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
explain why alpha emitters are not used as tracers for medical imaging (3)
- alpha is highly ionising
- alpha can kill healthy cells
- alpha would not be detected outside the body as it has a low penetrating ability
(3)
- alpha radiation is not suitable as it is absorbed by the plastic
- beta radiation is suitable as it shows a clear and gradual decrease in counts detected as the thickness increases
- gamma radiation is less suitable than beta, as it shows a smaller change in counts detected
- gamma is less sensitive to variation in thickness
describe how the workers at the factory could correct their recorded value to account for background radiation (factory uses radiation to monitor the thickness of plastic sheets) (3)
- record the count for a set period of time with no source present
- record the count with sources present for the same period of time
- corrected count = count - background count
the factory records the background radiation to be 1 count per second, the factory wants to maintain a plastic sheet thickness of 1.5 mm, calculate the corrected count for beta radiation to ensure the desired thickness is maintained
- background count in one minute = 1 x 60 = 60 cpm
- corrected count = 170 - 60 = 110 cpm
