Science 10
Chapter 7 - Radiation
Chapter 7, Radiation and Nuclear Energy
7.1 ELECTROMAGNETIC RADIATION
Radiation
-Energy in the form of electromagnetic waves
Electromagnetic wave
-Composed of both a varying electric field and a varying magnetic field. The two fields run at
a right angle to each other
Electromagnetic Spectrum
-Is a name that scientists give a bunch of types of radiation when they want to talk about them
as a group. Lists the types of radiation from low frequency to high frequency.
1
Science 10
Chapter 7 - Radiation
Wave length
-The length of 1 wave, the higher the frequency the shorter the wavelength

A radio’s wavelength is approx. 1m in length

A gamma ray’s wavelength is 0.000 000 000 000 001 m in length!
Electromagnetic radiation
Can be described in terms of a stream of photons, which are particles each traveling in a wavelike pattern and moving at the speed of light = 299 792 458 m / s. Each photon contains a certain
amount of energy, and all electromagnetic radiation consists of these photons.
The only difference between the various types of electromagnetic radiation is the amount of
energy found in the photons. Radio waves have photons with low energies, microwaves have a little
more energy than radio waves, infrared has still more, then visible, ultraviolet, X-rays, and ... the most
energetic of all ... gamma-rays.
2
Science 10
Chapter 7 - Radiation
7.2 RADIATION IN ATOMS
Radioactive
-Any atom that emits radiation from their nuclei
-Three types of radiation are emitted from a nuclei - alpha, beta and gamma
Alpha: composed of 2 protons and 2 neutrons and have a charge of +2
- Are helium nuclei
Beta: high energy electrons and have a charge of -1
Gamma: a form of electromagnetic radiation and are not made of particles
- can penetrate very deep into objects
Isotopes
Review – atomic number = protons and electrons
- atomic mass minus atomic number = neutrons
-Atoms of the same element that have different mass numbers, due to the number of neutrons in the
nucleus.
Example : Carbon 12 has 6 protons and 6 neutrons
Carbon 13 has 6 protons and 7 neutrons
Carbon 14 has 6 protons and 8 neutrons
Radioactive Decay
The unstable nuclei emit radiation and decompose over time
Alpha Decay Emit alpha particles
Alpha particles are helium nuclei, therefore it emits 2 protons and 2 neutrons
Example
Uranium  Helium and Thorium
238
92
U
4
2
He + 234
90 Th
3
Science 10
Chapter 7 - Radiation
Beta Decay
Emit high energy electrons
Example
Carbon  electron and Nitrogen
14
6
C  01 e + 14
7 N
Carbon will lose 1 electron (e-1) therefore 6 – (-1) = 7
Gamma Decay
Does not give off a particle, there is no change to the nucleus
Emits excess energy from the nucleus
Half-life
The time required for half of the nuclei to decay
Therefore, after 1 half life, exactly half of the original starting material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
Half-life
The time required for half of the nuclei to decay
Therefore, after 1 half life, exactly half of the original starting material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
4
Science 10
Chapter 7 - Radiation
If you point a Geiger counter at a radioactive substance for a period of time,
you'll notice that the reading on the meter decreases as you watch. This is
shown on the graph.
The radioactivity from some substances dies away very fast - perhaps in a
few microseconds. Others take thousands of years before you'll notice that
the radioactivity had decreased at all.
In theory, every radioactive substance should stay slightly radioactive for
ever - the graph should never actually fall to zero. This means that we can't
usefully talk about the "life" of a radioactive source.
Instead, we use the idea of "half-life".
This is the time it takes for the radioactivity to fall by half.
This graph shows what
would happen with an
imaginary radioactive
substance.
Notice that the
radioactivity falls by half
every 2 hours.
Thus we say that this
imaginary substance has a
half-life of 2 hours.
The count rate coming from a radioactive source depends on how many unstable atoms it contains.
That's the number of un-decayed atoms.
If the count rate has fallen by half, then the number of unstable atoms has fallen by half.
A typical exam question may be "A radioactive substance has a half-life of 2 hours. How
much of the substance will remain after 6 hours have passed?"
