Module 6 Standard Answers

Question 1

Explain in terms of movement of electrons how the capacitor plates acquire an equal but
opposite charge.

Answer 1

• Electrons move from one plate to the other plate, making the plate they leave positive and the
plate that they arrive at negative.
• The number of electrons that are removed from one plate is the same as the number of
electrons that are deposited on the other plate.

Question 2

Explain how a capacitor stores energy but does not store charge.

Answer 2

• On a capacitor, work is done to separate the positive charges onto one plate and negative
charges onto the other plate.
• Energy is stored within the electric field between the capacitor’s oppositely charged plates.
• A capacitor has an equal magnitude of positive and negative charges and so the total charge
on a capacitor is zero. Therefore, it does not store charge.

Question 3

Describe and explain the purpose of a dielectric.

Answer 3

• A dielectric is an insulating material which is placed between capacitor plates.
• It decreases the electric field strength between a capacitor’s parallel plates, increasing its
capacitance

Question 4

Strong electric fields can cause a spark. Explain how the electric field causes the atoms
in the air to become conducting.

Answer 4

• The electric field causes an electric force to act on the electrons and nucleus in the atom. This
electric force acts on the electron and nucleus in opposite directions (as they are oppositely
charged).
• The electric field causes electrons to be stripped off the atom.

Question 5

Describe what is meant by an electric field and a magnetic field. State the differences
between the forces experienced by charged particles in these fields.

Answer 5

• An electric field is a region of space where a force is experienced by a charged particle,
whereas a magnetic field is a region of space where a force is experienced by a current-
carrying conductor, moving charge or permanent magnet.
• In an electric field, the electric force acts parallel to the field lines, with a magnitude that is
independent of the speed of the particle.
• In a magnetic field, the magnetic force acts perpendicular to the field lines, with a magnitude
that is directly proportional to the particle’s speed.

Question 6

Explain why the speed of charged particles travelling in a uniform magnetic field does
not change despite the force acting on the charged particles.

Answer 6

• The magnetic force acts perpendicularly to the velocity/direction of motion (towards the centre
of a circle).
• No work is done by the magnetic force on the charged particles.
• So, their kinetic energy and speed does not change.

Question 7

Explain why a repulsive force acts on a permanent bar magnet as it is pushed into a coil
(or whenever there is a change in the number of field lines passes through an area).

Answer 7

• As the magnet enters the coil, there is a change in the magnetic flux linkage.
• By Faraday’s Law �𝜀𝜀=
−Δ𝜙𝜙
Δ𝑡𝑡 �, an emf is induced in the coil.
• As the coil is complete (no cuts), there is an induced eddy current through the coil.
• By Lenz’s Law, the induced current through the coil generates an opposing magnetic field (it
opposes the change in magnetic flux linkage).
• So, the magnet experiences a magnetic force which opposes its motion

Question 8

Explain the shape of the induced emf vs time graph for a magnet moving through a coil.

Answer 8

• The induced emf is directly proportional to the rate of change of magnetic flux linkage, by
Faraday’s Law.
• The emf changes from positive to negative because the rate of change of magnetic flux
linkage changes sign (the flux linkage increases and then decreases).
• The emf becomes zero because the rate of change of magnetic flux linkage is zero when the
magnet is in the middle of the coil.
• The second peak has a larger negative amplitude because the rate of change of magnetic
flux linkage is greater when the magnet leaves the coil, as it is travelling with a greater speed.
• The two pulses have different widths as the magnet accelerates through the coil.
• The area under each of the two regions is the same as the total change of magnetic flux
linkage on entering the coil is the same as the total change of magnetic flux linkage on leaving
the coil.

Question 9

The primary coil of a transformer is connected to an alternating voltage supply.
Explain…
[i] how an emf is induced in the secondary coil.

Answer 9

• A changing current in the primary coil gives rise to a changing magnetic flux linkage in the
core.
• The soft iron core of the transformer links this magnetic flux linkage to the secondary coil.
• The changing magnetic flux linkage through the secondary coil induces an emf in the
secondary coil, by Faraday’s Law.

Question 10

The primary coil of a transformer is connected to an alternating voltage supply.
Explain…

[ii] why thermal energy is generated in the core.

