RADIOISOTOPES AT WORK
Video: Radioisotopes and radiotherapy
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Student questions
(possible assessment task)
Radioisotopes
1. What are isotopes of an element? How are the isotopes of an element always the same? How are they different from each other?
2. How do radioisotopes differ from other, more common isotopes of the same atom?
3. A radioactive isotope emits radiation and energy to become more stable. List the different kinds of emissions and include their properties such as charge, relative mass, penetrating power and ionizing strength.
Radioisotopes in medicine
4. What properties of gamma radiation make it useful for looking inside our bodies?
5. How are radioisotopes used in nuclear imaging?
6. Why would doctors and other scientists use different tagged compounds in different situations?
7. How are abnormal tissues detected?
8. 99mTc is a radioactive isotopic compound commonly used in diagnostic imaging. 99m Tc has a half-life of 6hrs. What is meant by the term half-life?
9. Why does 99mTc relatively short half-life make it a suitable radioisotope to use in medicine?
10. We are constantly exposed to many forms of radiation. Examine the pie charts shown in the video to determine the source of ionising radiation.
11. How does ionizing radiation affect living tissue?
12. What type of radiation is used to kill cancer cells?
13. What type of radiation is used in nuclear imaging?
Radioisotope manufacture
14. How are artificial radioisotopes made?
15. Explain how 99mTc is prepared.
Radiation safety
16. What safety precautions are taken by radiation workers to reduce their long-term exposure to radiation?
Planar imaging
17. Most bone injuries that you may be familiar with are examined using X-rays. Why then are bone scans used that employ a radioisotope to produce the image?
Tomographic imaging
18. What does SPECT stand for?
19. Describe the procedure known as SPECT.
20. What does PET stand for?
21. Describe the procedure known as PET.
22. What is a positron?
23. What tissues is PET scanning ideal at looking at?
Radioisotope manufacture – the cyclotron
24. How are radioisotopes made in a cyclotron?
Answers to student questions
1. Isotopes are nuclides with the same number of protons but different number of neutrons. Isotopes have same atomic number but different mass number.
2. Radioisotopes are unstable isotopes, where their nuclei decay to a more stable state or type of nuclei, giving off matter and energy as radiation.
3. Alpha particles can be describes as helium nuclei. They are positively charged (a 2- neutron and 2-protons package, therefore overall +2 charge, relatively massive compared with beta particles), capacity to penetrate materials is not great and readily ionize particles in their path.
4. Beta particles are fast moving single-charged particles. They are smaller and lighter and cause less ionisation per unit of distance and therefore travel further.
5. Gamma rays have no charge and mass. They travel further, are less ionising but highly penetrating.
6. High-penetrating properties (and less ionising).
7. A radioisotope is introduced into the body as a tracer. It is tagged with a compound that can be traced as it moves through the body or undergoes chemical reactions, by detecting the intensity of the emitted radiation. A detector outside the body measures the radiation to record the distribution of the tracer and the information is used to form an image.
8. Different tagged compound concentrates in a specific organ of regions of the body.
9. Abnormal tissue takes up more or less radioisotope than the tissue around them. They therefore give off more or less radiation, producing a dark or light area on the image.
10. The time taken for the decay of one-half of the original sample of atoms is called the half-life of a radioactive material. 99mTc’s radiation is reduced by half with every 6-hour period.
11. High activity and rapid decline in activity limits the exposure of the radiation to the patient.
12. 20% Earths crust, 25% radon gas give off by rocks and soil, 10% found naturally in food, 10% Cosmic Rays from Sun and outer space, 35% medical and industrial use.
13. Ionising radiation can kill cells or change the way they function.
14. High doses of radiation from beta particles.
15. Low dose of gamma radiation.
16. In nuclear reactors (or cyclotrons, discussed later in video). In a nuclear reactor materials used to make radioisotopes are placed at different depths within the reactor. They are bombarded by neutrons within the core. Neutrons are captured.
17. In a nuclear reactor. 235U captures a neutron and splits giving 99Mo and various other elements. 99Mo undergoes beta decay to give 99mTc, which must be used quickly due to it’s a short half-life.
18. Keeping their distance (due to intensity being inversely proportional to the square distance), shielding, limiting time of exposure.
19. X-ray photographs mainly detect structural changes, not changes in the function of the bone due to stress reaction, which is what is wrong with the horse.
20. Single photon emission computed tomography
21. Camera moves around patient detecting gamma rays from many different angles. Gamma emissions are converted into a series of images via a mathematical process.
22. Positron emission tomography.
23. Patients are injected with radioisotope that decays by emitting a positively charged beta particle, which travels only a few millimetres before colliding with an electron. They cancel each other out and emit two gamma rays. This gamma ray pair, with their equal energy travelling in opposite directions (due to conservation of energy and momentum), are detected and their intensity is measure via a camera.
24. Positively charged beta particle.
25. 18F is a positron emitter often used in PET. It can be chemically bound with glucose. PET is ideal for looking at tissues that use a lot of glucose for energy (that is, brain, heart).
26. Accelerated charged particles travelling at high velocities are directed or beamed at target substances. On collision with nuclei in the target, nuclear reactions occur that transform the material into unstable radioisotopes.