5
Science 10
Chapter 7 - Radiation
Thus, for a substance with a half-life of 2 hours, 1/8 of the original atoms will remain after 6 hours.
Note that this also means that 7/8 of the atoms will have decayed in that time.
Take another look at the graph above, you'll see that after 6 hours the activity has fallen from 8,000 to
1,000; i.e. it's fallen to 1/8 of the starting value.
Question 1:
A radioactive substance has a half-life of 30 minutes. What fraction of the atoms will
not have decayed after 1 hour?
Answer:
The half-life of the substance is 30 minutes.
That means that 1 hour is 2 half-lives for the substance.
After one half-life the activity will fall to 1/2 of the
starting value, after a second half-life it will have fallen
to half of that - i.e. a quarter.
So one quarter of the original atoms remain.
6
Science 10
Question 2:
Another substance has a half-life of 3 hours.
decayed after 6 hours?
Answer:
Chapter 7 - Radiation
What fraction of the atoms will have
The half-life is 3 hours, so 6 hours is 2 halflives.
After 2 half-lives only one quarter of the
original atoms remain, which means that
three-quarters of them have decayed.
Question 3:
A researcher measures 200 counts per minute coming from a radioactive source at
midday. At 3 o'clock, she finds that this has dropped to 25 counts per minute.
What is the half-life of the radioactive source?
Answer:
After 3 hours, the count rate has fallen from 200
to 25 counts per minute
Calculate the number of half lives there is from
200 to 25
200 – 100 -50 - 25
so this means that three half lives have passed.
If 3 half-lives are 3 hours, then the half-life is one
hour.
7
Science 10
Chapter 7 - Radiation
Chapter 7, Radiation and Nuclear Energy
7.1 ELECTROMAGNETIC RADIATION
Radiation
-Energy in the form of electromagnetic waves
Electromagnetic wave
-Composed of both a varying electric field and a varying magnetic
field. The two fields run at a right angle to each other
Electromagnetic Spectrum
-Is a name that scientists give a bunch of types of radiation when they
want to talk about them as a group. Lists the types of radiation from
low frequency to high frequency.
8
Science 10
Chapter 7 - Radiation
Wave length
-The length of 1 wave, the higher the frequency the shorter the
wavelength
 A radio’s wavelength is approx. 1m in length
 A gamma ray’s wavelength is 0.000 000 000 000 001 m in length!
9
Science 10
Chapter 7 - Radiation
Electromagnetic radiation
Can be described in terms of a stream of photons, which are particles
each traveling in a wave-like pattern and moving at the speed of light = 299
792 458 m / s. Each photon contains a certain amount of energy, and all
electromagnetic radiation consists of these photons.
The only difference between the various types of electromagnetic
radiation is the amount of energy found in the photons. Radio waves have
photons with low energies, microwaves have a little more energy than radio
waves, infrared has still more, then visible, ultraviolet, X-rays, and ... the
most energetic of all ... gamma-rays.
Electromagnetic radiation (including visible light) travels 149
million kilometers (93 million miles) from the sun to Earth in about 8
minutes. In contrast, an automobile speeding at 100 kilometers per
hour (60 miles per hour) would require 177 years to make the same
one-way trip.
In only one second, light can circumnavigate the Earth seven times.
10
Science 10
Chapter 7 - Radiation
7.2 RADIATION IN ATOMS
Radioactive
-Any atom that emits radiation from their nuclei
-Three types of radiation are emitted from a nuclei - alpha, beta and
gamma
Alpha: composed of 2 protons and 2 neutrons and have a charge of +2
- Are helium nuclei
Beta: high energy electrons and have a charge of -1
Gamma: a form of electromagnetic radiation and are not made of
particles
- can penetrate very deep into objects
Isotopes
Review – atomic number = protons and electrons
- atomic mass - atomic number = neutrons
-Atoms of the same element that have different mass numbers, due to the
number of neutrons in the nucleus.
