Slides summarising work covered in unit4 of the Intermediate2 Physics course

1. In unit 4 we will learn about energy from the nucleus and its applications. *

2. What do you know? How do we get energy from the nucleus? What do we mean by energy? What do we mean by nucleus? What do we use it for? What do we know? *

3. Ionising Radiations are used in many medical applications including X-rays and sterilising hospital equipment. They are also used in many non medical applications and it is important in many fields of work to understand radiation dose and safety. Nuclear reactors are used in the production of around 11% of the world’s energy production, and to power some military ships and submarines.

7. Baggage scanning

8. Smoke Detectors Smoke alarms contain a weak source made of Americium-241. Alpha particles are emitted from here, which ionise the air, so that the air conducts electricity and a small current flows. If smoke enters the alarm, this absorbs the alpha particles, the current reduces, and the alarm sounds. Am-241 has a half-life of 460 years.

9. Radioactive Dating Animals and plants have a known proportion of Carbon-14 (a radioisotope of Carbon) in their tissues. When they die they stop taking Carbon in, then the amount of Carbon-14 goes down at a known rate (Carbon-14 has a half-life of 5700 years). The age of the ancient organic materials can be found by measuring the amount of Carbon-14 that is left.

10. Leaking Pipes Radioactivity is used in industry to detect leaks in pipes.

11. To have a good understanding of radioactivity we need to know a bit about the structure of the atom

12. What do atoms look like? They are very small! Atoms are the smallest possible particles of the elements which make up everything around us

13. Structure of the atom nucleus proton neutron electrons

14. Structure of the atom nucleus proton neutron electrons

15. The relative masses and charges of these particles are given below 1/ 2000 1 1 MASS -1 Electron 0 Neutron +1 Proton CHARGE PARTICLE

17. The atoms of a particular element are identical: All carbon atoms have 6 protons in the nucleus and 6 orbiting electrons. *

21. Atoms contain protons , which are positive as well as electrons , which are negative

22. Normally atoms have equal numbers of protons and electrons and are therefore neutral

27. The picture below shows an ALPHA PARTICLE, consisting of 2 protons and 2 neutrons

28. Imagine that an ALPHA PARTICLE passes through a neutral atom – this will be shown in slow motion! electron

29. An electron has been knocked out of the atom. This atom is now positively charged – it is a POSITIVE ION.

32. The alpha particle that is emitted has a lot of energy and can damage human cells. A big atom releases an alpha particle to make itself more stable. *

34. Summary * An alpha particle is made up of two protons and two neutrons. It is the largest of the three ionising radiations. It has a lot of energy. What are alpha particles?

37. This is what happens inside the nucleus. *

38. Summary * A beta particle is a fast moving, high energy electron. The electron is released from the nucleus when a neutron changes into a proton plus electron. It is very very small. What are beta particles?

40. Gamma ray It is the most energetic of all three radiations. It is therefore the most penetrating – the most difficult to stop. *

41. * Gamma rays are high energy electromagnetic waves. They travel at the speed of light. What are gamma rays?

45. ALPHA PARTICLES are relatively large and cause a lot of ionisation + + + + + + + + + + + + - - - - - - - - - - - -

46. BETA PARTICLES are smaller, so they cause less ionisation + + + + - - - -

47. GAMMA RAYS cause least ionisation of all + -

52. Several cm of lead What material is sufficient to absorb gamma rays? A few millimetres of aluminium What material is sufficient to absorb beta particles? Paper What material is sufficient to absorb alpha particles?

53. The least. Gamma particles are most dangerous when outside the body because they can easily travel into the body. But they’re least dangerous when inside because they can escape. How much ionisation do gamma particles cause? Medium. Less than alpha, more than gamma. How much ionisation do beta particles cause? The greatest amount. Alpha particles are most dangerous when inside the body (but least dangerous outside – they can be stopped with paper!) How much ionisation do alpha particles cause?

55. Quick Recap Uncharged. Absorbed by lead. Charge and absorption A few m α Range in air What is this radiation? Symbol Type of radiation

59. Geiger Muller Tube The tube is filled with argon gas. Where else is argon gas used?

60. Geiger Muller Tube Around 400 V is applied to the thin wire.

61. Geiger Muller Tube The thin window alllows radiation to enter. Radiation causes ionisation of the gas – what do we mean by this?

62. Geiger Muller Tube Ions produce electrical pulses which are counted and displayed.

63. Geiger Muller Tube We can either display total counts and use a timer to determine counts per second, or use a rate meter, which displays counts per second.

64. Geiger Muller Tube Radiation Ionisation in tube (lots of electrons) Discharges central wire Counted as a pulse *

65. How the Geiger Muller tube works

69. Photographic Fogging Why are there different materials in the film badge?

70. Photographic Fogging Different radiations pass through or are absorbed by different materials. *

72. Alexander Litvinenko Poisoned using extremely rare radioactive substance Polonium-210 – which is 250000 more toxic than hydrogen cyanide. Swallowing a dose less than 1/10 th the size of a Smartie is lethal for a grown adult male.

