Nuclear Fission
Spring 2013
UCSD
Physics 12
Physics 12
UCSD
Spring 2013
UCSD
Spring 2013
Lecture 16
Physics 12
3
2
Physics 12
UCSD
Spring 2013
Q
4
1
Nuclear Fission
Spring 2013
Physics 12
UCSD
proton
Poof!
Physics 12
UCSD
electron
neutron
Spring 2013
UCSD
anti-neutrino
5
Physics 12
Spring 2013
Q
6
Physics 12
UCSD
A
Z
XN
12
€6 C6
14
6 C8
235
92 143
238
92 146
239
94
145
U
U
Pu
€
€
Spring 2013
Lecture 16
7
Spring 2013
€
€
€
Q
8
2
Nuclear Fission
Spring 2013
UCSD
Physics 12
Physics 12
UCSD
Chart of the Nuclides
β+
3
α
2
Z
β-
1
0
Spring 2013
UCSD
9
Physics 12
Spring 2013
UCSD
10
Physics 12
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
Spring 2013
Lecture 16
11
Spring 2013
12
3
Nuclear Fission
Spring 2013
Physics 12
UCSD
Physics 12
UCSD
Barium and Krypton represent just one of many potential outcomes
Spring 2013
UCSD
13
Physics 12
Spring 2013
14
Physics 12
UCSD
Bottom line: at thermal energies (arrow), 235U is 1000 times more likely
to undergo fission than 238U even when smacked hard
Spring 2013
Lecture 16
15
Spring 2013
3×Q
16
4
Nuclear Fission
Spring 2013
UCSD
Spring 2013
UCSD
Physics 12
17
Physics 12
Physics 12
UCSD
Spring 2013
18
Physics 12
UCSD
•  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
Spring 2013
Lecture 16
19
Spring 2013
20
5
Nuclear Fission
Spring 2013
UCSD
Physics 12
Physics 12
UCSD
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)
235U
daughter 1
daughter 2
Spring 2013
UCSD
Spring 2013
Lecture 16
21
Physics 12
23
Spring 2013
stable nuclide
radioactive (unstable) nuclide
Physics 12
UCSD
Spring 2013
22
Q
24
6
Nuclear Fission
Spring 2013
UCSD
Spring 2013
Lecture 16
Physics 12
25
7