Reactions Nuclear Microscopic cross sections
Duderstadt and Hamilton pp 3-19
Macroscopic to microscopic world
Cutaway of PWR pressure vessel and Internals.
Nuclear chain reaction
Neutron +
235
U fission products + more neutrons + energy
There are many reactions a neutron can have. We will look at individual nuclear reactions.
If I were a neutron
My world would be mostly empty space.
Two types of nuclear reactions
Radioactive decay nucleus spontaneously decays and emits a particle (-alpha, -beta, or -gamma)
Neutron-nuclear collisions neutron collides with a nucleus and is scattered or absorbed.
Nomenclature
A Z
X such as C or
12 6
235 92
U
Z is the atomic number A is the atomic mass N = A-Z is the number of neutrons Nuclei with the same Z and different A are called isotopes. 235 238 E.g. 92U and 92U
1 1 2 3 H and 1 H and 1 H
Nuclear Collision Reactions
a+b c+d
1 0
a(b, c)d
236 92
n + 235U 92
235 92
U +
U (n, ) 236U 92
Absorption and emission of energy
E = mc
2 2
Q = ( M a + M b ) ( M c + M d ) c Q > 0 exothermic Q < 0 endothermic
Most important reactions
Nuclear fission 0
n+ (n,fission)
1 X
A Z
A1 Z1
X+
A2 Z2
X + neutrons + 200 MeV
Radiative capture (n, )
1 0
n+ X (
A Z
A+1 Z
X)
*
A +1 Z
X +
Scattering (n,n) or (n,n)
1 0 1 0
n + ZA X 01n + ZA X elastic scattering (n,n) n + X n + ( X ) 01n + ZA X +
A Z 1 0 A Z *
inelastic scattering (n,n')
Microscopic Cross section
Consider a beam of mono-energetic neutrons of intensity I neutrons / cm2 s incident on a very thin wafer of material such that there are NA atoms per centimeter squared. The rate of neutron nuclear collisions is proportional to the neutron beam intensity I and the areal density of nuclei NA. We call the constant of proportionality the neutron...