Lecture 9 Nucleus - Forces ASTR 340 Fall 2006 Dennis Papadopoulos

FIRST IN CLASS EXAM ON THURSDAY OCT PM. BRING CALCULATOR. YOU CAN HAVE ONE PAGE OF NOTES EXAMS COVERS ALL LECTURES – GO OVER THE POWERPOINTS IN WEB, CHAPTERS 1- 4 AND CHAPTER 6 PAGES

Table 13-1, p.465

Mass-Energy Equivalence PREVIEW E=mc 2 EQUIVALENCE OF MASS AND ENERGY MASS+ENERGY CONSERVED MASS TRANSFORME INTO ENERGY AND ENERGY INTO MASS E=9x10 16 (m/kg) Joules From Lecture 5 we found energy of a 1kg (e.g. steak) 4.5 MJ (1000 cal) In chemical reactions we get an efficiency of transforming mass into energy approximately 4.5x10 6 /9x10 16 =5x Chemical bond – Electromagnetic Force – e.g. NaCl In chemical reactions only the energy stored in outer electrons is released Nucleus does not play any role

Covalent bond

Fig. 13-3, p.468 Nucleus involves only protons and neutrons (nucleons) Electrostatic repulsion of protons balanced by the nuclear force. Strong but short range – nearest neighbor. The Nuclear Force

Fig. 13-4, p.469

Binding Energy: A nucleus is dismantled by removing a nucleon at a time and the amount of work done in the process is measured. Next if we next reassemble the nucleons in the form of the original nucleus, an amount of energy equal to the work done would be released. This is the called the binding energy of the nucleus. It indicates how tightly bound is. Key quantity is the binding energy per nucleon. It is the binding energy divided by the number of nucleons. Curve of the binding energy

Nuclear Binding Energy

Fusion - Fission

Fusion - Issues

Fusion Cycles

CNO Cycle

Fig , p.478 Fission

Chain Reaction

DOUBLING TIMES Doubling time Growth factor = = = = x x x10 24 Critical Mass Energy per U 235 fission 235 MeV

Fig. 14-6, p.514

Table 13-3, p.483

Energy per nucleon required to put together the nucleus of an element as a function of the mass number

Fig , p.481

Radioactivityalpha decay Ra(226,88)->Rn(222,86)+He(4,2) U(238,92)->Th(234,90)+He(4,2) Beta decay C(14,6)->N(14,7)+e - +

Fig , p.485

Fig , p.482 Radioactive Dating U 238 ->Pb 206 determines when rocks were solidified 3.9 byears, meteorites 4.6 byears

Fig , p.516

Fig a, p.522

Fig b, p.522

Fig , p.523

Fig , p.524

Fig , p.525

Fig , p.526

Fig , p.537

Fig , p.538

Fig. 14-5, p.512