Nuclear Fission Spring 2013

Lecture 16 1

UCSD Physics 12 UCSD Physics 12

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Nuclear Fission Spring 2013

Lecture 16 2

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neutron

proton

anti-neutrino

electron Poof!

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€

ZA XN

€

612C6

€

614C8

€

92235U143

€

92238U146

€

94239Pu145

Q

Nuclear Fission Spring 2013

Lecture 16 3

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Chart of the Nuclides

Z

3

2

1

0

β+

β-

α

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source: http://www.epa.gov/radiation/understand/calculate.html 1 mrem carries 0.000055% chance of developing cancer: 350 mrem/yr expect cancer in 5000 years

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Barium and Krypton represent just one of many potential outcomes

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Bottom line: at thermal energies (arrow), 235U is 1000 times more likely to undergo fission than 238U even when smacked hard

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Nuclear Fission Spring 2013

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•  Iron (Fe) is at the peak •  On the heavy side of iron, fission delivers energy •  On the lighter side of iron, fusion delivers energy •  This is why normal stars stop fusion after iron •  Huge energy step to be gained in going from

hydrogen (H) to helium-4 via fusion

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235U

daughter 1

daughter 2

stable nuclide radioactive (unstable) nuclide

daughter nuclei from fission are neutron-rich, and β- decay toward black (stable) nuclei some can fall outside of neutron “drip line” in white region (don’t have to be right on red line)

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