Question 2
2
Question 2(c)
2(c)
Positronium is highly unstable, and after a very short period of time it becomes gamma radiation.
Question 2(c)(ii)
2(c)(ii)
State one medical application of the process described in (c)(i).
Answer
PET scanning B1
Question bank
A-Level CAIE Physics 24 3 Pet Scanning Question Bank
Practice A-Level CAIE Physics 24 3 Pet Scanning questions by syllabus topic with past-paper context, marks, difficulty and question previews on Eduninja.
Question 9
9
Fluorine-18 \(\left({ }_{9}^{18} \mathrm{~F}\right)\) is a radioactive nuclide that is used as a tracer in positron emission tomography (PET scanning). Fluorine-18 decays to a nuclide of oxygen ( O ) according to
Question 9(a)
9(a)
Question 9(a)(i)
9(a)(i)
State what is meant by a tracer.
Answer
material introduced into the body and (position in body) can be detected or absorbed by the tissue (being studied) B1
Question 9(b)
9(b)
Question 9(b)(i)
9(b)(i)
Explain how the radioactive decay of fluorine-18 results in the emission from the body of the gamma-ray photons that are detected during a PET scan.
Answer
positrons (emitted in the decay) and electrons annihilate B1 mass of particles becomes energy of gamma photons B1
Question 9(b)(ii)
9(b)(ii)
Explain how the detection of the gamma-ray photons is used to produce an image of the tissue being examined.
Answer
arrival times of photons are processed B1 image built up of tracer concentration in the tissue B1
Question 11
11
Question 11(a)
11(a)
Positron emission tomography (PET scanning) makes use of a tracer containing a radioactive material that decays by positron emission.
Question 11(a)(i)
11(a)(i)
State what is meant by a tracer.
Answer
substance introduced into the body B1 absorbed by tissues (being studied) B1
Question 11(a)(ii)
11(a)(ii)
State the name of the particles that are emitted from the body and detected by the detectors during PET scanning.
Answer
gamma photons B1
Question 11(b)
11(b)
Explain how the particles in (a)(ii) are created from positrons.
Answer
positrons (emitted) interact with electrons (in tissue) B1 positron is antiparticle of electron B1 (pair) annihilation (between the two) / matter turns into energy B1
Question 11(c)
11(c)
Positrons can be artificially created by a process in the laboratory that is the reverse of the process in (b). This process creates both a positron and an electron moving at the same speed in opposite directions. Suggest why two of the particles in (a)(ii) are needed to create one positron.
Answer
(same mass therefore) combined momentum of electron and positron is zero B1 photons have momentum so must be two of them (to conserve momentum) B1
Question 11
11
Positron emission tomography (PET scanning) obtains diagnostic information from a person. The information is used to form an image.
Question 11(a)
11(a)
PET scanning uses a tracer. Explain what is meant by a tracer.
Answer
substance containing radioactive nuclei that is introduced into the body or substance containing radioactive nuclei that is absorbed by the tissue being studied B1
Question 11(b)
11(b)
PET scanning involves annihilation.
Question 11(b)(i)
11(b)(i)
Explain what is meant by annihilation.
Answer
a particle interacting with its antiparticle so that mass is converted into energy B1
Question 11(b)(ii)
11(b)(ii)
State the names of the particles involved in the annihilation process.
Answer
electron(s) and positron(s) B1
Question 11(c)
11(c)
Question 11(c)(i)
11(c)(i)
Calculate the total energy released in one annihilation event in (b). energy =
Answer
\[ \begin{aligned} \mathrm{E}=2 \mathrm{mc}^{2} =2 \times 9.11 \times 10^{-31} \times 3.00 \times 10^{-82} =1.64 \times 10^{-13} \mathrm{~J} \end{aligned} \] A1
Question 11(d)
11(d)
Explain how the gamma photons are used to produce an image.
Answer
Any 3 from: - the two gamma photons travel in opposite directions - gamma photons detected (outside body / by detectors) - gamma photons arrive (at detector) at different times - determine location of production (of gamma) - image of tracer concentration in tissue produced B3