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Radioactivity encompasses ideas about powerful (and
natural) processes which can be hazardous in various ways. The
energy comes from the direct transfer of some of the nuclear
mass of atoms into energy. It is radioactivity (fission) that
keeps the interior of the Earth hotter than we would otherwise
expect - and (fusion) which generates the energy we receive
from the sun.
1.1 Understanding Radioactivity
Radioactivity is a topic with a huge potential for
misconceptions and fears, so it is perhaps a good thing that
it does not appear before key stage 4 of the National
Curriculum. It is included in the new specifications for GCSE
from 2006. This short unit identifies some of the obstacles
science tutors will need to be aware of as they support the
next generation of secondary school science teachers.
- There can be confusion between 'radiation' (eg alpha
& beta particles and gamma radiation, emitted from
radioactive sources), 'radioactivity' (the phenomenon) and
'radioactive substances' (the actual materials that emit
radiation). [Note: Of these three forms of ‘radiation’
only gamma is a form of electromagnetic radiation. It is
very high energy, short wavelength radiation, which
as you might expect penetrates deeply into most materials.
Alpha radiation consists of streams of fast moving
positively charged particles that are the nuclei of helium
atoms. Beta particles are very fast moving electrons
(negatively charged). Since both α and β
particles come from the nucleus of the radioactive atom
they change the atomic number of the atom concerned and
thus the atom changes to that of a different element.
γ-radiation emission does not change the element, it is
simply a way
in which a very excited nucleus can lose energy.]
- A very serious confusion between 'irradiation' (the act
of having radiation impact on a substance, where it may be
reflected, pass through, or be (partially) absorbed) and
'contamination' (where the actual material that is
radioactive contaminates another material)
- There is also considerable confusion of the various
units used to quantify 'activity' and 'dose'.
- Finally few people seem to be aware of the relatively
high background radiation we are all exposed to all our
lives, and the relatively small contribution human-induced
radiation usually makes to this background dose. This
should be a reassuring thought with nuclear power coming
back in favour.
The web resource Radioactivity
is a multimedia resource developed to give trainee teachers an
understanding of the key ideas. It is written for adults, but
is pitched at about GCSE standard, so will be of use for both
the teachers in training and their KS4 pupils. Radioactivity
was developed from the Science
Issues CD
1.2
Radioactivity and the National Curriculum.
According to the 1999 KS4 National Curriculum Programme of Study Radioactivity (Science 4 para 6)
http://www.nc.uk.net/ - students should be taught:
-
that
radioactivity arises from the breakdown of an unstable
nucleus
-
about some sources of the ionising radiation found in all
environments
-
the characteristics of alpha and beta particles and of gamma radiation
-
the meaning of the term 'half-life'
-
the beneficial and harmful effects of ionising radiation on matter
and living organisms
-
some uses of radioactivity, including radioactive dating of rocks.
And
in the new specifications for GCSE from 2006, the QCA
requires: http://www.qca.org.uk/11881.html
3.7 All specifications with the title GCSE Science should
set the skills, knowledge and understanding, outlined in
paragraph 3.6, entirely in the context of:
3.7 (iii) energy, electricity and radiations
c) radiations, including ionising radiations, can transfer energy
And:
At least half of each specification with the title GCSE Additional Science should set the skills, knowledge and understanding, … in the context of the following content.
(iii) Physics
b) Nuclear changes
Nuclear changes within unstable atoms cause random emissions of particles. Nuclear changes also cause the emission of energy in the form of useful and dangerous radiation.
Clearly radioactivity has and will play an important part in the KS4 science curriculum, yet many science teachers will have had little exposure to the ideas in their undergraduate years (though they will have had background exposure to the real stuff, of course!). In this short section we will focus on the barriers faced not only by our pupils in school, but also by many of our science teachers in training. Even if they are do not teach the radioactivity topic in their teaching careers they all should have a clear understanding of the concepts above to enable them to avoid the confusions of paragraph 1.1.
This section is summarized from a paper by Edward Prather (2005), which began by summarising previous research into students’ misunderstandings about radioactivity. Much of this work has been done by Millar, often in collaboration:
As suggested in the introduction, this research showed that one of the common difficulties that students experience when trying to learn about radiation and radioactivity was an inability to differentiate properly between the concepts of irradiation and contamination. (p.345)
These students often stated that objects exposed to radiation would either become sources of radiation or have radioactive properties. Some of these students describe ionizing radiation as having the same properties as radioactive materials.(p.345)
Prather’s own research was undertaken on graduate students of geology who were trying to understand how radio-dating worked, and he targeted students' understanding of the role the atom plays in the radioactive decay process. (p.346)
Many of his students explained radioactive instability and decay in terms of electrostatic charge imbalance, and he devised this multiple-choice (plus reason) question to follow their ideas up in a larger sample (p.250):
Circle the statement(s) which characterize(s) what happens during radioactive decay.
