- The atomic model has evolved over time based on new evidence and experiments. Early thinkers proposed ideas including Democritus' atomic theory of small indivisible particles. John Dalton later proposed atoms of different elements have distinct properties. J.J. Thomson discovered the electron and proposed the plum pudding model. Rutherford's gold foil experiment showed the atom's small, dense nucleus. Niels Bohr incorporated electron orbits into his model. Later, Schrodinger and others developed the concept of electron clouds. Chadwick discovered the neutron in 1932, completing the standard atomic model.

3. I
II
III
IV
History of Atom
Nuclear and Radioactivity
Natural Radioactive Sereis
Application of Radioactivity
V Interaction of Radiation with Matter

6. 460 – 370 BC
Democritus
proposes
the 1st atomic
theory
History of the Atom - Timeline
Antoine Lavoisier
makes a substantial
number of contributions
J.J. Thomson
discovers the
electron and
proposes the
Plum Pudding
Model in 1897 1871 – 1937
to the field of
Chemistry
1766 – 1844
John Dalton
proposes his
atomic theory in
1743 – 1794 1803
0
1856 – 1940
Niels Bohr
proposes
the Bohr
Model in
1913
1887 – 1961
Ernest Rutherford
performs the Gold Foil
Experiment in 1909
1885 – 1962
James
Chadwick
discovered
the neutron
in in 1932
Erwin
Schrodinger
describes
the electron
cloud in 1926
1891 – 1974
1700s
1800s
1900s
Click on picture for more information

7. Democritus
(460 BC – 370 BC)
Proposed an Atomic Theory (along
with his mentor Leucippus) which
states that all things are small, hard,
indivisible and indestructible
particles made of a single material
formed into different shapes and
sizes.
He named the smallest piece of
matter “atomos,”
meaning “not to be cut ”

8. ATOMOS
-To Democritus, atoms were
small, hard particles that were all
made of the same material but
were different shapes and sizes.
-Atoms were infinite in number,
always moving and capable of
joining together
-Aristotle did not support his
atomic theory

9. Aristotle and Plato favorted
the earth, fire, air and
water approach to the
nature of matter. Their
ideas held a way
because of their
eminence as
philosophers. The
atomos idea was buried
for approximately
2000 years

10. John Dalton
(1766 – 1844)
-In 1803, proposed the first scientific Atomic
Theory which states:
.All substances are made of atoms; atoms
are small particles that cannot be created,
divided, or destroyed.
.Atoms of the same element are exactly
alike , and atoms of different elements are
different
.Atoms join with other atoms to make new
substances
-Calculated the atomic weights of many various
elements (36 element)
-Was a teacher at a very young age
-Was color blind

11. John Dalton’s Periodic Table

12. J.J. Thomson
(1856 – 1940)
.Proved that atom can be divided into
smaller parts
.While experimenting with cathode-ray
tubes, discovered corpuscles, which were
later called electrons
.Stated that the atom is neutral
.In 1897, proposed the Plum Pudding Model
which states that atoms mostly consist of
positively charged material with negatively
charged particles (electrons) located
throughout the positive material.
. Won a Nobel Prize.

13. Plum pudding
+
+
-
- -
+
-
-
+
-
-
-
-
10-10m
+
+
+
+
+
+
+
+
+
+
+
+
Positively charged
porridge
Negatively charged
raisins (plums)

14. A Cathode Ray Tube

15. Ernest Rutherford
(1871 – 1937)
In 1909, performed the Gold Foil Experiment
and suggested the following characteristics of the
atom:
o It consists of a small core, or nucleus, that
contains most of the mass of the atom
o This nucleus is made up of particles called
protons, which have a positive charge
o The protons are surrounded by negatively
charged electrons, but most of the atom is
actually empty space
 Did extensive work on radioactivity (alpha & beta
particles, gamma rays/waves) and was referred to
as the “Father of Nuclear Physics”
 Won a Nobel Prize
 Was a student of J.J. Thomson
 Was on the New Zealand $100 bill

17. Rutherford’s experiment Involved firing a stream of tiny positively charged
particles at a thin sheet of gold foil (2000 atoms thick)
Most of the positively charged “bullets” passed right
through the gold atoms in the sheet of gold foil
without changing course at all.
Some of the positively charged “bullets,” however, did
bounce away from the gold sheet as if they had hit
something solid.
He knew that positive charges repel positive charges.
A very few get deflected greatly , Even fewer get bounced
of the foil and back to the left.

