Nuclear Physics
An overview
Dr. Sajid Khan
Assistant Professor,
Physics Department, KUST
The Atom
The atom consists of two parts:
1. The nucleus which contains:
protons
neutrons
2. Orbiting electrons.
Discovering the Nucleus
• In I9II Ernest Rutherford
proposed that the positive
charge of the atom is
densely concentrated at
the center of the atom,
forming its nucleus
• Experiment involves
counting the number of
alpha particles that are
deflected through various
scattering angles φ. Experimental arrangement
proposed by Rutherford.
Explaining the Deflections
• To deflect the alpha
particle backward, there
must be a large force
• This force could be
provided if the positive
charge, instead of being
spread throughout the
atom, were concentrated
tightly at its center
Result
In Rutherford's words: "It
was quite the most
incredible event that ever
happened to me in my life.
It was almost as incredible
as if you had fired a 15-inch
shell at a piece of tissue
paper and it came back
and hit you."
The basic building blocks of the nucleus
are the proton and the neutron.
A
Z
X
A = number of protons + number of neutrons
Z = number of protons
A – Z = number of neutrons
Number of neutrons = Mass Number – Atomic Number
Nuclear Properties
Nuclear Terminology
• Nuclei (plural of nucleus) are made up of protons and neutrons
• The number of protons in a nucleus
(called the atomic number or proton number of the nucleus) is
represented by
the symbol Z
• The number of neutrons (the neutron number) is represented by
the symbol N.
• The total number of neutrons and protons in a nucleus is called its
mass number A
𝑨=𝒁+𝑵
• Neutrons and protons collectively called nucleons
• Representing nuclides, example 197Au
• Nuclides with the same atomic number Z but different neutron numbers N
are called isotopes of one another
Some Properties of Selected
Nuclides
Organizing the Nuclides
• Isotopes of an element have same number of
electrons and same chemical properties
– Fit into the same box in the periodic table.
• The nuclear properties of the isotopes of a given
element are very different from one isotope to
another.
– periodic table is of limited use to the nuclear physicist
• the nuclides are organized on a nuclide chart
Stable Nuclides-Green
Radionucles-Beige
Z > 83, No stable nuclides
Nuclear Binding Energy
∆𝑬𝒃𝒆 = (𝒎𝒄𝟐) − 𝑴𝒄𝟐
∆𝑬𝒃𝒆
∆𝑬𝒃𝒆𝒏 =
𝑨
Type equation here.
Nuclear Energy Levels
• The energy of nuclei, like
that of atoms, is
quantized. That is, nuclei
can exist only
in discrete quantum
states, each with a well-
defined energy.
• The emitted photon has
energy in the gamma-ray
region of electromagnetic
spectrum.
The Nuclear Force
Strong nuclear force
• Stronger than coulomb force to overcome the
repulsion of protons.
• Short range
• Charge independent.
Radioactive Decay
• Statistical process
• Spontaneous emission of particle or
electromagnetic radiation from the atom
• Unaffected by temperature, pressure, physical state,
etc
• Conserves total energy, linear and angular
momentum, charge, mass number, lepton number,
etc.
Decay Rate and Half Life
−𝑑𝑁
= λ𝑁
𝑑𝑡
λ is disintegration constant, has characteristic
value for every radionuclide.
− λ𝑡
𝑁 = 𝑁𝑜𝑒
Half-life T1/2of a radionuclide is the
time at which N reduced to one-half of its initial
𝑙𝑛2
value 𝑇1/2 =
λ
Alpha Decay
A4
A
Z XN Z2 X N 2 He γ
4
2
Intensity (Orb. Units)
5.0 5.5 6.0 6.5 7.0 7.5
Energy (MeV)
Beta Decay
b: change a neutron to a proton (negatron decay)
A
Z XN Y A
Z 1 N 1 b
b is an electron
b: change a proton to a neutron
A
Z XN Y A
Z 1 N 1 b
β+ is an anti-electron or positron
EC: electron capture, change a proton to a neutron
A
Z XN e Y A
Z 1 N 1
Beta Decay Spectrum
The disintegration energy Q is shared-in varying
proportions-between the emitted electron and neutrino
Gamma Decay
Bismuth-214. The daughter isotope is a more stable (lower-energy)
version of the original bismuth-214.
Radiation Dosage
Absorbed dose: (Energy transferred per unit mass
1 Gy = 1 J/Kg
Dose Equivalent: express the biological effect by
multiplying the absorbed dose (in grays or rads) by a
numerical RBE factor (from relative biological
effectiveness.
• X rays and electrons, for example, RBE – 1, slow
neutrons, RBE - 5; alpha particles, RBE : l0
• SI unit of dose equivalent is the sievert (Sv)
• Recommended dose limit 5 mSv
Energy from the Nucleus
• Energy from wood, coal
atomic source; rearrangement
of outer electrons to get more
stable atoms
• Energy from nucleus (e.g
Uranium)
Rearrangement of nucleons
into more stable configuration
Energy Comparison
Nuclear Fission
𝟐𝟑𝟓𝑼 + 𝒏 → 𝟏𝟒𝟎𝑿𝒆 + 𝟗𝟒𝑺𝒓 + 𝟐𝒏 + 𝑸
𝑸 = 𝒕𝒐𝒕𝒂𝒍 𝒇𝒊𝒏𝒂𝒍 𝒃𝒊𝒏𝒅𝒊𝒏𝒈 𝒆𝒏𝒆𝒓𝒈𝒚 − (𝒕𝒐𝒕𝒂𝒍 𝒊𝒏𝒕𝒊𝒂𝒍 𝒃𝒊𝒏𝒅𝒊𝒏𝒈 𝒆𝒏𝒆𝒓𝒈𝒚)
Chain Reaction
Controlled and Uncontrolled Chain
Reaction
• On earth, nuclear fission
reactions take place in
nuclear reactors, which use
controlled chain reactions to
generate electricity.
• Uncontrolled chain reactions
take place during the
explosion of an atomic bomb
Nuclear Fusion
• Nuclear fusion is the
combining of two nuclei
with low masses to
form one nucleus of
larger mass.
• Nuclear fusion
reactions are also
called thermonuclear
reactions
Cont…
• Fusion reactions exist in
stars.
• Our sun is a good example
of a thermonuclear (fusion)
reaction.
• It is very challenging to
create fusion reactions on
earth since they need
temperatures above one
million degrees Celsius in
order to take place.
