Transcript Detection of Ionising Radiation

Ionising Radiation: Risks and
Applications
Martin Jones
Email: [email protected]
1
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
Low
51% Radon
Gas
14% Medical
Ionising Radiation
0.5% Nuclear Industry
10% Cosmic Rays
11.5% Food
High
2
Environmental Radiation
o Naturally occurring radiation atoms may be of terrestrial or
extraterrestrial origin
Extraterrestrial : Cosmic radiation comes from space
Ionising Radiation
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
3
Extraterrestrial Radiation
Ionising Radiation
Radiation from space interacts in the Earths atmosphere
The Northern Lights (Aurora borealis)
4
Extraterrestrial Radiation
Ionising Radiation
Northern Lights (Aurora borealis) as seen
from space
Southern Lights (Aurora australis) as
captured from a NASA satellite
5
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
Ionising Radiation
g
o Thorium emits beta particles and
gamma rays
o Thorium can be contained in rock
b
6
Radiation All Around Us
o The substances used in building materials contain radioactive
nuclides:
Wood :
40K
Red Brick :
Sand :
40K, 226Ra, 232Th, 238U
40K, 232Th, 238U
Concrete :
40K, 226Ra, 232Th, 238U
o The level of radiation varies depending on where in the world they are found
Ionising Radiation
- 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
7
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
Ionising Radiation
o
226Ra
is chemically similar to calcium
- absorbed by bones
- you are radioactive
8
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)
Ionising Radiation
- Fast moving electrons
- Moderately penetrating – stopped by aluminium
- gamma rays (g)
- High frequency EM waves
- Highly penetrating
Penetration of 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.
Ionising Radiation
a particle
Electron
10
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
Ionising Radiation
= radioactive
At start there are
16 radioisotopes
After 1 half life half
have decayed.
There are 8
remaining
= stable
After 2 half lives
another half have
decayed. There are
4 remaining
After 3 half lives
another 2 have
decayed. There are
2 remanining
11
Half-Life
o How can we work out the half-life of a radioisotope?
We can plot a graph of activity against time
Ionising Radiation
1 Half-Life
2 Half-Lives
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…
8
4
2
1
8
8
8
8
…of the
sample was
uranium
Ionising Radiation
1 half life
later…
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.
13
Radioactive Dating
We have seen how radioactive decay can be used for dating. A common
example is Carbon dating
- living organisms contain radioactive
- when they die, they stop absorbing
-
14C
14C
and it decays away
decays with a known half-life of 5600 years
By measuring how much
ago something died
Ionising Radiation
14C (created by cosmic radiation)
14C
has decayed scientists can work out how long
Radioactive dating can be used to
estimate the age of fossils
14
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
Ionising Radiation
- this is ionisation
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
15
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
- medical imaging
Nuclear Bombs
- We can treat illnesses using radiation
- radiotherapy
o It allows us to watch TV, turn on lights etc
Ionising Radiation
- 20% of our electricity is provided by nuclear power
In order to use radiation we must be
very aware of the dangers!
Nuclear Power
16
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
- this can damage bodily functions
• Radiation damages DNA breaking bonds
- this kills cells
Ionising Radiation
- 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
17
External Effects
Hydrogen peroxide production in the eye
Radiation Burns
Hair Loss
Ionising Radiation
Mutation
18
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
Ionising Radiation
- 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
19
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
Ionising Radiation
Small doses of radiation seem
to reduce the risk of death!!
Seems strange but it MIGHT be true
20
Applications
The 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
Smoke Detector
a
Ionising Radiation
a
21
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
Ionising Radiation
lung
tumour
heart
lung
spine
22
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
Ionising Radiation
lung
tumour
heart
lung
spine
23
Applications
Medical Imaging
Ionising Radiation
Basically, letting doctors see inside the human body without cutting people open!
Patients injected with
Radioactive substance
CT image – X-rays shone
onto patient
24
Applications
Ionising Radiation
tumours
Reduced brain activity due
to Alzheimer’s disease
Cancerous tumours in the
upper body
25
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
Ionising Radiation
- destroying cancer - radiotherapy
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?
o We need some way of detecting it and working out how much there is
- count rate
o We know radiation interacts with matter
Ionising Radiation
- causes ionisation
o We can use these interactions to aid detection
- allow radiation to interact in some kind of material
- observe the effects
27
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
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
28
Radiation Monitoring
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
Ionising Radiation
o The radiation dose the person wearing it
received is calculated
Q
How do we know if the radiation
was beta or gamma?
Film badge for
radiation monitoring
29
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
B la ck pa per
Ph otog raph ic film
Bottom part of film NOT affected by
radiation
Ionising Radiation
Q
3 m m thic k a lu m iniu m
A
What kind of radiation has this
badge been exposed to?
Beta Radiation
30
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)
Ionising Radiation
Argon filled tube
The spark in the gas can be
amplified and sent through a
speaker to give the “clicking”
sound
A Geiger-Muller tube
+ve voltage on wire
31
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
Ionising Radiation
These type of radiation detectors
are used in hospital scanners
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
Ionising Radiation
o New developments in detection systems
32
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
Ionising Radiation
o We can also use
- Geiger counters
- scintillation detectors