PHYSICS – Radioactive Decay
LEARNING
OBJECTIVES
Core
• State the meaning of radioactive
decay
• State that during α- or β-decay the
nucleus changes to that of a different
element
•
Use the term half-life in simple
calculations, which might involve
information in tables or decay
curves
•
Recall the effects of ionising
radiations on living things
Describe how radioactive materials
are handled, used and stored in a
safe way
•
Supplement
•
Use equations involving nuclide notation
to represent changes in the composition
of the nucleus when particles are
emitted
•
Calculate half-life from data or decay
curves from which background radiation
has not been subtracted
Radioactive decay
Radioactive decay
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Radioactive decay
When a nucleus decays it becomes
more stable, but the loss of protons and
neutrons makes it a different element.
The original nucleus is called the parent
nucleus. The nucleus formed is known
as the daughter nucleus. Both are
called the decay products.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Radioactive decay
When a nucleus decays it becomes
more stable, but the loss of protons and
neutrons makes it a different element.
The original nucleus is called the parent
nucleus. The nucleus formed is known
as the daughter nucleus. Both are
called the decay products.
Mass number (nucleon
number) = total number of
nucleons (protons +
neutrons) in the nucleus
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
4
2He
Radioactive decay
When a nucleus decays it becomes
more stable, but the loss of protons and
neutrons makes it a different element.
The original nucleus is called the parent
nucleus. The nucleus formed is known
as the daughter nucleus. Both are
called the decay products.
Mass number (nucleon
number) = total number of
nucleons (protons +
neutrons) in the nucleus
Atomic number (proton
number) also shows the
relative charge on the
nucleus.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
4
2He
Radioactive decay
When a nucleus decays it becomes
more stable, but the loss of protons and
neutrons makes it a different element.
The original nucleus is called the parent
nucleus. The nucleus formed is known
as the daughter nucleus. Both are
called the decay products.
Mass number (nucleon
number) = total number of
nucleons (protons +
neutrons) in the nucleus
Atomic number (proton
number) also shows the
relative charge on the
nucleus.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Alpha particle
4
2He
+ +
4
2α
Four nucleons,
relative charge of
+2
Radioactive decay
When a nucleus decays it becomes
more stable, but the loss of protons and
neutrons makes it a different element.
The original nucleus is called the parent
nucleus. The nucleus formed is known
as the daughter nucleus. Both are
called the decay products.
Mass number (nucleon
number) = total number of
nucleons (protons +
neutrons) in the nucleus
Atomic number (proton
number) also shows the
relative charge on the
nucleus.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Alpha particle
4
2He
+ +
4
2α
Four nucleons,
relative charge of
+2
Beta particle
0
-1
β
An electron,
charge of -1
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
Let’s have a look
at some
examples!
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
When radium-226 decays, it does so
by emitting an alpha particle. This
means that the ‘daughter’ nucleus now
has 2 protons and 2 neutrons less than
it did before. We can write this as a
nuclear equation.
Let’s have a look
at some
examples!
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
When radium-226 decays, it does so
by emitting an alpha particle. This
means that the ‘daughter’ nucleus now
has 2 protons and 2 neutrons less than
it did before. We can write this as a
nuclear equation.
Let’s have a look
at some
examples!
226
88
Ra
222
4
86
2
Rn + α
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
When radium-226 decays, it does so
by emitting an alpha particle. This
means that the ‘daughter’ nucleus now
has 2 protons and 2 neutrons less than
it did before. We can write this as a
nuclear equation.
Let’s have a look
at some
examples!
226
88
Ra
222
4
86
2
Rn + α
A new element, radon, has
been formed from the
decay of the radium.
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
Thorium-232 also undergoes
radioactive decay, again with the loss
of an alpha particle (helium nucleus).
Let’s have a look
at some
examples!
232
90
Th
228
4
88
2
Ra + α
The element radium has
been formed from the
decay of the thorium.
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
Both examples
involved alpha
decay. Let’s now
look at an
example of beta
decay
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
In beta decay, a neutron changes into
a proton plus an electron. The proton
stays in the nucleus and the electron
leaves the atom with high energy. The
mass number remains unchanged (one
neutron lost, one proton gained) but
the atomic number increases by one.
Both examples
involved alpha
decay. Let’s now
look at an
example of beta
decay
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
In beta decay, a neutron changes into
a proton plus an electron. The proton
stays in the nucleus and the electron
leaves the atom with high energy. The
mass number remains unchanged (one
neutron lost, one proton gained) but
the atomic number increases by one.
Both examples
involved alpha
decay. Let’s now
look at an
example of beta
decay
14
6
C
14
0
7
-1
N + e-
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
In beta decay, a neutron changes into
a proton plus an electron. The proton
stays in the nucleus and the electron
leaves the atom with high energy. The
mass number remains unchanged (one
neutron lost, one proton gained) but
the atomic number increases by one.
Both examples
involved alpha
decay. Let’s now
look at an
example of beta
decay
14
6
C
14
0
7
-1
N + e-
The element nitrogen has
been formed from the beta
decay of the carbon.