Answer 10

• The changing magnetic flux linkage in the core generates eddy currents in the core, by
Faraday’s Law.
• This induced current in the core causes heating / power dissipation, by P = I2R

Question 11

Explain how the features of a transformer’s core reduce energy losses and improve its
efficiency.

Answer 11

[i] a continuous loop
• This confines the magnetic field lines produced by the primary coil to the core.
• This prevents the loss of magnetic flux linkage in the secondary coil.
[ii] soft-iron
• AC in the primary coil magnetises and de-magnetises the core continuously, which requires
energy.
• Soft iron is easily magnetised but does not stay magnetic, reducing energy dissipation.
[iii] laminated
• Reduces the magnitude of the eddy currents in the core.
• Reduces power dissipation in the core, by P = I2R.

Question 12

State advantages and disadvantages of the use of alternating voltage / current for the
transmission and use of electrical energy.

Answer 12

• Advantage: Voltages can be changed easily and efficiently.
• Advantage: High voltage transmission reduces power losses.
• Disadvantage: Cables require greater insulation.

Question 13

Explain why the emf of the supply / primary coil and the emf induced in the secondary
coil of a transformer are not in phase.

Answer 13

• The magnetic flux linkage in the core is in phase with the emf of the supply / primary coil.
• By Faraday’s Law, the emf induced in the secondary coil is directly proportional to the rate of
change of magnetic flux linkage.
• So, the emf of the supply / primary coil is not in phase with the emf induced in the secondary
coil.

Question 14

Describe how the Rutherford / alpha-particle scattering experiment provides evidence
for the existence, charge and size of the nucleus.

Answer 14

• Most of the alpha particles aimed at the gold foil passed straight through, and some were
deviated through small angles.
• Hence, most of the atom is empty space.
• A very small number of alpha particles were scattered through large angles (more than 90°).
• As the alpha particle is positively charged, this showed the existence of a tiny positive nucleus
(size/diameter ≈ 10-14 m).

Question 15

State the typical values for…

Answer 15

• Nuclear radius ≈ 10-15 m
• Atomic radius ≈ 10-10 m
• Mean nuclear density ≈ 1017 kg m-3
• Mean atomic density ≈ 103
– 104 kg m-3

Question 16

Explain why, during the closest approach of an alpha particles, the gold nucleus has a
velocity, and the alpha particle does not.

Answer 16

• There is a repulsive electric force between the gold nucleus and the alpha particles.
• Linear momentum is conserved for this interaction since there are no external forces acting.
• The initial kinetic energy of the alpha particle is transformed into electrical potential energy.

Question 17

Describe the nature and range of the three forces acting on protons and neutrons in the
nucleus.

Answer 17

Gravitational Force:
• This force is attractive and long ranged.
• This force obeys the inverse square law.
Strong Nuclear Force:
• This force is attractive between 0.5 - 3 fm and repulsive at distances below 0.5 fm.
• This force is short ranged.
• This force acts between quarks (and bosons).
Electrostatic / Electromagnetic Force:
• This force is repulsive between protons (since they are both positively charged).
• This force does not act between neutrons, or between a proton and a neutron (since neutrons
have zero charge).
• This force is long ranged.

Question 18

Suggest why two gamma photons move in opposite directions with equal energy after
annihilation (assuming the positron and electron had negligible kinetic energy).

Answer 18

• Before annihilation, the total momentum of the positron and electron is zero. By conservation
of momentum, the total momentum of the two gamma photons produced after annihilation must
also be zero.
• As the gamma photons have equal magnitudes of momentum, they have equal energies

Question 19

Proton

Answer 19

uud
Q:+1
B:+1
L:0
S:0

Question 20

Anti-Proton

Answer 20

ūūd
Q:-1
B:-1
L:0
S:0

Question 21

Neutron

Answer 21

dud
Q:0
B:+1
L:0
S:0

Question 22

Anti-Neutron

Answer 22

(All anti) dud
Q:0
B:-1
L:0
S:0

Question 23

Up

Answer 23

u
Q:+2/3
B:+1/3
L:0
S:0

Question 24

Anti-up

Answer 24

ū
Q:-2/3
B:-1/3
L:0
S:0

Question 25

Down

Answer 25

d
Q:-1/3
B:+1/3
L:0
S:0

Question 26

Anti-down

Answer 26

Anti d
Q:+1/3
B:-1/3
L:0
S:0

Question 27

Strange

Answer 27

s
Q:-1/3
B:+1/3
L:0
S:-1

Question 28

Anti-strange

Answer 28

Anti s
Q:+1/3
B:-1/3
L:0
S:+1

Question 29

Electrons (e-)

