nuclear physics
TRANSCRIPT
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
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180
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190
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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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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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+ 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)
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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.
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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
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- 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
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′
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--
Incoming photonCollides with
electron
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--
Electron is ejected from atom
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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?