P4 Radiation for Life
- Created by: Jen677
- Created on: 18-11-16 19:12
Item P4a: Sparks
Like charges repel, and opposite charges attract
Electrostatic effects are caused by the transfer of electrons:
- A positive charge due to lack of electrons
- A negative charge due to an excess of electrons
Atoms or molecules that become charged are ions
Static electricity can be dangerous when:
- In atmospheres where explosions could occur, such as flammable gases
- In situations where large quantities of charge could flow through the body to earth
They can be avoided in the following ways:
- Earthing of an object
- Standing on insulating mats/insulating soles on shoes
- Bonding fuel tankers to aircrafts
- Filling with an inert gas
Item P4a: Sparks
Static electricity can also be a nuisance because:
- Dust and dirt are attracted to insulators, such as tv screens
- Clothes made from synthetic materials tend to cling
Anti-static sprays, liquids and cloths help to reduce the problem of static electricity because they are made from conducting materials and they carry away electric charge. Stopping a build up of charge
Item P4b: Uses of electrostatics
Static electricity is used in dust precipitators, to remove smoke particles:
- Dust passes through high voltage charged metal grids or past charged rods
- So dust particles become charged, as they either gain or lose electrons
- Dust particles induce a charge on the earthed metal plates
- So dust particles are attracted to plates
- Plates are struck and dust falls to collector
Static Electricity is used in spray painting:
- Spray gun charged
- Paint particles charged the same so repel giving a fine spray and coat
- Object to be painted charged oppositely to paint so attracts paint into the shadows of the object, giving an even coat and less waste
If the object to be painted isn't charged the paint moves onto it but the object becomes charged from the paint, gaining the same charge. So further paint droplets are repelled
the object to be painted is given to opposite charge.If the paint is negatively charged- having gained electrons, the object needs to lose electrons
Item P4b: Uses of electrostatics
Defibrillation= A procedure to restore a regular heart rhythm by delivering an electric shock through the chest wall to the heart
- Two paddles are charged from a high voltage supply
- Good electrical contact with patients chest
- Charge passed through patient to make heart contract
- Care taken not to shock operator
Power=Energy/Time
Item P4c: Safe electricals
A variable resistor/rheostat can be used to change the current in a circuit
- Longer wires have more resistance
- Thinner wires have more resistance
- As temperature increases resistance increases
Voltage is measured in volts using a voltmeter connected in parallel:
- For a fixed resistor,current increases as voltage increases
- For a fixed voltage, current decreases as resistance increases
Resistance is measured in ohms
Resistance= Voltage/Current
V=IR I=V/R
Item P4c: Safe electricals
Live Wire-Carries the high voltage=Brown
Neutral=Completes the circuit=Blue
Earth= A safety wire to stop the appliance coming live=Green/Yellow
Earth Wires and fuses stop a person receiving a shock if they touch a faulty appliance. As soon as the case becomes live a large current flows in the earth and live wires and fuse blows
A fuse reduces the risk of fire if the appliance develops a fault:
- Too large a current causes the fuse to melt
- Preventing flow of current
- Prevents flex overheating and causing a fire
- Prevents further damage to an appliance
- A resettable fuse called a circuit breaker doesn't need to be replaced to restore power,
Double insulated appliances don't need earthing as the appliance is a non-conductor and cannot become live.
Power=Voltage x Current
Item P4d: Ultrasound
Ultrasound is sound above 20000 Hz which is a higher frequency than humans can hear. It travels as a pressure wave containing compressions and rarefactions.
Compressions=Particles pushed together, increasing pressure
Rarefaction= Particles further apart than usual, decreasing pressure
Item P4d: Ultrasound
Features of longitudinal sound waves:
- · Can’t travel through a vacuum. The denser the medium, the faster a sound wave travels
- · The higher the frequency the smaller the wavelength
- · The louder the sound, the more energy is carried and the larger the amplitude
Ultrasound can be used to break down kidney stones:
- A high powered ultrasound beam is directed at the kidney stones
- the ultrasound energy breaks the stones down into smaller pieces
- The tiny pieces are then excreted from the body
Ultrasound can be used for body scans:
- At each boundary between different tissue some ultrasound is reflected and the rest is transmitted. The returning echoes are recorded and used to build up an image of the internal structure. The depth of the structure is calculated using distance=speed x time.
- The proportion reflected at each interface depends on the densities and the speed of sound. If the tissues are very different most of the ultrasound is reflected
Item P4e: What is radioactivity?
Radioactive substances decay naturally, giving out alpha, beta and gamma radiation
Nuclear radiation causes ionisation by removing/gaining electrons from atoms
Half Life=Average time taken for half the nuclei in a radioactive sample to decay
Radioactive decay is a random process, and it isn't possible to predict when a nucleus will decay.
Alpha particles are good ionisers as they are the largest particles emitted in radioactive decay. Meaning they are more likely to strike atoms of the material they are passing through ionising them
Item P4e: What is radioactivity?
