Nuclear physicsBombs, power plants

Radioactive decay

• Requires a metastable nucleus, such as 238U.

Radioactive decay

• Requires a metastable nucleus, such as 238U.

• 238U is essentially 234Th + 4He (particle).

Radioactive decay

• Requires a metastable nucleus, such as 238U.

• 238U is essentially 234Th + 4He (particle).

• Because of q.m., has a wave function

Radioactive decay

• Requires a metastable nucleus, such as 238U.

• 238U is essentially 234Th+ 4He (particle).

• Because of q.m., has a wave function

• Decay occurs by tunneling.

Half life

• Any radioactive nucleus can decay at any moment.

• Half life is related to probability:– Low prob. -> long half

life

– High prob. -> short half life

Decay examples

238 234 492 90 2

14 14 06 7 1

, 4.5 billion years

, 5700 years

U Th He

C N e

Half-life is the time it takes half the material to decay.

Carbon used for dating (formerly) living things.

Where do the elements come from?

Stability diagram

Heavy elements can fissioninto lighter elements.

Light elements can undergofusion into heavier elements.

Elements from helium to iron were manufactured in the cores of stars by fusion. Heavier elements are metastable and were made during supernovae explosions.

Uranium decay sequence(one path)

Uranium decay sequence(one path)

Radon is the first isotope in the sequencethat is a gas. Uranium occurs naturally in thesoil around here, but is not a direct problem because the soil shields the alphas. However, radon, being a gas, rises into our homes causing lung cancer.

Fission

• Hitting a radioactive nucleus with a neutron can cause it to split into several pieces: FISSION. Energy is released.

• If you have enough, chain reaction!

1 235 236 * 140 94 10 92 92 54 38 0

1 235 236 * 141 92 10 92 92 56 36 0

2

3

n U U Xe Sr n

n U U Ba Kr n

Chain reaction

For reaction to be self-sustaining, must haveCRITICAL MASS.

Fission bomb

Nuclear reactors

Risks of nuclear power

• Reactor explosion

Risks of nuclear power

• Reactor explosion

Risks of nuclear power

• Reactor explosion

• Radiation release from plant.

• Storage– Leakage

• inert ceramics fix

– Inadvertent entry

• Terrorist threat

Risks of nuclear power

• Reactor explosion

• Radiation release from plant. -- TMI

• Storage– Leakage

• inert ceramics fix

– Inadvertent entry

• Terrorist threat• Processing accidents

We do not have to worry aboutreactor fuel stolen for bombs, becauseit is not sufficiently enriched.

Tokaimura, Japan

• Japan’s nuclear industry’s first critical accident.

• Inadvertent critical mass• Container size: 16 kg

instead of 2.4• Container shape

September 28, 1999

10 liters16 kg

Two of three workers died within seven months.

How safe is nuclear power?

• Nuclear power’s track record shows it is among safest energy sources.– Wind and hydroelectric are

limited.

– Coal is dangerous (pollution kills).

– Solar would require huge construction, with accompanying construction accidents.

Can we make it safer?

• Yes!– Better training and on-site

monitoring by agents paid by government, not power companies.

– In the event of accident, can almost completely eliminate radiation danger with iodine tablets. Buy your own!

Advantages of nuclear power

• No pollution (except thermal, like any heat engine)

• No lung cancer, emphysema, etc.

• No greenhouse effect• Fewer mining

accidents than coal.

Fusion

• Light nuclei more stable when combined.

• Tremendous energy release.

• Hydrogen bombs• Fusion power?