76. The gamma camera

80. This scan is produced after a few hours of the patient being injected with an isotope that emits gamma radiation. A detector is moved around the body and a computer produces an image. Dark areas show high concentrations of radiation coming from those parts. This indicates increased blood flow to these parts. Tumour fast growing hence increased blood supply

81. If a radioisotope that emits alpha radiation is used, no particles can be detected outside the body – why not? Alpha radiation will be stopped within a few centimetres. Internal organs will be seriously damaged.

82. Isotopes that emit gamma radiation must be used – why? Since gamma rays will pass through the body (and out) while doing the least damage.

98. Activity Activity (Bq) Number of nuclei decaying Time (s)

101. Dosimetry: Absorbed Dose Absorbed dose – units? Energy (J) Mass (kg)

102. Dosimetry ABSORBED DOSE (D) is the energy absorbed PER UNIT MASS of absorbing tissue. 1 Gy = 1 J/kg Units are GRAYS (Gy)

103. Dosimetry 60.0 Typical dose to a tumour over a six week period 5.0 Dose which if given to whole body in a short period would prove fatal in half the cases 3.0 Gamma rays which would just produce reddening of skin 0.05 CT Scan 0.00015 Chest X-ray Absorbed dose (Gy) Radiation Treatment

105. EQUIVALENT DOSE (H) is a quantity which takes into account the TYPE OF RADIATION. Unit of equivalent dose is sieverts (Sv) W R is the WEIGHTING FACTOR of the particular radiation

106. Typical Equivalent Dose 15.0 Astronaut in space for one month 2.0 Renogram 2.0 Annual exposure of aircraft crew 2.0 Bone Scan 1 to 3.5 CT Scan 4.0 Stomach X-ray 2.0 Spine X-ray 0.1 Chest X-ray Equivalent dose (mSv) Investigation

107. How much is a sievert (Sv)? If 100 people received a dose of 1 Sv, 4 would die as a result. This is the type of dose you’d receive after a nuclear accident. We normally work in millisieverts (mSv = Sv ) or microsieverts ( μ Sv = Sv)

112. 1 mSv is about 100 times the radiation you experience when you travel by aircraft on holiday. If you are part of the aircrew, you will experience larger amounts due to the amount of travel. There are regulations about total flying times which take into account exposure to radiation.

113. In the UK people receive an average of 2 mSv each year from background sources (cosmic rays, radon gas etc). Members of the public – an additional 5 mSv each year Legal limits have been set on the additional dose equivalent which people can receive: Workers exposed to radioactivity - an additional 50 mSv each year

114. Background Radiation Life on Earth has evolved to cope with this. Your cells have self-repairing mechanisms which allow them to survive relatively unscathed. The amount of background radiation varies considerably around Britain, as shown on the map. You can see that it is particularly high in Cornwall, because of the types of rock there.

122. Radioactive Decay & Half Life Sketch a graph of activity against time Time (s) Activity (Bq))

124. Background Radiation If we are measuring the activity of a source we must always take off the background radiation For example: We measure background radiation at 2 counts each second. We then introduce a source and find that there are 47 counts each second. What is the radiation due to the source? Source radiation = total radiation – background radiation Source radiation = 47 – 2 = 45 counts each second.

125. Draw out this table Counts per second Continue to 250 seconds 40 30 20 10 0 Corrected count rate Time (s)

128. What makes a good graph?

129. Measuring the Half-Life of a radioactive source Read the time taken for the activity to half. You can choose any starting point. T 1 T 2 The half life is found by calculating T 2 -T 1 . Time (s) Activity (Bq))

130. Measuring the Half-Life of a radioactive source T 1 T 2 Time (s) Activity (Bq))

131. Construct a table like this: Average half-life = ……………. s 40 80 35 70 30 60 Half-life (s) T 2 (s) T 1 (s) 2 nd activity 1st activity

132. Radioactive Decay and Half Life

134. 1/32 37.5 50 1/16 75 40 1/8 150 30 ¼ 300 20 ½ 600 10 1 1200 0 Fraction of initial count rate Count rate (counts/sec) Time elapsed (mins)

139. Radiation Safety

143. Radiation Safety What safety precautions should be taken when working with radioactive sources?

150. Is nuclear power renewable or non-renewable? Strictly non-renewable because the uranium fuel is a finite resource. At the current rate of use the existing reserves will last a long time. The ‘spent’ fuel can be re-processed and used again. Nuclear Power

151. A lot of energy is produced per kilogram of uranium. - 1 kilogram of coal produces 30 million Joules 30 x 10 6 J or 30 MJ - A kilogram of uranium produces 5 million million Joules 5 x 10 12 J of energy. Nuclear Power – What are the advantages?

152. Nuclear power plants generate relatively little carbon dioxide so contribute little to global warming. Technology is readily available and well established. It is reliable. Large amount of electricity can be generated by one plant. Produces small amount of waste. Nuclear Power – What are the advantages?

153. In the UK, about 50% of energy is created from nuclear sources. In France it is about 70%. Nuclear Power – do we rely on it?

