Nuclear Radiation
N5 Physics
The Atom
The Atom
! Learning Intention
! In this lesson we will learn about the structure of the atom, what
nuclear radiation is, and why some atoms are radioactive.
! Success Criteria
! Draw a diagram of an atom showing the location of protons,
neutron and electrons.
! State the number of protons that are in the nucleus of a particular
atom in the periodic table.
! Explain why some atoms are radioactive.
The Plum Pudding Model
! J.J Thomson, the man who discovered the electron, purposed
the plum pudding model of the electron in 1904
The Bohr Model
! Purposed by Niels Bohr in
1904. His model had a
positively charged centre
with electrons orbiting just
like the solar system.
The Atom
! Atoms are the building
blocks of matter.
! Atoms are made from 3
particles: Protons, Neutrons
and Electrons
! Protons and Neutrons are
found in the nucleus (centre)
of the atom.
! Electrons are found orbiting
around the nucleus
Protons, Neutrons & Electrons
Particle
Symbol
Proton
p
Relative Charge
Mass
1
+
Neutron n
1
0
Electron e
0
-
! Protons and Neutrons have the
same mass. They give the
atom its mass.
! A Proton is positively charged,
while a neutron has no
electrical charge.
! Electrons are very light,
negatively charged particles.
! Electrons do have a mass but
its so small we assume it is
zero for our calculations.
The Periodic
Table of Elements
The Periodic Table lists all the
different atoms that exist. Each of
these elements have a different
atom.
Different elements have different
numbers of protons, neutrons and
electrons in the atoms.
Atomic Number
! The atomic number tells us
how many protons are in the
nucleus of that elements’
atom.
! It also tells us the number of
electrons orbiting the
Nucleus.
! Carbon is Atomic Number 6:
A Carbon Atom has 6
protons and 6 electrons
Mass number
! The mass number tells us
the number of protons +
neutrons in the nucleus.
! To find the number of
Neutrons in an atom:
! Neutrons = Mass Number –
Protons
!
! Carbon has mass number
12 so there are 6 Neutrons
Summary
! Atomic Number = Number of
Protons in the atom
! Mass Number = Number of
protons + neutrons in the
atom
!
! Number of Neutrons = Mass
number – number of protons
Building atom models
! Using the materials provided build the following Atoms using
your periodic table to find the atomic number and mass
number. Show the teacher each time you complete one.
!
!
!
!
!
!
Hydrogen
Boron
Oxygen
Helium
Potassium
What if the nucleus of an atom
was a basket ball?
! If you were holding a basket ball and it was the nucleus of the
atom where would the electrons be?
The atom would
have a diameter of
14 miles!
Nanoscience
! Only within the last few years have scientists been able to
manipulate atoms to make new structures
The Atom
! Learning Intention
! In this lesson we will learn about the structure of the atom, what
nuclear radiation is, and why some atoms are radioactive.
! Success Criteria
! Draw a diagram of an atom showing the location of protons,
neutron and electrons.
! State the number of protons that are in the nucleus of a particular
atom in the periodic table.
! Explain why some atoms are radioactive.
Drawing Model Atoms
!Draw the following atoms into your jotter
!Lithium
!Nitrogen
!Carbon
!Carbon-14
!
!Explain why some atoms are
radioactive.
Lesson 2
Alpha, Beta & Gamma Radiation
Alpha, Beta & Gamma Radiation
! Learning Intentions
! In this lesson we learn about 3 kinds of nuclear radiation:- Alpha,
Beta and Gamma radiation
! Success Criteria
! Describe the nature of Alpha, Beta and Gamma radiation
! Describe how ionising each of the radiations are.
! Describe how each of the radiations can be absorbed.
Radioactive atoms
! Atoms that have a very large
nucleus can be unstable.
! Unstable nuclei will release
particles or energy in an
effort to become more
stable. These released
particles or energy is what
we call Nuclear Radiation.
Radioactive atoms
! An Isotope is an atom that
has an unusual number of
Neutrons in the nucleus
! Isotopes of atoms can also
be radioactive. Isotopes will
release nuclear radiation in
order to become more
stable.
! Carbon-14 is an Isotope of
Carbon (normally mass
number 12). It has 2 extra
Neutrons in the nucleus.
Alpha, Beta & Gamma
! When a radioactive atom
decays it can emit alpha,
beta and gamma radiation
! It may emit just one of these
or a combination of these.
