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Ionising Radiation: Risks and Applications
Martin Jones
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Environmental Radiation
1 Environmental Radiation There is radiation all around us but where does it come from? Some is manmade Some is naturally occurring Low High 51% Radon Gas 14% Ground and Buildings 14% Medical 11.5% Food 10% Cosmic Rays 0.5% Nuclear Industry Background Radiation in the UK Ionising Radiation
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Environmental Radiation
2 Environmental Radiation Naturally occurring radiation atoms may be of terrestrial or extraterrestrial origin Extraterrestrial : Cosmic radiation comes from space Cosmic radiation is passing through us all the time. It adds to the background count while also producing radioactive materials. Ionising Radiation The amount of cosmic radiation we experience increases the higher up we are
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Extraterrestrial Radiation
3 Extraterrestrial Radiation Radiation from space interacts in the Earths atmosphere Ionising Radiation The Northern Lights (Aurora borealis)
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Extraterrestrial Radiation
4 Extraterrestrial Radiation Northern Lights (Aurora borealis) as seen from space Ionising Radiation Southern Lights (Aurora australis) as captured from a NASA satellite
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Environmental Radiation
5 Environmental Radiation Naturally occurring radiation may be of terrestrial or extraterrestrial origin Terrestrial : Rocks which are primordial in origin were created during the big bang, around 14 billion years ago These rocks still exist today and are still emitting radiation e.g. Uranium, Thorium Ionising Radiation Thorium Ore g Thorium emits beta particles and gamma rays Thorium can be contained in rock b
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Radiation All Around Us
6 Radiation All Around Us The substances used in building materials contain radioactive nuclides: Wood : 40K Red Brick : 40K, 226Ra, 232Th, 238U Sand : 40K, 232Th, 238U Concrete : 40K, 226Ra, 232Th, 238U The level of radiation varies depending on where in the world they are found - Sand in some areas of India can be very radioactive A radiation survey in Germany found that radiation exposure was 33% higher indoors than outdoors Ionising Radiation
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7 Radiation in Food Radioactive materials are present in foods we eat every day - radionuclides absorbed by plants through soil Regions with high activity in soil produce foods with high activity Foods with highest amount of radiation include: - Brazil nuts - Coffee - Potatoes - Salt 226Ra is chemically similar to calcium - absorbed by bones - you are radioactive Ionising Radiation
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8 Radioactive Decay There are materials all around us that emit radiation - why are some atoms radioactive and others aren’t? Radioactivity is the spontaneous disintegration (decay) or nuclei Some atoms are said to be unstable They achieve stability by emitting radiation - alpha particles (a) - beta particles (b) - gamma rays (g) - He nuclei - Weakly penetrating - stopped by paper, air, skin… Penetration of radiation Ionising Radiation Isotope is an atom with a different number of neutrons Alpha is a He nucleus (2 protons and 2 neutrons) - Fast moving electrons - Moderately penetrating – stopped by aluminium - High frequency EM waves - Highly penetrating
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Radioactive Decay particle Electron Ionising Radiation
9 Radioactive Decay Ionising Radiation When radiation collides with neutral atoms or molecules it alters their structure by knocking off electrons. This will leave behind IONS – this is called IONISING RADIATION. particle Ionising Radiation Isotope is an atom with a different number of neutrons Alpha is a He nucleus (2 protons and 2 neutrons) Electron
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Radioactive Decay = radioactive = stable
10 Radioactive Decay Each time a radioactive decay occurs one radioactive nucleus disappears The Half-Life The HALF-LIFE of an atom is the time taken for half of the radioactive nuclei in the sample to decay = radioactive = stable Ionising Radiation If the amount of radiation keeps halving it will never go to zero At start there are 16 radioisotopes After 1 half life half have decayed. There are 8 remaining After 2 half lives another half have decayed. There are 4 remaining After 3 half lives another 2 have decayed. There are 2 remanining
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Half-Life How can we work out the half-life of a radioisotope?
