Units and Quantities in Radiation Protection

8/14/2019 Units and Quantities in Radiation Protection

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Units and Quantities inRadiation Protection


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Learning Objectives:

describe the different units & quantities

used in radiation protection

determine when to use the different units& convert one unit from the other

solve related problems in radiation

protection


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Activity

Indicates the number of radionuclides

disintegrating per second (dps or s-1)

The SI unit is the becquerel (Bq)

1 Bq = 1 disintegration per second


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Activity

Symbol is A

Unit is becquerel (Bq)

transformation (decay) of one atom persecond

Curie (Ci)- old unit of activity1 Ci = 3.7 x 1010Bq = 0.037 terabecquerel

(TBq)tera (T) = 1012

A


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Multiples & Prefixes of Bq

Multiple Prefix Abbreviation

1 ------- Bq

1,000,000 Mega (M) MBq

1,000,000,000 Giga (G) GBq

1,000,000,000,000 Tera (T) TBq

1 x 1015 Peta (P) PBq


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Relationship of Units of Activity

Becquerel (Bq) = 1 dps

Curie (Ci) = 3.7 x 1010dps

1 Ci = 3.7 x 1010 Bq

1 mCi = 3.7 x 10 7Bq

1 Ci = 3.7 x 10 4Bq


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Useful Conversions for Units of Activity

Curies to Becquerels Becquerels to Curies

1 Ci = 37 kBq 1 Bq = 2.7 x 10 -11Ci

1 mCi = 37 MBq 1 kBq = 2.7 x 10 -3Ci

1 Ci = 37 GBq 1 MBq = 2.7 x 10 -5Ci = 27 Ci

102= 37 TBq 1 GBq = 2.7 x 10 -2Ci = 27mCi

1 TBq = 2.7 x 10 Ci = 27 Ci


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Radiation Quantities

Energyof ionizing radiation (E)

Joule (J) SI unit

1 eV = 1.6 x 10 -19J


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Radiation Quantities(2)

Fluence() no. of particles passing thru aunit area

- measured in particles per m 2

Fluence rate ()no. of particles passingthru a unit area per unit time

(m -2s -1)

.


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Exposure(X) the amount of ionizationproduced in air by photon i.e. gamma and x-rays

Unit:

Roentgen( R)

SI unit

Coulomb per kg of air

1 R = 2.58 x 10 -4C/kg of air


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Kerma (k)

- kinetic energy released per unit mass of

absorber

- kinetic energyof charged particles

produced in an absorbing medium by

uncharged radiationUnit:

Joule/kg = Gray


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Dosimetric Quantities

Absorbed Dose(D) a measure of radiation energy absorbed per

unit mass of matter

SI Unit:

Gray(Gy) = J/kg

Old Unit:

Rad= radiation absorbed dose

1 Gy = 100 rad


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Absorbed Dose (D)

Symbol is D

Unit = gray (Gy);(1 joule per kilogram)

Some countries still

use the rad(= 0.01 Gy)

D


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Examples

Convert the ff absorbed dose & dose rate:

0.4 mrad to Gy

7.5 Gyh -1to radh-1


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Dosimetric Quantities (2)

Equivalent Dose(H)

A measure of the biological effects of a

particular type of radiation on organs ortissues

H = D x WR , WR= radiation weighting factor

Unit: Sievert(Sv)

1 Sv = 100 rem


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Equivalent Dose (H)

Takes into accountdifferent radiation types

Symbol is H

Unit = Sievert (Sv)

Some countries still use

the rem(= 0.01 Sv)

HH WRD


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Radiation weighting factor, W R

-a dimensionless variable to be applied to

the absorbed dose to provide an estimateof relative human hazard of low level

exposure encountered in radiation

protection practice from diff. types &

energies of radiation


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Radiation Weighting Factors

Type & Energy Range Radiation Weighting

Factor (WR)

particles, all energies 20

particles, all energies 1

& x-rays, all energies 1

Neutrons: < 10 keV

10 keV100 keV> 100 keV 2 MeV

> 2 MeV 20 MeV

> 20 MeV

5

1020

10

5


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Example 1

Convert the ff equivalent dose & dose rate

between old & new units:

0.25 mrem to Sv

0.3 mSvh-1

to remh-1


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Example 2

Convert the ff. absorbed doses in a particular

organ or tissue to equivalent doses:

2 mGy from particle

2 mGy from particle

2 mGy from rays Which of these would be the most damaging

to organs or tissues?