! An atom emits this radiation
in order to attempt to
become a stable atom.
Radiation types research
!Find out the following information
! What is the nature of each of the 3 radiation types
! Describe their range in air and give reasons for the
differences in range they have.
! Describe the level of ionisation they each cause and
reasons for the differences.
! Describe what materials can be used to absorb each of
the radiations.
!
!Write notes on the above into your jotter
Alpha, Beta and Gamma
Alpha α 2 protons (+ charge)
2 neutrons (0
charge)
!
!
!
Beta
β
An electron
( - charge)
!
Gamm γ An electromagnetic
a
wave.
Emitted from the
nucleus.
Emitted from the
nucleus when a
neutron changes into
a proton, emitting an
electron.
Emitted from the
nucleus.
Ionisation
! Ionisation occurs when an atom loses or gains an electron.
! Removing and electron creates a positive ion, and adding an
electron creates a negative ion.
! Alpha radiation is the most ionising since it is positively
charged, and therefore seeks electrons. If it removes an
electron a positively charged ion is left behind.
!24
Ionising Radiation
! When nuclear radiation
strikes a material it may
ionise some of the atoms in
the material.
! Ionisation is when electrons
are removed (or added) to
an atom.
! This can have a damaging
effect on the material if
enough ionisation occurs
Ionisation of living tissue
! Ionising radiation can
damage cells or even the
DNA in the cell nucleus
through ionisation.
! This usually results in the
death of the cell but
occasionally as a mutation
leading to cancers.
Lesson 3
Background Radiation
Alpha, Beta & Gamma Radiation
! Learning Intentions
! In this lesson we learn about natural background radiation and
some sources of radiation
! Success Criteria
! State that radiation is constantly around us
! Describe some sources of background radiation
Geiger–Müller tube
! The Geiger-Muller counter is a particle detector designed to
detect ionising radiation, such as alpha and beta as well as
gamma radiation
!
! It was invented by the German physicist Hans Geiger (codiscoverer of the atom nucleus) and later improved by his
student Walther Muller around 1908
Geiger–Müller tube
A Geiger–Müller tube is main
component of a Geiger
counter, a radiation detection
and measuring instrument. It
consists of a gas filled tube
containing electrodes,
between which there is an
electrical voltage, but no
current flowing. When ionising
radiation passes through the
tube, a short, intense pulse of
current passes "cascades"
from the negative electrode to
the positive electrode and is
measured or counted.
Radon Gas
! Radon is a naturally occurring radioactive gas and is
the largest source of background radiation.
! Exposure to excessive concentrations of Radon can
pose serious risks to health
! If you breathe in high concentrations of radon decay
particles they can damage your lung tissue
! Radon has been linked to lung cancer which
proceeds in exactly the same way as that caused
by smoking.
! Radon is a decay product of uranium
! Radon rises from the soil into the air
! Outdoors radon is diluted and poses a low risk
Types of Background Radiation
! There are two different types of background
radiation
Natural
Man Made
!
!
Natural
Cosmic rays
Food
Rocks (particularly
granite)
Radon gas
Hospitals
Nuclear bombs and testing
Nuclear power stations
accidents
Background Radiation
13% is from man
made sources
! Although radioactive
materials are associated
with power stations and
bombs, we live with
radioactive substances
all around us.
Nuclear Power
Cosmic Rays
Cosmic Rays are highly charged particles, originating from outer
space.
!
Cosmic ray particles, as they are now known, are understood to
arrive individually, not in the form of a beam.
A single particle will release a
secondary shower of particles
when they hit our atmosphere.
Most are simply protons and
electrons.
Dosimetry: Radiations effect on the
human body
Dosimetry: Radiations effect on the
human body
! Learning Intentions
! In this lesson we learn about radiations effect on the human body
and how it is measured.
! Success Criteria
! Correctly use the terms Activity, Absorbed Dose, Equivalent dose
and weighting factor.
! Apply your knowledge of these terms to calculate the effects of
radiation.
Radioactivity
! There are several different ways to
measure radiation. The activity of a
sample is measured in becquerels (Bq);
this measures the number of decays per
second.
!
! Named after Henri Becquerel who along
with Marie Curie and Pierre Curie won
the 1903 Nobel Prize in Physics for their
discovery of radioactivity.
!
