P4 – Radiation for life

1. P4 – Radiation for life NB This is not yet in its final form. Some material may be in duplicate.

2. Insulating materials can become charged when rubbed with another insulating material. • What are the two kinds of charge? • When some materials are rubbed they attract other objects: • small pieces of paper or cork to a rubbed comb or strip of plastic; • certain types of dusting brushes become charged and attract dust as they pass over it.

3. How is it possible to get an electrostatic shock from charged objects, such as synthetic clothing? • People can get electrostatic shock if they become charged and then become earthed, • such as when they walk over thick carpet and touch a metal door handle • touching water pipes after walking a floor covered with an insulating material e.g. vinyl. • Static electricity can be described in terms of the electrons: • positive charge is due to? • negative charge is due to?. • Like charges _________________and unlike charges ________________.

4. Electrostatic phenomena are caused by the transfer of electrons. • Static electricity can be dangerous when: • in atmospheres where explosions could occur e.g. inflammable gases or vapoursor with high concentrations of oxygen; • in situations where large quantities of charge could flow through the body to earth. • Static electricity can be a nuisance: • dirt and dust attracted to insulators (plastic containers, TV monitors etc); • causing clothing to “cling”.

5. The chance of receiving an electric shock can be reduced by: • correct earthing; • use of insulating mats; • using shoes with insulating soles. • Why is it necessary to earth lorries containing inflammable gases and liquids and powders before unloading? • How can anti-static sprays, liquids and cloths help reduce the problems of static electricity?

6. Static electricity can be useful: • restarting a heart when it has stopped (defibrillator); • photocopiers/laser printers; • removing dust from smoke in chimneys; • paint spraying. Electrostatic dust precipitator

7. Defibrillator • paddles charged; • good electrical contact with patient’s chest; • charge passed through patient to make heart contract; • care taken not to shock operator. • Electrostatic dust precipitators to remove smoke particles etc from chimneys: • metal plates/grids put into chimneys; • connected to a high PD • dust particles attracted to plate/grid; • dust attracts together to form larger particles; • dust falls back down chimney when particles are heavy enough. • Paint spraying: • spray gun charged; • paint particles charged; • repel giving fine spray; • object charged oppositely to paint; • attracts paint; • even coat, less waste, shadows painted.

8. Uses of Electrostatics • Defibrillators – restarts a heart • Paint Spraying • Dust Precipitators • Photocopiers & Laser Printers 4 uses

9. 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.

10. 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

11. What is required for a circuit to work? • An earthed conductor cannot become live – why? • What is a resistors, and what can it be used for? • Plug wiring • live – ____________; • neutral – _____________; • earth – ____________________. • A circuit breaker is a fuse that can be reset – why is this more useful than a normal fuse? • Objects and appliances that are “double insulated” do not need earthing – why?

13. What is a variable resistor? • What is the equation that links current, potential difference (pd) and resistance? • For a given resistor, current increases as pd increases and vice versa; for a fixed pd, current decreases as resistance increases and vice versa. • Functions of the live, neutral and earth wires • live – carries the high voltage; • neutral – the second wire to complete the circuit; • earth – a safety wire to stop the appliance becoming live.

14. The unit of resistance is the Ohm, Ω. Resistance, current and voltage (potential difference) are related by this equation: • resistance (Ω ) = voltage (V) / current (A) • Example: • Question What is the resistance of a bulb that has 0.4A of current flowing through it when a potential difference of 2V is put across it? • voltage = current x resistance • current = voltage / resistance • Example • Question What potential difference causes a current of 3A to flow through an 80Ω resistor?

15. How does a wire fuse work? • A wire fuse reduces the risk of fire if the appliance develops a fault: • too large a current causes the fuse melt; • preventing flow of current; • prevents flex overheating and causing fire • prevents further damage to appliance.

16. 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 +!)

17. A V A Circuit to measure resistance A variable resistor varies the current in the circuit Resistance = Potential difference ÷ Current R = V ÷ I The component which is having its resistance measured An ammeter measures Current in Amps A voltmeter measures Potential Difference in Volts

18. Ohm’s Law Cover up what you want to find V ÷ ÷ • “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 Ω. • So R = V ÷ I, also V = I x R and I = V ÷ R R x I

19. Fuses come in various values; 2A,3A,5A,13A. A 13Amp fuse blows when current through it exceeds 13Amps Mains Electricity • Live (brown) brings supply to house • Neutral (blue) isreturn 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.

20. Ultrasound is a longitudinal wave, what is the other type of wave called? • Define the following words: • amplitude; • wavelength; • frequency; • compression; • rarefaction. • Ultrasound can be used in medicine: • to look inside people by scanning the body; • to break down kidney and other stones; • to measure the speed of blood flow in the body.