-
A valence electron is emitted from an atom.
-
Some combination of protons and neutrons are emitted from the nucleus.
-
An electron is emitted from the nucleus.
-
A valence electron drops to a lower energy level, releasing energy (emits a photon).
-
A proton or neutron drops to a lower energy level, releasing energy (emits a photon).
-
Other (specify):
Explain your reasoning for each statement you circled.
Only a quarter of his sample gave responses which only involved the nucleus (B, C and E). Even with these students they often thought that only coulombic forces were involved, and were unaware of the ‘strong’ nuclear force.
[Note: In all nuclei beyond hydrogen the ‘strong’ nuclear attractions are able to overcome the coulombic repulsions between positively charged protons
(fundamental
forces). It is a balance between the number of protons and neutrons in the nucleus that allows some nuclei to be stable and prevents others from existing. At the edge of the stable region for most elements there are isotopes that can exist but whose nuclei can also become more stable by losing alpha or beta particles – and changing to the nucleus of another element.]
In a further set of interviews and questions Prather found that his students thought that either the mass and/or volume of a radioactive material would decrease by half in the period of a half-life. Using such terms as radioactive ‘decay’ seemed to suggest that the atoms disappeared so even for those students who did have an understanding of radioactivity that involves the atom, they often also predict that half of the radioactive object will disappear after a half-life. (p.353)
http://www.nagt.org/nagt/jge/abstracts/sep05.html.
It is likely that pupils will be taught radioactivity in one go as part of their GCSE course, so the idea of progression is not so significant here. However, it is important that students are familiar with concepts such as electrons; nucleus (protons and neutrons); (relative) atomic mass; atomic number and the Periodic Table. Children are likely to come to their GCSE session with some (popular) ideas about the dangers of radioactivity, and they will have some knowledge of the electronic structure of the atom. It is these two bits of prior knowledge that are likely to predispose the pupils to build up the misconceptions described above:
- a confusion of nuclear processes with the electrostatic events associated with the chemistry of the atom,
- a lack of appreciation of the background levels of radiation which
surround us all
- a fear of radiation and the thought that irradiated objects will become radioactive (the irradiation/contamination confusion) – although irradiated objects are often damaged and may become chemically changed.
Schools do keep radioactive sources for teachers to demonstrate to their pupils. There are strict regulations relating to the storage and use of these materials, and tutors and trainees should read the advice from
CLEAPSS carefully.
These are the necessary guides from CLEAPSS.
R92 The Measurement of Radioactivity. 02/01
L93 Managing Ionising Radiations and Radioactive Substances. (Explains the requirements of the latest Ionising Radiations Regulations. The important process of regular monitoring (now a legal
requirement for every radioactive source) is explained in detail. Model local rules and risk assessments for the most commonly used radioactive sources are included.)
08/01
PS46A Radiation Protection in School Science: Guidance for Employers - Information for LEAs.
04/05
PS46B Radiation Protection in School Science: Guidance for Employers - Information for independent schools & colleges (including foundation & voluntary-aided schools).
05/05
Student teachers should not attempt to handle radioactive sources in school with children unless under the guidance and tuition of the school’s radiation officer [Radiation Protection Adviser (RPA)], but if they can be trained to use sources safely during their ITE so much the better.
References:
- Prather E. (2005) Students' Beliefs About the Role of Atoms in Radioactive Decay and Half-life
Journal of Geoscience Education, v. 53, n. 4, September, 2005, p. 345-354.
- Eijkelhof H. M. C, and Millar R., 1988, Reading about Chernobyl: the public understanding of radiation and radioactivity, School Science Review, v. 70, p. 35-41.
- Millar R., Klaassen K. and Eijkelhof H., 1990, Teaching about radioactivity and ionizing radiation: an alternative.
- Millar R., 1994, School students' understanding of key ideas radioactivity and ionizing radiation, Public Understanding of Science, v. 3, p. 53-30.
Web Resource:
Radioactivity: This programme on Radioactivity can be used at Key-stage 4 and A Level, but anyone with an interest in Radioactivity and its uses will also find the content useful. Animation is used throughout to enhance the understanding of sometimes difficult concepts, and it contains a number of built-in elicitation
questions [author: George Burch].
Section Developed by:
Keith Ross, University of Gloucestershire with additional material from Alan Goodwin.
January 2006
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