acads (08-006) covered keywords contamination, decontamination, dose equivalent, effective dose,...

ACADs (08-006) Covered

Keywords contamination, decontamination, dose equivalent, effective dose, committed dose, absorbed dose, exposure dose, committed dose equivalent, committed effective dose equivalent, radiation exposure limits, airborne radiation, 10CFR20, 10CFR100, NRC, time distance shielding, shielding, exposure control, buildup, protective clothing, ALARA, deep, shallow.

Description This module explains the legal requirements to ensure radiation exposure is controlled. Legal limits are discussed along with the ways to limit exposure.

1.1.8.4.4 1.1.8.4.5 3.3.1.10 3.3.3.9 3.3.3.11 3.3.3.14

3.3.4.8 3.3.4.12 3.3.4.13 3.3.4.14 3.3.6.13 3.3.7.4

3.3.8.9 3.3.8.10 3.3.8.11 3.3.8.18 3.3.9.8.1 3.3.9.16

3.3.9.21 3.3.9.26 3.3.10.13 3.3.11.8 3.3.11.13.8 3.3.11.20.4

3.3.12.1 3.3.12.3 3.3.12.18 3.3.14.20.1 3.3.14.20.2 3.3.14.20.3

3.3.14.20.4 3.3.14.20.5 4.9.9 4.9.10 4.10.3 4.11.5

4.11.7 4.11.8 4.11.9.1 4.11.9.2 4.11.9.3 4.11.10

4.12.2 4.14.6.1 4.14.6.2 4.15.1 4.16.2 3.3.4.8

Overview

• Legal standards and administrative procedures to protect radiation workers from the hazards of radiation exposure

• All employees in nuclear industry required to comply with certain federal government regulations with respect to radiation protection

• Plants licensed by the Nuclear Regulatory Commission (NRC) must meet all established radiation protection criteria

NET 130Module 4: Protection Against

Radiation2

NET 130 Module 4: Protection Against Radiation 2

Overview• Protection from Radiation

– Time-distance-shielding concept• If exposure time is minimized, dose is minimal• Shielding: when time and distance criteria are impractical

– Decontamination (external)– Protective clothing

• Internal contamination and resulting exposure is difficult to measure• Not all of the effects of radionuclides that may get into the body are

known• Once radioactivity enters the body, only natural biological processes and

radiological decay can remove it.• To avoid this hazard, respiratory protection equipment is worn to prevent

inhaling airborne radioactivity in designated areas.


Radiation3


Overview• Actual incidents involving overexposure have

contributed to knowledge about radiation damage.– Results studied and policies established to prevent

recurrence– Can be avoided by:

• Proper application of established procedure• Being aware of changing plant conditions• Adhering to basic exposure reduction principles of time, distance,

and shielding– Studies of long-term effects still being conducted

• Measures have been devised and implemented to prevent exposure to unnecessary radiation, even at low dose levels.– Refer to SOERs 85-3 and 01-1


Radiation4


Natural Background Radiation: Cosmic

• Everyone is inevitably exposed• Sources:

– Cosmic– Terrestrial– Internal

• Cosmic– From sources external to the earth, mainly the sun– Exposure depends on latitude and altitude– At 70deg latitude and sea level, dose rate from cosmic

rays measures about 28 mrem/year


Radiation5


ALTITUDE COSMIC RADIATION

Sea Level 33 mR/year (53 on open ocean)

5000 ft 40 mR/year

10000 ft 80 mR/year

15000 ft 160 mR/year

20000 ft 300 mR/year

300 miles 5000 mR/year

Natural Background Radiation: Terrestrial• In the air: Radon isotopes and their daughters

– Products of uranium-238 and thorium-232 decay• In water: Radium-226 and Radium-228 • In the Earth

– Common minerals used as building materials• Granite can cause 150 mrem exposure per year• Limestone: 20 mrem/yr

– Monazite• Mineral in rock or sand form• Contains thorium -- can produce high background levels• India: about 100000 people receive a dose of 1500 mrem/yr• Brazil: 30000 people receive about 1000 mrem/yr• In some cases, peak dose rates are on the order of 23000 mrem/yr

– Uranium: Typical uranium miner receives 5000 mrem/yr• A person living in a wood house is exposed to about 104 mrem/yr of

natural background radiation• A person living in a brick and concrete house is exposed to about 145

to 300 mrem/yrNET 130

Module 4: Protection Against Radiation

6NET 130 Module 4: Protection Against Radiation 6

Image source:

Wikimedia.org

(public domain)

Natural Background Radiation: Internal

• Exposure from radioactive materials that are inside the body naturally.

• Dose rate typically about 26 mrem/yr• Potassium-40 accounts for about 90% of the

total

• The average estimated dose rate per person for all types of background radiation combined is approximately 125 mrem/year


Radiation7


Man-Made Radiation and Legal Limits• Protection from natural background radiation is

impossible• Legal limits for protection are specifically for man-made

radiation only• Major sources

– Medical diagnosis and therapy• X-rays alone: average American is exposed to 50 mrem/yr whole body

and up to 1000 mrem/yr local dose– Nuclear weapon testing– Some consumer products

• Television sets, cigarettes, and watches contribute a few mrem/yr– Industrial exposure

• Legal standards apply only to occupational exposure– People employed in industries where exposure to man-made

(non-background) radiation occursNET 130Module 4: Protection Against

Radiation8


Average Annual Exposure

Human-Made Radiation Sources:

70 mRem/year

Naturally-Occurring Radiation Sources:

300 mRem/year


Radiation9

Human-Made Sources• Power generation

– Nuclear– Coal– Gas

• Nuclear weapons testing• Medical

– X rays– Chemotherapy– etc

• Industrial• Consumer products

– Lantern mantles– Cigarettes– etc


Radiation10


Legal Standards for Rad. Protection: 10CFR

• Nuclear Regulatory Commission (NRC)– Licenses and regulates the nuclear industry– Derives authority from Title 10 of the Code of Federal Regulations

• 10 CFR presently consists of about 180 parts• Parts that specifically address radiation:

– Part 19 (10CFR19): “Notices, Instructions, and Reports to Workers; Inspections”

– Part 20 (10CFR20): “Standards for Protection Against Radiation"– Part 100 (10CFR100): “Reactor Site Criteria”

• Each licensed facility is legally required to comply with all regulations in Title 10, or be subject to civil penalties.

• Every single individual employed in the nuclear industry should understand how he/she is legally protected.


Radiation11


10CFR19• Details workers’ rights and responsibilities in regard to radiation

exposure• Establishes requirements concerning radiological working

conditions• Outlines options available to workers to ensure compliance • Each licensee (e.g., a nuclear power plant) is required to post

conspicuously within the facility the following documents:– Regulations in 10CFR19 and 10CFR20– The facility's license and all associated amendments– Operating procedures– Notice of violations of radiological working conditions and response from

licensee• If posting not practical, may post a description and location of the

document• Must also post Form NRC 3, “Notice to Employees in Restricted

Areas” frequented by employeesNET 130



10CFR19• Licensee required to furnish exposure information to any

individual upon request• Workers are to be kept informed of the status of radioactive

materials or radiation levels in "restricted areas"• All employees are to be trained in health protection procedures

involving radiation exposure• NRC may conduct inspections of physical working conditions,

activities, and records of the plant.• Employees may be consulted during inspections, or they may

report any possible violations to the inspector• In the event that an individual suspects violations of 10CFR

regulations, he/she may request an inspection– A worker is permitted to conduct an inspection with the NRC– Complaint must be warranted– Arguments may be presented at an informal hearing instead of an

inspection– Name of person making complaint is withheld unless the individual

authorizes its releaseNET 130



10CFR100• “Reactor Site Criteria”• Regulations concerning public safety in the event of a

major accident• Criteria used in evaluating a site for new nuclear

deployment (NND – new reactor construction)– Intended use of reactor– Application of engineering standards to design– Safety features and radioactive release boundaries– Population density and land use– Physical characteristics such as seismology, meteorology,

geology, and hydrology• NRC makes an evaluation for each new site and issues

construction license if acceptableNET 130



• Exclusion Area– Area surrounding the reactor– Licensee has authority to determine all

activities including exclusion or removal of personnel and property from area

• Low Population Zone– Area immediately surrounding Exclusion

Area– Contains residents, the total number and

density of which are such that there is a reasonable probability that protective measures could be taken on their behalf in the event of a serious accident


Radiation15


10CFR100

Reactor

Exclusion

Low Population

Zone

Area

• Establishes industry standards and routine requirements for protecting plant personnel and the public from radiation hazards.

• Maintain radiation exposures and radioactive releases As Low As Reasonably Achievable (ALARA)

• Defines terms used in the regulations– Definitions are exact and must be known by

operators– See “Vocabulary” section


Radiation16


10CFR20

Units of Radiation Dose• Occupational Dose

– Dose received by an individual during course of employment, in activities/duties that involve exposure to radiation and/or radioactive materials

• Exposure Dose– Units of Roentgen (R)– Measurement of the exposure to ionizing radiation equivalent

to 2.58 E-4 coulombs/kg of air

• Absorbed Dose– Units of Rad or gray (1 gray = 100 rad)– Measurement of the amount of energy deposited (absorbed)

in a material, equivalent to 100 ergs/gm.


Radiation17


• Dose Equivalent (DE) DE = (Absorbed Dose) x (QF) Unit of Roentgen equivalent man (Rem) or Sievert (1 Sv =

100 Rem) Expresses the effects of all types of radiation on a

biologically equivalent basis

• Effective Dose Equivalent (EDE) EDE = (DE) x (WT)] WT = Tissue weighting factor Estimate of the effect of a localized partial-body exposure

on the whole body For a partial-body dose equivalent, multiply by WT for that

particular tissueNET 130Module 4: Protection Against

Radiation18


Units of Radiation Dose


Radiation19


Tissue or Organ WT (NRC) WT (ICRP)

Gonads 0.25 0.2Bone Marrow (Red) 0.12 0.12

Colon 0.12Lung 0.12 0.12

Stomach 0.05Bladder 0.05Breast 0.15 0.05

Esophagus 0.05Liver 0.05

Thyroid 0.03 0.05Skin 0.01

Bone Surface 0.03 0.01Remaining Tissues and Organs 0.30 0.05

Whole Body 1

TISSUE WEIGHTING FACTORS

• Committed Dose Equivalent (CDE) Once a radionuclide has been deposited in the body,

exposed person is “committed” to the dose resulting from the decay of that radionuclide so long as it is present in the body

Committed dose = dose occurring over the next 50 years (for radiation workers) or 70 years (for general public) after deposition

• Committed Effective Dose Equivalent (CEDE) CEDE = [(CDE) x (WT)]


Radiation20



• Collective Dose– Means for expressing the societal impact of

radiation exposures to population groups– Product of # of people exposed and their average

dose– Expressed in terms of “person-Sv” or “person-

Rem"– Collective dose equivalent

• Calculated based upon specific tissues or organs

– Collective effective dose equivalent• Calculated in terms of the whole body equivalent


Radiation21



• Deep Dose Equivalent (DDE)– Applies to external whole body exposure– Dose equivalent at tissue depth of 1 cm

• Shallow Dose Equivalent (SDE)– Applies to the external exposure of the skin or an

extremity– Dose equivalent at tissue depth of 0.007 cm

averaged over an area of 1 cm2

• Total Effective Dose Equivalent (TEDE)– Sum of the DDE (external exposure) and the CEDE

(internal exposure)NET 130




Radiation Exposure Limits• Occupational Exposure

– 10CFR20 establishes occupational exposure limitations for individuals in restricted areas

– Station Management for local plant also establishes site administrative limits

• Minors– Annual occupational dose limits for minors are

10% of the annual dose limits specified for adult workers.


Radiation23



Radiation24


10CFR20 Limitation State Admin Limits

N (age) x 1000 mrem or 5000 mrem/year

Pregnant females limit is the same as the Federal limitations.

TODE: Total Organ Dose Equivalent to Any Organ

50000 mrem/year to any organ 40000 mrem/year to any organ

LDE: Eye Dose Equivalent to the Lens of the Eye

15000 mrem/year to the lens of the eye

12000 mrem/year to the lens of the eye

SDE, WB: Shallow Dose Equivalent, Whole Body

50000 mrem/year 40000 mrem/year

SDE, ME: Shallow Dose Equivalent, Max Extremity to Any Extremity

50000 mrem/year 40000 mrem/year

TEDE: Total Effective Dose Equivalent

500 mrem/year ALARA awareness limit extendible to 1000 mrem by individual. