QUANTITIES AND UNITS USED IN RADIATION PROTECTION

H.L ANIL RANJITHHEAD, DIVISION OF RADIATION PROTECTION

ATOMIC ENERGY AUTHORITY

QUANTITIES:

ARE MEASURABLE CHARACTETISTICSEg LENGTH, DOSE ETC.

UNITS

ARE USED TO DESCRIBE THE QUANTITYEg METERS, GRAYS ETC.

RADIATION UNITS

• TO MEASURE RADIOACTIVITY• TO EXPRESS ENERGY OF

RADIATION EMITED• TO EXPRESS AMOUNT OF

ENERGY DEPOSITED IN THE BODY

• TO QUANTIFY BIOLOGICAL DAMAGES TO IRIDIATED TISSUES

ACTIVITY

• NO.OF DESINTEGRATIONS PRE SECOND

• 1Bq = 1 dis/s

• ORDER OF MAGNITUDE

THE CURIE

1 Curie (Ci) = Activity of 1g of 226Ra

1g of 226Ra disintegrate 3.7x1010 atoms per second

1 Ci = 3.7 x 1010 dis/s

1 Ci = 3.7 x 1010 Bq

1 Ci = 37 GBq

ENERGY OF RADIATION

ELECTRON VOLTS

1eV = 1.6 X 10 –19 J COBALT- 60 RADIOACTIVE MATERIAL EMITS TWO GAMMA RADIATIONS OF ENERGIES 1.17 MeV AND 1.32 MeV.

DOSE

USES AS A GENERIC TERM THAT CAN APPLY TO ANY OF THE RELEVANT

DOSIMETRIC QUANTIES

EXPOSURE

IN A GENERIC SENSE TO MEAN THE PROCESS OF BEING EXPOSED TO

RADIATION

Exposure Unit

•Is a measure of ionization produced in air

•Is used only for X and radiation

•Is valid for quantum energy less than 3 MeV

X Unit

1 X unit = 1 C/kg air

One exposure unit is defined as that quantity of x or gamma radiation that produces in air, ions carrying 1 coulomb of change( of either sign) per kg air.

Exposure Exposure is measured under conditions of electronic

equilibrium For photon energies above about 3 MeV, the ranges of

secondary electrons become a significant fraction of the photon attenuation lengths and the departure from equilibrium may be significant

Thus, exposure is not defined above photon energies of 3 MeV

Roentgens (2/3)

• Is symbolized by R

• was used as the exposure unit before SI system was adopted

• is still being used.

Roentgen

Is defined as the quantity of x or gamma radiation that produces ions carrying one statcoulomb of charge of either sign per cubic centimeter of air at STP. Charge of the electron=1.6x10-19C =4.8x10-10sC

1C =3x109 sC

13

KERMA

KERMA (Kinetic Energy Released in a Material):– Is the sum of the initial kinetic energies of all charged

ionizing particles liberated by uncharged ionizing particles in a material of unit mass

– For medical imaging use, KERMA is usually expressed in air

SI unit = joule per kilogram (J/kg) or gray (Gy)

1 J/kg = 1 Gy

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Mean absorbed dose in a tissue or organ

The mean absorbed dose in a tissue or organ DT is the energy deposited in the organ divided by the mass of that organ.

ABSORBED DOSE(1/2)• MEASURES THE ENERGY

DELIVERED TO ANY MATERIAL

• IN RADIATION PROTECTION THE MATERIAL CONCERNED IS

THE TISSUE OR ORGAN OF THE HUMAN BODY

ABSORBED DOSE(2/2)

• DEFINED AS THE “ENERGY ABSORBED

PER UNIT MASS OF ANY MATERIAL”

• UNIT USED “GRAY” OR “RADS”

1GRAY (Gy) = 1J/kg

1RADS = 100 ergs/g

100 RADS = 1 Gy

EQUIVALENT DOSE(1/2) QUANTIFY THE BIOLOGICAL DAMAGE TO THE ORGAN OR

TISSUE IRRIDIATEDThe same dose levels of different radiations (ie photons and neutrons) do not have the same level of biological effect

