Radioactivity - students' ideas and educational research
Students' ideas on radioactivity
Students always come to the physics lab with a range of pre-conceptions and ideas about the world around them. The points below are some of the most common ideas students have about radioactivity according the Millar et al. (1990):
- Radiation is conserved
- When radiation is absorbed it is somehow stored inside the absorber
- Irradiation and contamination are not clearly distinguished
An added problem is that students often find sub-atomic explanations of radioactivity. According to Klaassen et al. (1990), students have no secure understanding of the particulate model of matter and show “severe difficulties” with atomic and sub-atomic level explanations of radioactivity. However, this approach seems to be the prominent way to treat radioactivity in many textbooks and schemes of work.
So, Millar et al. (1990) propose the following strategies to elicit students' ideas:
- Differentiate clearly between radiation and radioactive materials, and between irradiation and contamination
- Practical work and demonstrations can be tricky, so draw bridging analogies with other types of radiations
- Make use of loose forms of expression in newspapers and children’s answers – can students spot the inaccuracies?
Proposed teaching sequence
To support learners' progress through radioactivity Millar et al. (1990) propose to teach radioactivity through four stages:
- Phenomenological orientation
- Qualitative macroscopic treatment
- Quantitative macroscopic treatment
- Microscopic treatment
This sequence should help students ease into the most abstract and complex by starting from concepts and contexts that are more familiar to their own experience.
In this stage of the sequence students should explore real world contexts and links to Science Capital. Teachers should try to draw analogies and explanations from pupils' own experiences, e.g. x-rays, radiation in the news, as well as comparing nuclear radiation with other types of radiation, like sound, light, infrared, UV, etc.
Students should also begin to explore the penetrating power of radiation and the relationship between strength and distance from the source.
Qualitative macroscopic treatment
In this stage, examples and teaching activities should aim at developing the following ideas:
- Radiation is not conserved
- Irradiated objects near a close source do not subsequently emit radiation
- The radiation absorbed by these objects can cause damage to them
- The distinction between irradiation and contamination
The above concepts can be taught and (to some extent) demonstrated without the need for qualitative analysis.
Quantitative macroscopic treatment
By this stage students should be able to consider and take measurements involving macroscopic effects of radiation. Millar et al. (1990) propose the teaching points below for a qualitative macroscopic treatment.
- Measurements of quantities associated with radiation and radioactive materials
- Ask about their ‘strength’ and the rate of change of this ‘strength’
- Leading to activity and half-life
- How much damage to the receiver is caused by the radiation absorbed? - dose equivalent
When using microscopic treatment students should be ready to analyse the microscopic effects of nuclear radiation, for example:
- What happens to a source and receiver when radiation is emitted and absorbed?
- How can radiation cause and cure cancer?
- Need an atomic level model - emissions and absorptions of radiation by nuclei result in changes in the nuclear structure
- Leading to nature of radiation, ionisation, radical formation, damage to DNA…