18. -The atom similar to the solar system (the central
core around which the great distances negatively
charged electrons)
-The atom mostly vacuum (because The atom is
not solid and the size is too small for the size of the
nucleus The atom)
-The mass of the atom is concentrated in the
nucleus (because the mass of the electrons is very
small compared to the mass of the nucleus of
protons and neutrons components)

19. Niels Bohr
(1885 – 1962)
-In 1913, proposed the Bohr Model,
which suggests that electrons travel around
the nucleus of an atom in orbits or definite
paths. Additionally, the electrons can jump
from a path in one level to a path in another
level (depending on their energy)
-Won a Nobel Prize
-Worked with Ernest Rutherfor

20. Niels Bohr’s Model (1913)
Electrons orbit the
nucleus in circular
paths of fixed energy
(energy levels).

21. Erwin Schrodinger
(1887-1961)
-In 1926, he further explained the nature
of electrons in an atom by stating that the
exact location of an electron cannot be
stated; therefore, it is more accurate to
view the electrons in regions called electron
clouds; electron clouds are places where the
electrons are likely to be found
-Did extensive work on the Wave formula
“Schrodinger equation”
-Won a Nobel Prize

22. Wave Model

23. James Chadwick
-Realized that the atomic mass of
most elements was double the
number of protons  discovery of
the neutron in 1932
-Worked on the Manhattan Project
-Worked with Ernest Rutherford
-Won a Nobel Prize
(1891 – 1974)

24. Progression of the Atomic Model
-
-
-
- +
-
++ EElleeccttrroonn CClloouudd
-
-
The structure of an atom, according to: Democritus &
ErrJnJw.eNaiJnsme. t iS elTsRsc h uhBCotromhhoheadsrrdoinfwngoiercdrk
John Dalton
+
-
- -
-
-
-
-
-
-
-
-

27. The first 92 elements on the table exist naturally.
The rest –which extended to 118 elements- were created
by scientists in atomic nuclei collision with the aid of
particle accelerators.

28. Isotopes
- Each element is characterized by atoms containing a fixed numbers of
protons .denoted by the atomic number Z , in the nucleus and an equal
numbers of orbital electrons to ensure the electrical neutrality
In addition to protons, the nucleus contains a variable number N of
electrically neutral neutrons.
Atoms of an element with different number of neutrons , but fixed number
of protons are known as ISOTOPES (there are more than 3000 isotopes
known ,but about 10% of those are stable)
-
-
-
Nuclides with the same N and different Z are called ISOTONES
Nuclides with the same mass numbers A are known as ISOBARS.

29. Isotopes
are atoms of the same element that differ in the number of
neutrons in their nuclei. A nucleus with a particular composition
A
is called a nuclide and is represented by X
Zwhere
: X =
Z =
A =
chemical symbol of the
element
atomic number
mass number or the number of
protons and neutrons in the nucleus
A nucleon is a neutron or proton; the mass number of
a nucleus is the number of nucleons (protons and
neutrons) it contains.
NOTE

30. How many protons, neutrons and electrons in each of the
following:
protons neutrons electrons
23Na
14N
38Ar
35Cl
36Cl-1
56Fe
Protons Neutrons Electrons
6 6 6
6 7 6
6 8 6
11 12
7
11
7 7
18 20 18
17 18 17
17 19 18
26 30 26

32. -Protons and neutrons are packed together tightly so that the
nucleus takes up only a tiny part of an atom.
-If an atom were the size of a football stadium, its nucleus
would be the size of a marble!

33. Despite taking little space, the nucleus contains
almost all the mass of the atom.

34. A proton or neutron has about 2,000 times the
mass of an electron.

35. “Why do protons stay together
when positive charges repel each
35
other?”
The main reason is because of a
force called Strong Force.
Opposes the electrostatic
force.

37. The force that makes protons and neutrons
attract each other and stay together.
100 times
stronger than the
electric force
Only works when
particles are close
Within the incredibly small nuclear size, the two strongest forces
in nature are pitted against each other. When the balance is
broken, the resultant radioactivity yields particles of enormous
energy

39. The Strong Force is exerted by
anything with mass (protons and
neutrons) to attract other masses
together and works within a very
short distance.
it is not an inverse square force
like the electromagnetic force.
Neutrons act as insulation, since
they have no charge, but have the
strong force to bring other
nucleons (protons and neutrons)
39
together.

