Lecture 1 basic nuclear physics 1 - basic atomic structure

1. IAEA
Basic Nuclear Physics
Basic Atomic Structure
Day 1- Lecture 1
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2. IAEA
Objective
• To discuss about the structure of the atom
including the Neutron, Proton and
Electron
• To learn about the Atomic Number,
Atomic Mass, nuclear stability and
radioactive or unstable nuclei
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Contents
• Atom
• Nucleus
• Electron Binding Energy
• Periodic Table of the Elements
• Isotopes
• Nuclear Stability
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4. IAEA
Atom
 positively charged
(+) protons,
 uncharged neutrons
and
 negatively charged
(-) electrons
The atom is
composed of:
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Atom
Thomson’s Model Rutherford’s Model
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Atom
Bohr’s Model
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Nucleus
Protons and neutrons together
form the nucleus of the atom.
The nucleus determines the
identity of the element and its
atomic mass.
Proton and neutrons have essentially the same mass but
only the proton is charged while the neutron has no
charge.
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8. IAEA
Protons
Protons are positively charged
particles found inside the nucleus
of an atom. Each element has a
unique atomic number (a unique
number of protons).
Proton number never changes for any given element. For
example, oxygen has an atomic number of 8 indicating
that oxygen always has 8 protons.
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Neutrons
Neutrons are the other particle
found in the nucleus of an atom.
Unlike protons and electrons,
however, neutrons carry no
electrical charge and are thus
"neutral."
Atoms of a given element do not always contain the same
number of neutrons.
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10. IAEA
Electrons
Electrons are negatively charged
particles that surround the nucleus
in “orbits” similar to moons orbiting
a planet.
The sharing or exchange of electrons between atoms
forms chemical bonds which is how new molecules and
compounds are formed.
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11. IAEA
ELECTRON BINDING ENERGY
• Electrons exist in discrete “shells” around the
nucleus (similar to planets around the sun)
• Each shell represents a unique binding energy
holding the electron to the nucleus
• The shells are designated by letters (K, L, M,
N …) where K, the shell closest to the nucleus,
has the largest binding energy, so the K
electron is the most tightly bound
• Maximum number of electrons in each shell: 2
in K shell, 8 in L shell …

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Particle Symbol Mass (kg) Energy (MeV) Charge
Proton p 1.672E-27 938.2 +1
Neutron n 1.675E-27 939.2 0
Electron e 0.911E-30 0.511 -1
Summary of the Atom

13. IAEA
Atomic Mass Unit (amu)
Where 1 amu is
approximately equal to
1.6605 x 10-24 grams
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14. IAEA
Atomic Mass Unit (amu)
The atomic mass of the proton and the neutron is
approximately:
Proton = 1.6726 x 10-24 grams = 1.0073 amu
Neutron = 1.6749 x 10-24 grams = 1.0087 amu
Thus, the neutron is just a little heavier than the
proton.

15. IAEA
Atomic Mass Unit (amu)
The difference in the mass of the neutron and the
proton can be understood if we assume that the
neutron is merely a proton combined with an
electron forming a neutral particle slightly more
massive than a proton alone.
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16. IAEA
Atomic Mass Unit (amu)
The atomic mass of the electron is approximately:
Electron = 9.1094 x 10-28 grams = 0.00055 amu
Thus, the electron has a much smaller mass than
either the proton or the neutron, 1837 times
smaller or about 2000 times smaller.

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Elements
The number of protons in an atom dictate the
element.
For an uncharged atom, the number of
electrons equals the number of protons.

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10 Most Abundant Elements
Element Symbol Protons Relative % of Earth’s Mass
Oxygen O 8 46.6
Silicon Si 14 27.7
Aluminum Al 13 8.1
Iron Fe 26 5.0
Calcium Ca 20 3.6
Sodium Na 11 2.8
Potassium K 19 2.6
Magnesium Mg 12 2.1
Titanium Ti 22 0.4
Hydrogen H 1 0.1
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19. IAEA
In 1869, Russian chemist Dmitri
Mendeleev first described an
arrangement of the chemical
elements now known as the
periodic table.
The periodic table displays all
chemical elements systematically
in order of increasing atomic
number (the number of protons in
the nucleus).
Periodic Table of the Elements
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Rare Earth
Elements
Actinide Series
Lanthanide Series
Periodic Table of the Elements
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Sample Element - Zirconium
40
Zr
Zirconium
91.2
Electron Shell Configuration:
K 1s-2 2
L 2s-2 2p-6 8
M 3s-2 3p-6 3d-10 18
N 4s-2 4p-6 4d- 2 10
O 5s-2 2
10 + 18 + 12 = 40
K
L
M
N
O
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23. IAEA
Sample Element - Zirconium
Name: Zirconium
Symbol: Zr
Atomic Number: 40
Atomic Mass: 91.224 amu
Melting Point: 1852.0 °C
Boiling Point: 4377.0 °C
No. of Protons/Electrons: 40
No. of Neutrons: 51
Classification: Transition Metal
Phase at Room Temperature: Solid
Density @ 293 K: 6.49 g/cm3
Color: Grayish
Date of Discovery: 1789
Discoverer: Martin Klaproth
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Isotopes
Atoms of an element
that have a different
number of neutrons
in the nucleus are
called isotopes of
each other.
Xy
Z
A
Xy = element symbol
A = atomic mass (neutron + protons)
Z = atomic number (protons)
isotope notation
typically written as:
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Isotopes
The number of
protons and
electrons remain
the same.
But the number of
neutrons varies.
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26. IAEA
Isotopes
There are many
isotopes. Most have
more neutrons than
protons. Some are
stable but most are
unstable
(radioactive).
equal number of protons and neutrons
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Nuclear Stability
• A stable or non-radioactive nuclide is one
whose atoms do not decay
• If one plots the stable nuclei, an interesting
pattern emerges (shown in next slide)
• The graph in the next slide shows a plot of
neutron number N vs atomic number Z for
the stable nuclei
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N > Z
The Line of Stability
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Nuclear Stability
 For the heaviest stable nuclei, N is about
1.5 times Z
 The presence of the extra neutrons
overcomes the positively charged protons’
tendency to repel each other and disrupt
the nucleus
 The nucleus is held together by a poorly
understood force, the Nuclear Force
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30. IAEA
The nuclear force is an extremely short-
range force
It acts over a maximum distance of about
two proton diameters
The nuclear force is responsible for the
binding energy that holds the nucleus
together
Nuclear Stability
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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
Unstable Nuclei
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Radionuclides undergo a process called
radioactive transformation or disintegration
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
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33. IAEA
Some Common Radionuclides
Naturally occurring 235U and 238U
60Co, 137Cs, 90Sr found in nuclear power
plants
192Ir used in radiography
99mTc used in nuclear medicine
131I used in treatment of thyroid conditions
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34. IAEA
Summary
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35. IAEA
Where to Get More Information
 Cember, H., Johnson, T. E, Introduction to Health
Physics, 4th Edition, McGraw-Hill, New York (2009)
 International Atomic Energy Agency, Postgraduate
Educational Course in Radiation Protection and the
Safety of Radiation Sources (PGEC), Training Course
Series 18, IAEA, Vienna (2002)
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