154. Nuclear power stations produce radioactive waste – which can be harmful to us and the environment. The waste must be stored safely for many years – sealed and buried. Nuclear Power – What are the disadvantages?

155. Chernobyl demonstrated the risks of this type of technology. Nuclear power is reliable, but a lot of money has to be spent on safety - if it does go wrong, a nuclear accident can be a major disaster. People are increasingly concerned about this - in the 1990s nuclear power was the fastest growing source of power in much of the world. In 2005 it was the second slowest-growing. Nuclear Power – What are the disadvantages?

156. There are 3 main types of power station: THERMAL POWER STATION NUCLEAR POWER STATION HYDROELECTRIC POWER STATION

157. Each type has the same basic plan Thermal Hydro-electric Nuclear Turbine kinetic energy Generator kinetic to electrical energy Coal is burned chemical energy to heat Water behind dam potential energy to kinetic Nuclear reaction nuclear energy to heat

160. 4. Turbines – these have hundreds of blades. The steam from the boiler hits the blades and turns the turbine. The turbine has a shaft attached to it. As the turbine turns so does the shaft. The shaft from the turbine is connected to the generator.

162. 5. Generator

163. 5. Generator – the generator is made up of large electromagnet and coils of wire. The electromagnet is attached to the shaft from the turbine and turns inside the wire coils. As the electromagnet turns an electrical current is produced in the coil of wire.

165. 6. Transformer

166. 6. Transformer – the transformer increases the voltage of the electricity from 20 000 V to 275 000 V. This allows the electricity to be transported efficiently through the electrical transmission system.

167. 7. Cooling Tower – after the steam has turned the turbine it is piped to the condenser. Cold water is pumped from the cooling towers where it is used to cool the steam. After circulating round the condenser the cooling water which is now about 10 ºC warmer, flows back to the cooling tower. The water is cooled by air and then falls back down to the bottom of the cooling tower to be recycled through the condenser (8) again. Some of the heat from the water is released into the air in the form of water vapour which you can see coming out of the top of the tower.

168. 7. Cooling Tower – after the steam has turned the turbine it is piped to the condenser . Cold water is pumped from the cooling towers where it is used to cool the steam. After circulating round the condenser the cooling water which is now about 10 ºC warmer, flows back to the cooling tower. The water is cooled by air and then falls back down to the bottom of the cooling tower to be recycled through the condenser (8) again. Some of the heat from the water is released into the air in the form of water vapour which you can see coming out of the top of the tower.

171. A Conventional (Fossil Fuel) Power Station Energy Changes

173. Energy Efficiency Why is the useful energy out always less than the total energy input? Units?

174. Efficiency It can be useful to consider the energy each second rather than total energy. What would the equation be for efficiency using energy each second?

175. Efficiency (as a percentage) The efficiency of a power station (or any machine) tells us how much of the input energy is converted to useful output energy. Energy that is LOST has been converted to less useful forms such as heat.

176. Efficiency

177. Fuel Consumption To determine the amount of fuel required: Note that power is energy each second so for a given power output we can find the fuel needed each second.

178. Like fossil fuels, uranium is mined. A lengthy (and expensive) process is required to extract the uranium from the ore. Nuclear Power

179. Inside the Nuclear Power Station http://science.howstuffworks.com/nuclear-power2.htm

180. Inside the Nuclear Power Station In place of the boiler found in a conventional power station, there is a reactor. Heat energy produced during nuclear fission is carried by carbon dioxide gas to a heat exchanger where it heats water, turning it into steam. The steam drives a generator to produce electrical energy. The steam is cooled (turned back into water) and pumped round for reuse.

184. A Chain Reaction

185. A Chain Reaction The 2 neutrons released during the nuclear fission can go on to bombard further uranium nucleii which causes further nuclear fission releasing even more neutrons which can in turn go on to produce more fission An uncontrolled chain reaction is used in a nuclear bomb In a nuclear power station the rate of reaction is controlled using boron control rods which can be lowered into the reactor and absorb the neutrons that induce the fission process.

187. The Graphite Moderator When the neutrons are emitted after fission they are moving very fast. They will not be able to be “captured” by other nuclei so fission will not occur. If they are slowed down there is a greater chance that fission will occur. This is done using a graphite moderator – collisions with graphite atoms slow the neutrons down.

189. The Control Rods The amount of electrical power required will vary with peak demand during the day and lower demand at night. Rods of boron absorb additional neutrons and control the number available for fission. They can be raised and lowered as necessary, and provide an important safety feature. In the event of an accident, all rods are lowered to absorb neutrons and stop the chain reaction.

190. Coolant The heat produced during the reaction must be removed from the reactor. This is done using the coolant – normally carbon dioxide. The carbon dioxide is continually heat, then passes the heat to water via the heat exchanger. The water turns to steam, which drives the turbine.

194. Energy Changes in a Nuclear Power Station Note that in conventional fossil fuel power stations AND in nuclear power stations the energy source is used to raise steam to drive turbines to drive the electricity generator.