P4 Overview radiation for life

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P4 Overviewradiation for life

• GCSE Additional Science Y 11

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Uses of Electrostatics

• Defibrillators restarts a heart
• Paint Spraying
• Dust Precipitators
• Photocopiers Laser Printers

4 uses
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Paint Spraying

• Spray Gun is charged all of the paint gets the
  same charge
• Like charges repel paint particles spread out
  giving a fine spray
• Object being painted is given the opposite charge
  paint is attracted to object and sticks to it.
• Advantages less wasted paint even coat of
  paint awkward places are painted.

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Electrostatic Dust Precipitators

• Removes harmful smoke particles from a chimney.
• Metal grid/wires placed in chimney
• Grid connected to high voltage supply
• Dust particles attracted to metal grid
• Dust particles stick together
• Large particles fall down chimney
• Soot used to make building blocks

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Current Electricity

• Electric Circuits must be COMPLETE to allow
  electricity to flow from to terminals on a
  cell/battery.
• A Cell provides POTENTIAL DIFFERENCE (Voltage) in
  VOLTS. This provides the FORCE to move the charge
  carriers (in wires electrons in electrolysis
  ions)
• The resulting flow of charge is called CURRENT
  measured in AMPS.
• Current always flows from to (even though the
  electrons flow from to !)

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A Circuit to measure resistance
Resistance Potential difference Current
R V I
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Ohms Law
Cover up what you want to find

• For a metallic conductor at constant
  temperature, the ration of Potential difference
  (V) to Current (I) is constant.
• The constant is called Resistance, R measured in
  ohms, symbol O.
• So R V I, also V I x R and I V R

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Mains Electricity
Fuses come in various values 2A,3A,5A,13A. A
13Amp fuse blows when current through it exceeds
13Amps

• Live (brown) brings supply to house
• Neutral (blue) is return path to power station
• Earth (green and yellow)
• carries current to 0V if the casing becomes
  live. This blows the FUSE which cuts off the
  supply.
• Fuse is in series with the Live wire.

A circuit-breaker is a re-settable fuse which can
be re-set at the flick of a switch These have
replaced fuse wire in the main fuse box.
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Ultrasound - sound waves beyond the human hearing
range

• Range of human hearing is 20 20,000Hz so beyond
  that is Ultrasound

Sound waves are LONGITUDINAL the vibrations of
the particles are in the same direction as the
wave
Compression particles in wave squashed
together Rarefaction particles in wave spread
out. Wavelength distance occupied by one
complete wave (unit metres) Frequency number
of complete waves per second (unit
hertz) Amplitude maximum distance a particle
moves from its normal position.
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Uses of Ultrasound

• Check the condition of a foetus
• Investigate heart and liver problems
• Look for tumours in the body
• Break down kidney stones and stones elsewhere in
  the body
• Measure the speed of blood flow in vessels when a
  blockage of a vein or artery is suspected
• Cataract surgery

Non medical uses dentists shake plaque and
dirt off teeth
jewellers clean delicate pieces of
jewellery and watches
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Radiotherapy and Diagnosis

• Gamma rays ?
• High frequency/energy electromagnetic waves
  emitted from the nucleus of a radioactive isotope
• Very penetrating can pass into the body to
  treat internal organs
• Can damage living cells over exposure should be
  avoided

• X rays
• High frequency/energy electromagnetic waves
  emitted when high speed electrons are decelerated
• Very penetrating
• Can damage living cells
• An X-ray machine can produce and control X-rays
  of different energies so some X-rays can have
  higher energy than ? rays

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Alpha, Beta and Gamma emissions
Ionisation the ability to remove an electron
from an atom, causing the atom to become
charged. Alpha has 2 charges so has a great
ionising effect, beta has 1 charge so a lesser
ionising effect.
Alpha and Beta particles are not good inside the
body they cannot escape from inside so dont
swallow any remember Mr Litvinienko? killed
with Polonium 210, an alpha emitter!
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Using Gamma radiation

• Treating cancer large doses can kill and
  destroy cancer cells. A gamma knife is rotated
  around a cancer to give the cancer a high dose
  but the healthy tissue a low dose. Side effects
  of this kind of therapy can be unpleasant but
  slows down the growth of the cancer.
• Sterilising hospital equipment Gamma kills
  bacteria and prevents the spread of disease.

Radiographers carry out procedures using X-rays
and nuclear radiation. Lead prevents tissue
absorbing radiation.
Tracers some radioactive isotopes (in very low
doses!) can be injected into the body to
highlight places where a cancer may be
growing. Common isotopes are Technetium 99
and Iodine - 123
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Radioactivity - discovered by Becquerel and
researched by Pierre Marie Curie (among others)

• Some atoms naturally break up because the nuclear
  forces holding them together are not strong
  enough.
• Radioactive substances decay naturally and give
  out Alpha (a), Beta (ß) and Gamma (?) radiation.
• Radioactivity is a random process that cannot be
  controlled by external conditions such as
  temperature, pressure etc. Neither can the decay
  be predicted.
• Radioactivity is detected usually with a
  Geiger-Müller (GM) tube and a ratemeter.
• Activity is measured by counting the average
  number of nuclei that decay every second, unit
  Becquerels (Bq).

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Half Life

• The time taken for the activity of a sample to
  fall to one half of its original activity,
• OR
• The time for half of the atoms in a radioactive
  isotope to have decayed.
• It is different for every radioisotope

A Typical Decay curve
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Alpha Decay
Remember A is the mass number protons
neutrons Z is the
proton number number of protons OR electrons

• An alpha particle (or helium nucleus) contains 4
  nucleons (2p 2n)
• When a is emitted, A decreases by 4, Z
  decreases by 2
• The new element formed is two places lower in the
  Periodic table than the original radioisotope.
• 92U 2a 90Th

238
4
234
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Beta Decay -1ß
0

• A beta particle is a high energy electron
• emitted from the nucleus (!)
• This is because a neutron decays to a proton,
  an electron and a bit of antimatter
• When ß- is emitted, A does not change
• Z increases by 1
• (because it has an extra proton).
• 6C -1ß 7N
• A new element is formed that is one place higher
  in the periodic table than the original
  radioisotope.

14
0
14
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Background Radiation

• This is ionising radiation that is always present
  in the environment.
• The level of background radiation is low and does
  not cause harm.
• E.g. Granite contains small amounts of Uranium
  which decays to Radon, a radioactive gas.
• Sources (7) radioactivity in the air radiation
  from Space (cosmic rays) rocks food medical
  uses nuclear power nuclear weapons testing
  (these last two make up just 1).

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Uses of Radioactivity

• Alpha is used in Smoke detectors Americium-241
• Beta is used to monitor the thickness of paper
  Strontium-90
• Gamma is used to treat cancer to search for
  leaks from pipes to check welds in castings.

• Dating
• Uranium/Lead levels are used to date rocks VERY
  OLD!
• Potassium/Argon levels date rocks up to about
  100,000 years old
• Carbon 14/Carbon12 levels are used to check
  organic material up to 60,000 years old

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Nuclear Fission

• U235 can become unstable when bombarded with
  neutrons.
• It accepts a neutron, becomes U236, which decays
  readily to Kr92, Ba141 and extra neutrons. (These
  may go on to strike the nuclei of other atoms
  causing further fission reactions
• a CHAIN REACTION).
• It also releases massive amounts of energy!!!

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A Nuclear Power Station
Control Rods in a reactor core
The output of a Nuclear Reactor is controlled
by A graphite moderator between the fuel rods
slows down fast-moving neutrons Boron control
rods absorb neutrons and so control the rate of
fission.