Transcript P4 Radiation for Life

06/04/2017
Radiation for Life
OCR Additional Science
W Richards
P4a: Sparks
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Static Electricity
An introduction – click here
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Static Electricity
Static electricity is when charge “builds up” on an object and
then stays “static”. How the charge builds up depends on what
materials are used:
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Short Static Experiments
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Try the following quick static electricity experiments:
1) Rubbing a balloon on your jumper and “sticking” it to the
wall
2) Charging a plastic rod by rubbing it with a cloth and then
holding it near the water from a smooth-running tap
3) Charging a plastic rod and trying to pick up small pieces of
paper (or someone else’s hair!) with it
4) Rubbing a balloon on someone else’s head – you might want
to ask their permission first…
Can you explain what you saw in each of these experiments?
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Static Electricity
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Static Electricity in Lightning
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Van de Graaf generators
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When a charge is neutralised by
the movement of electrons either
from the Earth or to the Earth
we call this “earthing”
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Dangers of Static – fuelling lines
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P4b: Uses of Electrostatics
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Using Static in Paint Sprayers
Connected to
negative voltage
Connected to positive
voltage
1) Why is the paint sprayer given a negative charge?
2) Why is the car given a positive charge?
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Uses of Static – Smoke Precipitators
Chimney
Negatively
charged
plates
Positively
charged
grid
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Uses of Static - Defibrillators
How do defibrillators work?
P4c: Safe Electricals
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Electric Current
Electric current is a flow
of negatively charged
particles (i.e. electrons).
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Note that
electrons go
from negative
to positive
By definition, current is “the
rate of flow of charge” and
it is larger through shorter,
wider wires
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Resistance
Resistance is anything that will RESIST
a current. It is measured in Ohms, a
unit named after me. Basically, longer
wires have more resistance and wider
wires have less resistance.
Georg Simon Ohm
1789-1854
The resistance of a component can be
calculated using Ohm’s Law:
Resistance
(in )
=
V
Voltage (in V)
Current (in A)
I
R
An example question:
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Ammeter
reads 2A
A
V
Voltmeter
reads 10V
1) What is the resistance across
this bulb?
2) Assuming all the bulbs are the
same what is the total resistance
in this circuit?
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More examples…
3A
6V
12V
3A
2A
4V
2V
1A
What is the
resistance of
these bulbs?
Resistance
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Resistance is anything that opposes an electric current.
Resistance (Ohms, ) =
Potential Difference (volts, V)
Current (amps, A)
What is the resistance of the following:
1) A bulb with a voltage of 3V and a current of 1A.
3
2) A resistor with a voltage of 12V and a current
of 3A
4
3) A diode with a voltage of 240V and a current of
40A
6
4) A thermistor with a current of 0.5A and a
voltage of 10V
20
Wiring a plug
1. Earth
wire
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4. Live
wire
5. Fuse
2. Neutral
wire
3. Insulation
The neutral wire of a plug is used
to complete the circuit.
6. Cable
grip
The Earth wire of a plug keeps the
device safe by stopping the
appliance becoming “live”
Fuses
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Fuses are _______ devices. If
there is a fault in an appliance
which causes the ____ and
neutral (or earth) wire to cross
then a ______ current will flow
through the _____ and cause it
to _____. This will break the
_______ and protect the
appliance and user from further
_____.
Words – large, harm, safety, melt, live, circuit, fuse
Circuit breakers
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Residual Current Circuit Breakers
(RCCBs) are often used with fuses. They
have some advantages over fuses:
1) They are safer – they don’t get hot
2) They react more quickly
3) They can be switched off for repairs
4) They are easy to reset
5) Each RCCB is attached to a certain
circuit, so if one switches off you can
see which circuit has a fault
Earth wires
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Earth wires are always used if an appliance has a _____ case.
If there is a _____ in the appliance, causing the live wire to
______ the case, the current “_______” down the earth wire
and the ______ blows. Earth wires are not needed if a device
is “double insulated”.
Words – fuse, fault, metal, surges, touch
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Power and fuses
Power is “the rate of doing work”.
The amount of power being used in
an electrical circuit is given by:
Power = voltage x current
in W
in V
in A
P
V
I
Using this equation we can work out the fuse rating for any
appliance. For example, a 3kW (3000W) fire plugged into a
240V supply would need a current of _______ A, so a
_______ amp fuse would be used (fuse values are usually 3,
5 or 13A).
