FUSION AND FISSION
All matter is made of atoms.
Atoms contain:
- Electrons
-Atomic nucleus: the nucleons
Nucleons are protons and neutrons
Protons + charge
Neutrons 0 charge
Electrons – charge
mass = 1 amu
mass = 1 amu
mass = 0.00055 amu
In the Universe, there are
4 fundamental interactions
[also called the 4 fundamental forces]
All matter containing atoms are bound together
by the gravity force. [stars, galaxies, etc]
The electrons and the protons of an atom are
bound together by the electromagnetic force.
The nucleons are bound together by the strong
force. This force is strong enough to overcome
the electromagnetic repulsion of the protons for
each other.
The fourth force is the weak force. This force
is responsible for fusion and fission.
In ordinary chemical reactions, only electrons
are transferred or shared between atoms.
In nuclear reactions, the nucleus of an atom
changes.
Fusion: light nuclei forced together fuse and
release energy.
Fusion occurs in the core of stars. When the
critical amount of mass accretes, and there is
sufficient temperature [due to KE] fusion
begins.
The combined nuclear mass of a fused atom is
less than the sum of the parts.
The difference in mass is predicted by the
Einstein equation: E = mc2
c = speed of light
m = mass
E = energy
The missing mass is converted into binding
energy, that holds the particles together.
Fission: A massive nucleus like U-235 breaks
apart [fissions] to produce two or more lighter
nuclei.
Fission occurs in the rocks in the mantle.
90% of the heating of the core is due to
radioactivity.
The sum of the parts is less than the whole,
because some of the mass is released as energy.
[Einstein equation]
fission produces three types of radiation:
alpha, beta , gamma
alpha = = helium nucleus = 2p +2n
The nucleus emits a particle containing 2
protons and 2 neutrons
beta = = an electron = 1eA neutron in the nucleus breaks into a proton
plus an electron and then the electron is
emitted.
n = p + egamma =  = a photon
high energy photons emitted from the nucleus.
writing equations for radioactivity:
number of nucleons is conserved
[mass number is conserved.]
Example:
Alpha radiation: U-238
Write alpha particle as 24He or 24
238
92
U  H + ?
ENERGY
balance the number of protons and nucleons

238
U  H + 90234Th + ENERGY
92
Beta decay: Iodine-131
Write the beta particle as
131
53
I-10e- +
0
-1
e-
? + ENERGY
balance the number of protons and nucleons
131
53
I -10e- +
131
54
Xe + ENERGY