Turnbull High School
Physics Department
Unit 1 :- Waves and Radiation
Section 4: Electromagnetic Spectrum
and Radiations
Name:
Class:
1
National 4
Electromagnetic Spectrum and Radiations
• I can describe applications and hazards associated with
electromagnetic radiations.
• I can describe approaches to minimising risks associated with
electromagnetic radiations.
• I can identify natural and artificial sources of nuclear radiation
and associated medical and industrial applications.
• I can explain some the pros and cons of generating electricity
using nuclear fuel.
• I can make comparisons of risk due to nuclear radiation and
other environmental hazards.
• I can describe how to manage the risks associated with
radiation.
2
National 5
Electromagnetic Spectrum and Radiations
• I can state the relative frequency and wavelength of radiations
in the electromagnetic spectrum
• I can state some typical sources and applications of radiations in
the electromagnetic spectrum.
• I can state the relationship between the frequency and energy
associated with a form of radiation.
• I can state that all radiations in the electromagnetic spectrum
travel at the speed of light
• I can describe the nature of alpha, beta and gamma radiation in
terms of relative effect of ionization, absorption, shielding.
• I can identify sources of background radiation.
• I can calculate absorbed dose, equivalent dose and make
comparisons of equivalent dose due to a variety of natural and
artificial sources.
• I can describe some applications of nuclear radiation.
• I can state that activity is measured in Becquerel’s.
• I can give a definition of Half-life.
• I can make use of graphical or numerical data to determine the
half-life of a source.
• I can give a qualitative description of fission and fusion,
emphasising the importance of these processes in the generation
of energy.
3
The Electromagnetic Spectrum
Energy often travels through space in the form of electromagnetic
waves. This family of waves include:
Long wavelength
Low frequency
Short wavelength
High frequency
They all travel through space at a speed of 3 x 108 m s−1
(300 000 000 m s−1). Each member of the electromagnetic spectrum
has a different ___________ and _____________.
Radio and Television
Mobile telephones (microwaves), radio and
television are examples of long-range
communication which do not need
_________ between the transmitter and
the receiver. These signals travel as waves
and so carry _________. They also travel
very quickly - their speed in air is
300 000 000 ms−1 (___________ms−1).
4
Experiment 1
What you need: Battery, file, radio.
battery
file
What to do:
Switch on the radio and place it near the file. Scrape the end of the
wire quickly over the file. Move the radio further away and again
scrape the wire over the file.
Questions:
1. What effect does scraping the file have on the radio?
__________________________________________________
2. How far apart can you move the radio and the file and still hear
the effect?
__________________________________________________
3. There are no wires joining the file to the radio - how does the
signal travel to the radio?
__________________________________________________
5
Experiment 2
What you need: Radio, I-pod, aluminium foil, plastic bag.
What to do:
• Switch on the radio and tune to a station - then wrap it in
aluminium foil.
• Switch on the I-pod and wrap it in aluminium foil.
• Repeat using the plastic bag instead of the aluminium foil.
Questions:
1. Can radio waves pass through metal foil?
2. Can radio waves pass through plastic?
3. Would this radio work well inside a metal train or car?
4. How is a car radio able to pick up radio waves?
5. What happens when the I-pod is wrapped in foil?
6
Tuning
Radio sets and Television sets are able to receive signals
from many different stations. To keep the signals
separate, each station transmits on a different
______________ (and therefore different frequency).Inside radio
sets and television sets there are tuning circuits which when altered
accepts only _____ signal and ignores all the rest.
Experiment 3
What you need: Radio set
Tune into some of the stations listed below. Complete the
table.
Working
Station
Radio Scotland
Radio 1
Radio Clyde
Clyde 2
Radio 4
Atlantic
Wavelength
370 m
275 m
261 m
Frequency
810 kHz
1089 kHz
102.5 MHz
1515 m
1190 m
252 kHz
7
Wave Band
MW
MW
MW
Fm
LW
LW
Microwaves
Microwaves are used in satellite communication or short
range terrestrial (on Earth) communication.
Microwaves have smaller wavelengths than Radio and T.V. waves and
so can’t _____________ around objects.
Microwaves are also used for
__________________________________________
__________________________________________
__________________________________________
8
Do you consider mobile phones to be safe?
The use of mobile phones is a good example of a scientific
controversy. Recent research studies have produced tentative
evidence that mobile phones may have long-term health effects.
However, this is by no means certain and the radiation produced by
mobile phones falls well below current safety guidelines.
Activity
1. Find the website – www.peep.ac.uk
2. Read each webpage on this topic in turn carefully
3. Look at the extra links and interviews
4. Considering evidence for and against the use of mobile phones,
use this framework to construct a reasoned argument and
present it in a suitable format. Use the cues below to help you.
I think that................................................
The evidence to support this idea is.....
The evidence supports me because........
Arguments against me are........................
I would counter these arguments by........
9
Tutorial 1
1. Our eyes can detect visible light with wavelengths
ranging from 400 nm to 700 nm. Light with a wavelength of
around 400 nm is violet in colour. Red light has a wavelength of
around 700 nm.
[1nm = 1x10-9m]
Calculate the frequencies of violet light and red light.
2. The human body gives out microwaves of wavelength 9 cm which
can be detected by a small aerial placed in contact with the skin.
These microwaves allow doctors to measure the temperature of
organs inside the body.
Calculate the frequency of microwaves emitted from the body.
10
Satellite Communication
Microwaves, radio waves and TV waves can be
transmitted all around the world and even through
space using a network of satellites carrying dish aerials. Receiving
dishes collect in many signals and reflect them onto one point called
the focus.
Experiment 4
What you need: Raybox kit, curved reflector, labpack, ruler
Place a set of slits in the beam to produce three parallel rays of light
- draw in what happens to the rays.
11
1. What happens to the beam of light after it hits the mirror?
2. Where is the light brightest?
3. Where should the receiving aerial be placed so that it receives the
strongest signal from the dish?
Satellite dishes can also be used to transmit waves in a parallel beam
which can be easily directed.
T
12
Visible Light - Lasers
A laser produces an intense _________ of
_________ in ______ direction.
Lasers have various uses in medicine. For example:
Vaporising Cancer
Tumours
Laser Scalpel
Eye Surgery
Removing
Tattoos/Birth Marks
13
Infrared
All ______ objects give off invisible ‘heat rays’ called
infrared radiation. Infrared radiation travels at
___________________________.
Special infrared cameras can be used to take colour photographs
called _______________ using this radiation instead of light.
In medicine, thermograms of a patient’s body show areas of
different temperature as different ____________. Doctors have
found that malignant tumours are ____________ than healthy
tissue and show up clearly on thermograms.
Infrared radiation is used in a different way by physiotherapists.
They use this radiation to penetrate the skin and heat muscles and
tissues. Heat causes healing to occur more quickly.
Infrared light is also used in Nightvision devices, and in astronomy,
imaging at infrared wavelengths allows
observation of objects obscured by
interstellar dust.
14
Experiment 5
What you need: Light source, triangular prism, infrared
detector, multimeter.
What to do:
1. Position the triangular prism on a white sheet of paper.
2. Shine a single narrow beam of light into the prism and alter the
angle of incidence until a visible spectrum is produced.
3. Move the detector infrared detector beyond the red end of the
visible spectrum.
4. Monitor closely the reading on the meter and explain why the
meter reading increases beyond the red end of the spectrum.
15
Experiment 6
What you need: safety goggles, metal gauze, Bunsen
burner, tongs, cement mat, infrared detector, infrared
camera.
What to do:
1.
Hold the metal guaze in the tongs.
2. Heat the gauze in the Bunsen flame until it glows red hot.
3. Remove the guaze from the flame and let it cool until the red
glow just disappears.
4. Hold the gauze in front of the radiation sensor. Note how the
detector reading increases when the gauze is brought close to it.
5. Your teacher will repeat the experiment replacing the infrared
detector with a digital camera.
Experiment 7
What you need: Infrared thermometers
What to do: Use an Infrared thermometer to measure various
temperatures around the lab.
16
Ultraviolet
Ultraviolet is another type of invisible radiation which
travels at _______________________.To keep healthy, our bodies
need the ultraviolet radiation to produce _______________ to help
the body obtain calcium from food.
Too much ultraviolet light on the skin produces _____________.
Excessive use of sun beds may cause _________ _________.
Ultraviolet radiation is used in the treatment of Jaundice in babies
and certain skin diseases such as acne.
17
Fluorescence
Some chemicals glow and emit visible light when they absorb UV. This
is used in shops to test credit card and banknotes as they have codes
marked on them that cannot be seen in normal light but glow under a
UV lamp
Industry uses fluorescent plastic food seals on some products to allow
automatic checks for tampering.
Experiment 8
What you need: Ultraviolet lamp, "Invisible ink"
security marker, various banknotes, credit cards, white shirt, soap
powder, highlighter ink, UV beads.
What to do:
Use the ultraviolet lamp to examine each of the samples.
18
X-rays
X-rays are invisible rays which _________ photographic
film when they hit it and travel at ________________________.
X-rays pass through body tissues like skin, fat and muscle fairly
easily, but are more readily absorbed by __________.
Medical X-rays
X-rays are used in two main areas in
medicine – diagnosis and treatment.
•
X-rays are used to diagnose
illness, or damage to bones or
other tissues inside the body.
•
High energy X-rays are used to
intentionally damage cancerous cells.
When X-rays hit the photographic plate
on the other side of the patient, they
blacken the photographic film, and so
the image of the foot would be fairly
dark, with lighter areas for the bone.
Any break in the bone lets
X-rays
through and may show up as a dark
crack.
19
People who work with X-rays must be protected from the X-rays.
They use lead screens to block the X-rays, they stand as far as
possible from the machine and they wear special photographic film
badges which monitor their exposure
X-rays may also be used to look for problems in organs or the
intestine. Patients swallow a liquid which absorbs X-rays - a ‘barium
meal’. The X-rays are detected electronically, processed by a
computer and produce an image on the monitor.
X-rays Photographs
Experiment 9
What you need: X-ray transparencies.
What to do: Hold the X-ray transparency up to light – identify which
part of the body has been X-rayed.
1. Why is X-ray film put in light tight containers?
2. If X-rays of wavelength 3 x 10−11 m are used for on a patient
calculate their frequency?
3. What advantages can you think of in using continuous X-ray
pictures?
20
Computed Tomography
Computed tomography uses a sophisticated X-ray machine
known as a CAT scanner to give a clear image of a selected slice
through the body. The X-rays travel at right angles to the body’s
length as shown below, and the source and detector rotate around
the body to give readings for all directions.
The data is fed into a computer which then builds up a picture of the
organs in each slice. The picture is then displayed on a TV screen.
The main advantages of computed tomography compared with normal
X-ray photographs are
• a three dimensional picture of the part of the body being
studied (hence nothing is hidden)
• moving pictures can be obtained.
21
Gamma Radiation (γ)
Gamma radiation, also known as gamma rays is an invisible
electromagnetic radiation with _______ energy, which
can pass through thick layers of most materials.
Treating Cancer - Radiation Therapy
Cancers are growths of cells which are out of control. The radiation
____________ the cancer cells which then stop reproducing. The
cancer or tumour then _____________.
__________ cells can also be damaged by radiation, and so the
applied dose has to be very accurately calculated.
The apparatus is arranged so
that it can rotate around the
couch on which the patient lies.
This allows the patient to be
irradiated from different
directions.
The tumour receives a maximum
radiation dose from the beam, while
the skin and other tissue receive as
little unwanted radiation as possible.
