Today: Fusion & Review

Exam #3 is a week from today!

1/3 millimeter

Electron Microscope Image of MEMS Force Sensor

Quiz 8

Quiz 8

Chemical reactions involve interactions of electrons

The nuclei do not change, elements remain the same!

Quiz 9

Discuss!

Quiz 9

These have atomic mass number zero

Quiz 9

A question probably on the next quiz

(Which has more mass?)

Protons and neutrons weigh LESS when bound together!

Mo

re d

ecre

ase

in m

ass

+

0

+++ 0

+

+

00 00 Carbon-12 nucleus,

Mass = 12 u (by definition)

+

0

Single free protonMass = 1.007825 u

Single free neutronMass = 1.008665 u

You need to ADD energy to takeapart a C-12 nucleus

Uranium-235 decreases in mass during fission

One possible fission reaction is:

U-235 + neutron Ba-141 + Kr-92 + 3 neutrons

Ending mass = 99.9% of starting mass0.1% Missing mass = kinetic energy of products

(and some gamma rays)

Fission of 1000 kilograms of Uranium-235 releases 1 kilogram of mass energyEquivalent to a few days of U.S. electrical needs

(true: free neutrons do increase in mass)

Clicker question—Mass energy available

Which reaction can potentially release more energy per nucleon

A) More energy can be released per fission event

B) More energy can be released per fusion event

Immediately, Nuclear Fusion was recognized as an even greater source of energy

High mass atoms can yieldenergy via nuclear fission

Low mass atoms can yieldenergy via nuclear fusion

Energy availablefrom U-235

Energy availablefrom

hydrogen fusion

And of course, hydrogen is a very abundant element!

Fusion power first harnessed for weapons

Hyrdrogen fusion initiated by “conventional” fission bombs

Fusion bombs or “H-bombs” 100’s of times more powerful than fission bombs

User:Boostin on wikipedia

Fission energy took 18 months to harnessWe are still waiting for fusion power!!!

Conceptually, fusion is as simple as fissionE.g. the sun shown above

In practice, fusion is way way way way way way way way harder to control in a machine(fusion weapons work well, but not good for a reactor)

ITERMagnetic confinementfusion experiment

The sun is a successfulfusion reactor

http://www.youtube.com/watch?v=SQ9j2cajRo4&feature=related

Remember to study quizzes for exam!

One topic that we will cover is diffraction and interference of light. Let’s review a little by looking at applications.

We stopped lecture here, because I became confused about exam #3 topics! Exam #3 DEFINITELY contains interference!