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Physics 2 > 22) Dosimetry > Flashcards

22) Dosimetry Flashcards

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1
Q

Dosimetry

A

Studies the quantities describing the effect of ionising radiation on matter and the methods of their measurement and calculation

Application in medicine
Radiography
Nuclear medicine
Radiobiology

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2
Q

Biological effects of ionising radiation

A

Due to the part of the radiation energy which is transferred to the medium

The energy leaving the medium with the radiation produces no effect

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3
Q

Absorbed dose D

A

The energy deposited by the ionising radiation per unit mass of the medium

D= 🔺E/🔺m
Units is gray Gy
I rad = 0.01 Gy

Biological effect increases with the absorbed dose

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4
Q

Absorbed dose rate Pd

A

The rate at which the absorbed rate is accumulated

P_D = 🔺D/🔺t

Biological effect increases with the absorbed dose rate

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5
Q

Equivalent dose rate H

A

The absorbed dose weight by the quality factor Q of the ionising radiation

H=QD

Realative biological effectiveness is Q

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6
Q

Quality factor Q

A 
Radiation.        Energy.         Q
Photon             
Beta               
Proton           Above 2 MeV
Neutron         Below 10 Kev
                      100 Kev - 2 MeV
Alpha

BOOOOOK

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7
Q

Equivalent dose rate P_H

A

The rate at which the equivalent dose rate is accumulated

P_H= 🔺H/🔺T

Measurement is Sv/s

Biological effect increases as equivalent dose rate increases

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8
Q

Exposure x for x rays and gamma rays

A

Total charge for the ions of one polarity produced by the radiation in unit mass of the air

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9
Q

Exposure rate Px

A

The rate at which exposure is accumulated

PX = 🔺x/🔺T

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10
Q

Dose exposure relationship

A

Absorbed dose of a photonic radiation proportional to the exposure X

D=FX

F is exposure dose conversion factor

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11
Q

Conversion factor f

A

Measure of energy absorbed by the irradiated medium

It is proportional to the coefficient of the medium

Depends on the energy and the type of medium

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12
Q

Conversion factor f for tissues

A

Low energy is photoeffect
Conversion factor for bone is larger than soft tissue

Medium energy is Compton effect
The conversion factor is equal for all tissues

High energy is e- -e+
Conversion for bone is somewhat larger

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13
Q

Dosimetric instrument

A

Decide used to measure dosimetric quantities

Dosimeter
Measures dose exposure and rates
Radiometer
Measures activity of radioactive sources

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14
Q

Types of dosimetric detectors

A

Ionisation detector

Scintillation detector

Semiconductor detector

Chemical detector

Thermoluminescent detector

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15
Q

Ionisation detector

A

Gas filled tube with electrodes
.
Electrical conductivity of gas increases with ioniszing radiation

The disadvantage is that amount of ions produces in gases and tissues is different

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16
Q

Ionisation chamber

A

DRAWING

the raid iron ionises the gas and current flows in circuit

Current is proportional to exposure rate

17
Q

Quartz fiber dosimeter

A

Small ionisation chamber
No power supply

Ionisation of the gas reduces the charge of the electrodes

18
Q

Proportional counter

A

Average frequency of electric pulses is proportional to the activity of the radiation source

19
Q

Geiger counter

A

Each ion produces a strong electric current and the voltage between the electrode drops

The average frequency of the electric pulse is proportional to the activity of the radiation source

Used as radiometer only

20
Q

Scintillation detectors

A

Ionisation radiation produces fluorescence in the material of the detector

Disadvantage is that they’re not tissue equivalent

Frequency is proportional to dose rate
Magnitude depends on the type and energy of the ionising particle

21
Q

Semiconductor detectors

A

Ionisation radiation increases the electrical conductance of the semiconductor material

Disadvantage is that they’re not tissue equivalent

22
Q

Chemical detectors

A

Radiation initiates a chemical reaction
Advantage is that it’s tissue equivalent

Disadvantage is that it has low sensitivity

23
Q

Photographic detectors

A

Photograaphic films are sensitive to radiation

Darkening of the film depends on the absorbed dose

Disadvantaged is low accuracy

24
Q

Thermoluminescent detectors

A

The atoms excited by the radiation remain excited for long period of time

When crystal is heated it’s released as luminescent photons

Very sensitive

25
Q

Natural background radiation

A

Cosmic radiation

Ionisizing radiaiton

26
Q

Natural background radiation

A

Cosmic
Bulgaria is 300 usv/a
World is 400 usv/a

Terrestrial
Bulgaria 2000usv/a
World 2400usv/a

27
Q

Technogenic radiation

A

Radiography 1400

Nuclear medicine 110

Global fallout 5

Occupation exposure 4

Fossil fuel power station 2

Nuclear power station 2

28
Q

Background radiation

A

Natural
B is 2300
W is 2800

Technogenic
B is 1500
W is 800

Overall background rad
Add them up

29
Q

Natural background radiation

A

Cosmic
Bulgaria is 300 usv/a
World is 400 usv/a

Terrestrial
Bulgaria 2000usv/a
World 2400usv/a

30
Q

Technogenic radiation

A

Radiography 1400

Nuclear medicine 110

Global fallout 5

Occupation exposure 4

Fossil fuel power station 2

Nuclear power station 2

31
Q

Background radiation

A

Natural
B is 2300
W is 2800

Technogenic
B is 1500
W is 800

Overall background rad
Add them up

32
Q

Photographic detectors

A

Photograaphic films are sensitive to radiation

Darkening of the film depends on the absorbed dose

Disadvantaged is low accuracy

33
Q

Thermoluminescent detectors

A

The atoms excited by the radiation remain excited for long period of time

When crystal is heated it’s released as luminescent photons

Very sensitive

34
Q

Natural background radiation

A

Cosmic radiation

Ionisizing radiaiton

35
Q

Radiation protection

A

Minimising exposure to ionising radiation of workers to the lowest reachable levels

ALARA principle

36
Q

Compromise

A

The use of ionising radiation brings benefit

So you minimise the exposure not eliminate

Higher exposure to a small percentage of the population may be tolerated

37
Q

Exposure limits

A

Occupational
50-100 nAv/a

Individual
5mSv/a

General public
1msv/a

38
Q

Principles of radiation protection

A

Use ionising radiation if the results can’t be achieved by any other method

Establish that exposure limits are at the lowest reasonable achievable value

39
Q

Methods of radiation protection

A 
Ensure safe working conditions 
Time 
Amount 
Sheilding 
Distance 
Provide regular dosimetric screening and medical monitoring

Physics 2 (7 decks)

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