Nuclear Physics
Atomic Structure
Bohr Model
Protons (atomic # Z)
• Positively charged
• Located in the nucleus
– Mass = 1.6726 x 10 -27 kg
• All atoms of an element have the same number of
protons, whether they are radioactive or not.
• Dictates position on periodic table and chemical
identity
• Protons and Neutron, and their associated forces,
affect an atom’s radioactive properties
Neutrons
• No charge
• Located in the nucleus
• 1800 times as heavy as an electron.
– Mass= 1.6749 x 10 -27 kg
• Neutron + proton = Nucleon
Electrons
• Negatively charged
– Neg. charge of 1.6022 x 10-19 Coulomb
– Mass = 9.109 x 10-31 kg
• Orbit around the nucleus
• Determine atom’s chemical properties
• Less mass
• Higher energy?
Electron Shell Configuration
Sl.No
Electron Shell
Maximum
Capacity
1
K Shell
2 electrons
2
L Shell
8 electrons
3
M shell
18 electrons
4
N shell
32 electrons
ELECTRON VOLT
• Base unit of energy
• Amount of energy acquired by an electron
when accelerated through an electrical
potential of 1V.
Atomic Shorthand
X = Chemical Symbol
A= Atomic mass
Z= Number of protons
Subtract A-Z to find the number of neutrons.
Chemical Shorthand
• X= elemental atom
A
Z
X
• Z= Atomic Number
• # of protons
• N= Neutron Number
N
• A= Mass Number
• Z+N
• Total number of nucleons
Mass Unit
• Universal mass unit: equal to ½ the mass of a
Carbon atom
1.66054 x 10 -27 kg
• Atomic Mass Unit (AMU)
1/12 mass of stable Carbon-12 atom
One AMU is about the same as one proton, and also
about the same as one neutron.
One AMU is 1.66x10-27 kg
Vocabulary words
• Valent Electrons: outer electrons that interact to form
molecules
• Valence: is an atom’s ability to lose or gain an e- so that it can
achieve a stable e- configuration. Usually determined by the
number of e- in outermost shell (valence shell)
– Octet Rule: Most stable form of atom. Main-group
elements tend to undergo reactions that leave them with
8 outer shell e-. They react in such a way that they attain
an e- configuration like an inert gas in which the s and p
orbitals are filled in their valence e- shell (ns2np6)
Vocabulary words
• Atom: smallest part of an element with the same
chemical properties. Contains 3 types of elementary
particles: p+, n, e• Element: An element is a fundamental substance that
cannot be chemically broken down any further.
• Molecules :are formed from combinations of elements
• Matter: Molecules make up matter
2
E = mc
E= energy
M= mass
C= speed of light (3 x 108m/sec)
Matter and Energy are directly related, matter
can be turned into energy and energy can be
turned into matter.
Quantum Theory
• Subatomic particles-tiniest things we know
• Collaborative effort by early 20th century
physicists: Niels Bohr, Erwin Schrodinger,
Wolfgang Pauli, Max Born, Max Planck,
Werner Hiesenberg
• Explains the nature and behavior of matter
and energy on the atomic and subatomic
levels.
Quantum theory
• the study of the jumps from one energy level
to another as it relates to the structure and
behavior of atoms.
May the Forces be with You
• Nature consists of mainly matter and the
forces that govern the behavior of matter
• Force is a term related to interaction between
different parts of matter
– Gravitational
– Electromagnetic
– Weak
– Strong
The Forces
• Gravitational: result of the mass of matter
(holds the solar system together, helps create
centrifugal force)
• Electromagnetic: dominate role in holding
atoms together and interactions between
atoms, molecules, biomolecules, etc
• Strong: hold a nucleus together (p-p, n-n, p-n)
• Weak: nuclear transformation
Gravitational
• Best described in Einstein’s Theory of Relativity
• force proportional to masses of interacting bodies
and inversely proportional to the square of the
distance between them
• Newton's law of universal gravitation simplifies to
F = mg, where m is the mass of the body and g is a
constant vector with an average magnitude of
9.81 m/s2. The acceleration due to gravity is equal
to g.
Gravitational
• every object in the universe exerts a
gravitational force on everything else.
• The effects of gravity depend on two things:
the mass of two bodies and the distance
between them.
• is about 10-36 times the strength of the strong
force
Electromagnetism
• has both attractive and repulsive properties
that can combine or cancel each other out
• two charges: positive and negative
• keeps atoms together: the positively charged
nucleus and the negatively charged electrons
attract each other
• messenger particle of electromagnetism is the
photon
Magnetism
• A magnetic field describes a volume of space
where there is a change in energy.
– a magnetic field is produced whenever an electrical
charge is in motion.