Answer 29

Q:-1
B:0
L:+1
S:0

Question 30

Positrons (e+)

Answer 30

Q:+1
B:0
L:-1
S:0

Question 31

Electron neutrino (Ve)

Answer 31

Q:0
B:0
L:+1
S:0

Question 32

Anti-electron neutrino

Answer 32

Q:0
B:0
L:-1
S:0

Question 33

Alpha Decay

Answer 33

Strong nuclear
≈1cm
Stopped by paper

Question 34

Beta decay

Answer 34

Weak nuclear
≈1m
Stopped by aluminium (5mm)

Question 35

Gamma Decay

Answer 35

Infinite range
Stopped by a lot of lead

Question 36

Describe what is meant by the random and spontaneous nature of radioactive decay.

Answer 36

• The decay cannot be induced; it occurs without external influence
• It is impossible to predict when a nucleus will decay.

Question 37

Two isotopes undergo alpha decay and emit different amounts of energy. Explain which
isotope has a larger decay constant.

Answer 37

• The parent nucleus which emitted alpha particles of larger energy was less stable and more
likely to decay.
• The isotope of this parent nucleus has the larger decay constant.

Question 38

Suggest why measuring the mass and activity of a radioactive isotope is not an accurate
method for determining its half-life if the half-life ≈ 1 hour.

Answer 38

• There would be significant/large decay of the source whilst taking measurements.

Question 39

Describe carbon-dating.

Answer 39

• Living organisms (plants) take in carbon (CO2) whilst they are alive. When they die, they stop
taking in carbon.
• Some of this carbon will be carbon-14. The ratio of carbon-14 to carbon-12 for the dead
object is determined; that is A.
• The current (today’s) ratio of carbon-14 to carbon-12 is determined; that is A0.
• The age of the sample is found, using A = A0 e-λt
.
• As the activity of the sample is small, it must be measured over a long time period and then
averaged, as a long time is needed to build up enough data to determine an accurate age

Question 40

Explain the major limitations of carbon-dating.

Answer 40

• The ratio of carbon-14 to carbon-12 is assumed to be constant. This is unlikely to be correct,
as the amount of CO2 in the atmosphere is continuously changing.
• Very old samples (>105 years) have such a low activity that their activity might be comparable
(similar in size) to the background activity. So, their activity cannot be differentiated from the
background.

Question 41

Explain why the total mass of the individual protons and neutrons of a particular
nucleus is different from the mass of that nucleus

Answer 41

• The mass of the nucleus is less than the total mass of the individual protons and neutrons.
This difference between these two masses is known as the mass defect.
• The nucleus has a binding energy; energy must be supplied in order to separate the
individual protons and neutrons of a nucleus.

The binding energy=the mass defect x c^2

Question 42

Describe nuclear fission and fusion. Explain how these reactions can provide energy.

Answer 42

• Fusion is the joining together of lighter nuclei in order to make heavier nuclei.
• Fission occurs when a thermal (slow moving) neutron is absorbed by a massive nucleus,
causing it to split into two daughter nuclei, and one or more fast moving neutrons.
• In fission or fusion, the total mass decreases. By ∆E = ∆mc2
, total binding energy increases.
• Energy is produced in the form of kinetic energy and electromagnetic energy / photons

Question 43

Explain why nuclei with less than 56 nucleons cannot provide energy by fission / why
nuclei with more than 56 nucleons cannot provide energy by fusion.

Answer 43

• For a reaction to release energy, the binding energy per nucleon must increase.
• The total energy released from a fission or fusion reaction is equal to the increase in the total
binding energy during this reaction.
• If nuclei with less than 56 nucleons fissioned / more than 56 nucleons fused, the binding
energy per nucleon (and total binding energy) would decrease. This is impossible, unless
external energy is supplied

Question 44

Explain the role of fuel rods in a nuclear reactor and suggest suitable materials.

Answer 44

• Fuel rods contain the fissile material.
• Suitable material for fuel rod cylinder: Titanium.
• Suitable material for fissile material: Uranium-235.

Question 45

Explain the purpose of a moderator in a nuclear reactor and suggest a suitable material.