22
Summary of radiations and detectors
Radiation Type
detector
TV and Radio waves
aerial and receiver
Microwaves
aerial and receiver
Infrared
photodiode
Visible light
human eye and photographic film
Ultraviolet
photographic film and fluorescent material
X-rays
photographic film
Gamma rays
photographic film and Geiger-muller tube.
23
Tutorial 2
1. A patient is suffering from pains in his knees. The doctor in the
hospital takes a thermogram of the knees and detects an
inflammation of the joints caused by arthritis. The infra red
radiation being given out by the knees has a frequency of
5 x 1012 Hz.
Calculate the wavelength of this radiation.
2. The ancient Egyptians used ultraviolet radiation from the sun’s
rays to treat the skin complaint acne. Ultraviolet light is still
used today in hospital to treat acne.
Calculate the wavelength of UV light of frequency 8·8 x1016 Hz.
24
3. X – rays are widely used in medicine and dentistry.
4.
John is having an X-ray taken of one of his teeth. The dentist
sets up the X-ray apparatus and goes to stand behind a lead
screen. The X - rays used have a frequency of 2 x1017 Hz.
(a)
Calculate the wavelength of these X-rays.
(b)
How long will it take for these X -rays to travel 10 cm
from the X- ray machine to John’s tooth?
(c)
Why did the dentist stand behind a lead screen?
25
Nuclear Radiation
Alpha, Beta and Gamma Radiation
The Atom
Atoms are the smallest possible particles of the elements. Atoms
make up everything around us. The three main particles which make
up atoms are
All atoms have a tiny central nucleus which has a _________ charge.
We can imagine the ____________ charged electrons to be circling
around this, rather like planets around the sun. The nucleus contains
the ___________ protons and the neutrons, which are
_______________.
Ionisation
Ionisation is the break up of a neutral
atom into a positive ion and an electron.
The electrons near the outside of the
atoms are very light, and can easily be
knocked away from the atom. This can
happen if radiation from a radioactive substance passes nearby.
Because radiations from radioactive substances make ions so easily,
they are often called ____________ ____________.
26
Ionising Radiations
When the alpha or beta or gamma radiation passes
through a material they lose _________ by colliding with
the atoms of the material. Eventually the radiations lose so much
_________ that they cannot get through (____________) the
material and so are ____________.
Alpha particles: (α
α) are the nuclei of helium atoms. They have 2
neutrons and 2 protons in the nucleus and are therefore
___________ charged.
Alpha particles will travel about 5 cm through the air before they are
fully absorbed. They will be stopped by a sheet of paper. Alpha
particles produce the greatest ionisation.
Beta particles: (β
β) are fast moving electrons and so are
___________ charged.
Beta particles can travel several metres through air and will be
stopped by a few millimetres of aluminium. They cause less ionisation
than alpha particles.
Gamma rays: (γγ) have ____ mass or charge and carry energy from
the nucleus leaving the nucleus in a more stable state.
Gamma rays can only be stopped by a very thick piece of lead. They
travel at the speed of light and very little ionisation.
27
Detecting Radiation
Geiger-Muller Tube
The Geiger-Muller tube is a detector which use the effects of
ionisation to measure the amount of radiation present.
The central wire inside the cylindrical tube is kept at a high voltage
of about +400 V compared with the outer case. When radiation
enters the tube and produces a few ions, these are accelerated
towards the central wire. As they pass through the low-pressure gas,
they bump into atoms at high speed and knock out many more
electrons off. When they reach the central wire they send a pulse of
current round the circuit. These pulses are counted electronically by
the scalar or ratemeter, and so the amount of radiation being
detected by the G-M tube is measured.
28
Measuring Background Radiation
Experiment 10
What you need: A Geiger-Muller tube, a scalar meter
What to do:
Switch on the counter for one minute and measure the amount of
radiation detected in the lab during this time. Reset the counter and
repeat the experiment twice more. Complete the table using your
own results and seven more obtained by other groups.
Measurement
number
1
2
3
4
5
6
7
8
9
Counts in 1
minute
Are all the values the same?
