hazards and uses of radioactivity (topic 4) Flashcards
- y
- least ionising
- penetrates through the body
- is a gas so can be breathed in
- longer shelf life
- food can be supplied from around the world
- less likely to get food poisoning
alpha - stopped by paper
beta - travels 1 metre
gamma - travels at speed of light
- higher in village B
- by 6 units
describe the structure of the three main types of ionising radiation (3)
- alpha - helium nuclei (or 2 protons and 2 neutrons)
- beta - high speed electron
- gamma - high energy electromagnetic wave
explain the precautions that must be taken when handling radioactive materials (2)
- limit the time of exposure
- maintain a safe distance from the source
- use shielding materials such as lead
- handle with tongs
- suitable protective clothing
describe how radioactive tracers are used in medical imaging (2)
- radioactive tracer is injected OR radioactive tracer is ingested
- radiation emitted by the tracer is detected, creating an image of the area being examined
a patient is given a dose of technetium-99m with an initial activity of 296 MBq, calculate the activity of the tracer after 18 hours
- 18 hours = 3 half lives
- initial activity = 296 MBq
- after 1 half life - 6 hours = 148 MBq
- after 2 half lives - 12 hours = 74 MBq
- after 3 half lives - 18 hours = 37 MBq
describe how radioactive substances are used in radiotherapy for cancer treatment (2)
- radioactive sources emit ionising radiation
- that damages cancerous cells (or kill cancer cells)
describe how radioactive substances are used in smoke detectors
- alpha particles ionise the air
- creating a current
- this current is interrupted when smoke enters the detector
- triggering the alarm
describe the potential safety concerns related to the use of alpha radiation in smoke detectors (2)
- alpha particles are highly ionising
- harmful if ingested or inhaled
describe the precautions and safety measures taken to minimise the risks associated with using alpha-emitting sources in smoke detectors (2)
- alpha has a low penetrating capability so wont be able to get outside the smoke detector
- alpha has a very low range in air
- alpha source is enclosed, preventing direct exposure to alpha radiation
- the amount of radioactive material used in smoke detectors is very small
describe the relationship between the counts detected and the thickness of the aluminium sheets (2)
- as the thickness increases, the counts detected decrease
- in a non-linear way
- thickness is inversely proportional to the counts detected
explain how beta radiation is used to measure the thickness of materials in this application (3)
- radioactive source that emits beta particles is placed on one side of the material
- geiger-Muller tube is placed on the opposite side of the material
- as the thickness varies, the number of beta particles that are detected varies
explain how radioactive tracers are used to detect leaks in pipelines (3)
- radioactive material is placed into the pipeline fluid
- detectors placed along the pipeline to monitor the radiation levels outside the pipe
- an increase in radiation levels detected indicates position of a leak
Describe the advantages and safety precautions of using radioactive tracers for leak detection in pipelines.
advantages:
- ability to detect leaks in inaccessible or underground pipes
- high sensitivity for leak detection
safety precautions (max 2 marks):
- must use a radioactive isotope with a suitable-half life to prevent unnecessary long term radiation levels
- radioactive sources must be stored in suitable containers such as lead lined boxes
- radioactive sources must be handled with care
explain what is meant by background radiation and give one source of background radiation (2)
- low level radiation that is present in the environment at all times
- cosmic rays
- natural radioactive materials in the earth
- human-made sources like medical tracers
- some foods
a student places an alpha source near a Geiger-Muller tube and records a count of 185 in 30 s, calculate the corrected count rate (in counts per minute)
radium-223 can be put inside the body to treat cancers, radium has a half-life of 11.4 days and emits alpha radiation, explain why radium-223 is suitable for use inside the body to treat cancers
- alpha is highly ionising
- alpha kills cancer cells
- alpha does not penetrate very far in the body
- half-life is long enough for the treatment to take effect
- half-life is short enough that the radiation does not need to be removed (or half-life is short enough that it won’t last very long in the body)
9 MBq
beta
explain what is meant by a half-life of 6 hours (1)
activity of the sample will half every 6 hours (or number of radioactive parent nuclei halves every 6 hours)
the radiographer wants the activity of the tracer to be less than 1 MBq after one day, calculate the maximum initial activity of the tracer if it is to have an activity of less than 1 MBq after one day
- number of half lives = 24 ÷ 6 = 4
- activity after 4 half lives = 1 MBq
- activity after 3 half lives = 2 MBq
- activity after 2 half lives = 4 MBq
- activity after 1 half life = 8 MBq
- initial activity = 16 MBq