! More than a century on their papers are
still radioactive
Radioactivity Formula
The activity of a source is the rate at
which a radioactive source decays
A, Activity (Bq) =
N, number of Disintegrations
t, time (s)
A=N
t
Absorbed Dose
! The activity is of limited use when considering the effect
of the radiation. When a radioactive source decays, it
gives out energy. This energy can cause damage to the
material.
!
! The absorbed dose is the energy absorbed per unit mass
of the absorbing material. The absorbed dose (measured
in grays, Gy) measures the energy deposited in each
kilogram of material it passes through.
D, Absorbed Dose (Gy) = E, Energy absorbed (J)
m, mass of absorbing
material (kg)
D=E
m
Weighting Factor
!
! Each type of radiation (α,β,γ) is given a radiation
weighting factor, Wr. The Weighting factor allows
the ability of different types of radiation to damage
living cells to be compared.
!
! The weighting factor does not have a unit because
it is not a physical quantity but rather a number that
gives the relative harm done to cells.
Radiation
Alpha α
Beta β
Gamma γ
Fast neutrons
Radiation Weighting factor (wr)
20
1
1
10
Equivalent Dose
The damage to a biological system depends on the type of
radiation as well as how the energy that it releases is
distributed. The equivalent dose (measured in Sieverts) is
a measure of the biological effect of radiation and takes
into account the type of radiation as well as how the
radiation is distributed i.e radiation of the same energy may
have a greater effect on soft tissue than bone.
H=DWr
H, Equivalent Dose (Sv) = D, Absorbed Dose (Gy) x
Wr, Radiation Weighting Factor (no unit)
Radioactivity Formula
A, Activity (Bq) =
N, number of Disintegrations
t, time (s)
D, Absorbed Dose (Gy) = E, Energy absorbed (J)
m, mass of absorbing
material (kg)
H, Equivalent Dose (Sv) = D, Absorbed Dose (Gy) x Wr, Radiation Weighting Factor (no unit)
H=DWr
Effects on the human body
! A gastrointestinal series X-ray investigation
exposes the human to 14 mSv
! Recommended limit for volunteers averting a
major nuclear escalation - 500 mSv (according to
the International commission on Radiological
Protection)
! Recommended limit for volunteers rescuing lives
or preventing serious injuries - 1000 mSv
(according to the International commission on
Radiological Protection)
The Effect on the Body
! 250 to 1000mSv can effect the intestinal track causing nausea
and vomiting.
! 1000 to 3000 mSv - nausea is mild to severe, no appetite,
considerably higher susceptibility to infections. Injury to the
following will be more severe - spleen, lymph node and bone
marrow. The patient will most likely recover, but this is not
guaranteed.
! 3,000 to 6,000 mSv - nausea much more severe, loss of
appetite, serious risk of infections, diarrhoea, skin peels,
sterility. If left untreated the person will die. There will also be
haemorrhaging.
! 6,000 to 10,000 mSv - Same symptoms as above. Central
nervous system becomes severely damaged. The person is
not expected to survive.
! 10,000+ mSv - Incapacitation. Death. Those who do survive
higher radiation doses have a considerably higher risk of
developing some cancers, such as lung cancer, thyroid
cancer, breast cancer, leukemia, and cancer of several
International Nuclear Event Scale
Fission and Fusion
Fission and Fusion
Research current applications and developments of
fission and fusion reactions to generate energy
What is nuclear fission? (diagram)
!
What is nuclear fusion? (diagram)
!
How can these reactions be useful to generate
energy?
!
Which different methods are used to control
these reactions?
Tokamak Fission Atomic Bomb Fusion Cold Fusion ITER NIF
Nuclear Fission
Nuclear Fusion
What the world needs now
is nuclear energy. True or
False?
National 5: Radioactivity
What the world needs now is
nuclear energy. True or False?
! Make two columns in your jotter with the headings For and
Against.
! When listening to the debate make notes on points for and
against Nuclear Power.
! We will then discuss as a class the Pros and Cons of nuclear
power and discuss our own opinions
Environmental Impact
! Unlike fossil fuel plants,
which spew tons of carbon
dioxide into the atmosphere
each year, nuclear power
plants don't produce
smoke.The iconic images of
white plumes rising from
cooling towers show nothing
more than steam.
! Nuclear power is considered
carbon-free and produces
more electricity than other
renewables like solar and
wind.
! Nuclear power requires
uranium, which must be mined
and transported to power
plants.
! Then there is the significant
issue of radioactive waste,
which isn't biodegradable and
is extremely dangerous. Most
plants store nuclear waste in
steel-lined concrete basins
filled with water, where it
remains radioactive for
thousands of years.