40. Binding Energy
The experimental
observations show
that the mass of a
nucleus is always less
than the sum of
masses of its
constituent protons
and neutrons.
40

41. This “missing mass” is called as Mass Defect. This “missing mass” is
converted to energy according to Einstein’s E=mc2 and this energy is
called as “Nuclear Binding Energy”. The greater the nuclear binding
41
energy, the more stable is the atom.

42. Nucleus Binding Energy
We can define the binding energy of nucleus as it’s the energy
needed to separates the nucleus into it’s constituent component
nucleons .

43. 43

44. Nuclear stability
As a general rule, a nucleus
will need a neutron/proton
ratio of 3:2 (or 1.5:1) in order
to stay together.
This rule is more precise for larger
nuclei.
Of all known isotopes of
natural elements (about 1500),
only 250 of them are stable.
44

45. All of these stable isotopes
have an atomic number in
between 1 and 83. , Nucleons
exist in different energy
45
levels, or shells, in the
nucleus.
The numbers of nucleons that
represent completed nuclear
energy levels -2, 8, 20, 28,
50, 82, and 126- are called
magic numbers

46. 46
- Nuclei which do not fall on the line
of stability tend to be unstable or
“radioactive”
- They are called “radionuclides”
- A few radionuclides do fall on the line of
stability but their rate of decay is so slow that for
all practical purposes they are stable

47. Unstable Nuclei
 Radionuclides undergo a process called radioactive
transformation
 In this process, the nucleus emits particles to adjust
its neutron (N) to proton (Z) ratio
 This change in the N to Z ratio tends to move the
radionuclide toward the line of stability

48. All elements with atomic numbers greater than 83 are
radioisotopes meaning that these elements have unstable
nuclei and are radioactive. Elements with atomic numbers of
83 and less, have isotopes (stable nucleus) and most have at
least one radioisotope (unstable nucleus). As a radioisotope
tries to stabilize, it may transform into a new element in a
process called transmutation.

50. Discovery of radioactivity
In 1896, Henri Becquerel
accidentally left pieces of
uranium salt in a drawer on a
photographic plate. When he
developed the plate, he saw
an outline of the uranium salt
on it. He realized that it must
have given off rays that
darkened the film.

51. Discovery of Po and Ra
Marie Skłodowska Curie
(1867-1934)
Marie, and her husband Pierre,
analyzed a ton of Uranium ore.
After removing the uranium
the radioactivity increased.
This led to the discovery of
Polonium, more radioactive
than uranium, named after
here home country of Poland.
After removing the Polonium
the radioactivity increased
again. This led to the
discovery of a small amount in
their hand of Radium, so
radioactive that it glowed in
the dark.

52. Radioactive Decay
spontaneous disintegration of a nucleus into a slightly lighter & more
stable nucleus, accompanied by emission of particles, electromagnetic
radiation or both

53. In this process, an unstable “parent” nuclide P is
transformed into more stable “daughter”
nuclide D through various processes .

54. Types of Radioactive Decay
There are many types of
radioactive decay such as :
Alpha (α)
decay
Beta – minus (β̄ )
decay
Gamma
emission (훾)
Beta-plus (β+ )
decay Electron capture ( εc
)
nternal
conversion (IC)
Isomeric
transition (IT)
Special beta-decay
processes (β-n,β+α,β+p)
Neutron decay
Proton decay (P) (N)
Spontaneous
fission (SF)

55. Alpha particle emissions:
Helium nucleus: 2 protons and 2
neutrons, +2 charge.
For large, unstable nucleus which
needs to reduce both the number
of protons and the number of
neutrons.
210
84  
Pο Pb He 4
2
206
82
Example:

57. Beta particle emissions:
Electron emission, -1 charge.
For unstable nucleus which needs to
reduce the number of neutrons.
A neutron is converted into a proton
and an electron, the electron is given
off as a beta particle.
14
6   
C N β 0
1
14
7
Example:

59. Beta-plus emissions:
Positron emission, +1 charge.
For unstable nucleus which needs to
reduce the number of protons.
A proton is converted into a neutron
and a positron, the positron is emitted.
10
6   
C B β 0
1
10
5
Example:

61. Gamma emissions:
High energy electromagnetic waves
(photons) like visible light, except with
a shorter wavelength.
For high energy nucleus when it jumps
down from an excited state to a ground
state.
3
2  
He He γ 3
2
Example:

63. Electron capture:
An inner orbit electron combines with a proton and
forms a neutron.
For unstable nucleus which needs to reduce the
number of protons.
7
4   
Be e Li 7
3
0
1
Example:

64. Electron capture •

66. Type of Radioactivity
Natural Artificiall
-Collision of two
particles or collision of
a particle like neutron
with the atomic
nucleus.
-May generate the
unstable element from
a stable one.
-Nuclear Fission
-Nuclear Fusion
-Spontaneous
emission.
-By unstable nuclei of
particles or
electromagnetic
radiation, or both.
-Resulting in the
formation of a stable
isotope.