Answer 45

• Fission reactions produce fast-moving neutrons.
• A moderator slows down these fast-moving neutrons. It does not absorb these neutrons.
• The fast-moving neutron collides inelastically with a moderator nucleus, so the neutron’s
kinetic energy, and speed, decreases.
• Slow-moving (thermal) neutrons have a greater probability of inducing fission.
• Suitable material for moderator: Water (also a coolant) or graphite.

Question 46

Explain the purpose of control rods in a nuclear reactor and suggest a suitable material.

Answer 46

• Control rods absorb some of the neutrons produced during fission.
• The control rods are inserted into the reactor to allow an average of one neutron from a
previous reaction to cause subsequent fission reactions.
• Suitable material for control rods: Boron.

Question 47

Explain why a proton must have a very high velocity to fuse with another proton. How
can this typically occur at temperatures lower than 107K?

Answer 47

• As one proton approaches another proton, it experiences an electrostatic repulsive force that
slows it down (since both protons are positively charged).
• The proton must have a very high velocity in order to get close enough to the second proton
for the attractive short range strong nuclear force to act and fuse these two protons together.
• At 107K, some nuclei have a kinetic energy greater than the mean translational kinetic energy
and so have a greater velocity than vrms, by the Maxwell-Boltzmann distribution.
• These nuclei will have a large enough energy to overcome the electrostatic repulsive force.

Question 48

Suggest why control rods become hot when they absorb neutrons in a nuclear reactor.

Answer 48

• The particles and neutrons emitted from a nuclear reaction have kinetic energy.
• The range of the neutrons in the control rods is short and so the neutrons lose kinetic energy
in the control rods.
• When neutrons are absorbed in the control rods, their kinetic energy is converted into thermal
energy.

Question 49

Discuss the physical properties of nuclear waste that make it dangerous.

Answer 49

• Nuclear waste is radioactive for a long time.
• Therefore, it causes ionisation, which is harmful to life

Question 50

Explain what is meant by a non-invasive technique and state some of its advantages.

Answer 50

• Non-invasive techniques require no cutting / incision of the body and so no surgery is
required.
• There is a lower risk of infection or scarring.
• There is less trauma, such as bruising or bleeding.

Question 51

State the main properties of X-ray photons

Answer 51

• They can travel in a vacuum.
• They travel at the speed of light in a vacuum.
• They have no charge.
• They have no rest mass.
• They are highly ionising.

Question 52

Describe how X-ray photons are produced in an X-ray tube/machine.

Answer 52

Electrons are accelerated through a high potential difference.
• These high-speed electrons hit a metal surface.
• The kinetic energy of these electrons is transferred into X-ray photons.

Question 53

When high-speed electrons hit a metal
surface, this spectrum of X-ray radiation is
emitted.

continuous distribution of wavelengths

sharp cut-off at a short wavelength

Answer 53

• Electromagnetic radiation is produced whenever
charged particles are accelerated.
• The electrons hitting the metal have a distribution of accelerations, and therefore a
distribution of energies.
• All the electron’s energy is converted into a single photon when it hits a metal surface, so the
emitted photons will have a distribution of energies / wavelengths.

• The shortest wavelength corresponds to the greatest electron acceleration (therefore the
greatest electron energy and photon energy).
• As all the electron’s energy is converted into a single photon, via a one-to-one interaction.

Question 54

Explain the principles behind the use of X-rays for imaging internal body structures.

Answer 54

• An X-ray beam is directed through the body onto a detector plate.
• Different soft tissues absorb/attenuate the beam by different amounts.
• This results in contrasting amounts of darkening of a photographic film, producing an image
of the internal body structures.

Question 55

State interaction mechanisms between X-ray photons and matter, and describe what
happens during the mechanism to the X-ray photon interacting with a single atom.

Answer 55

• Simple scattering: The X-ray photon scatters off an electron with no change to its energy, as it
does not have enough energy to remove the electron from the atom.
• Photoelectric effect: The X-ray photon provides enough energy to remove an electron from
the atom and provides kinetic energy to the electron. This is the dominant mechanism for
hospital X-ray machines.
• Compton scattering/effect: The incoming X-ray photon collides/interacts with an electron in
the atom. The electron is ejected from the atom and the X-ray photon is scattered with a lower
energy / frequency.
• Pair production: The incoming X-ray photon disappears and produces an electron-positron
pair.