Power and fuses
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Copy and complete the following table:
Appliance
Power rating
(W)
Voltage (V)
Toaster
920
230
Fire
2000
230
Hairdryer
300
230
Hoover
1000
230
Computer
100
230
Stereo
80
230
Current
needed (A)
Fuse needed
(3, 5 or 13A)
Power and fuses
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Copy and complete the following table:
Appliance
Power rating
(W)
Voltage (V)
Current
needed (A)
Fuse needed
(3, 5 or 13A)
Toaster
920
230
4
5
Fire
2000
230
8.7
13
Hairdryer
300
230
1.3
3
Hoover
1000
230
4.3
5
Computer
100
230
0.43
3 or 1
Stereo
80
230
0.3
3 or 1
P4d: Ultrasound
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Waves- Some definitions…
1) Amplitude – this is
“how high” the wave is:
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
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Transverse waves are
when the displacement
is at right angles to
the direction of the
wave (e.g. light and
other electromagnetic
waves)…
Displacement
Transverse vs. longitudinal waves
Displacement
Direction
Direction
Longitudinal waves
are when the
displacement is
parallel to the
direction of the wave
(e.g. sound waves)…
Where are the compressions and rarefactions?
Ultrasound
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Ultrasound is the region of sound above 20,000Hz – it can’t
be heard by humans. It can be used in pre-natal scanning:
How does it work?
Ultrasonic waves are partly _________ at the boundary as they pass from
one _______ to another. The time taken for these reflections can be
used to measure the _______ of the reflecting surface and this
information is used to build up a __________ of the object.
Words – depth, reflected, picture, medium
Other uses of ultrasound
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1) Breaking down kidney stones
Ultrasonic waves break kidney
stones into much smaller pieces
2) Cleaning (including teeth)
Ultrasound causes dirt to vibrate
dirt off without damaging the object
Why is ultrasound better than X-rays?
Ultrasound can be used instead of X-rays because they are
able to produce images of soft tissue and they do not damage
living cells.
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P4e: What is Radioactivity?
The structure of the atom
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ELECTRON –
negative, mass
nearly nothing
NEUTRON –
neutral, same
mass as
proton (“1”)
PROTON –
positive, same
mass as
neutron (“1”)
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Introduction to Radioactivity
Some substances are classed as “radioactive” – this means that
they are unstable and continuously give out radiation:
Radiation
The nucleus is more stable after emitting some radiation – this
is called “radioactice decay” and the activity is measured in
“Becquerels (Bq)”.
Types of radiation
Unstable
nucleus
New
nucleus
Alpha
particle
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1) Alpha () – an atom decays into a new
atom and emits an alpha particle (2
protons and 2 ______ – the nucleus of a
______ atom)
2) Beta () – an atom decays into a new
atom by changing a neutron into a
_______ and electron. The fast moving,
Beta high energy electron is called a _____
particle particle.
Unstable
nucleus
New
nucleus
Unstable
nucleus
New
nucleus
3) Gamma – after  or  decay surplus
______ is sometimes emitted. This is
called gamma radiation and has a very
high ______ with short wavelength.
The atom is not changed.
Gamma
radiation
Words – frequency, proton,
energy, neutrons, helium, beta
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Changes in Mass and Proton Number
Alpha decay:
241
Am
95
237
Np
93
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2
α
Beta decay:
90
Sr
38
90
Y
39
β
-1
Ionisation
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Radiation is dangerous because it “ionises” atoms – in other
words, it turns them into ions by “knocking off” electrons:
Alpha radiation is the most ionising (basically, because it’s the
biggest). Ionisation causes cells in living tissue to mutate,
usually causing cancer.
Half life
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The decay of radioisotopes can be used to measure the
material’s age. The HALF-LIFE of an atom is the time
taken for HALF of the radioisotopes in a sample to decay…
= radioisotope
At start
there are 16
radioisotopes
After 1 half
life half have
decayed
(that’s 8)
= new atom formed
After 2 half
lives another
half have
decayed (12
altogether)
After 3 half
lives another
2 have
decayed (14
altogether)
A radioactive decay graph
Activity (Bq)
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“1 Becquerel” means “1
radioactive count per second”
Time
A radioactive decay graph
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Count
1 half
life
1 half
life
1 half
life
Time
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P4f: Uses of Radioisotopes
Background Radiation
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13% are
man-made
Radon gas
Food
Cosmic rays
Gamma rays
Medical
Nuclear power
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Background Radiation by Location
In 1986 an explosion occurred at the Chernobyl nuclear power
plant. Here is a “radiation map” showing the background
radiation immediately after the event:
Other “risky” areas could be mining underground, being in a
plane, working in an x-ray department etc
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Uses of radioisotopes - tracers
A tracer is a small amount of radioactive material used to
detect things, e.g. a leak in a pipe:
Gamma
source
The radiation from the radioactive source is picked up above
the ground, enabling the leak in the pipe to be detected.
