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Measuring the radioactivity of an object [3]:
- measure the background radiation
- measure the radiation with the object in position
- subtract the background radiation from the object's
Radioactive absorption test
Penetrating power of α radiation [2]
- stopped by paper and skin
- travels a few cm in air
Penetrating power of β radiation [2]
- stopped by thin sheets of aluminium
- travels tens of cm in air
Penetrating power of γ radiation [2]
- stopped by thick lead
- travels more than a km in air
Ionisation
when radiation knocks electrons out of a substance
Irradiated
an object that has been exposed to ionising radiation
Radioactive contamination
the unwanted presence of materials containing radioactive atoms on other materials
What can ionising radiation do to a living cell?
damage or kill the cell
What else causes ionisation? [3]
- x-rays
- fast-moving protons
- fast-moving neutrons
What type of radiation has the highest ionising power?
alpha radiation
Why is alpha radiation dangerous in the body? [2]
- it is highly ionising
- it cannot penetrate the skin and escape
How do workers protect themselves when working with ionising radiation? [3]
- keeping far away from source (e.g. using special tools)
- spending as little time as possible in at-risk areas
- shielding behind thick concrete barriers or lead plates
How can β radiation be used to monitor thickness? [3]
- metal is put between rollers
- a Geiger tube and a source of β radiation are placed either side of the metal
- the count rate depends on the thickness and so it can be monitored and controlled
How do smoke alarms use α radiation? [3]
- alpha particles are sent into a gap in the circuit
- the particles ionise the air and create a current across the gap
- smoke absorbs the ions and the current drops, causing the alarm to sound
Activity (of a radioactive source)
the number of unstable atoms in the source that decay per second
The unit of activity
Becquerel (Bq)
1 Bq =
1 decay per second
Parent atom
the atom that undergoes radioactive decay in a nuclear reaction
Count rate
number of counts per second
The count rate is ... to the activity of the source
proportional
Count rate against time
Half-life
length of time required for half of the radioactive atoms in a sample to decay/count rate to halve
count rate after n half-lives =
initial count rate ÷ 2ⁿ
Radioactive decay is ... but you can predict ...
random, how many atoms will decay in a given time
Radioactive tracer
a radioactive material that is added to a substance so that its distribution can be detected later
How are radioactive tracers used to detect kidney blockage? [3]
- sensors are placed against kidneys
- radioactive substance would flow in and out of a normal kidney
- in a blocked kidney, the reading stays up as the substance cannot leave
Why is radioactive iodine used to detect kidney blockage? [3]
- has a half-life of 8 days; long enough for test, decays within around a week
- emits gamma so it can be detected outside
- decays into stable product
Gamma camera
a camera that detects gamma rays from nuclei directly in front of it
What are gamma cameras used for?
to take images of internal body organs
How is a gamma camera used? [4]
- patient is injected with gamma-emitting radioactive isotope
- substance is absorbed into organ
- gamma rays pass through holes in lead grid in front of detector
- half-life long enough to take image, but mostly decayed afterwards
How is gamma radiation used to destroy cancerous tumours? [4]
- narrow beam of gamma radiation is directed at tumour
- emitted from isotope of cobalt
- half-life of five years
- gamma is used as it penetrates deeper than beta
Radioactive implants
tiny rods or seeds that emit beta or gamma radiation and slowly irradiate a tumour
Film badge
a device containing photographic film that registers the wearer's exposure to radiation
Where does background radiation come from? [6]
- cosmic rays
- food and drink
- ground
- medical
- air (radon)
- nuclear weapons and reactors
