Science at Work in Healthcare
Post – 16 Science Education Pack
Key Stage 5 Physics
Lesson Plan 5 – Nuclear Medicine
Lesson aim
To familiarise students with the use of radioactive isotopes in medical imaging.
Lesson objectives
Students will be expected to:
· Work safely with a radioactive isotope.
· Take activity measurements of the isotope and calculate its half life.
· Identify the isotope and research some of its properties.
Lesson Outcomes
By the end of this lesson:
· All students must be able to understand the principles and limitations of using radioactive isotopes for medical imaging. They should also understand the concepts of half life and the decay constant.
· Most students should be able to use measurements of activity over time to plot a graph and then use the graph to ascertain the half life of the isotope.
· Some students may be able to understand the use of calculus and logs in the mathematical treatment of radioactive decay.
Time Required
Approximately two hours for the testing, research and presentation of results.
Note
This practical will require the use of an isotope generator. For the purposes of this lesson plan it is assumed that a Cs-137/Ba-137m isotope generator is being used.
While carrying out this practical please ensure that the manufacturer’s instructions are followed and that any use complies with the relevant health and safety regulations covering your institution.
It is recognised that most schools or colleges will only possess one, or possibly two, isotope generators, each of which will require a 20 to 30 minute recharge period between uses. For this reason it is suggested that this practical is used as part of a wider circus of activities.
Specification links
Board / Unit / Spec.AQA
Physics A / 1 / 3.1.1 (particles and radiation)
3.1.2 (energy levels and photon emission)
3 / Investigative and practical skills
5 / 3.5.1 (radioactive decay and nuclear instability)
Also general relevance to Unit 5B-Medical Physics
6 / Investigative and practical skills
AQA
Physics B / 1 / 3.1.2 (radioactive decay)
3 / Investigative and practical skills
4 / 3.4.3D (medical imaging)
5 / 3.5.3A (medical imaging with radioactive tracers)
6 / Investigative and practical skills
Edexcel
(concept approach) / 3 / Exploring physics
4 / 4.5 (atomic structure)
5 / 5.4 (radioactive decay)
6 / Experimental physics
Edexcel
(context approach) / 3 / Exploring physics
4 / 10.5 (atomic structure)
5 / 11.3 (uses and applications of radioactive materials)
6 / Experimental physics
OCR
Physics A / G483 / Practical skills in physics
G485 / 5.3.1 (atomic structure)
5.3.3 (radioactive decay)
G486 / Practical skills in physics
OCR
Physics B
(Advancing Physics) / G493 / Physics in practice (research into the use of a particular material)
G494 / RF 1.1 (radioactive decay and half life calculations)
G495 / FP 2.1 (atomic structure and energy levels)
FP 2.2 (radioactive decay)
G496 / Researching physics
Materials and equipment required
Per student
· Resource Sheet 5.1 – Imaging with Radioactive Tracers
· Resource Sheet 5.2 – Half life and the Decay Constant
Per pair of students
· An isotope generator or aliquot of Ba-137m solution
· Gloves, goggles and lab coat
· GM tube and counter
· A clamp and stand for holding the GM tube
· Stopwatch
· Suitable power supply if necessary for GM tube
· Shielding material
· 1 copy per student of:
o Resource Sheet 5.3 – Isotope Testing
o Resource Sheet 5.4 – Measuring Half Life
Students will also need access to an internet connected computer.
Prior knowledge required
Students should be aware of the different types of ionising radiation and their properties. They should also be aware of the definition of terms such as isotope, atomic number, atomic mass etc.
Students should also be familiar with standard deviation and its application to error calculations.
They should be aware that a nuclear isomer is a metastable state of the atomic nucleus caused by the excitation of one or more nucleon and that this state is denoted by adding a lower case ‘m’ next to the element’s atomic mass number. E.g. 99mTc or Tc-99m denotes the metastable nuclear isomer of Technetium-99.
Lesson structure
Intro activity:
· Give each student a dice and ask them to roll it . Ask them if there is anyway they can accurately predict the outcome. Then ask if they are able to make any reliable predictions about the results of the whole groups’ rolls. This can then lead into a discussion about half life and how it is used to characterise radioactive isotopes.