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Uses of radioactivity – smoke detectors
Smoke detectors
Alpha
emitter
+ve electrode
-ve electrode
Alarm
Ionised air particles
If smoke enters here a
current no longer flows
Uses of radioactivity – dating rocks
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Question: Uranium decays into lead. The half life of uranium is
4,000,000,000 years. A sample of radioactive rock contains 7 times as
much lead as it does uranium. Calculate the age of the sample.
Answer: The sample was originally completely uranium…
1 half life
later…
1 half life
later…
1 half life
later…
8
8
4
8
2
8
1
…of the
sample was
uranium
Now only 4/8 of
the uranium
remains – the
other 4/8 is lead
Now only 2/8 of
uranium remains
– the other 6/8
is lead
Now only 1/8 of
uranium remains
– the other 7/8
is lead
8
So it must have taken 3 half lives for the sample to decay until only 1/8
remained (which means that there is 7 times as much lead). Each half
life is 4,000,000,000 years so the sample is 12,000,000,000 years old.
An exam question…
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Potassium decays into argon. The half life of potassium is
1.3 billion years. A sample of rock from Mars is found to
contain three argon atoms for every atom of potassium.
How old is the rock?
(3 marks)
The rock must be 2 half lives old – 2.6 billion years
Carbon Dating
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The amount of the isotope Carbon-14 present in the air has
not changed for thousands of years. Therefore scientists can
use it to help calculate how old something is. Consider, for
example, a fossilised tree:
1) When the tree died it
stopped exchanging carbon-14
with the atmosphere
2) As time went on the
amount of carbon-14
decreased as it decayed
3) The amount of current
activity can then be compared
to a living tree to work out
how old it is
P4g: Treatment
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X-Rays and Gamma Rays
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X-rays and gamma rays are similar in
that they have similar wavelengths and
they are both ionising but they are
produced in different ways.
Gamma rays are given out from the
nucleus of radioactive materials
whereas X-rays are made by firing
high-speed electrons at metal targets
and are therefore easier to control.
X-ray images are possible because the
absorption of X-rays depends on the
material’s thickness and density.
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Uses of Radioactivity - sterilisation
Gamma rays can be used to kill and sterilise
germs without the need for heating. The
same technique can be used to kill microbes
in food so that it lasts longer.
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Uses of Radioactivity - Treating Cancer
High energy gamma radiation can be
used to kill cancerous cells.
However, care must be taken in
order to enure that the gamma
radiation does not affect normal
tissue as well.
During radiotherapy gamma rays are
focused on the tumour and rotated
around the patient with the tumour
at the centre, thereby limiting
damage to non-canerous tissue.
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Uses of radioactivity – medical tracers
As well as using tracers to
find leaks in pipes, tracers
can also be used in
medicine to highlight
problem areas within a
body by using a radiation
detector:
What sort of half life
would you want a medical
tracer to have?
Medical radioisotopes are produced by placing materials in a
nuclear reactor and they become radioactive by absorbing
extra neutrons.
Exposure to Radiation
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People like me work with radiation a lot so
we need to wear a “dosimeter” to record
our exposure to radiation:
Radiation dose is
measured in units called
“sieverts” (Sv).
P4h: Fission and Fusion
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How Power Stations Work
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1) A fossil fuel is burned in the boiler
2) Water turns to steam and the steam drives a
turbine (in some gas poer stations the air is
heated directly)
3) The turbine turns a generator
4) The output of the generator is connected to a
transformer
5) The steam is cooled down in a cooling tower and
reused
Nuclear power stations
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Notice that the heat from these reactions is used to heat
water and turn it into steam, which then drives turbines.
Nuclear fission
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More
neutrons
Neutron
Uranium or
plutonium
nucleus
Unstable
nucleus
New nuclei
(e.g. barium
and krypton)
Chain reactions
Each fission reaction releases
neutrons that are used in further
reactions. A nuclear bomb is basically
a chain reaction that has gone out of
control!!
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Fission in Nuclear power stations
These fission reactions occur in the fuel
rods and they become very hot. Water (a
coolant) cools the rods (which then turns
to steam) and the control rods are moved
in and out to control the amount of fission
reactions taking place.
Nuclear Fusion in stars
Proton
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Neutron
Nuclear fusion happens in stars but it’s not possible to use it
in power stations yet as it needs temperatures of around
10,000,000OC and very high pressures.
Cold Fusion
Stanley Pons and Martin
Fleishmann
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In 1989 we claimed that we
had enabled “cold fusion”,
i.e. we had created fusion
reactions in lab
temperatures. However,
no one else could verify our
findings so our theories
have not been accepted.