(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 $\left({ }_{9}^{18} \mathrm{~F}\right)$ 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

{ }_{9}^{18} \mathrm{~F} \longrightarrow{ }_{P}^{Q} \mathrm{X}+{ }_{8}^{R} \mathrm{O} \text {. }

(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 ]

Question 2

Question 2(c)

Question 2(c)(ii)

Question 9

Question 9(a)

Question 9(a)(i)

Question 9(b)

Question 9(b)(i)

Question 9(b)(ii)

Question 11

Question 11(a)

Question 11(a)(i)

Question 11(a)(ii)

Question 11(b)

Question 11(c)

Question 11

Question 11(a)

Question 11(b)

Question 11(b)(i)

Question 11(b)(ii)

Question 11(c)

Question 11(c)(i)

Question 11(d)