67. What is a
radioactive
series ?
And How many
series?

68. What is a decay series?
Sometimes when a nucleus decays, the product is not stable
(radioactive isotope) and it will decay.
The series of disintegration until a stable nuclide is reached is called a
decay series.
퐴1 → 퐴2 → 퐴3 → ⋯ → 퐴푛 휆1 휆2 휆3 휆푛
Radioactive series
Stable end
product In general
휆1 > 휆2 > 휆3 > ⋯ > 휆푛

69. How many series?
There are four natural decay chains:
Uranium series: 238
92U  206
82Pb
Actinium series : 235
92U  207
82Pb
Thorium series : 232
90Th  208
82Pb
Neptunium series : 241
94Pu  209
82Pb
HALF-LIFE STABLE END PRODUCT
yr
MASS SERIES PARENT
NUMBER
208
82Pb 232 1.39× 1010
90Th 4n Thorium series
209
82Pb 241 2.25× 106
94Pu Neptunium
series
4n+1
206
82Pb 238 4.51× 109
92U 4n+2 Uranium series
209
82Pb 235 7.07× 108
92U 4n+3 Actinium series

70. 70 annexeh@yahoo.co.in

72. The members of this
series are not
presently headed found by
in
nature because the
half-life of the longest
lived isotope in the
series is short
compared to the age
of the earth
Neptunium-241
241
94Pu  209
82Pb

73. In fact
Three radioactive series were recognized (Uranium , Actinium and
Thorium)
In which
heavy elements loss mass and changed their
atomic number in successive steps.
The changes ending only when the element
became a stable isotope of lead

74. Radioactivity
series
Uranium, Actinium , and Thorium occur in three natural decay
series, headed by uranium-238, uranium-235,
Importance
and thorium-232, respectively
The Radionuclides in these three series are
approximately in a state of equilibrium, in which
the activities of all radionuclides within each
series are nearly equal.
In Nature

75. • If the half life of the parent is longer than that of the
daughter , then after a certain time a condition of
equilibrium will be achieved .
• that is the ratio of the daughter activity to the parent
activity will become constant .
• In addition the decay rate of the nuclide is then
governed by the half life or disintegration rate of the
parent

77. headed by
uranium-238
parent Daughter
238
92U  206
82Pb

79. headed by
uranium-235
parent Daughter
235
92U  207
82Pb

81. headed by
thorium-232
parent
232
90Th
Daughter
 208
82Pb

82. I Terresial Earth Crust
Rocks and soil
II Cosmic Ray
Distant supernovae
 Uranium
 Thorium
 Actinium
III Internal Sources
Radon

86. RADIATION
Ionizing Non-Ionizing
Heavy
• Electron
• positron
• 휶 − 풑풂풓풕풊풄풍풆
• Proton (p)
light
energy transferred may be
sufficient to knock an electron
out of an atom.
Ionizing
photons particle
휸 − 풓풂풚 
풙 − 풓풂풚
charged uncharged

87. several terms are used to
describe the change in energy
of a particle and the absorbing
medium
 The stopping power (S) the
loss of energy from a
particle over a path length
(dx).
 Linear energy.
 Range.

88. Photon-beam Interactions
Process Definition
Attenuation Removal of radiation from the beam by the matter. Attenuation may
occur due to scattering and absorption
Absorption The taking up of the energy from the beam by the irradiated material. It
is absorbed energy, which is important in producing the radiobiological
effects in material or soft tissues.
Scattering refers to a change in the direction of the photons and its contributes to
both attenuation and absorption
Transmission Any photon, which does not suffer the above processes is transmitted.

89. Attenuation of a photon beam by an absorbing material is
caused by five major types of interactions :
Coherent
scattering
Attenuation
Photoelectric
effect
Compton
effect
Pair
production
Photo
disintegration

90. Interaction of light charged
with matter particles
 Interaction of electron with matter
When the energetic electrons penetrate the target material
The electron lose their kinetic energy by to mechanisms
Collision loss Radiative loss
 Inelastic collisions
 Elastic collisions

91.  Inelastic collisions Of electrons
• when the incident electron penetrate the
target atom , the electron lose their energy .
• The interaction with bound atomic electron
 elastic collisions Of electrons
In this collision , the electron collides with a particle of
identical mass (atomic number) but in this case there is no
lose in the energy.