· Explain that this type of work would be carried out by a medical physicist.
· Students can fins out more about the work of medical physicists at www.nhscareers.nhs.uk.
10 mins approx
Practical:
· Before starting the practical activity, students should be aware of the hazards involved in using radioactive materials and how to handle them safely.
· In this practical, students will take on the role of NHS medical physicists and analyse a short lived gamma source and decide whether it would be suitable for use in medical imaging.
· The practical is designed to deliver a set of specific subject related learning outcomes and to also demonstrate the application of physics in a real-world context, allowing students to learn about some aspects of the role of medical physicists in the NHS.
· Issue the students with the following resource sheets:
o Resource Sheet 5.1 – Imaging with Radioactive Tracers
o Resource Sheet 5.2 – Half life and the Decay Constant
o Resource Sheet 5.3 – Isotope Testing
o Resource Sheet 5.4 – Measuring Half Life
· Students will use the GM tube and counter to firstly take a reading of the background radiation. They will then take readings of the activity of their sample, correcting for the background count, and use this to plot a graph of activity against time. From this graph students will be able to read off the observed half life of the sample.
· Students can then plot the natural logarithm of corrected counts per minute against time. The gradient of the resulting straight line graph will give them the decay constant, from which they can also calculate the half life of their sample. This can then be compared with the observed half life.
· Students will need to consider whether the measured half life of their sample makes it suitable for nuclear imaging. They will then need to do some guided research on the internet regarding the chemical properties of their sample and whether it is something that could be safely introduced into the body of a patient.
Resource Sheet 5.3 – Isotope Testing will help with the research aspect of the task.
· Students produce a short presentation. The key points that students need to consider here are:
o What type of radiation does the isotope emit and is it suitable for this kind of use?
o Is the half life suitable? How does it compare with the half lives of isotopes already used for this purpose?
o Would the use of this isotope require changes to the way imaging is carried out? Would making these changes be beneficial?
o How safe is the isotope for use with humans? Is it possible to make predictions on how it might behave inside the human body based on its chemical properties?
o What further testing would you recommend?
90 mins approx
Plenary activity:
· Students can present their findings back to the group. The group should be encouraged to question the recommendation.
· Presentations should be no more than 5 minutes in length and should show clearly how the data collected from testing of the devices supports any conclusion.
· Point out that although this scenario is indicative of what a medical physicist might do, in real life a tracer would be thoroughly tested by its manufacturer before being released for use in a clinical environment.
20 mins approx
Extension/Homework
· Students could select one of the radioactive tracers listed in the table in Resource Sheet 5.1 – Imaging with Radioactive Tracers and carry out some research to explain why that particular tracer is used for that particular type of imaging. This work could consider the half life of the particular tracer and also its toxicity and how it reacts with molecules in the body.
Risk assessment
It is the responsibility of the supervising teacher to carry out all risk assessments with regard to this activity and to make sure that any such risk assessment complies with the requirements of the particular institution in which it is being conducted.
Technician Notes
Preparation
Please read Resource Sheet 5.3 – Isotope Testing and Resource Sheet 5.4 – Measuring Half Life.
Each pair of students will require the following:
· An isotope generator or aliquot of Ba-137m solution
· Gloves, goggles and lab coat
· GM tube and counter
· A clamp and stand for holding the GM tube
· Stopwatch
· Suitable power supply if necessary for GM tube
· Shielding material
Although students should be capable of using the isotope generator themselves in certain cases it may be preferable for the generator to be operated by a technician. Given the short half life of Ba-137m, samples cannot be prepared prior to the lesson and should be produced as requested by the students performing the experiments.
You may need to carry out the experiment prior to the lesson to determine a suitable level of shielding for your particular source.
Sourcing the Parts
Details of the particular isotope generator referred to in this practical are given in the table below. It is possible to source the same or equivalent components from other suppliers.
Component / Supplier / Supplier website / Part No.Cs-137/Ba-137m Isotope Generator / Timstar / www.timstar.co.uk / RA75815
Extraction liquid / Timstar / www.timstar.co.uk / RA75820