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DDOSE CONCEPTS, QUANTOSE CONCEPTS, QUANTIITTIIES AND UNES AND UNIITSTS,, BASBASIIC PRC PRIINCNCIIPLES AND PLES AND PRIMARY PRIMARY
METHODS OF RADMETHODS OF RADIIATATIION PROTECTON PROTECTIIONON
DDOSE CONCEPTS, QUANTOSE CONCEPTS, QUANTIITTIIES AND UNES AND UNIITSTS,, BASBASIIC PRC PRIINCNCIIPLES AND PLES AND PRIMARY PRIMARY
METHODS OF RADMETHODS OF RADIIATATIION PROTECTON PROTECTIIONON
Module IVModule IV
Module IV - 2
Radiation Radiation exposureexposure
Traditional unit: Roentgen (R) = 2.58x10-4 coulomb/kg
= 1esu/cm3
Module IV - 3
Absorbed dose (D)Absorbed dose (D)
Energy imparted to matter from any type of radiation
D: absorbed dose
E: energy absorbed by material of mass ‘m’
Module IV - 4
Units of Units of aabsorbed bsorbed ddoseose
The SI unit: gray (Gy)
1 Gy = 1 joule/kilogram
Old unit : rad
1 Gy=100 rad
Module IV - 5
Equivalent dose Equivalent dose (H(HTT))
Accounts for biological effect
per unit dose
radiation weighting absorbed
factor ( WR ) X dose (D)
HT = WR x D
X
Module IV - 6
Radiation weighting factorsRadiation weighting factors (W (WRR))
ICRP 60 (1991)
Radiation type and energy range
WR
Photons (X-rays and gamma-rays) all energies Electrons, all energies Neutrons <10 keV 10-100 keV >100 kev to 2 MeV 2-20 MeV >20 MeV Protons >20MeV Alpha-particles, fission fragments
1 1 5 10 20 10 5 5 20
Module IV - 7
Unit of Unit of equivalent equivalent ddose ose
SI unit: sievert (Sv)HT (Sv) = WR x D (Gy)
Old unit: rem (roentgen equivalent man)
HT (rem) =( WR) x D (rad)
1 Sv = 100 rems
Module IV - 8
Effective dose (E)Effective dose (E)
Risk related parameter, taking relative radiosensitivity of each organ and tissue into account
E(Sv)= ΣT WT x HT
WT : tissue weighting factor for organ T
HT : equivalent dose received by organ or tissue T
Module IV - 9
Tissue and organ Tissue and organ weighting factorsweighting factors
Organ or tissue Tissue weightingfactor (WT)
GonadsRed bone marrowColonLungStomachBladderBreastLiverOesophagusThyroidSkinBone surfaceRemainder
Total
0.20.120.120.120.120.050.050.050.050.050.010.010.05
1.0
Module IV - 10
Conversion between units Conversion between units used in radiation protectionused in radiation protection
Physicalquantity
SI unit Non-SIunit
Relationship
Activity
Exposure
AbsorbeddoseEquivalentdose
becquerel
coulomb/kg
gray (=J/kg)
sievert
curie (Ci)
roentgen ®
rad
rem
1 Bq=2.7x10-11 Ci1 Ci=3.7x1010Bq1 mCi=37 MBq1 R=2.58x10-4 C/kg1C/kg=3876 R1 Gy=100 rad1 rad=1 cGy1 Sv=100 rem1 rem=10 mSv
Module IV - 11
Committed equivalentCommitted equivalent ddose ose HHTT(t)(t)
and cand committed ommitted eeffective ffective ddose E(t)ose E(t)
Module IV - 12
Averted dose
Averted dose
Projected dose
Projected Projected and aand avertablevertable dose dose
Module IV - 13
Collective effective dose Collective effective dose ((SS))
Total radiation dose incurred by population
Ei: average effective dose in the population subgroup i
Ni: number of individuals in subgroup i
Unit: man-sievert (man.Sv)
i
ii NES .