Radiation weighting factor, wR(related to radiation quality)

EQUIVALENT DOSE(2/2)

• BIOLOGICAL EFFECTS OF AN EXPOSURE ON A ORGAN OR TISSUE DEPEND ON:

• ENERGY TRANSMITTED TO THE ORGAN OR TISSUE BY RADIATION

• HAMFULNESS OF THE TYPE OF RADIATION INVOLVED (DEGREE OF POWER OF IONIZATION)

Radiation weighting factors, wR

1 Type and energy ranges

Radiation

weighting

factor, wR

115

10 20105 5

Photons, all energiesElectrons and muons, all energiesNeutrons, energy < 10 keV

10 keV to 100 keV100 keV to 2 MeV> 2 MeV to 20 MeV> 20 MeV

Protons, other than recoil protons, energy > 2

MeVAlpha particles, fission fragments, heavy nuclei

20

1) All values relate to the radiation incident on the body, or, for internal sources, emitted from the source.

Neutron radiation weighting factors30

25

20

15

10

5

0

wR

Neutron energy - MeV10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102

ICRP Recommendation

ICRP Approximation

EFFECTIVE DOSE

Different body tissues have different biological sensitivities to the same radiation type and dose

Tissue weighting factor, wT

EFFECTIVE DOSE• MEASURES THE RISK OF

BIOLOGICAL DAMAGE TO WHOLE BODY TAKING THE RADIOSENSITIVITIES OF TISSUE IRRIDIATED IN TO ACCOUNT

• MEASURES THE RISK REGARDLESS OF EXPOSURE INVOLVED.( INTERNAL, EXTERNAL, PARTIAL OR TOTAL)

• MEASURES IN THE UNIT OF.

“SIEVERT”( Sv )

Roentgen (3/3)

1R = 0.0087 J/kg of airIR = 0.0087 Gy = .87 RadIR = 0.0096 J/kg in TissueIR = 0.0096 Gy in TissueIR = .96 Rad in Tissue1 R = 1 Radfor x and rays IR = 1 rem = .01 Sv

Multipliers of the equivalent dose to an organ or tissue to account for the different sensitivities to the induction of stochastic effects of radiation.

Tissue or organ wT Tissue or organ wT

Gonads 0.20 Bone marrow (red) 0.12 Colon 0.12 Lung 0.12 Stomach 0.12 Bladder 0.05 Breast 0.05 Liver 0.05 Oesophagus 0.05 Thyroid 0.05 Skin 0.01 Bone surface 0.01 Remainder 0.05 TOTAL 1.00

Tissue weighting factors

Committed Dose

Is a useful subsidiary dosimetric quality to express dose to body during certain time following an intake of radioactive material to the body.

Note : The dose delivery to the body during the above period is at varying rates.

Committed Equivalent Dose

Defined as the time integral of the equivalent dose rate and denoted by HT( )

= integration time in years following the intake.

If t is not specified

Integration time is taken as

50 years for adults

70 years for children

  

Committed equivalent dose: The quantity H(), defined as;

 

where to is the time of intake, HT(t) is the equivalent dose rate at time t in an organ or tissue T and is the time elapsed after an intake of radioactive substances.When is not

specified it will be taken to be 50 years for adults and to age 70 years for intakes by children.

H H t dtTt

t

o

o

.

Committed effective dose:

The quantity E(), defined as ;

 

where HT() is the committed equivalent dose to tissue T over the integration time and WT is the tissue weighting

factor for tissue T. When is not specified it will be taken to be 50 years for

adults and to age 70 years for intakes by children.

E W HT TT

.

Collective Dose(1/2)

Is used to express dose to a group or a population.

Takes account of the no of people exposed to a source and the average dose to the individual.

