Applied radiation science and technology

Question 1

Name of the process which causes electrons to be emitted from the filament in the cathode

Answer 1

Thermionic emission

Question 2

Material which makes the coiled filament in the cathode and target in the anode

Answer 2

Tungsten

Question 3

Name two ways in which the intensity of X-ray production can be increased

Answer 3

Energy of incident electrons need to be increased, can be achieved by two ways:
1. Increased current supplying the filament
2. increase voltage supplying the electrodes which creates larger electric field strength

Question 4

Advantages of tungsten

Answer 4

Highly durable, high melting point, high atomic number

Question 5

Two types of radiation produced

Answer 5

Bremstrallung and Characteristic

Question 6

Bremstrallung radiation

Answer 6

Incident electron is fired towards the atom of the target material. Interacts with the electrostatic forces of attraction of the nucleus causing it to change its direction of motion. This change causes a loss in energy and attenuation of the incident electron. Loss in energy is given off as photons of X-rays. Degree of radiation emitted depends on level of attenuation of incident electrons. Resulting in a continuous spectrum of radiation.

Question 7

Characteristic radiation

Answer 7

Incident electron collides with orbiting electron in the target atom. Orbiting electron is fired off and creates a vacancy in an inner electron shell. Outer electron fills this vacancy resulting in an excess of energy due to inner shells requiring less energy. Excess energy is given off as photons of radiation. This is a specific amount and depends on the target atoms binding energies. This creates a line spectrum of radiation.

Question 8

Focussing hood purpose

Answer 8

Focussing hood has a negative potential difference across it which repels the electrons produced at the filament and causes them to form a focussed beam of electrons being fired towards the target.

Question 9

Vacuum

Answer 9

prevents oxidation of the electrodes and electrons colliding with air molecules reducing their net energy.

Question 10

Thermal cut out switch

Answer 10

Safety mechanism which is triggered when oil within the housing element expands due to overheating.

Question 11

Absorbed dose unit

Answer 11

Gray (Gy)

Question 12

what is 1 Gy equivalent to?

Answer 12

1 joule of energy per 1 kilogram of material

Question 13

absorbed dose meaning

Answer 13

measure of energy absorbed per unit mass of material being irradiated

Question 14

Dosimeter

Answer 14

A device used to measure the absorbed dose of ionising radiation.

Question 15

Give 3 ways in which dosimeters work?

Answer 15

1) ionisation chamber (uses either air or a semi conductor)
2) thermoluminescence
3)photographic film

Question 16

Summarise mechanism in which TLDs work:

Answer 16

Radiation causes electrons to gain energy and move from valence band to conduction band. electrons lose energy and fall into traps (impurities in the crystal). Heat is required to release trapped electrons. Produce light when released. light is an indication of radiation absorbed.

Question 17

Common material used in TDLs

Answer 17

Lithium fluoride with metal impurities

Question 18

what is Dose area product

Answer 18

DAP is total amount of radiation delivered to a patient by doing dose multiplied by area.

Question 19

Diamentor

Answer 19

device used to measure dose area product

Question 20

Dose reference levels

Answer 20

Average amounts of radiation delivered for different diagnostic procedures - a guide to what would be expected.

Question 21

What is a linac ionisation chamber

Answer 21

Used to measure total dose delivered to a patient - stops the linac when desired dose has been reached.

Question 22

Most commonly used semiconductor material

Answer 22

Silicon

Question 24

Absorbed dose meaning

Answer 24

Measure of energy absorbed per unit mass of material irradiated

Question 25

Unit of absorbed dose

Answer 25

Gray (Gy)

Question 26

What is 1Gy equivalent to?

Answer 26

1 joule of energy per kilogram of material

Question 27

What is the primary standard in terms of calibration

Answer 27

A measure of absorbed dose under carefully controlled conditions which local dosimeters can be calibrated against to ensure measurements are accurate and comparable

Question 28

Exposure

Answer 28

A measure of ionisation of air ( quantity of charge on ions per unit mass of air)

Question 29

Exposure units

Answer 29

Colombes per kilogram

Question 30

Thimble chambers

Answer 30

Detection devices which use the ionisation of air to measure absorbed dose of ionising radiation