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Effective Dose(E)

- a measure of the effect of a particular type of

radiation on organs or tissues

E T= H Tx W T, W T= tissue weighting factor


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Effective Dose (E)

Takes into account the

radiosensitivitiesof

different tissues or organs

Symbol is E

Unit = Sievert (Sv)

EE WTH


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Tissue weighting factor, W T

- multipliers used for radiation protection

purposes to account for the differentsensitivities of different organs & tissues to

the induction of stochastic effects of

radiation


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Tissue Weighting Factors (W T), ICRP 1990

Tissue W T

gonads 0.20

bone marrow 0.12

colon 0.12

lung 0.12

stomach 0.12

bladder 0.05

breast 0.05

liver 0.05

esophagus 0.05

thyroid 0.05

skin 0.01

bone surface 0.01

Remainder 0.05

ICRP-International Commission for Radiological Protection


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Recommended tissue weighting factors,

ICRP 2007Tissue W T Summation w T

Bone-marrow (red), Colon, Lung,

Stomach, Breast, Remainder tissues*

0.12 0.72

Gonads 0.08 0.08

Bladder, Oesophagus, Liver, Thyroid 0.04 0.16

Bone surface, Brain, Salivary glands, Skin 0.01 0.04

Total 1.00

* Remainder tissues: Adrenals, Extrathoracic (ET) region, Gall bladder, Heart, Kidneys,

Lymphatic nodes, Muscle, Oral mucosa, Pancreas, Prostate (M), Small intestine,

Spleen, Thymus, Uterus/cervix (F).


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Example

Calculate the effective dose resulting from 5

mSv equivalent dose to the ff organs/ tissues:

to the skin

to the thyroid

to the lung

to the gonads


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Committed Dose

dose accumulated by the body over 50 y

following intake of radionuclides (except inthe case of intakes by children where it is

defined as the dose accumulated until the age

of 70)


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Summary of Radiation Quantities

Quantity Symbol SI Unit SI unit

Name

Conversion

Energy E Joule (J) eV 1 eV = 1.6 x 1019J

Fluence Particles/sq. m.

Exposure X Coul/kg 1R= 2.58 x 10-4C/kg

kerma K Joule/kg Gray(Gy)

1 Gy = 1 J/kg


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Submultiples

1 Gy = 1 000 mGy = 1 000 000 Gy1 Sv = 1 000 mSv = 1000 000 Sv

In terms of old units:

1 Gy = 100 rad1 mGy = 100 mrad

1 Gy = 0.1 mrad

1 Sv = 100 rem

1 mSv = 100 mrem

1 Sv = 0.1 mrem


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Summary of Dosimetric Quantities

Quantity Symbol SI Unit SI Unit

Name

Conversion

Absorbed

Dose

D J/kg Gray

(Gy)

1 Gy = 100 rad

Equivalent

DoseH J/kg Sievert

(Sv)

1 Sv = 100 rem

Effective

DoseE J/kg Sievert

(Sv)

1 Sv = 100 rem


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Radiation Quantities & Units (Summary)

Equivalent

dose (Sv)

to a

particular

organ

Effective

dose (Sv)

to the

whole

body

Absorbed dose(Gy) to any medium

Fluence (particles per unit area)

Source(Activity: Bq)


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Tips to remember:

Roentgen: a measure of how much you

are exposed

gray (or rad): how much you absorb

sievert(or rem): how much biologicaldamage it does


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Measurement of RadiationRadiation monitoring instruments

Dose rate meter or survey meter

calibrated to read in microsieverts per hour or millirem perhour

Dosimeter

Measures the total dose accumulated by the instrument overa period of time

pocket or pen dosimeters-give direct or immediatereading of the dose

Film badge and thermoluminescent dosimeters-provide areading after processed by a laboratory

Surface contamination meterNeeded by users of unsealed sources

More sensitive detector to monitor spills and normallyprovides reading in counts per second (cps) or counts perminute (cpm)


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References

IAEA/ANSTO Module in Radiation Protection

Distance Learning Project

IAEA Post- Graduate Course in Radiation

Protection & Safe Use of Radiation Sources

(Lecture Materials)


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Documents

Units and Quantities in Radiation Protection