COLLECTIVE DOSE(2/2)

DEFINED AS,

THE PRODUCT OF THE NUMBER OF INDIVIDUAL EXPOSED TO A SOURCE AND THEIR AVERAGE DOSE

UNIT: MAN SIEVERT (man Sv)

Is there RADIATION in this room?

Background Radiation

•Natural Background Radiation•Background Radiation Due to Man Made Sources.

NATURAL BACKGROUND RADIATION

• TERRESTRIAL SOURCES• EXTRA TERRESTRIAL SOURCES ( COSMIC RADIATION )

Natural sources of radiation… (2.4 mSv.y-1)

Cosmic…(0.4 mSv.y-1)

…from earth’s crust (0.4 mSv.y-1)

…via ingestion (0.3 mSv.y-1)

…via inhalation (1.3 mSv.y-1)

C. Torudd ; Swedish Radiation Protection Institute

...internal

External terrestrial irradiation 0.4 mSv y- Varies considerably with soil and rock type

Unusually high background in a few places in e.g.•Esperito Santos, Brazil•Kerala, India•Guandong province, ChinaUp to 50 µGy h-1 compared to 0.1 µGy h-1

External extra terrestrial radiation (Cosmic radiation)Estimated spectrum of secondary particles in the atmosphere from cosmic radiation

Heinrich et al 1999 (0.4 mSv.y-1)

Cosmic radiationDose and ambient dose equivalent during a flight from Bangkok to Copenhagen

External irradiation: Natural background dose rates from external sources (mSv.y-1)

Internal irradiation via

inhalation, 1.2 mSv.y-1

(mainly indoor radon)

Reasons for elevated levels of indoor radon

•elevated levels of 238U and 232Th series in the ground

•building material with elevated levels of 238U and 232Th series

•tight houses (cold climate…)

Internal irradiation via

ingestion40K•abundance 0.0188% in potassium (K)(0.15 mSv.y-1)

Also•uranium and thorium series(0.15 mSv.y-1)

Man-made Radiation

• Cigarette smoke• Consumer products

– Building materials– Smoke detectors

• Industrial use• Medical use• Nuclear power • Nuclear fall out

…and artificial sources of radiation

Medical examinations…(0.4 mSv.y-1)

C. Torudd ; Swedish Radiation Protection Institute

…and more artificial sources of radiation

...and nuclear weapons(0.005 mSv.y-1

atmospherical tests)

Nuclear fuel cycle…(0.0002 mSv.y-1)

C. Torudd ; Swedish Radiation Protection Institute

Nuclear power

Nuclear weapons

© Chernobylinterninform 1996

Chernobyl accident, April, 1986

Practical concequencies of Chernobyl accident

Effects of radiation and accident situation•600,000-800,000 persons in cleaning up work•Approximately 200,000 persons evacuated•Large areas of land abandoned (30 km zone etc.)

Other effects:•Cost estimated to 100 billion USD

Health concequencies of Chernobyl accident

Effects of radiation and accident situationSeen:•Immediate death of 30 persons •1800 children diagnosed with thyroid cancer (1998)Statistically:•15,000 deaths in cancer (global)

Other factors influencing health:•Poor food supply, social concequencies, anxiety

Source Mean effective dose (mSv)Natural background 2,4Medical examinations 0,4Nuclear tests in the atmosphere 0,005Chernobyl accident 0,002Nuclear fuel cycle 0,0002

Individual exposure of the world’s population due to ionising radiation,

year 2000

UNSCEAR

DO WE NEED RADIATION PROTECTION ?

Drinking Hot Coffee

Excess Temperature = 60º - 37 = 23º1 sip= 3ml3x 23= 69 calories

Lethal Dose= 4GyLD 50/60 = 4 GyFor man of 70 kg

Energy absorbed = 4 x 70 = 280 Joules = 280/418= 67 calories = 1 sip

X-ray

We live with1-3 mSv

Can kill4000 mSv

Radiation

Where to stop, where is the safe point?What are the effects of radiation?

What can radiation do?DeathCancerSkin BurnsCataractInfertilityGenetic effects