Waves and Radiation: Nuclear radiation
Sample pages
Waves and Radiation
Nuclear radiation
The key concepts discussed in this spread are the nature of alpha radiation (α),
beta radiation (β), gamma radiation (γ) and the relative effects of ionisation,
absorption and shielding.
Types of nuclear radiation
Alpha (α) radiation
alpha particle
Beta (β) radiation
+
–
+
2 neutrons
Gamma (γ) radiation
beta particle = 1 electron
2 protons
gamma ray = energy wave
The atoms of radioactive substances emit radiation, and nuclear radiation is emitted from
the nucleus (centre) of an atom. Any radiation can be harmful, but it is also very useful
when used carefully, so it is important to know exactly how each type of radiation behaves.
VIDEO LINK
www.youtube.com/watch?fe
ature=endscreen&NR=1&v=I
jS0bTGCcJQ
Absorption and shielding of radiation
It is vital to know how far radiation can travel or penetrate before it is absorbed. Then
materials can be selected and used to shield humans from the radiation.
3 cm of aluminium
Sample pages
20 cm of air
Alpha (α) radiation
several cm of lead
Beta (β) radiation
Gamma (γ) radiation
A thin sheet of paper can absorb alpha radiation, but gamma radiation can even
penetrate several cm of lead.
Ionisation
ion
atom
α particle
dislodges electron
Don’t Forget
Although gamma radiation
travels the furthest and is the
most penetrating radiation,
alpha radiation does the most
damage over a very short
distance because of its strong
ionising capability.
Ionisation is when nuclear radiation changes atoms into ions.
Alpha radiation causes the most ionisation, and happens when an alpha
particle collides with an atom and removes an electron from the atom
which then becomes an ion (a charged particle).
Beta particles cause less ionisation than alpha, they are smaller particles.
Gamma radiation causes even less radiation, but because it is a ‘wave’ of energy, it can
travel through atoms without being absorbed.
Ionisation can be used deliberately for useful reasons:
•
•
•
to help diagnose or treat certain illnesses
to protect people – for example by its use in smoke detectors
in industry – for example to monitor the thickness of newspaper in a paper mill.
However, unexpected ionisation can be dangerous, and should be prevented.
cont
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Sample pages
α particle
Sample pages
The three types of nuclear radiation are:
Background radiation
VIDEO LINK
When the atoms of radioactive materials decay, they can give out alpha or beta or
gamma radiation.
www.youtube.com/
watch?v=Utpi5rFSVe0
Radioactive materials exist everywhere, and so there is always radiation around us,
called background radiation. When background radiation is measured, it measures
the Activity of a variety of sources in the particular area. The Activity is measured in
Becquerels (Bq).
Background radiation can be due to natural or artificial radiation.
Artificial Source
Annual
equivalent dose
μSv
mSv
Medical uses (X-rays)
250
0⋅250
Weapons testing
10
0⋅010
Nuclear industry (waste)
2
0⋅002
Other (job, TV, flights)
18
0⋅018
Total man-made sources
280
0⋅280
Natural Source
Annual
cosmic
equivalent dose
rays medical
mSv
radioactive μSv
foodgases in airgases
Radioactive
and
800
0⋅80
buildings (radon and thoron)
rocks
Rocks of the earth
400
0⋅40
medical
other
Total natural sources
1870
Absorbed Dose D
rocks
1⋅87
Online test
E
Absorbed Dose D
= –––
m
http://cloud4test.com/
hello/tests
Absorbed Dose is how much energy per kilogram from
radiation has been received. It depends on the mass of
biological material exposed to the radiation, and the
absorbed dose is measured in Grays (Gy).
Calculate the absorbed dose.
radioactive
gases
food
In food and our bodies
370
0⋅37
weapons
other
Cosmic rays from
spaceindustry 300
0⋅30
nuclear
weapons
nuclear industry
Example: A 2⋅5 kg sample of tissue receives 2mJ
of energy.
cosmic
rays
E
D=
–––
m
2 x 10–3
= ––––––––
2⋅5
=8 x 10–4 Gy (80 mGy)
Online test
http://cloud4test.com/
hello/tests
Equivalent Dose H
Equivalent Dose H = DwR
The effect of radiation on humans depends on the Absorbed Dose and the type of
radiation. Equivalent Dose measures this in Sieverts (Sv). Different types of radiation
are given a ‘radiation weighting factor’ (wR) depending on how harmful the effect is on
biological material like bone or tissue.
Example: A sample of tissue which received an
Absorbed Dose of 80 mGy was exposed to alpha radiation.
Alpha radiation has a radiation weighting factor of 20.
Calculate the Equivalent Dose.