22. The frequency of ultrasound is higher than the upper threshold of • human hearing. • What is the motion of particles in longitudinal and transverse waves? • In body scans ultrasound works by comparing the reflections from different layers • Ultrasound is used instead of x-rays • able to produce images of soft tissue; • does not damage living cells.

23. Ultrasound - sound waves beyond the human hearing range • Range of human hearing is 20 – 20,000Hzso 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.

24. 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

25. Nuclear radiation is used in medicine. See http://www.youtube.com/watch?gl=GB&v=7_24jzgLCpw • X-rays and gamma rays are electromagnetic waves. • Nuclear radiation can damage cells. • Gamma rays are used to treat cancer. • Nuclear radiation is used to sterilize hospital equipment. • The person in hospitals who takes x-rays and uses radiation is a?

26. Only beta and gamma radiation can pass through skin. • gamma rays are given out from the nucleus of certain radioactive materials; • X-rays are made by firing high speed electrons at metal targets; • X-rays are easier to control than gamma rays. • Beta or gamma emitters are used as tracers in the body. • Radioactive sources are used in medicine to treat cancer: • gamma rays focused on tumour; • wide beam used; • rotated round the patient with tumourat centre; • limiting damage to non-cancerous tissue.

28. Radioactive sources are used as tracers: • beta or gamma emitter; • drunk/eaten/ingested/injected into the body; • allowed to spread through the body; • followed on the outside by a radiation detector. • X-rays and gamma rays have similar wavelengths, but are produced in different ways • Radioactivity of an object is measured by the number of nuclear decays emitted per second. • Radioactivity decreases with time.

29. Radiation comes from the? • Radioactive substances decay naturally and giving out nuclear radiation in the form of alpha, beta and gamma. • Radioactivity as comes from the nucleus of an atom that is unstable. • An alpha particle is a helium nucleus, whilst a beta particle is a fast moving electron. • What is half-life?

31. When an alpha particle is emitted the following happens to a nucleus • mass number decreases by 4; • nucleus has two less neutrons; • nucleus has two less protons; • atomic number decreases by 2; • new element formed. • When a beta particle is emitted the following happens to the nucleus • nucleus has one less neutron; • nucleus has one more proton; • atomic number increases by one. • Simple equations can be constructed in terms of mass numbers and atomic numbers to represent alpha and beta decay.

33. There is background radiation in the environment which is always present. • Where does this background radiation come from? • Alpha sources are used in some smoke detectors.

34. Uses of tracers: • to track dispersal of waste; • to find leaks/blockages in underground pipes; • to find the route of underground pipes. • To find leaks in underground pipes • radioactive material put into pipe; • gamma source used so that it can penetrate to the surface; • progress tracked with detector above ground; • leak/blockage shown by reduces/no radioactivity after this point.

35. How does a smoke detector with an alpha source work? • Radioactivity can be used to date rocks (using uranium) • And old material (that contains carbon) • The measurements of the activity of radioactive carbon can lead to an approximate age for different materials: • the amount of Carbon 14 in the air has not changed for thousands of years; • when an object dies (e.g. wood) gaseous exchange with the air stops; • as the Carbon 14 in the wood decays the activity of the sample decreases; • the ratio of current activity from living matter to the activity of the sample leads to a reasonably accurate date.

37. What is the fuel in a nuclear power station? • What are the main stages in the production of electricity: • source of __________; • used to produce ___________; • used to produce electricity. • The decay of uranium can be a chain reaction. • Anuclear bomb is a chain reaction that has gone out of control. • How can materials be made radioactive?

38. Domestic electricity generated at a nuclear power station: • nuclear reaction; • producing heat; • producing steam; • turning a turbine; • turning a generator. • To allow uranium to release energy: • uranium nucleus hit by neutron; • causes nucleus to split; • energy released. • What is nuclear fission?

40. Nuclear fission produces radioactive waste, materials become radioactive when they absorb extra neutrons. • Chain reaction: • when each uranium nucleus splits more than one neutron is given out; • these neutrons can cause further uranium nuclei to split. • Scientists stop nuclear reactions going out of control: • rods placed in the reactor; • to absorb some of the neutrons; • allowing enough neutrons to remain to keep the process operating.

41. Radiotherapy and Diagnosis • 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 γ rays • Gamma rays γ • High frequency/energy electromagnetic wavesemitted 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

42. 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 don’t swallow any – remember Mr Litvinienko? – killed with Polonium 210, an alpha emitter!

43. 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

44. 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 (α), Beta (β) and Gamma (γ) 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).

45. 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

46. 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 α 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 2α + 90Th 238 4 234

47. Beta Decay-1β 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 β- is emitted, A does not change Z increases by 1 (because it has an extra proton). 6C -1β + 7N • A new element is formed that is one place higher in the periodic table than the original radioisotope. 14 0 14

48. 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%).

49. 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

50. Nuclear Fission • U235can 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!!!