Example : Carbon 12 has 6 protons and 6 neutrons
Carbon 13 has 6 protons and 7 neutrons
Carbon 14 has 6 protons and 8 neutrons
11
Science 10
Chapter 7 - Radiation
Radioactive Decay
The unstable nuclei emit radiation and decompose over time
Alpha Decay - Emit alpha particles - Alpha particles are helium nuclei, therefore it
emits 2 protons and 2 neutrons
Example;
Uranium  Helium and Thorium
238
4
2
U
92
He
+
234
90
Th
Beta Decay
Emits high energy electrons
Example;
Carbon  electron and Nitrogen
14
6 C

0
1e
+
14
7 N
Carbon will lose 1 electron (e-1) therefore 6 – (-1) = 7
Gamma Decay
Does not give off a particle, there is no change to the nucleus
Emits excess energy from the nucleus
12
Science 10
Chapter 7 - Radiation
Half-life
- The time required for half of the nuclei to decay
- Therefore, after 1 half life, exactly half of the original starting
material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
Half-life
The time required for half of the nuclei to decay
Therefore, after 1 half life, exactly half of the original starting material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
If you point a Geiger counter at a radioactive substance for a period of time,
you'll notice that the reading on the meter decreases as you watch. This is
shown on the graph.
The radioactivity from some substances dies away very fast - perhaps in a
few microseconds. Others take thousands of years before you'll notice that
the radioactivity had decreased at all.
In theory, every radioactive substance should stay slightly radioactive for
ever - the graph should never actually fall to zero. This means that we can't
usefully talk about the "life" of a radioactive source.
Instead, we use the idea of "half-life".
This is the time it takes for the radioactivity to fall by half.
13
Science 10
Chapter 7 - Radiation
This graph shows what
would happen with an
imaginary radioactive
substance.
Notice that the
radioactivity falls by half
every 2 hours.
Thus we say that this
imaginary substance has a
half-life of 2 hours.
The count rate coming from a radioactive source depends on how many unstable atoms it contains.
That's the number of un-decayed atoms.
If the count rate has fallen by half, then the number of unstable atoms has fallen by half.
A typical exam question may be "A radioactive substance has a half-life of 2 hours. How
much of the substance will remain after 6 hours have passed?"
Thus, for a substance with a half-life of 2 hours, 1/8 of the original atoms will remain after 6 hours.
Note that this also means that 7/8 of the atoms will have decayed in that time.
Take another look at the graph above, you'll see that after 6 hours the activity has fallen from 8,000 to
1,000; i.e. it's fallen to 1/8 of the starting value.
14
Science 10
Chapter 7 - Radiation
Question 1:
A radioactive substance has a half-life of 30 minutes. What fraction of the atoms will
not have decayed after 1 hour?
Answer:
The half-life of the substance is 30 minutes.
That means that 1 hour is 2 half-lives for the substance.
After one half-life the activity will fall to 1/2 of the
starting value, after a second half-life it will have fallen
to half of that - i.e. a quarter.
So one quarter of the original atoms remain.
15
Science 10
Question 2:
Another substance has a half-life of 3 hours.
decayed after 6 hours?
Answer:
Chapter 7 - Radiation
What fraction of the atoms will have
The half-life is 3 hours, so 6 hours is 2 halflives.
After 2 half-lives only one quarter of the
original atoms remain, which means that
three-quarters of them have decayed.
Question 3:
A researcher measures 200 counts per minute coming from a radioactive source at
midday. At 3 o'clock, she finds that this has dropped to 25 counts per minute.
What is the half-life of the radioactive source?
Answer:
After 3 hours, the count rate has fallen from 200
to 25 counts per minute
Calculate the number of half lives there is from
200 to 25
200 – 100 -50 - 25
so this means that three half lives have passed.
If 3 half-lives are 3 hours, then the half-life is one
hour.
16
Science 10
Chapter 7 - Radiation
Chapter 7, Radiation and Nuclear Energy
(student handout)
7.1 ELECTROMAGNETIC RADIATION
Radiation - ___________________________________________________________________
_____________________________________________________________________________
Electromagnetic wave
-
___________________________________________________________________
___________________________________________________________________________
Electromagnetic Spectrum
- ________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
17
Science 10
Chapter 7 - Radiation
Wave length
_________________________________________________________________________________

A radio’s wavelength is approx. 1m in length

A gamma ray’s wavelength is 0.000 000 000 000 001 m in length!