Question 56

Explain why contrast media are used in the diagnosis of stomach problems / improving
the X-ray image quality. Suggest a suitable element to use as a contrast medium.

Answer 56

• The contrast medium absorbs X-rays because it has a large attenuation coefficient.
• This is ideal for imaging the outline of soft tissues, and if there is a hole in the stomach, then
the contrast medium will show this by flowing through the hole.
• Suitable element: Barium or iodine.

Question 57

Explain the use of image intensifiers and aluminium filters to minimise the risk to patient
health when producing an X-ray image.

Answer 57

• Long-wavelength X-ray radiation is more penetrative in the body, posing a greater hazard to
health (so we need to minimise the patient’s exposure to this radiation).
• Intensifiers are sheets of material that contain phosphor which converts an X-ray photon into
many visible light photons. These visible light photons are absorbed by the photographic film
after passing through the patient.
• This enables the photographic film to be darkened more, so that a lower exposure to X-ray
radiation can be used.
• The aluminium filter absorbs the hazardous long wavelength X-ray radiation that would be
absorbed by the body (and not contribute to the image).

Question 58

Explain the difference between sharpness and contrast in X-ray imaging

Answer 58

• Sharpness: How well-defined the edges of structures are.
• Image’s sharpness is reduced by: the scattering of photons in the tissue; not using a lead
collimator tube; or using a wide X-ray beam.
• Contrast: The difference in the degree of darkening of the photographic film between
structures, due to their differing attenuation coefficients.

Question 59

Describe the operation of a computerised axial tomography (CAT) scanner.

Answer 59

• An X-ray beam passes through the patient at different angles as the X-ray tube rotates
around the patient.
• A thin, fan-shaped beam is used (1 mm - 10 mm thick).
• The X-ray tube / detectors are moved along the patient so that many 2D image slices through
the patient can be taken at many different angles.
• With the help of computer software, a 3D image can be built up.
• Soft tissues can then be identified.

Question 60

Explain how the production of a CAT scan image differs from that of an X-ray image.

Answer 60

• A simple X-ray produces a single 2D image slice.
• Whereas a CAT scan is a 3D image built up from many different 2D X-ray image slices, taken
at many different angles, so that the image can be rotated.
• As a CAT consists of many X-ray image slices, there is a much larger exposure with a CAT
scan.
• A powerful computer is required to store and process the huge quantities of data necessary to
build this 3D CAT scan image.

Question 61

State advantages of a CAT scan image over a conventional X-ray image.

Answer 61

• It is a 3D image, which allows the size, shape and position of tumours to be assessed better.
• It achieves better contrast between different soft tissues.

Question 62

State some of the disadvantages of a CAT scan.

Answer 62

• CAT scans rely on taking many X-ray image slices. The increased X-ray exposure to ionising
radiation carries increased risk to patient health.
• They are slower and more expensive than a traditional X-ray.
• They require the patient to remain very still during the scanning process (otherwise the image
will be blurred), which may be difficult for some patients (e.g. young children).

Question 63

Describe the piezoelectric effect. How is it used in an ultrasound transducer to emit and
receive ultrasound?

Answer 63

• Piezoelectric Effect: The application of an alternating pd across a crystal causes a vibration of
the crystal atoms.
• Emitting ultrasound: The piezoelectric crystal is connected to an alternating pd, making it
vibrate and emit ultrasound.
• Receiving ultrasound: Ultrasound makes the piezoelectric crystal vibrate and this produces an
alternating current / potential difference.

Question 64

Describe the principles of ultrasound scanning.

Answer 64

• A piezoelectric transducer is used to send pulses of ultrasound into the patient.
• This ultrasound signal is reflected at the boundaries between the tissues.
• The intensity of the reflected ultrasound signal depends on the acoustic impedances of the
materials at the boundary, which is linked to the type of tissue. The fraction of intensity that is
reflected is greater when the difference between the acoustic impedances is greater.
• The time between transmitting and receiving the ultrasound, and the speed of the ultrasound
in the tissue, are used to determine the depth of the tissue boundary:
depth = speed of ultrasound ×
1/2 time between transmitting and receiving ultrasound

Question 65

State what is meant by the acoustic impedance and explain its significance on the
reflection of ultrasound at the boundary between two media.