92.  Radiative collisions of electron
When an energetic electron penetrates the
target material (atom) and losses very lose to
the nucleus in the target material .
It is deviated by the electromagnetic
interaction so the incident electron losses
much kinatic energy and the proton will be
emitted .

93.  The interaction of positron
• When the positron penetrates the target atom
Two mechanisms may be occured
 Free annhilation
 The formation of
positronium atom

94. Interaction of heavy charged particles
with matter
 Interaction of 휶 − 풑풂풓풕풊풄풍풆 & 풑풓풐풕풐풏 풘풊풕풉 풎풂풕풕풆풓
The heavy charged particles interact with matter through
coulomb forces between their positive charge and the
negative charge of the orbital electrons of the absorbed
material .
The heavy charged particles pass through the target atom
and give up a part of into kinetic energy .

95.  Interaction of photon (훾 − 푟푎푦푠)
with matter
 Photoelectric effect
 Compton scattering
 Pair production

96. Photoelectric
effect
When the 훾 − 푟푎푦 푠 푠푡푟푖푐푘푒푠 abound
electron of the target material , so the
electron absorbs all the energy of the
incident 훾 − 푟푎푦푠 푤ℎ푖푐ℎ it is enough
to eject the electron from into orbit and
completely leave the atom
 the kinetic energy to the photo-electron.
. = w
K E h흊 _
W = The binding energy of the electron
and ½ mν2 is the kinetic energy of the
photo electron. Fig. : The photo electric effect
훾 − 푟푎푦 푎푟푒 푐표푚푝푙푒푡푒푙푦 푑푖푠푎푝푝푒푎푟푒

97. The incident 훾−푟푎푦 푖푛푡푒푟푎푐푡푠 푤푖푡ℎ 푎 푓푟푒푒 푒푙푒푐푡푟표
푛 푖푛 푡h푒 푡푎푟푔푒푡 푎푡표푚.
K.E=h흊 − 풉흊′
Before interaction After interaction
- -
-
Incoming photon
Collides with
electron
-
- -
-
Scattered Photon
-
Electron is
ejected from atom

98.  The free electron takes a part of energy of the incident 훾
− 푟푎푦 푎푛푑 푡ℎ푒 푎푡ℎ푒푟 푝푎푟푡 표푓 푒푛푒푟푔푦 표푓 훾
− 푟푎푦 푖푠 푠푐푎푡푡푒푟푒푡 푎푛 푎푛푔푙푒 휃
 The atomic electron has a sufficient energy which lead to
the ejection of this electron from atom and it is scattered
by an angle 휙 푤푖푡ℎ 푟푒푠푝푒푐푡 푡표 푡ℎ푒 푑푖푟푒푐푡푖표푛 표푓 훾 − 푟푎푦
If the angle by which the electron is scattered is
Φ and the angle by which the photon is
scattered is θ, then the following formula
describes the change in the wavelength (δλ)of
the photon:
λ2 – λ1 = δλ = 0.024 ( 1- cos θ) Å

99.  Pair Production:
When the photon with energy in excess of 1.02 MeV passes close to
the nucleus of an atom, the photon disappears, and a positron and
an electron appear.
 Annihilation:
These two particles collide, converting to 2 photons with equal energy of 511 kev.

100. When an x-ray or γ ray beam passes through a medium, interactions
occur between the beam and the matter.
Initially the electrons are ejected from the atoms of the absorbing
medium which in turn, transfer their energy by producing ionization
and excitation of the atoms along their path.
If the absorbing medium consists of body tissues,
sufficient energy may be deposited within the cells,
destroying their reproductive capacity.
Howeve
r,
most of the absorbed energy is converted into heat,
producing no biologic effect.

101. Matter
Photo electric
effect
Compton
Scatter
Pair
Photon
Production
Matter
Ionization
Excitation Heat
X-Rays Chemical Effects
Biological Effects
High Speed Electrons

102. Fig : Semilog plot showing exponential
attenuation of a monoenergetic photon
beam.
-When mono-energetic (mono-chromatic)
radiation passes
through any material, a reduction
in the intensity of the beam occurs,
This is known as attenuation.
-Attenuation occurs
exponentially, i.e. a given
fraction of the photons is
removed for a given thickness
of the attenuating material.

103. Any
Questions?