1. Assumptions in Bohr‘s Model
The two forces acting in the nucleus are:
A Coulomb force of repulsion between the
positively charged protons
The strong nuclear force that holds protons and
neutrons together.
o The combined effects of these two forces enable
only certain neutron to proton ratios to be stable.
(magic numbers)
3. Assumptions in Bohr‘s Model
The nucleus contains positively charged protons (each
1.6E-19 C) and neutrally charged neutrons.
What is a Coulomb?
The coulomb (symbol: C) is the SI derived unit of electric
charge. It is defined as the charge transported by a steady
current of one ampere in one second: 1C = 1A x 1s
Examples
The charges in static electricity from rubbing materials
together are typically a few microcoulombs.
The amount of charge that travels through a lightning bolt is
typically around 15 C, although large bolts can be up to 350
C.
The amount of charge that travels through a typical alkaline
AA battery is about 5 kC = 5000 C = 1400 mAh. After that
charge has flowed, the battery must be discarded or
recharged.
According to Coulomb's Law, two point charges of +1
4. Assumptions in Bohr‘s Model
The mass of a protons is 1.6726E-24 g. Or
1.0073amu
The mass of a neutron is 1.6749E-24 g. Or
1.0087amu
5. Assumptions in Bohr‘s Model
The majority of an atom’s mass is contained
within a small, dense nucleus (on the order of 10
million tons / cm3).
6. Assumptions in Bohr‘s Model
The number of extranuclear electrons equals the
number of protons within the nucleus.
Each electron carries an electrical charge of -
1.6E-19 C
Thus, the net charge of an atom is zero.
Electrons have a mass around 9.11E-34 g.
Electrons orbit nuclei in fixed energy shells
(quantized orbits); with each shell having a
characteristic binding energy for a given element.
7. Atomic Mass Scale
Atomic mass units (amu) is its mass ―relative‖ to 12C
unbound, at rest, and in its ground state. By definition
12C has 12 amu;
1 amu equals the mass in 1/12 of a 12Catom. The
actual mass of one amu is based on the 6 protons, 6
neutrons, and 6 electrons in one 12C atom. 1 amu =
1.66E-24 g.
An atom‘s ―atomic weight‖ is its ―amu number‖; which
is its mass ―relative‖ to 12C or: atomic weight = 12 x
(mass a / mass c 12)
The atomic weight of an ―element‖ is a weighted
average, accounting for the natural abundance of all
8. Radiation & Radioactivity Definitions
Radioactivity: the spontaneous process by
which unstable atoms emit or radiate excess
energy from their nuclei, and thus, change or
decay to atoms of a different element or to a
lower energy state of the same element.
Radionuclide: unstable atomic species which
spontaneously “decay” and emit radiation.
9. DEFINITIONS
Radiation: high energy particles and
electromagnetic rays emitted from atomic
nuclei during radioactive disintegration.
However, the term ―radiation” is also often
used instead of the longer term
“electromagnetic radiation” (aka
electromagnetic rays or photons), whether or
not they originate in the nucleus.
There are two broad categories of
electromagnetic radiation (ionizing and non-
ionizing). For example, x-rays originate
outside of nuclei and typically have sufficient
energy to ionize atoms.
10. Electromagnetic Radiation
Another term for ―photon‖ which is an
electromagnetic ―particle‖ that always travel in
waves at a velocity of 3E8 m/s in a vacuum. Each
particle has zero rest mass, no electric
charge, and an indefinitely long lifetime. The
energy of a photon is inversely proportional to its
wavelength.
E = hn
12. Ionizing Electromagnetic Radiation
Ionizing electromagnetic radiation consists of
photons possessing enough energy to completely
free electrons from atoms, thereby producing
ions. An ion is an atom which has lost or gained
one or more electrons, making it negatively or
positively charged.
13. Non-Ionizing Electromagnetic Radiation
Non-ionizing electromagnetic radiation consists of
photons that do not possess sufficient energy to
ionize atoms. However, non-ionizing
electromagnetic radiation may have enough
energy to excite electrons, that is cause them to
move to a higher energy state. Examples include
near ultraviolet rays, visible light, infrared
light, microwaves, and radio waves.