Answer 65

• The acoustic impedance is the product of the density of the medium and the speed of sound
in that medium (Z = ρc).
• The difference in acoustic impedance determines the fraction of incident intensity that is
reflected at the boundary between two media.

Question 66

What is meant by acoustic impedance matching?

Answer 66

The acoustic impedances of the media are similar, so that less ultrasound is reflected at a
boundary.

Question 67

Explain why a (coupling) gel is used between the ultrasound transducer and the
patient’s skin during a scan.

Answer 67

• Without the gel, practically all the ultrasound would be reflected at the air to skin boundary.
The gel allows the transmission of the ultrasound into the body by removing the air between
the transducer and the skin.
• The gel and the skin have similar acoustic impedances, so, with the gel, almost all the
ultrasound is transmitted into the body

Question 68

Explain the difference between an ultrasound A-scan and B-scan.

Answer 68

• An A-scan is one directional, whereas a B-scan takes place in different directions / angles.
• B-scans produce 2D or 3D images. They are built up of many A-scans.

Question 69

Describe and explain the principles of a B-scan.

Answer 69

• B-scans take place in different directions / angles.
• Ultrasound is reflected at the boundary between materials.
• The intensity of the reflected ultrasound signal depends on the acoustic impedances of the
materials at the boundary, which is linked to the type of tissue. The fraction of intensity that is
reflected is greater when the difference between the acoustic impedances is greater.

Question 70

Explain an advantage of using high frequency / short wavelength ultrasound for a scan.

Answer 70

Using a higher frequency / shorter wavelength provides greater resolution. This allows for
smaller structures to be detected.

Question 71

Explain how ultrasound is used to determine the speed of blood in an artery in the arm.

Answer 71

• The transducer is placed at an angle to the artery.
• Ultrasound pulses are reflected by moving blood cells.
• The frequency of ultrasound is changed, due to the Doppler effect.
• This change in frequency is related to the speed of blood.

Question 72

Explain what is meant by a medical tracer. Describe its use and suggest an example
element used.

Answer 72

• A radioactive substance is injected into the patient.
• This substance is absorbed by the organ/tissue.
• A gamma camera is used to detect the concentration of the medical tracer in a tissue/organ.
This can be used to identify irregularities in the function of the tissue/organ.
• Example element: Technetium-99m, Iodine-131, Fluorine-18, (NOT barium

Question 73

Why must a medical tracer primarily be a gamma emitter?

Answer 73

• Gamma radiation is not very ionising and so does little damage to cells.
• Gamma radiation is more penetrative and so will pass through the patient and be detected (it
is not absorbed by the patient

Question 74

Name and describe the function of the main components of a gamma camera. Suggest
how the image quality could be improved.

Answer 74

• Lead collimator tubes: Only gamma photons that travel along the axis of the tubes pass
through the collimator and are detected.
• Scintillator (sodium iodide) crystal: The incident gamma photon produces many visible light
photons.
• Photomultiplier tubes (photocathode and dynodes): An electrical pulse / electrons are
produced by each photon of visible light.
• Computer: The electrical pulse / electrons from the photomultiplier tubes are used to generate
an image.
• The quality of the image is improved by using narrower or longer collimators, or a longer
scanning time.

Question 75

Explain the basic principles of PET scanning, including how the image is formed.

Answer 75

• The patient is surrounded by a ring of gamma cameras/detectors.
• The positrons from the F-18 nuclei (β+ emitting tracer injected into patient) annihilate
electrons inside the body.
• The annihilation of a positron and an electron produces two identical gamma photons
travelling in opposite directions.
• The delay time between the detection of these two photons is used to determine the location
of the annihilation (which are areas of increased activity).
• A computer is connected to the gamma cameras/detectors and a 3D image is formed by the
computer using the electrical signals from the detectors.

Question 76

State some advantages of PET scanning.

Answer 76

• It is a non-invasive technique, so there is no risk of infection or scarring as a result of surgery.
• PET scans can be used to diagnose different types of cancers, to help plan heart surgery, and
to observe the function of the brain (such as Alzheimer’s disease).
• PET scans can be used to assess the effect of new medicines and drugs on organs.

Question 77

State some disadvantages of PET scanning.

Answer 77

• PET scanning is very expensive due to the facilities needed to produce the medical tracers.
• PET scanners are only found at larger hospitals, and only patients with complex health
problems are recommended for PET scans