I

II

III

IV

History of Atom

Nuclear and Radioactivity

Natural Radioactive Sereis

Application of Radioactivity

V Interaction of Radiation with Matter

Democritus proposes

the 1st atomic theory

460 – 370 BC

History of the Atom - TimelineAntoine Lavoisier

makes a substantial number of contributions

to the field of Chemistry

1766 – 1844

John Dalton proposes his

atomic theory in 18031743 – 1794

0

1856 – 1940

J.J. Thomson discovers the electron and proposes the Plum Pudding Model in 1897

1871 – 1937

Ernest Rutherford performs the Gold Foil

Experiment in 1909

1885 – 1962

Niels Bohr proposes the Bohr Model in

1913

1887 – 1961

Erwin Schrodinger

describes the electron cloud in 1926

1891 – 1974

James Chadwick

discovered the neutron in in 1932

170

0s

180

0s

190

0s

Click on picture for more information

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 ”

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

Aristotle and Plato favortedthe 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

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

John Dalton’s Periodic Table

.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 Modelwhich states that atoms mostly consist of positively charged material with negatively charged particles (electrons) located throughout the positive material.

. Won a Nobel Prize.

J.J. Thomson (1856 – 1940)

Plum pudding

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10-10m

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Positively chargedporridge

Negatively chargedraisins (plums)

A Cathode Ray Tube

Ernest Rutherford (1871 – 1937)

In 1909, performed the Gold Foil Experimentand suggested the following characteristics of the atom:o It consists of a small core, or nucleus, that

contains most of the mass of the atomo This nucleus is made up of particles called

protons, which have a positive chargeo 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

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.

Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil

without changing course at all.

A very few get deflected greatly , Even fewer get bounced of the foil and back to the left.

Rutherford’s experiment Involved firing a stream of tiny positively chargedparticles at a thin sheet of gold foil (2000 atoms thick)

-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)

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 jumpfrom a path in one level to a path in another level (depending on their energy)

-Won a Nobel Prize

-Worked with Ernest Rutherfor

Electrons orbit the

nucleus in circular

paths of fixed energy

(energy levels).

Niels Bohr’s Model (1913)

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

Wave Model

-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

James Chadwick (1891 – 1974)

Progression of the Atomic Model

The structure of an atom, according to: Democritus & John Dalton

J.J. ThomsonErnest RutherfordNeils BohrErwin SchrodingerJames Chadwick

+-- --

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+

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+

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+ Electron Cloud+ Electron Cloud

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.

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.

are atoms of the same element that differ in the number of

neutrons in their nuclei. A nucleus with a particular composition

is called a nuclide and is represented by ZX

Isotopes

A

where

: X =

Z =

A =

A nucleon is a neutron or proton; the mass number of

a nucleus is the number of nucleons (protons and

neutrons) it contains.

chemical symbol of the

element

atomic number

mass number or the number of

protons and neutrons in the nucleus

NOTE

How many protons, neutrons and electrons in each of the

following:

protons neutrons electrons23Na14N38Ar35Cl36Cl-1

56Fe

Protons Neutrons Electrons

6 6 6

6 7 6

6 8 6

11 12

7

11

77

18 20 18

17 18 17

17 19 18

26 30 26

-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!

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

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

other?”

The main reason is because of a

force called Strong Force.

Opposes the electrostatic

force.

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

Neutrons act as insulation, since they have no charge, but have the

strong force to bring other nucleons (protons and neutrons)

together.

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.

Binding Energy

40

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

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

energy, the more stable is the atom.

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

Nuclear stability

44

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.

45

All of these stable isotopes have an atomic number in

between 1 and 83. , Nucleons exist in different energy

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

- 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

- Nuclei which do not fall on the line

of stability tend to be unstable or “radioactive”

- They are called “radionuclides”

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

Unstable Nuclei

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.

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.

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.

spontaneous disintegration of a nucleus into a slightly lighter & more stable nucleus, accompanied by emission of particles, electromagnetic

radiation or both

Radioactive Decay

In this process, an unstable “parent” nuclide P is transformed into more stable “daughter”

nuclide D through various processes .

Types of Radioactive Decay

There are many types of radioactive decay such as :

Alpha (α) decay

Beta – minus (β ̄ ) decay

Gamma emission (𝛾)

Beta-plus (β+ ) decay Electron capture ( εc

)

nternalconversion (IC)

Isomeric transition (IT)

Special beta-decay processes (β-n,β+α,β+p)

Neutron decay (N)Proton decay (P)

Spontaneous fission (SF)

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.

HePbPο 4

2

206

82

210

84

Example:

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.

βNC 0

1

14

7

14

6

Example:

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.

βBC 0

1

10

5

10

6

Example:

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.

γHeHe 3

2

3

2

Example:

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.

LieBe 7

3

0

1

7

4

Example:

•Electron capture

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.

What is a

radioactive

series ?

And How many series?

Radioactive series

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.

𝐴1 → 𝐴2 → 𝐴3 → ⋯ → 𝐴𝑛𝜆1 𝜆2 𝜆3 𝜆𝑛

Stable end productIn general

𝜆1 > 𝜆2 > 𝜆3 > ⋯ > 𝜆𝑛

How many series?

