(a)
Positronium is highly unstable, and after a very short period of time it becomes gamma radiation.
[ 1 ]
(i)
State one medical application of the process described in (c)(i).
[ 1 ]
[Maximum number: 5]
Fluorine-18 (918 F) 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
918 F⟶PQX+8RO.
(a)
(i)
State what is meant by a tracer.
[ 1 ]
(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.
[ 2 ]
(ii)
Explain how the detection of the gamma-ray photons is used to produce an image of the tissue being examined.
[ 2 ]
(a)
Positron emission tomography (PET scanning) makes use of a tracer containing a radioactive material that decays by positron emission.
[ 3 ]
(i)
State what is meant by a tracer.
[ 2 ]
(ii)
State the name of the particles that are emitted from the body and detected by the detectors during PET scanning.
[ 1 ]
(b)
Explain how the particles in (a)(ii) are created from positrons.
[ 3 ]
(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.
[ 2 ]
[Maximum number: 7]
Positron emission tomography (PET scanning) obtains diagnostic information from a person. The information is used to form an image.
(a)
PET scanning uses a tracer.
Explain what is meant by a tracer.
[ 1 ]
(b)
PET scanning involves annihilation.
[ 2 ]
(i)
Explain what is meant by annihilation.
[ 1 ]
(ii)
State the names of the particles involved in the annihilation process.
[ 1 ]
(c)
(i)
Calculate the total energy released in one annihilation event in (b).
energy =
[ 1 ]
(d)
Explain how the gamma photons are used to produce an image.
[ 3 ]
0