Electromagnetic radiation
Can be described in terms of a stream of photons, which are particles each traveling in
a wave-like pattern and moving at the speed of light = 299 792 458 m / s. Each photon
contains a certain amount of energy, and all electromagnetic radiation consists of these
photons.
Electromagnetic radiation (including visible light) travels 149 million kilometers (93
million miles) from the sun to Earth in about 8 minutes. In contrast, an automobile speeding
at 100 kilometers per hour (60 miles per hour) would require 177 years to make the same
one-way trip. In only one second, light can circumnavigate the Earth seven times.
The only difference between the various types of electromagnetic radiation is _____________
_________________________________________________________________________________.
Radio waves have photons with low energies, microwaves have a little more energy than radio waves,
infrared has still more, then visible, ultraviolet, X-rays, and ... the most energetic of all ... gamma-rays.
18
Science 10
Chapter 7 - Radiation
7.2 RADIATION IN ATOMS
Radioactive
-__________________________________________________________________________
-Three types of radiation are emitted from a nuclei - alpha, beta and gamma
Alpha: composed of _________________________________ and have a charge of +2
- Are _______________ nuclei
Beta: _________________________________________________________________
Gamma: a form of electromagnetic radiation and are not made of particles
- can penetrate very deep into objects
Isotopes
Review : atomic number = protons and electrons
- atomic mass minus atomic number = neutrons
-Atoms of the same element that have different mass numbers, due to the number of neutrons in the
nucleus.
Example : Carbon 12 has 6 protons and 6 neutrons
Carbon 13 has 6 protons and 7 neutrons
Carbon 14 has 6 protons and 8 neutrons
Radioactive Decay
The unstable nuclei emit radiation and decompose over time
Alpha Decay Emit alpha particles
Alpha particles are helium nuclei, therefore it emits 2 protons and 2 neutrons
Example
19
Science 10
Chapter 7 - Radiation
Beta Decay
Emit high energy electrons
Example
Gamma Decay
Does not give off a particle, there is no change to the nucleus
_______________________________________________________________
Half-life
The time required for half of the nuclei to decay
Therefore, after 1 half life, exactly half of the original starting material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
If you point a Geiger counter at a radioactive substance for a period of time,
you'll notice that the reading on the meter decreases as you watch. This is
shown on the graph.
The radioactivity from some substances dies away very fast - perhaps in a
few microseconds. Others take thousands of years before you'll notice that
the radioactivity had decreased at all.
In theory, every radioactive substance should stay slightly radioactive for
ever - the graph should never actually fall to zero. This means that we can't
usefully talk about the "life" of a radioactive source.
Instead, we use the idea of "half-life".
This is the time it takes for the radioactivity to fall by half.
20
Science 10
Chapter 7 - Radiation
This graph shows what
would happen with an
imaginary radioactive
substance.
Notice that the
radioactivity falls by half
every 2 hours.
Thus we say that this
imaginary substance has a
half-life of 2 hours.
The count rate coming from a radioactive source depends on how many unstable atoms it contains.
That's the number of un-decayed atoms.
If the count rate has fallen by half, then the number of unstable atoms has fallen by half.
A typical exam question may be "A radioactive substance has a half-life of 2 hours. How
much of the substance will remain after 6 hours have passed?"
Thus, for a substance with a half-life of 2 hours, 1/8 of the original atoms will remain after 6 hours.
Note that this also means that 7/8 of the atoms will have decayed in that time.
Take another look at the graph above, you'll see that after 6 hours the activity has fallen from 8,000 to
1,000; i.e. it's fallen to 1/8 of the starting value.
21
Science 10
Chapter 7 - Radiation
Question 1:
A radioactive substance has a half-life of 30 minutes. What fraction of the atoms will
not have decayed after 1 hour?
Answer:
22
Science 10
Question 2:
Another substance has a half-life of 3 hours.
decayed after 6 hours?
Answer:
Chapter 7 - Radiation
What fraction of the atoms will have
Question 3:
A researcher measures 200 counts per minute coming from a radioactive source at
midday. At 3 o'clock, she finds that this has dropped to 25 counts per minute.
What is the half-life of the radioactive source?
Answer:
23