– The spinning and orbiting of the nucleus of an atom
produces a magnetic field as does electrical current
flowing through a wire.
– The direction of the spin and orbit determine the
direction of the magnetic field.
– motion of an electric charge producing a magnetic
field is an essential concept in understanding
magnetism
Magnetism
• All the electrons produce a magnetic field as they
spin and orbit the nucleus
• The direction of spin and orbit of the electron
determines the direction of the magnetic field.
• When two electrons are paired, they spin and
orbit in opposite directions. Since the magnetic
fields produced by the motion of the electrons are
in opposite directions, they add up to zero.
• The overall magnetic field strength of atoms with
all paired electrons is zero.
Coulombs Law
• Simplified: like charges repel, opposites
attract.
K = Coulombs law constant
Q =quantity of charge on objects 1 and 2
D= distance
F= force
Strong Force
• range is limited to subatomic distances
• Also called nuclear force
• keeps quarks together inside protons and
neutrons
• keeps protons and neutrons inside atomic nuclei
(binds nucleons).
• messenger particle is the massless gluon, so
named because it "glues" elementary particles
together
Weak Force
• only on the extremely short distance scales
found in an atomic nucleus
• stronger than electromagnetism, but its
messenger particles (W and Z bosons) are so
massive that they do not faithfully transmit its
intrinsic strength.
• responsible for radioactive decay
Force
Particle
Mass
force
Gravitational Force
Graviton
0
weak
Electromagnetic Force
Photon
0
weak
Weak Nuclear Force
Weak Gauge
Bosons
86, 97
strong
Strong Nuclear Force
Gluon
0
strong
THE UNIFICATION OF FORCES: Electromagnetic and gravitational forces get weaker as
you get further away while strong and weak get stronger.
Bosons are the particles which transmit the different forces between the matter
particles
Quantum Theory
• Stability of an atom is governed by nuclear
(strong and weak) and electromagnetic forces
• Strong is attractive
• Electromagnetic is repulsive
• Balance of these forces (attraction and
repulsion) must be maintained for stability
• Unbalanced = radioactive
Quantum Theory
• Wave particle duality
• changes in electric and magnetic fields are
always coupled, oscillating
• relationship between frequency and
wavelength
• distance per cycle × cycles per second =
distance per second = c
• The speed of electromagnetic radiation was
computed to be around 3×108 m/s
• Photons travel the same as light
• All photons travel at the speed of light.
solve for wavelength or frequency
Electromagnetic Spectrum
Plank’s Constant
• Max Plank: one of the founder’s of the quantum
theory, energy is not continuous
• 1900- discovered the physical constant reflecting
the sizes of energy quanta in quantum mechanics
• 6.626×10-34 J/Hz
• The Proportionality constant between energy (E)
of a photon and the frequency (v) of its associated
electromagnetic wave. (relation between energy
and frequency)
C= 3 x 10 8 m/s
Electromagnetic Radiation
• form of energy emitted and absorbed by
charged particles
• wave-like behavior as it travels through space.
• Photons-massless energy
• Gamma = higher frequency, shorter
wavelength, and higher energy
• Nuclear Binding Energy: the direct measurement of energy
it takes to hold the nucleons together and is determined
when the loss of mass is converted into energy released
during a nuclear reaction
• The energy holding the nucleus together. Some of the mass
of the nucleus is converted to energy to hold it together and
that is why the nucleus weighs less than if you would add
all the p+ and n together in the nucleus
ΔE = Δmc2
• Typical Binding Energy value is 6-9 MeV
– Amt of energy supplied to remove a single nucleon from the
nucleus
• The greater the binding energy, the more stable the
nucleus
Electron Binding Energy
The energy needed to completely remove an
electron from a shell of an atom
• Relative to the given shell
• Increases with the Z number…Why?
• Where is the binding energy the greatest?
Electron Binding Energy:
• Energy needed to move an electron to one
shell from another is equal to the difference in
binding energy.
• Greatest amount of energy at the inner most
shells (K shell)
Mass Deficit
• When a proton and neutron fuse together,
their new mass is less than the sum of the
individual parts.
• Mass deficit is the phenomenon wherein
nucleons, the protons and neutrons that are
being fused together to make up an atomic
nucleus, each give up a little mass.
• This is converted into binding energy
Quantum Theory
•Any imbalance of the forces governing an
atom can lead to ionization as it seeks
stability.
–What do you think will happen if energy is
imparted on an atom?
•What are some things an atom might do to try to
regain stability?
Quantum Theory
•What do you think will happen if a charged
particle interacts with an atom?
–What forces become unbalanced?
–What does the atom need to do to regain
stability?
For Next week…
•Complete handout
•Review conversions
•Study for Quiz