PAG 7.2 Investigating the Absorption of Ionising Radiation Flashcards
What safety precautions must be taken when working with a radioactive source?
- limit time of exposure
- warning signs should be displayed so people are aware that a radioactive source is in use
- keep an arm’s length away at all times, and only ever handle the source using long-handled tongs
How should a radioactive source be handled safely?
Long-handled tongs should be used to handle a radioactive source, and you should remain at least an arm’s length away from it at all times
How should a radioactive source be stored safely?
Radioactive sources should be locked away in a sealed lead container.
A hazard symbol should be visible on the container as well as at the location where it is stored.
What is the inverse square law of radiation
The intensity of the radiation is inversely proportional to the square of the distance from the source.
What device can be used to measure a radioactive count rate?
Geiger Counter or Geiger Muller Tube
When measuring the count-rate, what advantage come with measuring over a longer period of time?
The longer the period of time over which it is recorded, the lower the uncertainty will be
What preliminary recording should be taken before bringing the radioactive source into the lab?
Before bringing the radioactive source into the lab, the background radiation count should be taken
How should the background radiation count be accounted for in the experimental data?
The background count should be subtracted from the counts for each distance, the produce corrected counts.
How do you convert from a count to a count rate for a given distance
Count rate should be divided by the length of time over which it was taken to produce a count rate
What preliminary experiment could you carry out with the source before commencing the experiment?
Recordings could be taken to find the maximum thickness of lead for which you can get a reasonable count
Why is there likely to be systematic error in the distance measurements when carrying out this experiment?
The precise location of the radioactive source within the sealed capsule, and the precise location of ionisation in the GM tube are both unknown
Why may an old gamma source be unsuitable for this experiment?
Depending on the source’s half-life and its age, the activity of the source may have fallen to a level that is too low to obtain easily recordable counts over a large enough range of distances.
What is meant by the term ‘half-thickness’
The half-thickess is the thickness of lead required to reduce the count rate to half its initial value
Describe the nature of radioactive decay?
Radioactive decay is a random process, meaning you cannot predict which nuclei will decay next or when the next decay will occur
Why should repeat readings be taken?
Allow you to account for random fluctuations in radioactive decay be calculating average values
