The document discusses atomic models and nuclear physics. It provides information on: 1) Early atomic models including Dalton's billiard ball model, Thomson's plum pudding model, Rutherford's nuclear model, and Bohr's planetary model. 2) Experiments that led to discoveries about the structure of the atom including Thomson's cathode ray tube experiment, Rutherford's gold foil experiment, and Bohr's model of electron orbits. 3) Components of the nucleus including protons, neutrons, and isotopes. 4) Types of radiation including alpha, beta, gamma particles and their properties such as mass, charge, penetration and ionization. 5) Experiments that helped discover radiation and nuclear decay processes.

1. Particle and Nuclear Physics

2. The students should be able to:
• infer from the results of the α-particle scattering experiment the existence and small
size of the nucleus
• describe a simple model for the nuclear atom to include protons, neutrons and
orbital electrons
Learning Objectives

3. Atoms
A timeline of atomic models
1.Atomic model (1808)
2.Plum-pudding model (1904)
3.Nuclear model (1911)
4.Planetary model (1913)
5.Quantum mechanical model
(1926-present)

4. Dalton’s Early Atomic Model
• “Billiard Ball” model
• he envisioned atoms as
solid, hard spheres,
like billiard (pool) balls, so
he used
wooden balls to model them
Atoms

5. Atoms
The Cathode Ray Tube Experiment
Discovery of the Electron

6. Atoms
J.J. Thomson
He was the first scientist to
show the atom was made
of even smaller things
Electron
Used the Cathode ray tube
to discover electrons

7. Atoms
Using J.J Thomson’s Plum Pudding atomic model, Rutherford
predicted the alpha particles would pass straight through the gold
foil. This is because the alpha particles are more massive than
electron.
Aplha-Scattering Experiment

8. Atoms
Figure on the left show the apparatus used in
alpha-scattering experiment.
• The alpha particle (positively charged)
source was encased in the metal with a
small aperture, allowing a fine beam of
alpha particles to emerge.
• The alpha particles were known to be
smaller than a gold atoms and more
massive than electrons.
• The air in the apparatur was pumped out
to leave a vacuum. Alpha radiation is
absorbed by a few centimeter of air.
• One reason choosing gold was it can be
made into a very thin sheet or foil.
• The alpha particles were detected when
they struck a solid material. Each alpha
particle gave a tiny flash of light and were
counted by the experiment
Alpha-Scattering Experiment

9. Gold Foil Experiment Results
• Most of the alpha particles went straight
through the gold foil. Therefore, atoms are
mainly empty space.
• Some of the alpha particles were back-
scattered. Therefore, the centre of an atom
must have a positive charge and that repelled
the alpha particles, that is positively charged
• Sometimes an alpha particle bounced straight
back. Thus, the mass of the atom must be
concentrated in the centre. We now call the
central part of an atom, the nucleus
Atoms

10. Atoms
Ernest Rutherford
With his students, Geiger
and Marsden, discovered
the nucleus of a gold atom
with his “gold foil”
experiment.
alpha (α)- scattering
experiment

11. Atoms
Niels Bohr: Planetary Model
Bohr’s work agreed with the results of
experiments by other scientists.
SUGGESTION: electrons orbit the nucleus at
specific distance. He pictured atoms as miniature
solar systems
IMPORTANT!! Orbiting of electrons prevent the
atom from collapsing
We now call the “orbits”, energy level or shells

12. Atoms
Electrons and Energy Levels
The Nucleus is surrounded by electrons in energy level.
Energy levels which are further from the nucleus are at higher
energy than those which are closer to the nucleus.

13. Atoms
Electrons and Energy Levels
Electrons can change energy level if they gain or lose energy
• If the atom can now emit electromagnetic
radiation and the electron returns back to the
lower energy level.
If the atom absorb electromagnetic radiation, an
electron can move from a lower energy level to a
higher energy level
The atom is said to be EXCITED

14. Atoms
1. Electrons orbit the nucleus in
orbits that have specific size and
energy.
2. The energy of the orbit is related
to its size. The lowest energy is
found in the smallest orbit.
3. Electrons move between each
shell when gaining or losing
energy.
a) Gaining energyàelectrons
move to farther orbit from
the nucleus.
b) Losing energyàelectrons
move to closer orbit from the
nucleus.
Niels Bohr

15. Atoms
Protons and Neutrons
Further experiment by Rutherford found that
positive charge in the nucleus is actually made up of
small discreet positive particles called protons.
James Chadwick discovered that the nucleus also
contains neutrons. These have no charge, they are
neutral.

