Lecture 9 Nucleus - Forces

ASTR 340

Fall 2006

Dennis Papadopoulos

FIRST IN CLASS EXAM ON THURSDAY OCT. 5 3.30-5.00 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 165-173.

Table 13-1, p.465

Mass-Energy Equivalence

PREVIEW E=mc2 EQUIVALENCE OF MASS AND ENERGY

MASS+ENERGY CONSERVED

MASS TRANSFORME INTO ENERGY AND ENERGY INTO MASS

E=9x1016 (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 4.5x106/9x1016 =5x10-11

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 andthe 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 howtightly bound is.

Key quantity is the binding energy per nucleon. It is the bindingenergy divided by the number of nucleons.

Curve of the binding energy

Nuclear Binding Energy

Fusion - Fission

Fusion - Issues

Fusion Cycles

CNO Cycle

Fig. 13-12, p.478

Fission

Chain Reaction

DOUBLING TIMES

Doubling time Growth factor 1 21=2 2 22=4 4 24=16 10 210=1024 25 3.3x107

50 1.1x1015

80 1.2x1024

Critical Mass Energy per U235 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. 13-14, p.481

Radioactivity alpha decayRa(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. 13-16, p.485

Fig. 13-15, p.482

Radioactive Dating

U 238 ->Pb 206 determines when rocks were solidified

3.9 byears, meteorites 4.6 byears

Fig. 14-10, p.516

Fig. 14-14a, p.522

Fig. 14-14b, p.522

Fig. 14-15, p.523

Fig. 14-16, p.524

Fig. 14-17, p.525

Fig. 14-18, p.526

Fig. 14-26, p.537

Fig. 14-27, p.538

Fig. 14-5, p.512