15. Atomic Mass Scale
One mole = atomic weight-g and contains Avogadro’s
no. of particles.
Avogadro’s number = 6.0221415x1023 atoms (or
molecules).
Since one mole of an element is its atomic weight in
grams and will contain 6.0221415x1023 atoms, the
number of atoms in any given mass can readily be
computed. For example, since 12-g of 12C contains
6.0221415x1023 atoms as does 235-g of 235U:
100 g of 235U
contains 100/235 x 6.0221415x1023 =
2.56E23 atoms,
100 g of 12C, 100/12 x 6.0221415x1023 = 50.18E23
atoms.
16.
17. Relating Mass to Numbers of
Atoms
The Mole
A mole (abbreviated mol) is the amount of a
substance that contains as many particles as there
are atoms in exactly 12 g of carbon-12.
Avogadro‘s Number
Avogadro‘s number—6.022 1415 1023—is the
number of particles in exactly one mole of a pure
substance.
18. Relating Mass to Numbers of
Atoms, continued
Molar Mass
The mass of one mole of a pure substance is called
the molar mass of that substance.
Molar mass is usually written in units of g/mol.
The molar mass of an element is numerically equal to
the atomic mass of the element in atomic mass
units.
19. Relating Mass to Numbers of
Atoms, continued
Gram/Mole Conversions
• Chemists use molar mass as a conversion
factor in chemical calculations.
For example, the molar mass of helium is 4.00 g
He/mol He.
To find how many grams of helium there are in two
moles of helium, multiply by the molar mass.
4.00 g He
2.00 mol He = 8.00 g He
1 mol He
20. Relating Mass to Numbers of
Atoms, continued
Conversions with Avogadro‘s Number
• Avogadro‘s number can be used to find the
number of atoms of an element from the amount
in moles or to find the amount of an element in
moles from the number of atoms.
In these calculations, Avogadro‘s number is expressed
in units of atoms per mole.
21. Relating Mass to Numbers of Atoms,
continued
What is the mass in grams of 3.50 mol of the
element copper, Cu?
22. Relating Mass to Numbers of
Atoms, continued
A chemist produced 11.9 g of aluminum, Al-26.
How many atoms of aluminum were produced?
23. Relating Mass to Numbers of
Atoms, continued
How many atoms of plutonium-239 are present in
a bare-sphere critical mass of 10kg?
24. Energy and Mass
Einstein‘s famous E = mC2 equation shows the
relationship between mass and energy.
For 1 m, E = 1.66 x10-27kg *2.998 x 108 m/s2 = 1.492
x 10-10 J
Or = 931.5 MeV
So 1 AMU of mass = 931.5 MeV of energy
25. BINDING ENERGY
There is a complication, the whole does not equal
the sum of the parts. If you add the masses of all
the protons, neutrons and electrons in an atom
the predicted mass is ALWAYS more than the
measured mass.
This is the MASS DEFECT, D
D =ZMp + NMn + ZMe - Matom
26. Data
Where:
Mp, The mass of a proton: 1.0072766 m
Mn, The mass of a neutron: 1.0086654 m
Me, The mass of an electron: .0005486 m
Matom, The mass of the bound atom (varies by
isotope)
27. Example
Find the mass defect,D, and binding
energy, Q, for an 17O nuclide. It has 8
protons, 9 neutrons, and an atomic weight of
16.999133 amu
28. Oxygen 17
# Particles Mass each Total
8 p+ 1.0072766 8.0582128
9 no 1.0086654 9.0779886
8 e-1 .0005486 0.0043888
Total = 17.1405902
D= 17.1449790 - 16.999133 = 0.1414572 amu
0.145846 amu x 931.5 amu/ MeV = 131.77MeV
Or 135.85 / 17 = 7.75 MeV / nucleon
29. Mass Defect
The missing mass is believed to be converted to
energy that holds the nucleus together.
It is called binding energy, BE.
The Coulomb force of repulsion must be overcome
to allow so many p+ particles in the nucleus.