Module IV - 14
Sources and Sources and llevels of evels of rradiation adiation eexposure to xposure to
ppopulationopulation
Module IV - 15
Sources of Sources of rradiation adiation ddose to ose to ggeneral eneral ppopulationopulation
Module IV - 16
Background Background radiationradiation
•Terrestrial radioactivity
•Cosmic radiation
•Internal radioactivity
Natural background radiation doses in Europe
Module IV - 17
Terrestrial Terrestrial rradiationadiation::external and internal exposureexternal and internal exposure
U-238 Ra-222
Th-232 Ra-220
Module IV - 18
Cosmic Cosmic rradiationadiation
Module IV - 19
Internal Internal rradioactivityadioactivity
•Radioactivity in diet
•lead-210
•polonium-210
•potassium-40
Module IV - 20
AvAveerage ocupational radiation doses rage ocupational radiation doses received received duringduring various various types of types of workwork
‘Non-coal’
mining
16.3
mili
siev
erts
Dos
e in
mili
siev
erts
Module IV - 21
Dose Dose llimits imits rrecomended by ICRP ecomended by ICRP (1991)(1991) -- wwhole hole bbodyody
Occupationalexposure
Public exposure
50 mSv maximum in any 1 year 100 mSv in 5 years
5 mSv in any 5 consecutive years
(Working figure 20 mSv per year)
(Working figure 1 mSv per year
Module IV - 22
Dose Dose llimits imits rrecomended by ecomended by ICRP (1991)ICRP (1991) -- t tissuesissues
Annual doses to tissues Occupational Public
Lens of the eye
150 mSv 15 mSv
Skin (1cm2) 500 mSv 50 mSv
Hands and feet or individual organ
500 mSv
Module IV - 23
RRadadiiatatiion protecton protectiionon
Basic Basic pprinciples rinciples and and
primary methodsprimary methods
Module IV - 24
BasicBasic pprinciples of rinciples of rradiadiationation pprotectionrotection
Justification of practice
Optimization of protection
Individual dose limits
Module IV - 25
AALLAARRAA
As low as reasonablyachievable
Module IV - 26
Three basic factorsTimeDistanceShielding
Basic methods of protection against Basic methods of protection against
eexposurexposure to ionizing radiationto ionizing radiation
Module IV - 27
TimeTime
Exposure rate =10mGy/h
X Time = Total dose
1 hour = 10 mGy
2 hours = 20 mGy
Module IV - 28
DistanceDistance
Module IV - 29
Inverse Inverse ssquare quare llawaw
150 mSv/h0.06 mSv/h
d=50cm
Module IV - 30
ShieldingShielding
Module IV - 31
Shielding Shielding pphotonshotons
Module IV - 32
HalfHalf valuevalue layerlayer (HVL) (HVL)
Module IV - 33
Internal Internal eexposure xposure
Module IV - 34
InhalationInhalation
Module IV - 35
Ingestion/AbsorptionIngestion/Absorption
Module IV - 36
Protective clothingProtective clothing and and hand washinghand washing
Module IV - 37
Medical Medical eexposurexposureRelative effective dose and equivalent period of Relative effective dose and equivalent period of
exposure to natural background radiationexposure to natural background radiationEffective dose (mSv)
Equivalent period of natural radiation
Radiography
Chest 0.02 3 days
Pelvis 1.0 6 months
IVP 4.6 2.5 years
Barium studies 9.0 4.5 years
CT (Chest, Abdomen)
8.0 4 years
Nuclear Medicine
Thyroid imaging 1.0 6 months
Bone imaging 3.6 1.8 years
Module IV - 38
Review points Review points • Becquerel, coulomb per kilogram, gray, and sievert are part of International System of Units (SI).• Absorbed dose of radiation in SI units is expressed in gray. Ability of some types of radiation to cause more significant levels of biological damage taken into account with radiation weighting factor used to determine equivalent dose, expressed in sieverts
• Goal of radiation safety: keep radiation exposure as low as reasonably achievable (ALARA)