Radioactive decay
Use equations involving
nuclide notation to
represent changes in the
composition of the
nucleus when particles
are emitted
In this example of beta decay, iodine131 emits a beta particle to become
xenon.
Both examples
involved alpha
decay. Let’s now
look at an
example of beta
decay
131
53
I
131
0
54
-1
Xe + e-
The mass number remains
unchanged, and the proton
number (atomic number)
increases by 1.
Radioactive decay
Some types of
nucleus are more
unstable than others
and decay at a faster
rate.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Radioactive decay
Some types of
nucleus are more
unstable than others
and decay at a faster
rate.
10 Days
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Radioactive decay
Some types of
nucleus are more
unstable than others
and decay at a faster
rate.
10 Days
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
10 Days
Radioactive decay
Some types of
nucleus are more
unstable than others
and decay at a faster
rate.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
10 Days
10 Days
One half-life
One half-life
Radioactive decay
Some types of
nucleus are more
unstable than others
and decay at a faster
rate.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
10 Days
10 Days
One half-life
One half-life
HALF-LIFE is the TIME TAKEN for HALF of the
radioactive atoms now present to DECAY
Radioactive decay
Some types of
nucleus are more
unstable than others
and decay at a faster
rate.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Days
Nuclei
remaining
Half-life
0
64
0
10
32
1
20
16
2
30
8
3
40
4
4
50
2
5
Radioactive decay
Measurements taken with
a GM tube. Don’t forget
that you might need to
subtract figures for
background radiation!
70
x
Nuclei remaining
60
50
Radioactive decay
curve
40
x
30
20
x
10
0
x
0
10
20
30
Days
x
40
x
50
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Days
Nuclei
remaining
Half-life
0
64
0
10
32
1
20
16
2
30
8
3
40
4
4
50
2
5
Radioactive decay
Measurements taken with
a GM tube. Don’t forget
that you might need to
subtract figures for
background radiation!
70
x
Nuclei remaining
60
50
Radioactive decay
curve
40
x
30
20
x
10
0
x
0
10
20
30
Days
x
40
x
50
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Radioactive
isotope
Half-life
Radon-220
52 secs
Iodine-128
25 mins
Radon-222
3.8 days
Strontium-90
28 years
Radium-226
1602 years
Carbon-14
5730 years
Plutonium-239
24 400 years
Radioactive decay
In the early hours of 26 April 1986
one of the four reactors at
Chernobyl power station exploded.
Because of the long-lived radiation in
the region surrounding the former
Chernobyl Nuclear Power Plant, the
area won't be safe for human
habitation for at least 20,000 years.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
Radioactive
isotope
Half-life
Radon-220
52 secs
Iodine-128
25 mins
Radon-222
3.8 days
Strontium-90
28 years
Radium-226
1602 years
Carbon-14
5730 years
Plutonium-239
24 400 years
Radioactive decay
In the early hours of 26 April 1986
one of the four reactors at
Chernobyl power station exploded.
Because of the long-lived radiation in
the region surrounding the former
Chernobyl Nuclear Power Plant, the
area won't be safe for human
habitation for at least 20,000 years.
Radioactive decay is a random event –
The unstable nuclei in some materials
will break up, or disintegrate. It is
impossible to predict exactly which
nuclei will decay. This disintegration
of the nuclei is called radioactive
decay.
In a radioactive sample, the
average number of disintegrations
per second is called the activity.
The SI unit of activity is the
becquerel (Bq). For example,
100Bq = 100 nuclei disintegrating
per second.
Radioactive decay
Radioactive decay
Initial count rate = 600
counts per second.
Radioactive decay
Count rate falls to 200
counts per second after
25 minutes
Radioactive decay
If the initial count was
600, the half-life is 300
particles, which will be
after 16 minutes.
Radioactive decay
Initial count = 600, one
half life = 300, two half
lives = 150
Radioactive decay
Initial count = 600, one
half life = 300, two half
lives = 150
600
25
16
150
• Calculate half-life from data or decay
curves from which background
radiation has not been subtracted
Every half-minute a teacher records a count
rate of a radioactive substance. The
background count was 3Bq. Calculate the
corrected count rate and draw a graph for
these results.
Time in
minutes
Count rate
in Bq
0
52
0.5
33
1.0
27
1.5
21
2.0
18
2.5
14
3.0
13
3.5
12
4.0
8
4.5
9
Corrected count
rate in Bq
Radioactive decay
Supplement
• Calculate half-life from data or decay
curves from which background
radiation has not been subtracted
Every half-minute a teacher records a count
rate of a radioactive substance. The
background count was 3Bq. Calculate the
corrected count rate and draw a graph for
these results.
Time in
minutes
Count rate
in Bq
Corrected count
rate in Bq
0
52
49
0.5
33
30
1.0
27
24
1.5
21
18
2.0
18
15
2.5
14
11
3.0
13
10
3.5
12
9
4.0
8
5
4.5
9
6
Radioactive decay
Supplement
• Calculate half-life from data or decay
curves from which background
radiation has not been subtracted
Radioactive decay
Supplement
Time in
minutes
Count rate
in Bq
Corrected count
rate in Bq
0
52
49
0.5
33
30
1.0
27
24
1.5
21
18
2.0
18
15
2.5
14
11
3.0
13
10
3.5
12
9
4.0
8
5
4.5
9
6
Corrected count rate in Bq
Every half-minute a teacher records a count
rate of a radioactive substance. The
background count was 3Bq. Calculate the
corrected count rate and draw a graph for
these results.
