Transcript Nuclear Physics

A nucleus can be specified
By an atomic number and a
Mass number.
Mass
Number
(A)
Symbol
N
Atomic
Number
(Z)
Nitrogen
Name
14
7
The typical Nitrogen atom has
A mass number of 14.
It has 7 protons and 7 neutrons.
The atomic number never changes,
However the mass can change.
All atoms are electrically Neutral,
thus the number Of protons equals
the Number of electrons.
Symbol
Name
Explanation
A
Mass Number
The number of
nucleons
Z
Atomic Number
The number of
protons
N
Neutron Number The number of
neutrons
An isotope is when atoms of an
Element having the same atomic
Number but different
Neutron and mass number.
Hydrogen has 3 isotopes:
Hydrogen
Deuterium
Tritium
Scientists measure
Elements in AMU, or atomic
Mass units.
1 AMU = 1/12 (mass of Carbon)
= 1.66 X 10-24 g
So, one proton or one
Neutron are about
1 AMU each.
Nuclear reactions change
The composition of
An atoms nucleus!!
The strong nuclear force is
An attractive force that
Overcomes the electrical
Repulsion between protons.
Binding energy is the energy
Released when nucleons bind
Together to form a
Stable nucleus.
E=
2
mc
When a nucleus undergoes
Nuclear decay, only three types
Of radiation can be released…
Alpha
Beta
Gamma
NAME
IDENTITY
CHARGE
PENETRATION
ALPHA
α
He-4
NUCLEI
2+
LOW
BETA
β
ELECTRONS
1-
MEDIUM
GAMMA
γ
HIGH
ENERGY
X-RAY
NONE
VERY
HIGH
Everybody thinks that this is so
Hard, but there are only 2 rules…
The total of the atomic numbers on
The left is that same as the total
On the right because charge
Must be conserved.
The total of the mass numbers on
The left is the same as the total on
The right because mass must
Be conserved.
This is the nuclear equation
That describes the beta
Decay of iodine – 131.
131I
53
0β
 131
Xe
+
54
-1
The numbers ALWAYS balance!
One of the isotopes of radium,
226 Ra, decays by alpha
88
Emission. What is the resulting
Daughter element?
226
88
Ra 
222
86
Rn +
4
2
α
As things decay, it can
Be measured.
The SI unit of radioactivity is
The becquerel, Bq.
1 Bq = 1 decay per second
The half-life is the time required
To half the original nuclei
Of a radioactive material to
Undergo radioactive decay.
T½
0.693
=
Decay constant
The 1/2 life of a radium nucleus
is 5 X 1010s. A sample contains
3 X 10 16 nuclei. What is the decay
Constant for this decay? How
Many radium nuclei will decay
Per second?
Constant = 1.4 X 10-11
Activity = 420000 Bq
There are 2 types of nuclear
Reactions, fission & fusion.
Stable nuclei can be made
Unstable by bombarding them
With extra neutrons.
Heavy nuclei can undergo
Nuclear fission.
Nuclear fission is the breaking
Apart of a nucleus.
When nuclear fission occurs,
Neutrons are released and can
Trigger a chain reaction.
Light nuclei can undergo
Nuclear fusion.
Nuclear fusion is when two
Nuclei are squished together.
Stars work like this, up until
Iron - 58, (the most stable element).
Fusing elements after this require
Energy, thus are made in
A supernova.
All things in the universe are
Created by very, very tiny
Pieces of matter.
Many new particles have been
Produced in accelerators.
There are 4 fundamental
Interactions in nature…
Strong, Weak,
Electromagnetic & Gravitational
A force can be thought of as
Mediated by an exchange
Of particles.
Leptons are thought to be
Elementary particles.
Hadrons include mesons & baryons.
Hadrons are thought to be made
Of quarks.
There are 6 quarks…
Up, Down, Charm,
Strange, Top, Bottom.
The standard model can help
Explain the early universe.