Hazards & Uses of Radioactive Emissions & of Background Radiation Flashcards
All 18 cards in this deck
What is background radiation?
Low-level ionising radiation that is around us all of the time, from both natural and man-made sources.
Give two natural sources of background radiation.
Rocks (radon gas released from the ground) and cosmic rays from space.
Give two man-made sources of background radiation.
Fallout from nuclear weapons testing and fallout from nuclear accidents (e.g. Chernobyl); also medical X-rays and radiotherapy.
What is radiation dose measured in, and how does this unit relate to the millisievert?
Sieverts (Sv); millisieverts (mSv) sievert (Sv).
How can a person's occupation affect the radiation dose they receive?
e.g. an airline pilot
Some jobs involve extra exposure to radiation, so the dose is higher than average.
e.g. a pilot flies at high altitude, so receives more cosmic radiation.
How can location affect the level of background radiation?
e.g. living in an area with granite rock
Some places have higher background radiation than others.
e.g. granite releases more radon gas, so the background level and dose there are higher.
Why is a radioactive source with a very short half-life hazardous?
It has a very high activity, so it emits a lot of radiation per second and gives a large radiation dose in a short time.
Why is a radioactive material with a very long half-life hazardous?
Its activity decreases very slowly, so it stays radioactive and remains a hazard for a very long time (must be stored and monitored for many years).
True or false? An isotope with a long half-life is always more dangerous than one with a short half-life.
False. A long half-life means lower activity but the hazard lasts far longer; a short half-life means a much higher activity now, so the hazards differ rather than one always being greater.
True or false? Radioactive isotopes have half-lives ranging from tiny fractions of a second to billions of years.
True. Radioactive isotopes have a very wide range of half-life values.
Give two precautions used to reduce the radiation dose received when working near a radioactive source.
Increase the distance from the source (use tongs or a safety screen) and limit the exposure time; keep the source in a lead-lined box when not in use.
What are the steps to compare two half-lives given in standard form?
e.g. s and s
- Compare the powers of ten first: is bigger than
- Only if the powers are equal, compare the numbers in front
- So s is the longer half-life
How is nuclear radiation used to explore internal organs?
A radioactive tracer is injected or swallowed; it collects in the organ and the gamma radiation it emits is detected outside the body to give an image.
What type of emitter and what sort of half-life should a medical tracer have?
A gamma (or beta) emitter with a short half-life — long enough to complete the scan but short enough that the patient is not radioactive for long.
How is nuclear radiation used to destroy unwanted tissue from outside the body?
External radiotherapy: a beam of high-energy gamma rays (or X-rays) is aimed at the tumour from several directions, so the tumour gets the highest dose and healthy tissue less.
How is nuclear radiation used to control or destroy unwanted tissue from inside the body?
A radioactive source is placed in or next to the tumour (implanted seeds), or an isotope is swallowed or injected so it collects in the tissue and destroys it.
True or false? An alpha emitter is a good choice for a tracer injected to image an internal organ.
False. Alpha radiation cannot pass out of the body to be detected and is strongly ionising inside it; a gamma emitter is used.
When judging whether the risk of a medical scan or treatment is acceptable, what should the patient's radiation dose be weighed against?
The benefit (diagnosis or destroying a tumour) and the risk of the radiation damaging healthy cells and causing cancer; the dose can be compared with the background dose received over the same time.