There are four natural decay chains:

Uranium series: 23892U 206

82PbActinium series : 235

92U 20782Pb

Thorium series : 23290Th 208

82PbNeptunium series : 241

94Pu 20982Pb

STABLE END PRODUCTHALF-LIFEyr

PARENTSERIESMASS NUMBER

20882Pb1.39× 1010232

90Th Thorium series 4n

20982Pb2.25× 106241

94Pu Neptunium series

4n+1

20682Pb4.51× 109238

92UUranium series4n+2

20982Pb7.07× 108235

92UActinium series 4n+3

annexeh@yahoo.co.in70

The members of this series are not presently found in nature because the half-life of the longest lived isotope in the series is short compared to the age of the earth

24194Pu 209

82Pb

headed by

Neptunium-241

Three radioactive series were recognized (Uranium , Actinium and Thorium)

heavy elements loss mass and changed their atomic number in successive steps.

In fact

In which

The changes ending only when the element became a stable isotope of lead

Radioactivity

series

Importance

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.

Uranium, Actinium , and Thorium occur in three natural decay

series, headed by uranium-238, uranium-235,

and thorium-232, respectively

In Nature

• 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

23892U 206

82Pb

parent Daughter

headed by

uranium-238

23592U 207

82Pb

headed by

uranium-235

parent Daughter

23290Th

parent

headed by

thorium-232

Daughter

208

82Pb

I Terresial Earth Crust

II Cosmic Ray

III Internal SourcesDistant supernovae

Rocks and soil

Uranium Thorium Actinium

Radon

RADIATION

Heavy

• Electron• positron

• 𝜶 − 𝒑𝒂𝒓𝒕𝒊𝒄𝒍𝒆• Proton (p)

light

Ionizing Non-Ionizing

energy transferred may be

sufficient to knock an electron

out of an atom.

Ionizing

photons particle

𝜸 − 𝒓𝒂𝒚

𝒙 − 𝒓𝒂𝒚

unchargedcharged

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.

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. Itis 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.

Attenuation of a photon beam by an absorbing material is caused by five major types of interactions :

Attenuation

Coherent scattering

Photoelectric effect

Compton effect

Pair production

Photo disintegration

Interaction of light charged particleswith matter

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

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.

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 .

The interaction of positron

• When the positron penetrates the target atom Two mechanisms may be occured

Free annhilation The formation of

positronium atom

Interaction of heavy charged particleswith matter

Interaction of 𝜶 − 𝒑𝒂𝒓𝒕𝒊𝒄𝒍𝒆 & 𝒑𝒓𝒐𝒕𝒐𝒏 𝒘𝒊𝒕𝒉𝒎𝒂𝒕𝒕𝒆𝒓

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 .

Interaction of photon (𝛾 − 𝑟𝑎𝑦𝑠) with matter

Photoelectric effect

Compton scattering

Pair production

When the 𝛾 − 𝑟𝑎𝑦 𝑠 𝑠𝑡𝑟𝑖𝑐𝑘𝑒𝑠 abound electron of the target material , so the electron absorbs all the energy of the incident 𝛾 − 𝑟𝑎𝑦𝑠 𝑤ℎ𝑖𝑐ℎ it is enough to eject the electron from into orbit and completely leave the atom

the kinetic energy to the photo-electron.

K E h𝝊 _

W = The binding energy of the electron and ½ mν2 is the kinetic energy of the photo electron. Fig. : The photo electric effect

Photoelectric effect

. = w

𝛾 − 𝑟𝑎𝑦 𝑎𝑟𝑒 𝑐𝑜𝑚𝑝𝑙𝑒𝑡𝑒𝑙𝑦 𝑑𝑖𝑠𝑎𝑝𝑝𝑒𝑎𝑟𝑒𝑑

The incident 𝛾−𝑟𝑎𝑦 𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑠 𝑤𝑖𝑡ℎ 𝑎 𝑓𝑟𝑒𝑒 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑖𝑛 𝑡h𝑒 𝑡𝑎𝑟𝑔𝑒𝑡 𝑎𝑡𝑜𝑚.

K.E=h𝝊 − 𝒉𝝊′

-

--

Incoming photonCollides with

electron

--

--

Electron is ejected from atom

-

Scattered Photon

Before interaction After interaction

The free electron takes a part of energy of the incident 𝛾− 𝑟𝑎𝑦 𝑎𝑛𝑑 𝑡ℎ𝑒 𝑎𝑡ℎ𝑒𝑟 𝑝𝑎𝑟𝑡 𝑜𝑓 𝑒𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝛾− 𝑟𝑎𝑦 𝑖𝑠 𝑠𝑐𝑎𝑡𝑡𝑒𝑟𝑒𝑡 𝑎𝑛 𝑎𝑛𝑔𝑙𝑒 𝜃

The atomic electron has a sufficient energy which lead to the ejection of this electron from atom and it is scattered by an angle 𝜙 𝑤𝑖𝑡ℎ 𝑟𝑒𝑠𝑝𝑒𝑐𝑡 𝑡𝑜 𝑡ℎ𝑒 𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝛾 − 𝑟𝑎𝑦

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

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.

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.

Matter

Photo electric effect

Compton Scatter

Pair Production

Matter

Ionization

X-Rays Chemical Effects

Biological Effects

Excitation Heat

High Speed Electrons

Photon

Fig : Semilog plot showing exponentialattenuation 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 occursexponentially, i.e. a given fraction of the photons is removed for a given thickness of the attenuating material.

Any Questions?