Ionising Radiation: Risks and Applications Martin Jones Email: [email protected].
Apr 01, 2015
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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
Environmental Radiation
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There is radiation all around us but where does it come from?
Some is manmade
Some is naturally occurring
Environmental Radiation
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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 experience increases the higher up
we are
Extraterrestrial Radiation
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Radiation from space interacts in the Earths atmosphere
The Northern Lights (Aurora borealis)
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Extraterrestrial Radiation
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Southern Lights (Aurora australis) as captured from a NASA satellite
Northern Lights (Aurora borealis) as seen from space
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Environmental Radiation
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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
o Thorium emits beta particles and gamma rays
o Thorium can be contained in rock
Thorium Ore
Radiation All Around Us
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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
o A radiation survey in Germany found that radiation exposure was 33% higher indoors than outdoors
Radiation in Food
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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
- you are radioactive
Radioactive Decay
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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 ()
- beta particles ()
- gamma rays ()
- He nuclei
- Weakly penetrating - stopped by paper, air, skin…
- Fast moving electrons
- Moderately penetrating – stopped by aluminium
- High frequency EM waves
- Highly penetrating Penetration of radiation
Radioactive Decay
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Ionising Radiation
particle
Electron
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.
Radioactive Decay
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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
At start there are 16 radioisotopes
After 1 half life half have decayed.
There are 8 remaining
After 3 half lives another 2 have decayed. There are 2 remanining
After 2 half lives another half have decayed. There are 4 remaining
= radioactive
= stable
Half-Life
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o 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
Half-Life
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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.
8
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Answer: The sample was originally completely uranium…
…of the sample was
uranium
4
8
2
8
1
8
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.
1 half life later…
1 half life later…
1 half life later…
Radioactive Dating
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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
Radioactive dating can be used to estimate the age of fossils
Ionising Radiation : Summary
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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 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
o Some atoms emit radiation to achieve stability
- ionising radiation strips electrons from material it interacts in
- this is ionisation
Dangers and Applications
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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
- 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
Nuclear Power
Nuclear Bombs
In order to use radiation we must be very aware of the dangers!
Biological Effects
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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
- 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)
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
DNA molecule
External Effects
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Hydrogen peroxide production in the eye
Radiation Burns
Mutation
Hair Loss
Radiation Poisoning
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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
- death (within a month of ingestion)
o Resulting from alpha particles interacting within the body
- DNA damage
Radiation Hormesis
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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!!
Seems strange but it MIGHT be true
Applications
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The Smoke Detector
Smoke Detector
The black box contains a 241Am source– this emits alpha particles
o Smoke detectors operate using ionising radiation
o They contain an alpha emitting radionuclide
o A detector constantly measures the number of alpha particles reaching it
Applications
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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
spine
lung lung
tumour
heart
Applications
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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
spine
lung lung
tumour
heart
Applications
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Medical Imaging
Basically, letting doctors see inside the human body without cutting people open!
Patients injected with Radioactive substance
CT image – X-rays shone onto patient
Applications
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Reduced brain activity due to Alzheimer’s
diseaseCancerous tumours in
the upper body
tumours
Summary : Effects and Uses
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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
Radiation Monitoring
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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
- allow radiation to interact in some kind of material
- observe the effects
Radiation Monitoring
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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
Worlds first x-ray image
– Prof. Wilhelm Roentgen, 1895
The Discovery of Radiation
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 radioactive soil
Radiation Monitoring
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Film Badges
o Film badges are used to monitor the radiation dose workers in the nuclear industry receive
- Radiographers
- Dentists
- Pilots (recently)
o The film is checked on a regular basis
Film badge for radiation monitoring
How do we know if the radiation was beta or gamma?
Q
o The radiation dose the person wearing it received is calculated
Radiation Monitoring
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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
What kind of radiation has this badge been exposed to?
Q
Beta RadiationA
B la ck p a p er
P h o to g rap h ic film
3 m m th ic k a lu m in iu m
Top part of film affected by radiation
Bottom part of film NOT affected by radiation
Radiation Monitoring
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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)
The spark in the gas can be amplified and sent through a speaker to give the “clicking”
sound
A Geiger-Muller tube
Argon filled tube
+ve voltage on wire
Radiation Monitoring
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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 measuredThese type of radiation detectors
are used in hospital scanners
A scintillation crystal
Radiation Monitoring
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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
Summary : Monitoring
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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
- scintillation detectors
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