16. Atoms
A Simple Model of Atom

17. Atoms
1. Electrons don’t move around
the nucleus in orbits.
2. Electrons exist in specific
energy levels as a cloud.
3. The electron cloud is the
region of negative charges,
which surrounds the nucleus.
4. Orbital : The region with a
high probability of containing
electrons.
Schrodinger

18. Learning Objectives
The students should be able to:
1. distinguish between nucleon number and proton number.
2. understand that isotopes are forms of the same element with different
numbers of neutrons in their nuclei.
3. understand and use the notation !
"
𝑋 for the representation of nuclides.

19. Nuclei
Every elements has a symbol and these always has two numbers.
Proton number (Atomic number)
Proton have a positive charge but atom
have no overall charge.
This is because the number of electrons
is equal to the number of protons.
The negative charges on the electrons
cancel out the positive charges on the
protons.
Sodium atom contains 11 protons
so they also contains 11 electrons.

20. Nuclei
Every elements has a symbol and these always has two numbers.
Nucleon number (Mass number)
The Mass number tells us the total number of
protons and neutrons added together.
To calculate number of neutrons, substract the
atomic number from the mass number.
The mass number is always the biggest number.
It tells you the relative mass of the atom. It is
also always roughly double the atomic number.
Which means there’s about the same number
of protons as neutrons in any nucleus. For sodium atoms,
23 -11 = 12 Neutrons

21. Nuclei
Every elements has a symbol and these always has two numbers.

22. Nuclei
Think
Ø What is the same from the two atoms of sodium?...........................
Ø What is different between them?.............................................
Those two elements would all be classed as ISOTOPES of Sodium.
• How many protons are there?......
• How many neutrons are there?......
• How many protons are there?......
• How many neutrons are there?......

23. Nuclei
The number of protons in the nucleus of
an atom determines what element it is
Isotopes are atoms with the same
number of protons but a different
number of neutrons.
In the nucleus,
this one has 6
protons and 6
neutrons.
In the nucleus,
this one has 6
protons and 7
neutrons.
For an atom;
• The number of proton determines the
chemical properties
• The number of protons and the number
of neutrons determine the nuclear
properties

24. Nuclei and Radiation
Only one or two of an Isotopes elements are stable
The other isotopes tend to be radioactive,
which means that they decay into other
elements and give out radiation. This is where
all radioactivity comes from – unstable
radioactive isotopes undergoing nuclear decay
and spitting out high energy particles.

25. Learning Objectives
The students should be able to:
• understand that nucleon number and charge are conserved in nuclear processes
• describe the composition, mass and charge of α-, β- and γ-radiations (both β– (electrons) and
β+ (positrons) are included)
• understand that an antiparticle has the same mass but opposite charge to the corresponding
particle, and that a positron is the antiparticle of an electron
• state that (electron) antineutrinos are produced during β– decay and (electron) neutrinos are
produced during β+ decay
• understand that α-particles have discrete energies but that β-particles have a continuous range
of energies because (anti)neutrinos are emitted in β-decay
• represent α- and β-decay by a radioactive decay equation of the form !"
"#$
𝑈 → !%
"#&
𝑇ℎ + "
&
𝛼
• use the unified atomic mass unit (u) as a unit of mass

26. Radiation
Only one or two of an Isotopes elements are stable

27. Radiation
• An alpha particle, consisting of two protons
and two neutrons.
• An alpha particle is the same as a helium
nucleus.
• Alpha particles do not have any electrons. So
they have an overall charge of +2.
• Alpha particles have high mass compared
with beta particles.
• Alpha particle move with speed up to 0.1 x
speed of light
Alpha (α) Particles

28. Radiation
Beta (𝝱) Particles
A beta particle is an
electron which is ejected
from the nucleus at a very
high speed
Nucleus of an atom DOES NOT contains electron. Where does it come from???
A beta particle is formed inside the nucleus when a neutron changes into a
proton and an electron. With the proton stay in the nucleus and electron is
emitted at high speed

29. Radiation
Beta (𝝱) Particles FACTS
Ø Each beta particle is an electron.
Ø A relative charge of -1.
Ø A low mass compared with alpha
particles.
Ø Speed up to 0.9 x speed of light