What is the average background count in counts per minute?
29
10
Background radiation
Everyone is exposed to background radiation from natural and from
man-made radioactive material. Background radiation is always
present. Some of the factors affecting background radiation levels
are:
• Rocks which contain radioactive material, exposing us to ionising
particles
• Cosmic rays from the sun and outer space which emit lots of protons
which cause ionisation in our atmosphere
• Building materials containing radioactive particles and radioactive
radon gas from the soil and which collects in buildings, mainly due to
lack of ventilation.
• The human body which contains radioactive potassium and carbon.
• A person’s chosen occupation. Radiographers exposed to X-rays used
in hospitals and nuclear workers from the reactor.
Natural radiation
is by far the
greatest influence
on our exposure to
background
radiation.
30
Half-life
In any radioactive source, the activity decreases with
time because the number of unstable atoms gradually decreases
leaving fewer atoms to decay.
The half-life of a radioactive source is the time for the activity
to fall to half its original value.
To Find the Half Life of a Radioactive Source
1. Without the source being present measure the background count
rate with the Geiger counter.
2. Place the radioactive source in front of the Geiger Muller tube
and measure the total count rate (this is at t = 0).
3. Measure the count rate at regular intervals.
4. Correct all of the count rates for background radiation to find
the source count rate.
Source count rate = total count rate – background count rate
5. Draw a graph of source count rate against time.
6. Use the graph to find at least two values for the half-life of the
source (the time it takes for the count rate to half). Find the
average value for the half-life of the source.
(Instead of using the count rate of the source, the activity of the
source in Becquerels could be used)
31
Example
1. A Geiger-Muller tube and ratemeter were used to measure the
half-life of radioactive caesium-140. The activity of the source
was noted every 60 s. The results are shown in the table. By
plotting a suitable graph, find the half-life of caesium-140.
Time (s)
0
Count rate 70
(corrected)
(count/s)
60
120
180
240
300
360
50
35
25
20
15
10
From the graph the time taken to fall from 70 counts/s to 35
counts/s = 120 s
35 counts/s to 17.5 counts/s = 120 s
Average half life of caesium-140 = 120 s.
32
Tutorial 3
1. A radioactive tracer has an activity of 160 Bq. The tracer has a
half life of 5 hours and decays for 15 hours.
What is its final activity?
2. A radioactive source with a half life of 2.5 minutes decays for 10
minutes. The source has an initial activity of 64 kBq.
Calculate the final activity of the source.
3. A sample of radioactive uranium has an initial activity of 600
kBq. After 10 days its activity has dropped to 150 kBq.
Use this information to calculate the half life of the source.
33
4. The activity of an isotope varies with time as shown below. The
count rate is uncorrected for background radiation.
Count rate
230
190
160
130
110
95
80
70
0
1
2
3
4
5
6
7
(per minute)
Time
(hours)
The background count is 30 counts per minute.
a. Collect some graph paper from your teacher and lot a
corrected graph of activity against time for the isotope.
b. Calculate the half life of the isotope.
34
Dosimetry
Activity
The activity, A, of a radioactive source is the number of decays, N,
per second. It is measured
in Becquerel where:
1 Bq = 1 decay per second.
Number of Decays
Activity (Bq) = --------------------------Time (s)
N
A
t
Absorbed dose
The greater the transfer of radiation energy to the body the greater
the chance of damage to
the body. The absorbed dose, D, is the energy absorbed per unit mass
of the absorbing
material and is measured in grays, Gy.
1 Gy = 1 Joule per kilogram
Energy absorbed (J)
Absorbed dose (Gy) = ------------------------Mass (kg)
E
D
m
35
Tutorial 4
1. A radioactive source produces 100 disintegrations per
second. Calculate the activity in Becquerels.
2. A radioactive source produces 1000 disintegrations in
one minute. Calculate the activity in Becquerels.
3. The activity of a radioactive source is 1 MBq. How many
disintegrations would there be in one minute?
