CHEM 001C Lecture Notes - Lecture 20: Radioactive Decay, Radiocarbon Dating, Thermonuclear Weapon
CHEM 001C Lecture 20: Nuclear Chemistry
●Fission vs. Fusion
○Fission: large nuclei decaying into more stable nuclei + energy
■“Atom Bomb” 500 kilotons of TNT≈
●235
92U + n0 → 236
92U → Decay products + n0 + 3.2 x 10-11 J energy
○Fusion: combine smaller nuclei to produce more stable nuclei + energy
■“Hydrogen Bomb” 50 megatons of TNT≈
●2
1H + 3
1H → 4
2He + n0 + energy
●High temperatures needed to initiate reaction; thermally contained
plasma
●Benchtop Fusion (“Cold Fusion”)
○Fission in the sun: 1
1H + 1
1H → 2
1H + e- + neutrino + energy
○Taleyarkan Benchtop reaction: 2
1H + 2
1H → 3
1H + 1
1H + energy
■Neutrons that were detected had the same energy profile as that expected
for Californium-52, kept in Taleyarkan’s lab
●Nuclear Stability and Half-Life
○Radioactive decay: first order
process
■If we can determine the normal levels of carbon-14 in organisms, we can
use the half-life of carbon-14 decay to determine the age of fossilized
objects
●Radioactive Dating (Aging) Methods
○Radioactive decay → First order kinetics
■Plot of ln[ ] vs. t = linear
■ln( ) = -kt
[A]t
[A]0
○Nuclear reactions: “activity” instead of [ ], use # atoms/ nuclei
■ln( )= - t
(N)t
(N)0 λ
○First order kinetics: t1/2 = λ
0.693
○Radiocarbon dating
Document Summary
Fission : large nuclei decaying into more stable nuclei + energy. 235 92 u + n 0 236 92 u decay products + n 0 + 3. 2 x 10 -11 j energy. Fusion : combine smaller nuclei to produce more stable nuclei + energy. 2 1 h + 3 1 h 4 2 he + n 0 + energy. High temperatures needed to initiate reaction; thermally contained plasma. Fission in the sun: 1 1 h + 1 1 h 2 1 h + e - + neutrino + energy. Taleyarkan benchtop reaction: 2 1 h + 2 1 h 3 1 h + 1 1 h + energy. Neutrons that were detected had the same energy profile as that expected for californium-52, kept in taleyarkan"s lab. If we can determine the normal levels of carbon-14 in organisms, we can use the half-life of carbon-14 decay to determine the age of fossilized objects. Plot of ln[ ] vs. t = linear.