50 x
45
40
35
30
x
25
x
20
x
x
15
10
5
0
x
x
x
x x
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Time in minutes
• Calculate half-life from data or decay
curves from which background
radiation has not been subtracted
Radioactive decay
Supplement
Every half-minute a teacher records a count
rate of a radioactive substance. The
background count was 3Bq. Calculate the
corrected count rate and draw a graph for
these results.
Count rate
in Bq
Corrected count
rate in Bq
0
52
49
0.5
33
30
1.0
27
24
1.5
21
18
2.0
18
15
2.5
14
11
3.0
13
10
3.5
12
9
4.0
8
5
4.5
9
6
Corrected count rate in Bq
Time in
minutes
Use your graph to estimate the
half-life of the material
50 x
Original count = 49
45
40
35
30
x
Half of original count = 24.5
25
x
20
x
Half-life = 1 min
x
15
x
x x
10
5
x x
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Time in minutes
Ionising Radiation and Living Things
Ionising Radiation and Living Things
Alpha, beta and gamma
radiation will enter living cells
and collide with molecules –
these collisions cause ionisation,
damaging or destroying the
molecules.
Ionising Radiation and Living Things
Alpha, beta and gamma
radiation will enter living cells
and collide with molecules –
these collisions cause ionisation,
damaging or destroying the
molecules.
Lower doses cause
non-fatal damage to
cells, but can cause
them to become
cancerous, when they
divide uncontrollably.
Ionising Radiation and Living Things
Alpha, beta and gamma
radiation will enter living cells
and collide with molecules –
these collisions cause ionisation,
damaging or destroying the
molecules.
Lower doses cause
non-fatal damage to
cells, but can cause
them to become
cancerous, when they
divide uncontrollably.
Higher doses tend to kill cells
completely, causing radiation
sickness.
Ionising Radiation and Living Things
Alpha, beta and gamma
radiation will enter living cells
and collide with molecules –
these collisions cause ionisation,
damaging or destroying the
molecules.
Lower doses cause
non-fatal damage to
cells, but can cause
them to become
cancerous, when they
divide uncontrollably.
Higher doses tend to kill cells
completely, causing radiation
sickness.
The extent of the
harmful effects
depends upon two
things.
Ionising Radiation and Living Things
Alpha, beta and gamma
radiation will enter living cells
and collide with molecules –
these collisions cause ionisation,
damaging or destroying the
molecules.
Lower doses cause
non-fatal damage to
cells, but can cause
them to become
cancerous, when they
divide uncontrollably.
Higher doses tend to kill cells
completely, causing radiation
sickness.
The extent of the
harmful effects
depends upon two
things.
a) How much exposure there is to the radiation.
b) The energy and penetration of the radiation emitted – some
types are more hazardous than others.
Ionising Radiation and Living Things
Alpha radiation
cannot penetrate
through skin, so
outside the body
beta and gamma
radiation are the
most dangerous –
but both of these
are less ionising
than alpha and so
cause less
damage.
α
β
γ
Ionising Radiation and Living Things
Alpha radiation
cannot penetrate
through skin, so
outside the body
beta and gamma
radiation are the
most dangerous –
but both of these
are less ionising
than alpha and so
cause less
damage.
α
However, if alpha
particles get
inside the body
(ingested,
breathed-in) then
they can do much
more damage in a
very localised
area because they
are so strongly
ionising.
Ionising Radiation and Safety
Ionising Radiation and Safety
In the school laboratory
• Handle with tongs, avoid skin contact with a
source.
• Keep source as far away from the body as
possible.
• Avoid looking directly at the source
• Immediately return source to lead-lined box
when not required.
Ionising Radiation and Safety
In the school laboratory
• Handle with tongs, avoid skin contact with a
source.
• Keep source as far away from the body as
possible.
• Avoid looking directly at the source
• Immediately return source to lead-lined box
when not required.
In industry
•
•
•
Full protective suits prevent inhalation of radioactive
dust particles and direct skin contact
Use lead-lined suits, lead/concrete barriers, thick lead
windows to prevent exposure to gamma radiation.
Use of remotely controlled robot arms in highly
radioactive areas.
LEARNING
OBJECTIVES
Core
• State the meaning of radioactive
decay
• State that during α- or β-decay the
nucleus changes to that of a different
element
•
Use the term half-life in simple
calculations, which might involve
information in tables or decay
curves
•
Recall the effects of ionising
radiations on living things
Describe how radioactive materials
are handled, used and stored in a
safe way
•
Supplement
•
Use equations involving nuclide notation
to represent changes in the composition
of the nucleus when particles are
emitted
•
Calculate half-life from data or decay
curves from which background radiation
has not been subtracted
PHYSICS – Radioactive Decay