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Detection of Ionising Radiation

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					Ionising Radiation: Risks and
        Applications




                     Martin Jones

               Email: mj@ns.ph.liv.ac.uk
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                                   Environmental Radiation
                         There is radiation all around us but where does it come from?
                                 Some is manmade
                                 Some is naturally occurring


                           Background Radiation in the UK

                                        14% Ground and Buildings
                     51% Radon                                                           Low
                        Gas
                                                     14% Medical


                                                        0.5% Nuclear Industry
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                                                      10% Cosmic Rays
                                                                                         High



                                              11.5% Food
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                                 Environmental Radiation
                     o Naturally occurring radiation atoms may be of terrestrial or
                     extraterrestrial origin


                     Extraterrestrial : Cosmic radiation comes from space


                     o Cosmic radiation is passing through us all the time. It adds to the background
                     count while also producing radioactive materials.




                       The amount of cosmic radiation we
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                      experience increases the higher up we
                                       are
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                                Extraterrestrial Radiation
                     Radiation from space interacts in the Earths atmosphere
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                                                                 The Northern Lights (Aurora borealis)
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                                  Extraterrestrial Radiation




                     Northern Lights (Aurora borealis) as seen
                                   from space
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                          Southern Lights (Aurora australis) as
                             captured from a NASA satellite
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                                  Environmental Radiation
                     o 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


                     o These rocks still exist today and are still emitting radiation
                              e.g. Uranium, Thorium

                                                                                         Thorium Ore
                                                                             g

                       o Thorium emits beta particles and
                                 gamma rays
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                                                                                               b
                       o Thorium can be contained in rock
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                                  Radiation All Around Us
                     o 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




                     o The level of radiation varies depending on where in the world they are found
                              - Sand in some areas of India can be very radioactive
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                     o A radiation survey in Germany found that radiation exposure was 33% higher
                     indoors than outdoors
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                                                 Radiation in Food
                     o Radioactive materials are present in foods we eat every day
                                 - radionuclides absorbed by plants through soil

                     o Regions with high activity in soil produce foods with high activity


                     o Foods with highest amount of radiation include:
                                 - Brazil nuts
                                 - Coffee
                                 - Potatoes
                                 - Salt

                     o   226Ra   is chemically similar to calcium
                                 - absorbed by bones
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                                 - you are radioactive
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                                       Radioactive Decay
                     There are materials all around us that emit radiation
                              - why are some atoms radioactive and others aren‟t?


                      o Radioactivity is the spontaneous disintegration (decay) or nuclei
                      o Some atoms are said to be unstable
                      o They achieve stability by emitting radiation
                      - alpha particles (a)
                         - He nuclei
                         - Weakly penetrating - stopped by paper, air, skin…

                      - beta particles (b)
                         - Fast moving electrons
                         - Moderately penetrating – stopped by aluminium
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                      - gamma rays (g)
                         - High frequency EM waves
                         - Highly penetrating                                  Penetration of radiation
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                                       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.




                                                                                        a particle
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                                                    Electron
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                                          Radioactive Decay
                       o 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




                     At start there are    After 1 half life half    After 2 half lives    After 3 half lives
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                      16 radioisotopes        have decayed.          another half have      another 2 have
                                               There are 8          decayed. There are    decayed. There are
                                                remaining               4 remaining          2 remanining
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                                                 Half-Life
                     o How can we work out the half-life of a radioisotope?

                                 We can plot a graph of activity against time




                                        1 Half-Life



                                              2 Half-Lives
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                                                    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            1 half life               1 half life
                             later…                 later…                    later…

                       8                       4                        2                          1

                       8                       8                        8                          8

                       …of the        Now only 4/8 of the          Now only 2/8 of           Now only 1/8 of
                     sample was      uranium remains – the        uranium remains –         uranium remains –
                       uranium          other 4/8 is lead          the other 6/8 is          the other 7/8 is
                                                                         lead                      lead
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                       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
                     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
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                                              Radioactive dating can be used to
                                                 estimate the age of fossils
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                                Ionising Radiation : Summary
                     o 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


                     o Some atoms emit radiation to achieve stability

                             - ionising radiation strips electrons from material it interacts in
                             - this is ionisation
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                     o 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
                     o Ionising radiation is widely used in a range of applications
                     o It can be destructive

                              - Nuclear weapons
                     o It can cause illness or death
                     o It can be used to help people
                              - We can diagnose disease using radiation
                                                                                      Nuclear Bombs
                                        - medical imaging

                              - We can treat illnesses using radiation
                                        - radiotherapy

                     o It allows us to watch TV, turn on lights etc
                              - 20% of our electricity is provided by nuclear power
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                         In order to use radiation we must be
                              very aware of the dangers!
                                                                              Nuclear Power
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                                           Biological Effects
                      o Outside the body, gamma radiation is the most dangerous
                      o 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
                                                                                          DNA molecule
                               - 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)
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                     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
                     Hydrogen peroxide production in the eye



                                                               Radiation Burns




                     Hair Loss

                                           Mutation
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                                     Radiation Poisoning
                     Alexander Litvinenko
                     o Russian spy Alexander Litvinenko poisoned by ingestion of       210Po


                     o 210Po is naturally occurring and around 1million times more poisonous than
                     cyanide
                     o Initial effects may have included
                              - nausea, vomiting, fatigue, bleeding gums, hair loss

                     o Symptoms of radiation sickness – production of Hydrogen peroxide in body
                     o Then……
                              - gastro-intestinal failure
                              - destruction of red bone marrow - immune system fails
                              - shutdown of central nervous system
                              - multiple organ failure
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                              - death (within a month of ingestion)

                     o Resulting from alpha particles interacting within the body
                              - DNA damage
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                                     Radiation Hormesis
                     It might not all be bad news……can radiation be good for you?
                     o There are some studies which suggest that a little bit of radiation might
                     actually be good for you!
                     o Animals exposed to inhalation of uranium dust lived longer and had more
                     offspring than non-contaminated animals