11 Half-Life How can we work out the half-life of a radioisotope? We can plot a graph of activity against time 2 Half-Lives 1 Half-Life Ionising Radiation
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12 Half-Life Question: Uranium decays into lead. The half life of uranium is 4,000,000,000 years. A sample of radioactive rock contains 7 times as much lead as it does uranium. Calculate the age of the sample. Answer: The sample was originally completely uranium… 1 half life later… 1 half life later… 1 half life later… 8 4 8 2 8 1 8 Ionising Radiation …of the sample was uranium Uranium half life 4.5x10^9 years Pu241 died out – half life =14 years Now only 4/8 of the uranium remains – the other 4/8 is lead Now only 2/8 of uranium remains – the other 6/8 is lead Now only 1/8 of uranium remains – the other 7/8 is lead So it must have taken 3 half lives for the sample to decay until only 1/8 remained (which means that there is 7 times as much lead). Each half life is 4,000,000,000 years so the sample is 12,000,000,000 years old.
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Radioactive dating can be used to estimate the age of fossils
13 Radioactive Dating We have seen how radioactive decay can be used for dating. A common example is Carbon dating - living organisms contain radioactive 14C (created by cosmic radiation) - when they die, they stop absorbing 14C and it decays away - 14C decays with a known half-life of 5600 years By measuring how much 14C has decayed scientists can work out how long ago something died Ionising Radiation Radioactive dating can be used to estimate the age of fossils
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Ionising Radiation : Summary
14 Ionising Radiation : Summary There is radiation all around us it is in the environment, our food and even in our bodies some of it is manmade, most of it is natural some radiation comes from space some radiation comes from rocks all around us the level of background radiation varies with altitude Some atoms emit radiation to achieve stability - ionising radiation strips electrons from material it interacts in - this is ionisation Ionising Radiation Radioactive atoms decay with a fixed half life calculating this half life can help us identify the material we can use this half life for dating
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Dangers and Applications
15 Dangers and Applications Ionising radiation is widely used in a range of applications It can be destructive - Nuclear weapons It can cause illness or death It can be used to help people - We can diagnose disease using radiation - medical imaging - We can treat illnesses using radiation - radiotherapy It allows us to watch TV, turn on lights etc - 20% of our electricity is provided by nuclear power Nuclear Bombs Ionising Radiation In order to use radiation we must be very aware of the dangers! Nuclear Power
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16 Biological Effects Outside the body, gamma radiation is the most dangerous Inside the body, alpha particles are the most dangerous What happens inside your body? Radiation interacting in water produces Hydrogen peroxide (H2O2) - this makes you sick! Radiation causes ionisation inside the body damaging cells - this can damage bodily functions Radiation damages DNA breaking bonds - this kills cells - this can lead to genetic mutations - this can cause cancer (long term) DNA molecule Ionising Radiation There are both short term and long term effects of radiation exposure. The severity of the effects can depend on the amount of radiation, the type of radiation and whether it is internal or external
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External Effects 17 Hydrogen peroxide production in the eye
Radiation Burns Hair Loss Ionising Radiation Mutation
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Radiation Poisoning Alexander Litvinenko
18 Radiation Poisoning Alexander Litvinenko Russian spy Alexander Litvinenko poisoned by ingestion of 210Po 210Po is naturally occurring and around 1million times more poisonous than cyanide Initial effects may have included - nausea, vomiting, fatigue, bleeding gums, hair loss Symptoms of radiation sickness – production of Hydrogen peroxide in body Then…… - gastro-intestinal failure - destruction of red bone marrow - immune system fails - shutdown of central nervous system - multiple organ failure - death (within a month of ingestion) Resulting from alpha particles interacting within the body - DNA damage Ionising Radiation Potential antidote -
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19 Radiation Hormesis It might not all be bad news……can radiation be good for you? There are some studies which suggest that a little bit of radiation might actually be good for you! Animals exposed to inhalation of uranium dust lived longer and had more offspring than non-contaminated animals Death from Leukaemia in Hiroshima survivors Ionising Radiation Small doses of radiation seem to reduce the risk of death!! Seems strange but it MIGHT be true
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The black box contains a 241Am source– this emits alpha particles
20 Applications The Smoke Detector Smoke detectors operate using ionising radiation They contain an alpha emitting radionuclide A detector constantly measures the number of alpha particles reaching it The black box contains a 241Am source– this emits alpha particles Smoke Detector a Ionising Radiation a
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Applications Radiation Therapy spine lung tumour heart
