Presentation on theme: "Radiation True or False?"— Presentation transcript:
1Radiation True or False? You are being bombarded with radiation right now.You are giving off radiation right nowYour breakfast was irradiated with deadly radiationYou can see radioactivityYou can feel radioactivityRadioactive substances are only harmful if you touch themIf you are irradiated then you become radioactiveRadioactivity is not very usefulWe completely understand what causes radioactivityDo you know the three types of radioactivity. Write them down..TrueTrueTrue ??FalseFalseFalseFalseFalseFalse?
2PM S5 K1: Distinguish between stable and radioactive isotopes and describe the conditions under which the nucleus is unstable.
3? Alpha radiation - Helium nuclei Description: 2 neutrons, 2 protons (helium nuclei)Electric Charge:+2Relative Atomic Mass:4Penetration power:Stopped by paper or a few cm of airIonisation effect:Strongly ionisingEffects of Magnetic/Electric Field:Weakly deflectedHelium nuclei?
4Beta radiation - high energy electron Description: Electric Charge:-1Relative Atomic Mass:1/1860thPenetration power:Stopped by few mm of aluminiumIonisation effect:Weakly ionisingEffects of Magnetic/Electric Field:Strongly deflectedhigh energy electron
5Gamma radiation - Electromagnetic radiation Description: High energy electromagnetic radiationElectric Charge:Relative Atomic Mass:Penetration power:Reduced by several cms of lead or several metres of concreteIonisation effect:Very weakly ionisingEffects of Magnetic/Electric Field:NO deflectionElectromagnetic radiation
6Let’s have a look at some radioisotopes. Think about how we may be able to use them!
7The penetration power of the three types of radiation. Skin or paperstops ALPHAThin aluminiumstops BETAThick leadreduces GAMMAThin mica
8So what exactly does cause this radiation? . First we need to look at the structure of the atom
10How did you go? 6 protons 6 neutrons 6 electrons 6 protons 7 neutrons
11What do we call these? 6 protons 6 neutrons 6 electrons 6 protons
12IsotopesAtoms of the same element with different numbers of neutrons
13Isotopes Atoms of the same element with different numbers of neutrons Because they have the same number of electrons there is NO difference to their chemical behaviour.
14Stable and unstable Isotopes There are over 2000 different isotopes that have been discovered so far.Only 279 are stable – they do not emit radiation.The rest are unstable and are called radioisotopesThe nuclei rearrange to become more stable.As they do so they emit radiation.But which ones are unstable?Lets have a look at some of these isotopes.
15Stable and unstable Isotopes So why are some nuclei unstable?Some nuclei are unstable because of the proton to neutron ratio.For light elements, stable nuclei have a proton:neutron ration close to 1:1.For heavy elements the stable nuclei have a proton:neutro ratio close to 1:1.5
18Thickness Control Mill If not enough radioactivity is detected then the rollers compress to make the material thinner.This method is used in the manufacture of lots of sheet materials: plastics, paper, sheet steel.A radioactive source is on one side of the material and a detector on the other.If too much radioactivity is getting through, then the material is too thin and the rollers open up a bit to make the material thicker.Beta SourcedetectorHydraulicramElectronic instructions to adjust rollers.
19Leak detection in pipes The radioactive isotope is injected into the pipe. Then the outside of the pipe is checked with a Geiger-Muller detector, to find areas of high radioactivity. These are the points where the pipe is leaking. This is useful for underground pipes that are hard to get near.GM tubeThe isotope must have a short half life so the material does not become a long term problem.The radioactive isotope must be a gamma emitter so that it can be detected through the metal and the earth where the pipe leaks. Alpha and beta rays would be blocked by the metal and the earth.
20Cobalt-60 Sterilisation Gamma rays are used to kill bacteria, mould and insects in ood. Also used to kill bacteria on hospital equipment.This is useful particularly on packaged food or on plastic items which would be damaged by heat sterilisation.It can affect the taste and the vitamin content, but it lengthens the shelf life.Gamma Sourceunsterilisedsterilised
21Sterilisation Gamma Source unsterilised sterilised Cobalt-60 is used as it is a gamma emitter – very penetrating.It has a half life of 5.3 years so the machines can run cheaply without regular maintenance.You don’t need external power to produce the gamma rays as you do with x-raysCobalt-60 is held in a chemically inert form in a sealed container.When the cobalt-60 is exhausted it can easily be replaced.Gamma Sourceunsterilisedsterilised
22Radioactive half-life The average time taken for half of the substance to decay is called the radioactive half-life.
23What is the half life of Carbon-15? Radioactive half-lifeWhat is the half life of Carbon-15?
24PM S5 K5 – Identify one use of a named radioisotope: in industryIn medicinePM S5 K6 – Describe the way in which the above named industrial and medical isotopes are used and explain their use in terms of their chemical properties.(This is your homework – ask for a handout!Include something about half life in your answers.)Start by reading pCobalt-60 and Technetium 99 are easy to research but it is entirely up to you.
25Think about this!What happens if radiation is incident upon a living cell?Radiation can ionise cells which causes cellular damage.If the exposure is high, it can kill the cell.If the exposure is lower it can cause cancer.The higher the exposure, the higher the risk of cancer.
26PM S5 P6 – Use available evidence to analyse benefits and problems with the use of radioactive isotopes in industries and medicineRead p98 and from what you have learnt today make a list of benefits.Read p 101 and from what you have learnt today make a list of problems.
27Sensitive monitoring of inductrial processes PM S5 P6 – Use available evidence to analyse benefits and problems with the use of radioactive isotopes in identified industries and machines.Benefits:Non-invasive diagnostic proceduresTreatement of cancersSensitive monitoring of inductrial processesSterilisationNon-invasive examination of pipes / aircraft etc.Problems:Tissue damage for people exposedRisk of cancer if exposedGenetic damages to people exposedHard to dispose of some isotopes (long half-life)