30. Radiation
Gamma (𝛾) Rays
Gamma Rays are not particles
FACTS
ØGamma Rays are a type of
electromagnetic radiation
from nucleus
ØNo charge.
ØNo mass
ØTravel at the speed of light
After an alpha or beta decay, the nucleus is buzzing with energy. To get rid
of this energy, it gives out gamma radiation. Gamma ray is a wave at high
frequency carrying away a huge amount of energy

31. Radiation
Neutron Emission

32. Radiation
Properties of 𝛂, 𝛃, and 𝛄 Radiation

33. Radiation
Range in Air – 𝛂 Particles
𝛂 particles are large. The can travel
around 5 cm in air before they
collide with air particles and stop
• An 𝛂 particle, consisting of two
protons and two neutrons.
• An 𝛂 particle is the same as a helium
nucleus.

34. Radiation
Range in Air – 𝛃 Particles
A 𝛃 particle is an electron which is
ejected from the nucleus at a very
high speed
𝛃 particles can travel further. They
can reach around 15 cm in air before
stopping

35. Radiation
Range in Air – 𝛄 Rays
𝛄 Rays are a type of electromagnetic radiation
𝛄 radiation travel several metres in
air before stopping

36. Radiation
Energy Released
Radioactive substances release
energy when they decay.
Before they decay, this energy
is stored in the nucleus of the
atom, it is two forms:
1. An alpha particle or beta
particle is fast-moving. Both
particles have kinetic energy.
2. A gamma ray transfer energy
as electromagnetic radiation

37. Radiation
Atoms can lose electrons from their outer energy level
Atom absorb so much
enery, electron at the
outermost completely
leave the atom
Now we call this
positive ion rather than
atom since it has more
proton than electron
Ionisation

38. Radiation
Atoms can lose electrons from their outer energy level
Ionisation
• When an atom loses
one electron, the ion
now has a +1 charge.
• If an atom loses 2
electrons, the ion
now has a +2 charge.
NO overall charge Overall charge of +1

39. Radiation
Properties of Ionising Radiation
Radiation affects the matter it passes through by causing ionisation
Alpha Radiation Strongly Ionising
• The slowest moving
• Has the largest charge (+2)
As the alpha particles collide with atoms,
they may knock or drag electrons away
from the atom.
In the process, the alpha radiation loses
some of its kinetic energy. After many
ionisations, they loses all of its energy and
no longer has ionising effect

40. Radiation
Properties of Ionising Radiation
Radiation affects the matter it passes through by causing ionisation
Beta Radiation
Moderately Ionising
Less ionising compared to alpha radiation;
• The charge is less than that of an alpha
radiation (-1)
• It is moving faster, so that it is more
likely to travel straight past an atoms
without interacting with it.
Beta radiation can travel further through
air without being absorbed

41. Radiation
Properties of Ionising Radiation
Radiation affects the matter it passes through by causing ionisation
Gamma Radiation
Weakly Ionising
• The fastest moving
• Uncharged
Gamma radiation is the least readily
absorbed in air. Therefore, it is the
least ionising.

42. Radiation
Penetrating Power
Radiation
can pass
through solid
materials
Henry Bacquerel
discovered
radioacvtivity in 1896
The photographic film was blackened by
uranium compounds

43. Radiation
What materials
can STOP alpha,
beta and gamma
radiation?

44. Radiation
Different types of radiation can pass through (penetrate) different thickness
of materials
Penetrating Power
Alpha Radiation
Beta Radiation
Gamma Radiation

45. Radiation
Penetrating Power
A cloud chamber was used to show
the tracks of alpha particles in air
Alpha radiation is the most strongly
ionising, so it is the most easily absorbed
and the least penetrating
By the time the alpha particles have
travelled this far, they have lost virtually all
of their kinetic energy.
They are absorbed by a thin sheet of paper

46. Radiation
Penetrating Power
Beta Radiation
• Beta particles can travel fairly
easily through air or paper
• They are absorbed by a few
milimeter of metal, such as
aluminium
Gamma Radiation
• Since gamma radiation is the least strongly
ionising, it is the most penetrating
• Several centimeters of a dense metal like
lead can be used to absorb gamma rays.
• The intensity of gamma radiation
decreases gradually as it passes through
the lead