This Strong Nuclear Force accomplishes this but it‘s
range is only ~10-13 m
30. BE per Nucleon
The binding energy per nucleon can be calculated
for each isotope by dividing the total BE by the
number of nucleons.
The stability of a nucleus is a function of this
BE/nucleon
A plot of BE/nucleon vs atomic number shows the
most stable isotopes
31.
32. Magic Numbers
The ratio of odd to even numbers of protons and
neutrons show surprising trends
Even N, Even Z.........159 stable nuclides.
Odd N, Even Z......... 53 stable nuclides.
Even N, Odd Z......... 50 stable nuclides.
Odd N, Odd Z......... 5 stable nuclides.
33.
34. What is Radiation
Radionuclides undergo a process referred to as
decay (also known as transformation or transition)
During decay, a radionuclide changes its ratio of
protons and neutrons to a more stable
combination – it becomes a different nuclide
In the process some of it‘s mass is converted to
energy and is carried off by the radiation
35. What is Radiation
The physical characteristics of radiations include;
mass, charge, point of origin (where it‘s found)
There are two possible points of origin
Nucleus
Electron Cloud
Most radiations originating outside the nucleus
are not in the scope of this course, these
including…visible light, radio, etc.
36. What is Radiation
Radiations also can be characterized by their
effects on matter
When atoms are exposed to radiation they are
either created into ions or not, therefore we
classify radiation as either…
Ionizing
Non-Ionizing
In this course we are concerned only with ionizing
forms of radioactivity
37. What is Radiation
There are two major types of ionizing radiation
Particulate Radiation
Electromagnetic Radiation
Particulate Radiation is solid matter, consists of
particles, therefore has mass or substance
Electromagnetic Radiation is made up of waves
of pure energy, therefore having no mass
38. What is Radiation
There are three types of particulate radiation
Alpha
Beta
Neutron
Alpha radiation is made of 2 protons and 2
neutrons, therefore having an atomic mass of 4
(ionized helium nucleus)
Alpha radiation has a charge of +2 and as it
travels through air it ―ionizes‖ atoms
39. What is Radiation
The majority of alpha particles are emitted from
the nuclei of large atoms ~ 83 protons and up
The reason large atoms give off ―large‖ particles
i.e. alpha particles is because they are very
unstable therefore need to give off large amounts
of mass
A A-4
Z P Z-2 D + He
43. What is Radiation
Beta – Beta particles are made up of electrons
―born‖ in the nucleus
They can have either a + or – charge
Even though positive electrons are not supposed
to exist, under some circumstances they can be
produced in the nuclei of atoms
These positive electrons (positrons) are more
commonly known as antimatter
44. What is Radiation
Beta particles are a result of protons and
neutrons changing identity
When a neutron changes to a proton (neutron
conversion) a negative electron is emitted
When a proton changes to a neutron (positron
emission) a positive electron is emitted
45. What is Radiation
Every time a positron is produced, two 511 keV
(kiloelectronvolt) photons will also be produced.
When the positron has given up all, or almost
all, of its kinetic energy, it will combine with an
electron
The electron and positron annihilate each other –
their mass is completely converted into energy
53. Electron Capture
Sometimes when a nucleus will absorb an
orbiting electron
This is known as electron capture
A proton will be converted to a neutron without
the release of a positron
This will result in the release of an electron
neutrino
As outer electrons fill the lower energy level, x-
rays are produced
54. Internal Conversion
As the nucleus undergoes de-excitation in inner
electron can be kicked out of the electron cloud
Monoenergitic
This acts as a beta particle
Also, X-Rays are produced
55. What is Radiation
Neutrons are the last type of particulate radiation
that we will discuss
Neutrons have a mass of 1 AMU and ø charge
They are produced most commonly in nuclear
reactors from when atoms fission
56. What is Radiation
Now that we have looked at the types of
particulate radiation, we will now look at the types
of electromagnetic radiation
Remember electromagnetic radiation is waves of
pure energy for example; light, x-rays and all
other members of the electromagnetic spectrum
57. Electromagnetic Radiation
Gamma – Gamma rays are electromagnetic rays
of pure energy
They have no mass and no charge
Gamma rays are produced as a result of the de-
excitation of the nucleus of atoms that have given
off either an alpha or a beta particle
The gamma is actually emitted from the product
of the decay, but is attributed to the parent
nuclide
61. What is Radiation
Gamma, and X-rays are measured in KeV = 103
eV
Particulate Radiation is measured in MeV = 106
eV
62. Electromagnetic Radiation
Only a specific number of electrons is allowed in
each shell (energy level).
