) –Gamma: electromagnetic waves (  ) Alpha: radium and radon Beta: –Neutrino (to account for energy conservation) Gamma

9. Activity and half-life In given interval  t, a nucleus may decay  : decay constant Activity (absolute value) unit: Bq Decay law Half-life

10. 5 steps methods Draw and list quantitites Concepts and equations needed Solve in term of symbols Solve with numbers Checks values and units