Interactions, quality and intensity

Question 1

elastic scattering is also known as 2

Answer 1

Rayleigh, or coherent scattering)

Question 2

define elastic scattering 1

Answer 2

photon energy is less than the binding energy of orbital electrons of the attenuator, the photon may be deflected with no loss of energy

Question 3

state the angle of scatter And direction 2

Answer 3

<12 degrees forward

Question 4

Define the Photoelectric absorption? 2

Answer 4

photon is completely absorbed by an atom, resulting in ejection of an electron (photo electron) from its orbital with the atom remaining as a positive ion. KEphotoelectron = Ephoton - Binding Energy electron

Question 5

What happens when the photon energy is equal to the binding energy of the electron upon collision?

Answer 5

Absorption - energy is transfered from photon to electron which is ejected from its shell in the atom

Question 6

Define characteristic radiation 2

Answer 6

vacancy thus created from photoelectric absorption in the shell will be filled by electrons in other orbitals further from the nucleus performing a series of quantum jumps downwards.

Energy is loss in this process causing the production of characteristic xray photons

Question 7

If a vacancy is in the K shell and is filled from the L shell name the characteristic photon k shell filled by M 2

Answer 7

Ka Kb

Question 8

Describe an alternative to the emission of characteristic radiation regarding the ejection of an outer electron called 2

Answer 8

Auger electron

one of the inner shell e- is ejected via absorption leaving a vacant shell space. Hence creating a ion. the quantum jump of another electron down to the shell dissipates energy which causes an outer shell auger electron to be emmited.

Question 9

The Photoelectric absorption depends on two factors 2

Answer 9

1. atomic number of material
2. energy of incident photon

Question 10

Define compton scatter 1

Answer 10

incident x-ray photon losing some of its energy and changing direction

incident photn has the same if not a great amount of energy to the BE of e-.

Question 11

When is the compton electron given the most amount of energy? 1

Answer 11

photon is back scattered 180 degrees

Question 12

what is the formula for the total energy of the incident ELECTRON 1

Answer 12

E incident = E scattered + E electron

Question 13

Define pair production? 2

Answer 13

needs a minimum amount of energy to occur. incident photon interacts with the electric field of the nucleus and is completely absorbed. Causing th production of an electron and positron each with kinetic energy (511 kev). The incident electron needs to be above 1022kev.

Question 14

what two attributes make and xray beam? 2

Answer 14

high energy short wavelength

Question 15

define ionising? 1

Answer 15

able to eject electrons from their atoms.

Question 16

what is the charge of an atomn that has lost an e-? 1

Answer 16

positive

Question 17

What is and ion?1

Answer 17

atom which does not have an equal number of protons and electrons.

If an electron was ejected the atom would be a positive ion

Question 18

Define Intensity? 2

Answer 18

Intensity is defined as the total energy carried by the beam per second per unit area at right angles to the direction of travel. This is a measure of quantity of radiation flowing in unit time Intensity WM-2 = watts/area M2

Question 19

What device is used to measure intensity? state the unit 2

Answer 19

Air Ionisation chamber? C KG-1

Question 20

State three reasons for choosing to make measurements in air from the ionisation chamber ?

Answer 20

• It is readily available - Its composition is close to being universally constant - The mean atomic number of air (Z = 7.6) is very close to that of muscle/soft tissue (Z = 7.4). results in air will be closely similar to those of tissue.

Question 21

What happens to the intensity when the distance from the source is doubled? 1

Answer 21

reduce the intensity by one quarter.

Question 22

What factor effect variation in intensity 3

Answer 22

• X-rays are not emitted from a point source as the focal spot has a finite size. - They are not emitted equally in all directions as the anode heel effect causes the intensity to vary across the beam. - Absorption and scattering of the X-ray beam occur as it passes through air.

Question 23

What happens to the Intensity if the mas is doubled? 1

Answer 23

doubled

Question 24

State the relationship between Mas and Distence 1

Answer 24

MAS is inversely proportional Distence

mAs1 = FFD2

Question 25

Atomic number and attenuation 1

Answer 25

The higher the atomic number of the material, the greater the attenuation that will occur

Question 26

state the atomic number of the following copper alluminium lead

Answer 26

copper (Z = 29), aluminium (Z = 13) and lead (Z = 82)

Question 27

This describes the penetrating power of the X-ray beam 2

Answer 27

QUALITY The more high energy (shorter wavelength) photons that there are in the beam, the higher is its penetrating power

Question 28

comparing the penetrating power of X-ray beams 1

Answer 28

half-value layer

Question 29

Define the effective photon energy 2

Answer 29

Two X-ray beams with different spectra (and therefore qualities) can have the same half-value layer but their exposure rates would be reduced by unequal amounts by other thicknesses of the same material

Question 30

Explain what will happen with the resulting positron and electron from a pair production? 3

Answer 30

proceed to be either absorbed by the body and dissipate their energy

scatter or

not interact at all.

Question 32

What is the HVT of lead?

Answer 32

0.1mm

Question 33

What is the HVT in tissue?

Answer 33

30mm