Section 8

Question 1

What fundamental principle is in TLD

Answer 1

Reliance on trap states

Question 2

Explain the molecular level of TLD

Answer 2

Excited e falls into trap state
Heat gives e energy to reach conduction band
E releases and produces light

Question 3

What does the gas filled detector have and when does current/voltage flow?

Answer 3

2 electrodes in air
- current only flows if rad ionises gas
- response depends on supply voltage

Question 4

What are the gas filled detectors?

Answer 4

Ionisation, thimble and GM

Question 5

What are the features of ionisation chamber?

Answer 5

Plateau in graph - output indep of voltage
Low V - only primary ions collected

Question 6

What is the current in the ionisation chamber like

Answer 6

Small current - amplify and measure

Question 7

What are the chambers in the ionisation detector?

Answer 7

small chambers measure exposure of primary xray beam & large chamber to monitor scatter

Question 8

Is current proportional to in ionisation?

Answer 8

Radiation exposure - cannot count photons

Question 9

What is the voltage effect in ion.?

Answer 9

Unaffected by small variations in V

Question 10

What are the 2 disadv for ion?

Answer 10

Low intrinsic efficiency
Do not provide permanent record

Question 11

Electronic equilibrium

Answer 11

electrons leaving = # electrons entering

Question 12

Thimble chamber

Answer 12

Small Free air chamber with a central electrode

Question 13

The size of a Proportional chamber pulse is

Answer 13

proportional to the energy deposited by the radiation –> energy discrimination

Question 14

Geiger Muller has a large

Answer 14

voltage and a single ionising event can produce an avalanche of ionisation

Question 15

Saturation means

Answer 15

pulse size is independent of energy deposited –> energy discrimination

Question 16

GM disadvantages

Answer 16

Dead time (not desired); does not say what the radiation is

Question 17

GM advantages

Answer 17

Simple, rugged, fairly cheap

Question 18

Diodes

Answer 18

Semiconductor device with 2 layer - n and p

Question 19

N-type

Answer 19

Excess of negative charge

Question 20

P-type

Answer 20

Excess of positive charge

Question 21

Current is proportional

Answer 21

to dose rate (real time reading)

Question 22

In diodes, Sensitivity changes with

Answer 22

repeated use due to radiation induced damage

Question 23

MOSFET

Answer 23

Metal Oxide Silicon Field Effect Transistor

Question 24

Advantages of MOSFET

Answer 24

instant readout, no angular dependence, uniform energy response (exc at low e)

Question 25

Organic electronics

Answer 25

carbon chem - semiconductor material out of plastic