36
4. Calculate the absorbed dose when a 2 kg mass absorbs
0.1J of energy.
5. Calculate the mass of a worker who absorbs 0.2 J of
energy from a source with an absorbed dose of 3mGy.
37
The biological effects of radiation
All ionising radiation can cause damage to the body. The
risk of biological harm from an exposure to radiation depends on:
• the absorbed dose
• the kind of radiation
• the body organs or tissue exposed.
The body tissue or organs may receive the same absorbed dose from
alpha or gamma
WR
Type of Radiation
1
Beta particles/Gamma rays
10
Protons and Fast Neutrons
20
Alpha particles
Effects of radiation on living things
All living things are made of cells. Ionising radiation can kill or change
the nature of healthy
cells. This can lead to different types of cancer.
38
Equivalent Dose
When scientists try to work out the effect on our bodies of a dose of
radiation they prefer to
talk in terms of equivalent dose. The equivalent dose H is the product
of D and WR.
equivalent dose = absorbed dose x radiation weighting factor
H
D
WR
Equivalent dose (H) is measured in sieverts (Sv)
Absorbed dose (D) is measured in grays (Gy)
Radiation weighting factor (WR) has no units
Example
A worker in the nuclear industry receives the following absorbed
does in a year:
30mGy from Gamma radiation (WR =1)
300mGy from fast neutrons (WR = 10)
Calculate the equivalent dose for the year.
for Gamma
H = 30 x 10-3 x 1 = 30 x 10-3 Sv
for neutrons
H = 300 x 10-6 x 10 = 3.0 x 10-3 Sv
total
H = 30 x 10-3 + 3.0 x 10-3 = 33 x 10-3 Sv
39
Equivalent Dose rate
Sometimes it is important to monitor how quickly or bodies are
absorbing different types of radiations. In this situation we need to
calculate the equivalent dose rate.
Equivalent dose (H)
Equivalent dose rate (
)=
Time taken (t)
Equivalent dose rate is measured in sieverts per second or sieverts
per hour (Svs-1 or Svh-1)
Equivalent dose is measured in sieverts (Sv)
Time is measured in seconds or hours (s or h)
H
t
Example
A radiation worker spends 4 hours in a radioactive area. The worker
receives an equivalent dose of 8 mSv of radiation. Calculate the
equivalent dose rate.
=
8x10-3
4
= 2x10-3 Svh-1
40
Tutorial 5
1. An industrial worker receives an equivalent dose of
200microsieverts from alpha particles with a radiation weighting
factor of 20. Calculate the absorbed dose he is exposed to.
2. An unknown radioactive element has an absorbed dose of
500micrograys and gives an equivalent dose of 1millisieverts.
Calculate the radiation weighting factor of the material.
3. A patient has a dental X-ray which produces an absorbed dose of
0.3milligrays. Calculate the equivalent dose of this X-ray.
(WR=1 for X-rays)
41
4. A technician in a nuclear power station is exposed to several
types of radiation over a 150-hour working month.
She receives a dose 0.2 mGy due to exposure to fast
neutrons, 15 µGy due to α-particles, and an absorbed dose of
1mGy from gamma rays.
Calculate the technician’s total equivalent dose.
5. A radiation detector on an aircraft measures an equivalent dose
of 12mSv during a 3 hour flight. Calculate the equivalent dose
rate received by the passengers.
42
Safety with Radioactivity
• Always use forceps or a lifting tool to remove a
source. Never use bare hands.
• Arrange a source so that its radiation window points away from
the body.
• Never bring a source close to your eyes for examination.
• After any experiment with radioactive materials, wash your
hands thoroughly before you eat.
Reducing the dose equivalent
• Use shielding, by keeping all radioactive materials in sealed
containers made of thick lead. Wear protective lead aprons to
protect the trunk of the body.
• Keep as far away from the radioactive materials as possible.
• Keep the times for which you are exposed to the material as
short and as few as possible
Radioactive hazard warning sign
The sign should be displayed on all doors where radioactive
materials are stored.