21 Applications Radiation Therapy Radiotherapy treats cancer – destroying tumours through the use of radiation - typically, high energy X-rays are used The X-rays kill tumour cells by destroying their DNA Breaks in the DNA can stop the tumour cells multiplying However, this can also lead to the damage of healthy tissue surrounding the tumour spine lung tumour heart Ionising Radiation
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Applications Radiation Therapy spine lung tumour heart
22 Applications Radiation Therapy The radiation may be delivered from several angles to maximise damage to the tumour and minimise damage to surrounding tissue Dose is at a maximum at tumour location Dose ‘evenly’ distributed throughout healthy tissue spine lung tumour heart Ionising Radiation
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Applications Medical Imaging
23 Applications Medical Imaging Basically, letting doctors see inside the human body without cutting people open! Ionising Radiation Patients injected with Radioactive substance CT image – X-rays shone onto patient
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Applications tumours Reduced brain activity due to Alzheimer’s disease
24 Applications Reduced brain activity due to Alzheimer’s disease Cancerous tumours in the upper body tumours Ionising Radiation
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Summary : Effects and Uses
25 Summary : Effects and Uses Radiation can be dangerous - it can be cause sickness and death - it can cause ionisation inside the body and DNA damage - alpha particles are the most dangerous inside the body - gamma rays are the most dangerous outside the body Radiation can be used for……… - saving people from fires - smoke detectors - diagnosing disease – medical imaging - destroying cancer - radiotherapy Ionising Radiation
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26 Radiation Monitoring Q. We can’t see, hear, smell or taste radiation, so how can we tell if it is around us? Q. How do we know if someone is in danger from it? We need some way of detecting it and working out how much there is - count rate We know radiation interacts with matter - causes ionisation We can use these interactions to aid detection - allow radiation to interact in some kind of material - observe the effects Ionising Radiation
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Radiation Monitoring The Discovery of Radiation
27 Radiation Monitoring The Discovery of Radiation In 1896 Antoine Henri Becquerel discovered radioactivity He left photographic film in a drawer next to some rocks The next day the film had been exposed – film looked “foggy” The rocks contained uranium The photographic film is a very simple radiation detector/monitor Ionising Radiation When radiation hits the film it becomes fogged A radioactive leaf – the tree was in radioactive soil Worlds first x-ray image – Prof. Wilhelm Roentgen, 1895
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Film badge for radiation monitoring
28 Radiation Monitoring Film Badges Film badges are used to monitor the radiation dose workers in the nuclear industry receive - Radiographers - Dentists - Pilots (recently) The film is checked on a regular basis Film badge for radiation monitoring Ionising Radiation The radiation dose the person wearing it received is calculated How do we know if the radiation was beta or gamma? Q
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What kind of radiation has this badge been exposed to?
29 Radiation Monitoring Film Badges beta and gamma radiation have different penetrating power The badge may contain “filters” Filters may stop beta radiation but let gamma radiation through Top part of film affected by radiation Bottom part of film NOT affected by radiation Ionising Radiation What kind of radiation has this badge been exposed to? Q Beta Radiation A
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Radiation Monitoring Geiger Counters
30 Radiation Monitoring Geiger Counters A Geiger counter uses a Geiger-Müller tube and some kind of counter The Geiger-Muller tube is full of gas This gas becomes ionised when radiation hits it - very good for detecting alpha particles The counter counts how many times this happens per minute (or second) Argon filled tube The spark in the gas can be amplified and sent through a speaker to give the “clicking” sound Ionising Radiation A Geiger-Muller tube +ve voltage on wire
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These type of radiation detectors are used in hospital scanners
31 Radiation Monitoring Scintillation When radiation hits certain materials they produce flashes of light This is known as scintillation or fluorescence These materials can be used as radiation detectors The amount of light given off is measured These type of radiation detectors are used in hospital scanners Ionising Radiation A scintillation crystal
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Radiation Monitoring Aiport X-ray scanning systems
The current systems use X-ray scanning machines These detectors are currently the best available Unfortunately, not all the information we need is there Can see dense areas but not exact information on what exists New developments in detection systems Ionising Radiation
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32 Summary : Monitoring Radiation monitoring is important in order to protect people against harmful effects We can use the ionising nature of radiation to help us detect it We can use film badges - photographic film fogs (darkens) when radiation hits it - calculate dose of radiation someone has received - filters can be used to distinguish between beta and gamma We can also use - Geiger counters - scintillation detectors Ionising Radiation
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