                                                             Death from Leukaemia in
                                                               Hiroshima survivors




                                                                            Small doses of radiation seem
                                                                            to reduce the risk of death!!
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                                                                 Seems strange but it MIGHT be true
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                                                Applications
                     The Smoke Detector

                                                       o Smoke detectors operate using ionising radiation
                     The black box contains a
                     241Am source– this emits          o They contain an alpha emitting radionuclide
                          alpha particles              o A detector constantly measures the number of
                                                       alpha particles reaching it

                                                Smoke Detector
                                                                                    a


                                                                                        a
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                                               Applications
                      Radiation Therapy
                     o Radiotherapy treats cancer – destroying tumours through the use of radiation
                              - typically, high energy X-rays are used
                     o The X-rays kill tumour cells by destroying their DNA
                     o Breaks in the DNA can stop the tumour cells multiplying
                     o However, this can also lead to the damage of healthy tissue surrounding the tumour

                                                                         lung        heart            lung
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                                                                         tumour                  spine
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                                             Applications
                     Radiation Therapy
                     o The radiation may be delivered from several angles to maximise damage to
                     the tumour and minimise damage to surrounding tissue
                     o Dose is at a maximum at tumour location
                     o Dose „evenly‟ distributed throughout healthy tissue

                       lung          heart           lung
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                                                  spine
                       tumour
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                                              Applications
                     Medical Imaging
                     Basically, letting doctors see inside the human body without cutting people open!
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                                Patients injected with                             CT image – X-rays shone
                                Radioactive substance                                   onto patient
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                                       Applications




                                                                             tumours
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                     Reduced brain activity due
                       to Alzheimer’s disease

                                                  Cancerous tumours in the
                                                        upper body
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                                 Summary : Effects and Uses

                     o 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


                     o Radiation can be used for………
                             - saving people from fires - smoke detectors
                             - diagnosing disease – medical imaging
                             - destroying cancer - radiotherapy
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                                  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?



                     o We need some way of detecting it and working out how much there is
                              - count rate

                     o We know radiation interacts with matter
                              - causes ionisation

                     o We can use these interactions to aid detection
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                              - allow radiation to interact in some kind of material
                              - observe the effects
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                                   Radiation Monitoring
                     The Discovery of Radiation
                      o In 1896 Antoine Henri Becquerel discovered radioactivity
                      o He left photographic film in a drawer next to some rocks
                      o The next day the film had been exposed – film looked “foggy”
                      o The rocks contained uranium


                     The photographic film is a very simple radiation
                                   detector/monitor


                     When radiation hits the film it becomes fogged

                                            A radioactive leaf
                                            – the tree was in
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                                             radioactive soil


                                                                            Worlds first x-ray image
                                                                         – Prof. Wilhelm Roentgen, 1895
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                                   Radiation Monitoring
                     Film Badges
                     o Film badges are used to monitor the radiation dose workers in the nuclear
                     industry receive
                              - Radiographers
                              - Dentists                                              Film badge for
                                                                                   radiation monitoring
                              - Pilots (recently)


                     o The film is checked on a regular basis

                     o The radiation dose the person wearing it
                     received is calculated
Ionising Radiation




                     Q
                           How do we know if the radiation
                              was beta or gamma?
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                                   Radiation Monitoring
                     Film Badges
                     o beta and gamma radiation have different penetrating power
                     o The badge may contain “filters”
                     o Filters may stop beta radiation but let gamma radiation through


                                                                     Top part of film affected by radiation
                                              Black paper



                                                                     Bottom part of film NOT affected by
                                              Photographic film                   radiation



                                                                     Q
                                                                          What kind of radiation has this
Ionising Radiation




                                              3 mm thick aluminium         badge been exposed to?


                                                                     A
                                                                                   Beta Radiation
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                                    Radiation Monitoring
                     Geiger Counters
                     o A Geiger counter uses a Geiger-Müller tube and some kind of counter
                     o The Geiger-Muller tube is full of gas
                     o This gas becomes ionised when radiation hits it
                               - very good for detecting alpha particles
                     o 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
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                                                        A Geiger-Muller tube
                      +ve voltage on wire
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                                     Radiation Monitoring
                     Scintillation
                     o When radiation hits certain materials they produce flashes of light
                     o This is known as scintillation or fluorescence
                     o These materials can be used as radiation detectors
                     o The amount of light given off is measured
                                                                        These type of radiation detectors
                                                                          are used in hospital scanners
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                                       A scintillation crystal
                                   Radiation Monitoring
                     Aiport X-ray scanning systems
                     o The current systems use X-ray scanning machines


                     o These detectors are currently the best available


                     o Unfortunately, not all the information we need is there


                     o Can see dense areas but not exact information on what exists


                     o New developments in detection systems
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                                  Summary : Monitoring
                     o Radiation monitoring is important in order to protect people against harmful
                     effects


                     o We can use the ionising nature of radiation to help us detect it


                     o 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


                     o We can also use
                             - Geiger counters
Ionising Radiation




                             - scintillation detectors

				
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