43
Fission and fusion
Advantages of using nuclear power to produce electricity
• Fossil fuels are running out, so nuclear power provides a
convenient way of producing electricity.
• A nuclear power station needs very little fuel compared with a
coal or oil-fired power station. A tonne of uranium gives as much
energy as 25000 tonnes of coal. • Unlike fossil fuels, nuclear fuel
does not release large quantities of carbon dioxide and sulphur
dioxide into the atmosphere, which are a cause of acid rain.
Disadvantages of using nuclear power to produce electricity
• A serious accident in a nuclear power station is a major disaster.
British nuclear reactors cannot blow up like a nuclear bomb but
even a conventional explosion can possibly release tonnes of
radioactive materials into the atmosphere. (The Chernobyl
disaster was an example of a serious accident.)
• Nuclear power stations produce radioactive waste, some of
which is very difficult to deal with.
• After a few decades nuclear power stations themselves will have
to be disposed of.
44
Nuclear fission
A uranium nucleus can be split by a
neutron. This can produce two new
nuclei plus the emission of neutrons
and the release of energy.
Chain reaction
Once a nucleus has divided by fission, the neutrons that are emitted
can strike other neighbouring nuclei and cause them to split releasing
energy each time. This results in what is called a chain reaction as
shown below.
In a controlled chain
reaction, on average only
one neutron from each
fission will strike another
nucleus and cause it to
divide. This is what
happens in a nuclear power
station. In an uncontrolled
chain reaction all the
neutrons from each fission
strike other nuclei
producing a large surge of
energy. This occurs in
atomic bombs.
45
Fusion
Nuclear fusion is the process by which two or more
atomic nuclei join together, or "fuse", to form a single
heavier nucleus. This is usually accompanied by the release of large
quantities of energy. Fusion is the process that powers active stars,
the hydrogen bomb and some experimental devices examining fusion
power for electrical generation.
Many scientists are working to produce controlled nuclear fusion
reactions, but have not yet been successful. If they do succeed the
fuel and end products, hydrogen and helium, will not be dangerously
radioactive.
Nuclear fusion reactions require very high temperatures, such as
found in the core of the Sun. A few scientists have claimed to have
produced cold fusion reactions where they fused hydrogen into
helium at approximately room temperature. If they were possible,
such reactions would immensely help the world's energy problems.
However other scientists have been unable to duplicate the work and
the cold fusion claims have been discredited.
46
The nuclear reactor
There are five main parts of a reactor as shown in the diagram below:
47
The fuel rods are made of uranium which produces
energy by fission.
1. The moderator, normally made of graphite slows
down neutrons that are produced in fission, since a
nucleus is split more easily by slow moving neutrons.
2. The control rods are made of boron, and absorb neutrons when
lowered into the reactor, so that the reaction can be slowed
down. In the event of an emergency they are pushed right into
the core of the reactor and the chain reaction stops completely.
3. A cooling system is needed to cool the reactor and to transfer
heat to the boilers in order to generate electricity. British gascooled reactors use carbon dioxide gas as a coolant.
4. The containment vessel is made of thick concrete which acts as
a shield to absorb neutrons and other radiations.
Radioactive waste
Nuclear power stations produce radioactive waste materials, some of
which have half-lives of hundreds of years. These waste products are
first set in concrete and steel containers then buried deep
underground or dropped to the bottom of the sea. These types of
disposals are very
controversial.
Some scientists believe
the containers will keep
the radioactive material
safe for a long time, other
scientists are worried
that the containers will
not remain intact for a
sufficient time.
48
Unit 1: Electromagnetic Spectrum and Radiations
Additional notes
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Unit 1: Electromagnetic Spectrum and Radiations
Additional notes
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Unit 1: Electromagnetic Spectrum and Radiations
Additional notes
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Unit 1: Electromagnetic Spectrum and Radiations
Additional notes
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Unit 1: Electromagnetic Spectrum and Radiations
Additional notes
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