Cost
The pro and con arguments over the cost and the economics of nuclear power are
difficult to untangle. Ask 20 different experts and you will get 20 different answers.
! Nuclear power plants
produce more kilowatts than
coal, wind or solar for fewer
cents. As more plants are
built, it's expected that
construction costs will come
down, making the price of
nuclear-generated electricity
that much more attractive
! With construction comes
jobs, something few could
make a case against in the
current economic climate.
! While the electricity seems
cheaper up front, the
exorbitant costs of building
and maintaining plants must
be added into the equation -something industry experts
rarely do.
! Long-term storage of nuclear
waste is expensive and
dangerous.
Economics in Developing Nations
! Developing countries with
nuclear power plants
wouldn't have to rely on
expensive fossil fuels that
emit large volumes of carbon
dioxide.
!
! Global interest in investing in
nuclear power is high,
providing the potential to
pump money into emerging
economies and create jobs.
! Blanket assumptions that
expanding programs would
boost economies and solve
energy poverty doesn't
account for each country's
specific needs; issues like
power grids, skilled labor and
strong government policies
differ among governments.
! Concerns that radical
governments might develop
nuclear weapons runs deep.
Proliferation (increase in number of nuclear weapons)
! A ''dirty bomb'' can be built
! Commercial plants have large
with a relatively small amount stores of radioactive waste
of radioactive material but it
and keeping track of it is
would be incredibly difficult to difficult. This contributes to the
obtain it from a nuclear power threat of theft or sabotage.
plant. A tremendous amount ! Critics point to inadequate
of money would be needed
security regulations against
for training, bribes at borders
terrorist attacks by aircraft,
and transportation. Detection
boats or trucks
is another issue. Lead
shielding in a truck is
required for uranium to slip
through security detectors.
! In addition, heightened
security awareness has
tightened access to power
plants.
Safety
! Proponents of nuclear power
are steadfast in the belief that
modern nuclear power plants
pose no safety risk and are in
fact safer than coal-burning
plants.
! In the U.S. nuclear reactors
are contained in concrete
structures with walls four feet
thick
! Three Mile Island and
Chernobyl (which did not
have concrete containment
structures) were the only
major accidents in ''14,000
cumulative reactor-years of
commercial operation in 32
countries''
! Accidents do happen.
Instances of radioactive water
leeching into the ground have
occurred. In one case, several
million gallons of
contaminated water reached
drinking wells.
Half Life
National 5 Radiation
WHAT IS HALF-LIFE?
•
Radioactive decay is a spontaneous process that cannot be
controlled and is not affected by temperature.
•
However, each radioactive element has its own particular
decay rate, which is called the half-life.
!
!
The half-life of a radioactive element is the time
that it takes half the atoms in a sample to decay.
•
For example, the half-life of the isotope iodine-131 is 8 days.
•
This means that after 8 days half the atoms in a sample of
iodine-131 have decayed. 8 days later half the remaining
atoms have decayed and so on.
HALF LIFE
atoms
decayed atoms
HALF LIFE
Half-lives range from millionths of a second to millions of years. Some nuclei are more unstable than others and decay at a faster
rate.
Xenon-133 is a radioactive isotope used for studying lung function.
Why does its half-life of 5.2 days make it suitable for this use?
Uranium-235, which is
used in nuclear reactors
and nuclear weapons, has
a half-life of 710 million
years. Why is the use of
uranium-235 considered
controversial?
radioisotope
half-life
boron-12
0.02 seconds
radium-226
1602 years
uranium-235
710 million years
HALF LIFE
Half Life is defined as the time taken for the
activity of a radioactive source to fall to half
it’s original value.
e.g half life = 2 days means that every 2
days the activity of the source will half
If the activity of a source is 200Bq and the half
life is 1 hour after 1 hour the activity will be...
HALF LIFE
Half-life can be used to do many
useful calculations.
For example, the half-life of carbon-14 is 5,700 years. If a
fossil bone has a count of 25, and a piece of bone from a
living body has a count of 200, how old is the fossil?
After one half-life, the count will decrease by half to 100.
After the second half-life, the count decreases by half
again to 50.
After the third half-life, the count decreases to 25.
Three half-lives of carbon-14 have passed, so 3 x 5,700
years makes the fossil 17,100 years old.
ULTIMATE PHYSICS,
HEALTH PHYSICS,
PG 16