Radioactivity comes from the nucleus of an atom that is unstable
Alpha: Beta:
- Positively charged -Negatively Charged
- Has a large Mass -Very small mass
- Helium nucleus -Travels very fast
- helium gas around it -Is an electron
- 2 protons and 2 neutrons
During Decay Alpha: During decay beta:
- Mass number decreases by 4 -Mass number is unchanged
- Nucleus has 2 fewer neutrons -Nucleus has one less neutron
- nucleus has two fewer protons -Nucleus has one more proton
- Atomic number decreases by 2 -Atomic number increases by one
Item P4f: Uses of radioisotopes
Background radiation comes from waste products and man-made sources:
- Industry
- Cosmic Rays
- Rocks
- Radioactive waste from hospitals
When using a tracer to locate a leak in an underground pipe:
- Radioactive material put into pipe
- Progress tracked with detector above ground
- An increase in activity is detected in the region of the leak. Or no activity is detected after this point
A gamma source is used because the radiation is able to penetrate to the surface
Item P4f: Uses of radioisotopes
A smoke detector contains an isotope which emits alpha particles:
- Without smoke, the alpha particles ionise the air which creates a tiny current that can be detected by the circuit
- With smoke the alpha particles are partially blocked, so there is less ionisation-the change is detected and the alarm sounds
Some rocks such as granite contain traces of uranium:
- The uranium isotopes present in the rocks go through a series of decays, eventually forming a stable isotope of lead
- By comparing the amounts of uranium and lead present in a rock sample, its approximate age can be found. The proportion of lead increases as time increases. If there are equal quantities of uranium and lead the rock is 4500 million years old- one-half life
Carnon-14 is a radioactive isotope, that is present in all living things- by measuring the amount of Carbon-14, its approximate age can be found. When an object dies, no more Carbon-14 is produced. As the carbon-14 decays, the activity of the sample decreases. The ratio of current activity from living matter to the sample activity provides a reasonably accurate date
Item P4g: Treatment
Radiation emitted from the nucleus of an unstable atom can be alpha, beta or gamma:
- Alpha radiation is absorbed by the skin so is no use for diagnosis or therapy
- Beta radiation passes through the skin, but not bone. So its medical applications are limited but are used for example to treat eyes
- Gamma radiation is very penetrating and is used in medicine. Colbalt-60 is a gamma emitting radioactive material used to treat cancers
materials can be made radioactive when their nuclei absorb extra neutrons in a nuclear reactor. When nuclear radiation passes through a material it causes ionistaiton
Item P4g: Treatment
X-rays:
- X-rays are made by firing high-speed electrons at metal targets
- They are easier to control than gamma rays
- X-rays are gamma rays have similar wavelengths
- The rate of production of energy can be controlled
When x-rays pass through the body the tissues absorb some of the ionising radiation. The amount absorbed depends on the thickness and the density of the absorbing material
Gamma Rays:
- Gamma rays are given out from the nucleus of certain radioactive materials
- Can't change the gamma radiation emitted from a particular radioactive source
- When a nucleus of an atom of a radioactive substance decays, it emits an alpha or a beta particle and loses any surplus energy by emitting gamma rays
Item P4g: Treatment
A radioactive tracer is used to investigate inside the body without surgery:
- Beta or gamma emitter with a short half life
- Drunk/eaten or injected into body
- Allowed to spread through body
- Followed on the outside by a radiation detector
A radioisotope is used to destroy a tumour in the body:
- Gamma rays focused on tumour
- Wide beam used
- Rotated around the patient with tumour at centre
- Limiting damage to non-cancerous tissue
Item P4h: Fission and fusion
How domestic electricity is generated at a nuclear power station:
- Nuclear reaction
- Producing heat
- Heating water to produce steam
- Spinning a turbine
- Driving a generator
How uranium releases energy:
- Uranium nucleus hit by neutron
- Causes nucleus to split
- energy released
- More neutrons released
Item P4h: Fission and fusion
Nuclear Fission:
Fission is the reaction in nuclear power stations with a uranium isotope
When uranium fissions, a chain reaction starts. In a nuclear power station atoms of uranium-235 are bombarded with neutrons. This causes the nucleus to split releasing energy. the extra neutrons emitted cause further uranium nuclei to split. This is described as a chain reaction and produces a large amount of energy. A nuclear bomb is an example of a chain reaction that is not controlled
In a power station the reaction must be kept under control:
- Boron control rods are placed in the reactor
- To absorb some of the neutrons
- Allowing enough neutrons to remain to keep the process operating
- Graphite moderator between the fuel rods slows down the neutrons. Slow moving neutrons are more likely to be captured by other uranium nuclei
Item P4h: Fission and fusion
Nuclear fusion releases energy:
- Fusion happens when 2 nuclei join together
- fusion produces large amounts of heat energy
- Fusion happens at extremely high temperatures
Fusion for power generation is very difficult as it requires extremely high temperatures and these high temperatures must be safely managed. So power research is carried out under international joint venture to share costs, expertise and benefits
Conditions:
- In stars, fusion happens under very high temperatures and pressures
- Fusion bombs are started with a fission reaction
- For power generation exceptionally high temps and pressures would be needed
Cold fusion is not accepted as a realistic method of energy production as any results are impossible to verify
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