The number of electrons in the various shells
determines the chemical properties of the atom.
Electrons (like all particles) ―want‖ to occupy the
lowest possible energy level.
When an electron moves (undergoes a transition)
to a lower energy level, it must release energy.
63. What is Radiation
When an electron fills a vacancy in an inner shell
(moves to a lower energy level), this energy might
take the form of an x-ray.
X-rays (and gamma rays) have a high enough
energy to ionize atoms (remove electrons from
atoms) and are therefore considered a type of
ionizing radiation.
65. What is Radiation
Energy can be described as the ability to do work.
Two kinds of energy:
potential energy
Kinetic energy
Kinetic energy is the energy of motion (1/2mv2)
Basic unit: joule (J)
Special unit: electron volt (eV)
1 eV = 1.6 x 10-19 J
66. Units
Roentgen (R)
The roentgen is a unit used to measure a quantity
called exposure. This can only be used to describe an
amount of gamma and X-rays, and only in air. One
roentgen is equal to depositing in dry air enough energy
to cause 2.58x10-4 coulombs per kg. It is a measure of
the ionizations of the molecules in a mass of air. The
main advantage of this unit is that it is easy to measure
directly, but it is limited because it is only for deposition
in air, and only for gamma and x rays.
67. Curie (Ci)
The curie is a unit used to measure radioactivity. One
curie is the quantity of a radioactive material that will
have 37,000,000,000 transformations in one second.
Often radioactivity is expressed in smaller units like:
thousandths (mCi), one millionths (uCi) or even
billionths (nCi) of a curie. The relationship between
becquerels and curies is: 3.7 x 1010 Bq in one curie.
68. Rad (radiation absorbed dose)
The rad is a unit used to measure a quantity
called absorbed dose. This relates to the amount
of energy actually absorbed in some
material, and is used for any type of radiation and
any material. One rad is defined as the
absorption of 100 ergs per gram of material. The
unit rad can be used for any type of radiation, but
it does not't describe the biological effects of the
different radiations.
69. Rem (roentgen equivalent man)
The rem is a unit used to derive a quantity called
equivalent dose. This relates the absorbed dose in
human tissue to the effective biological damage of the
radiation. Not all radiation has the same biological
effect, even for the same amount of absorbed dose.
Equivalent dose is often expressed in terms of
thousandths of a rem, or mrem. To determine
equivalent dose (rem), you multiply absorbed dose
(rad) by a quality factor (Q) that is unique to the type of
incident radiation.
70. Becquerel (Bq)
The Becquerel is a unit used to measure a radioactivity.
One Becquerel is that quantity of a radioactive material
that will have 1 transformations in one second. Often
radioactivity is expressed in larger units like: thousands
(kBq), one millions (MBq) or even billions (GBq) of a
becquerels. As a result of having one Becquerel being
equal to one transformation per second, there are 3.7 x
1010 Bq in one curie.
71. Gray (Gy)
The gray is a unit used to measure a quantity called
absorbed dose. This relates to the amount of energy
actually absorbed in some material, and is used for any
type of radiation and any material. One gray is equal to
one joule of energy deposited in one kg of a material.
The unit gray can be used for any type of radiation, but it
does not't describe the biological effects of the different
radiations. Absorbed dose is often expressed in terms of
hundredths of a gray, or centi-grays. One gray is
equivalent to 100 rads.
72. Sievert (Sv)
The sievert is a unit used to derive a quantity called
equivalent dose. This relates the absorbed dose in
human tissue to the effective biological damage of the
radiation. Not all radiation has the same biological
effect, even for the same amount of absorbed dose.
Equivalent dose is often expressed in terms of millionths
of a sievert, or micro-sievert. To determine equivalent
dose (Sv), you multiply absorbed dose (Gy) by a quality
factor (Q) that is unique to the type of incident radiation.
One sievert is equivalent to 100 rem.
73.
74. Naturally Occurring Radionuclides
Naturally Occurring Radionuclides, NORM, are
present everywhere on earth. Their sources are:
Primordial radionuclides were contained in the
matter that condensed to form the earth.
Cosmic Rays very high energy radiation and
particles that come from space.
Cosmogenic radionuclides are formed by nuclear
reactions in the atmosphere.
75.
76. Cosmic Ray Produced
Radionuclides
Isotope Half Life Isotope Half life
10Be 2.7 E 9 y 36Cl 3.0 E 5 y
14C 5.7 E 3 y 32Si 7.1 E 2 y
3H 12.5 y 22Na 2.6 y
35S 87 d 7Be 53 d
33P 25 d 32P 14 d
77. Naturally Occurring Radionuclides (not in
decay chains)
244 Pu, Progenitor of 238 U, t ½ 80 E 6 y (now extinct)
129 I, Parent of 129 Xe, t ½ 16 E 6 y (now extinct)
40K, Parent of 40Ar & 40Ca, t ½ 1.3 E 9 y (40Ar = 1%
atmosphere)
87Rb, Parent of 87Kr, t ½ 48 E 9 y
78.
79. Radon in Nevada Hot Springs
Spring 22Rn (pCi/l) 238U (pCi/l)
Warm Springs 2900 0.09
63 oC
Crystal Springs 18 1.5
32 oC
Ash Springs 140 1.2
36 oC
Bailey‘s Hot 3560 3.5
Spring 42 oC
84. Historical
1903, Rutherford and Soddy developed the basic
radioactive decay equations.
1911, Rutherford proved the atom has a very tiny
nucleus.
1913, Fajans and Soddy demonstrated the existence
of isotopes.
86. Rutherford‘s a Scattering Experiment
This experiment showed that about 1 in every
20,000 a particles ―bounced back‖
Since a ‗s were much heavier than electrons the
uniform positive matrix Thomson proposed was
wrong.
(This is how we know the nucleus is so small. )
87. Historical
1897, J.J. Thomson measured the
charge/mass ratio of the electron.
1926, G. P. Thomson received the Nobel Prize for
discovering the electron, like light, had both
particle and wave nature.
89. Other History
Radioactivity of Rain
1902, Wilson found rain contained short lived
radionuclides.
1906, Rain from thunderstorms was found to be very
radioactive.
1908, 214Pb and 214Bi were identified in rain. (today
we know these are decay products of 222Rn)
90. Other History
Radioactivity of Hot Springs
1906, Boltwood found Radon 222 in water at Hot
Springs, AR.
Many spring, hot or cold, contain Rn and its daughter
isotopes.
The hot salt water, brine, produced with oil often
contains Radium and Radon
91. Historical
1918, Max Planck derives the constant, h.
1932, Chadwick discovered the neutron.
1938, Hahn and Strassman discovered nuclear
fission.
1940, Seaborg discovered Plutonium.
1941, First man made nuclear chain reaction.
92. Historical
1949, Libby develops the Carbon 14 nuclear
chronometer.
1956, Kuroda predicts a natural nuclear reactor
occurred somewhere on the earth.
1972, Natural ancient nuclear reactor discovered in
Africa.
93. GET THIS DOCUMENT
http://www.epa.gov/radiation/docs/402-k-07-
006.pdf
http://www.epa.gov/radiation/docs/402-k-
07-006.pdf
94. History of Nuclear Fission
The history of the discovery of nuclear fission is
fascinating. All the great players in nuclear
physics and chemistry were involved. The
account of how the information was secreted out
of Germany to this country, Einstein‘s letter to
President Franklin D. Roosevelt, the self imposed
secrecy of the scientists in Chicago, and the
extent of Japan‘s nuclear research is better than
any action thriller you can find today.