H= DwR
=8 x 10–4 x 20
=0⋅016 Sv (16 mSv)
Don’t Forget
THINGS TO DO AND THINK ABOUT
There are a variety of tasks that can be carried out either on your own or in a group to
explore this topic further. Why not have a go at:
•
Researching the extraction of naturally occurring radioactive materials and maybe
determine levels of background radiation in places near you?
•
Discuss or debate the risks and benefits of radioactivity in society or the biological
effects of radiation in a class environment with one group arguing for and another
against.
Activity in Bq.
Absorbed dose in Gy.
Equivalent dose in Sv.
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Energy and Electricity – Conservation of Energy
CONSERVATION OF ENERGY
The key concepts to learn in this topic are the principles of ‘conservation’ and ‘loss’ of
energy, applied to examples where energy is transferred between stores, the principle of
heat energy (Eh) and how to perform calculations with gravitational and elastic potential
energy (Ep) and kinetic energy (Ek) in situations involving conservation of energy.
VIDEO LINK
Energy is never destroyed but is always transformed (changed) into other stores
(types) of energy. For example, gravitational potential energy is often transformed into
kinetic energy:
http://www.youtube.
com/watch?v=BSWl_
Zj-CZs&feature=related
Potential energy
Kinetic energy
A bouncing ball dropped on to the ground illustrates how energy is transformed:
What happens when the
ball is dropped?
What happens when the ball stops
going up?
As the ball falls, if air
resistance is ignored then
all of the gravitational Ep is
transformed into Ek
When all of the Ek is transformed back
into gravitational Ep the ball will be at
the top of its bounce – but not at the
height it was dropped from because of
the Eh ‘lost’ when it changed shape.
Ep ≡ Ek
What happens when the ball
rebounds?
As the ball hits the ground,
it changes shape, and the
Ek transforms into elastic Ep
and some Eh
As the ball rebounds, the elastic Ep
transforms back into Ek and some Eh
and regains its shape. Then this Ek is
transformed into gravitational Ep as
the ball gets higher.
Each time the ball bounces, the lost energy means that the ball will rebound to a lower
height until eventually it loses all of its energy.
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Sample pages
What happens when the
ball hits the ground?
Sample pages
Heat energy is usually always produced whenever potential energy is transformed into
other stores of energy – whether heat energy is wanted or not. For example, in a car,
energy from fuel is transformed by the engine into useful kinetic energy but also into
wasted or ‘lost’ heat energy.
Sample pages
Energy conservation and loss
Sample pages
Energy and Electricity
Energy calculations
Online test
To calculate gravitational potential energy use Ep = mgh
To calculate kinetic energy use Ek =
½mv2
http://cloud4test.com/hello/
tests
This example illustrates how to calculate speeds, height and ‘lost’ energy:
A 600 g ball is dropped to the ground from a vertical height of 4 metres.
(a) Calculate the speed of the ball just as it collides with the ground. Ignore air resistance.
Energy is transformed from potential energy into kinetic energy as the ball falls.
Ep ≡ Ek
mgh= ½mv2
so v= ƒ
2gh
= E
2 × 9⋅8 × 4
Don’t Forget
Because Ep ≡ Ek ,to calculate
the final speed where Ep is
transformed into Ek then
the equation v = ƒ
2gh can
be used to calculate the
answer.
= 8⋅9 m s–1
(b)When the ball rebounds, it leaves the ground with a speed of 7∙4 m s–1.
Calculate the height the ball will return to.
v= ƒ
2gh
Don’t Forget
This rearranges to
h=
v2
To calculate the final
rebound height then the
2g
7⋅42
=
2 × 9⋅8
equation h =
v2
can be
2g
used to calculate the answer
= 2⋅8 m
(c) Calculate the energy lost when the ball collides with the ground.
Before the collision After the collision Energy lost during the collision
Ek = ½mv2
= ½ × 0⋅6 × 8⋅92
= 23⋅76 J
Ek = ½mv2
= ½ × 0⋅6 × 7⋅42
= 16⋅4 J
= Ek before – Ek after collision
= 23⋅76 – 16⋅4
= 7⋅4 J
Don’t Forget
Good advice: This lost energy
is usually transformed into
sound and heat. Sometimes
this heat energy can cause
the ball to become warm in
sports where there are lots
of ‘rebounds’ e.g. squash and
tennis.
THINGS TO DO AND THINK ABOUT
There are several other examples of everyday energy transformations, e.g.
A clock
pendulum
Water stored in a
reservoir which flows
downwards through
pipes to a generator in
a hydro electric power
station
Think of examples of energy transformations going on around you and consider the
energy loss which may occur in these transfers. Discuss and explain why processes are
not 100% efficient in terms of useful energy.
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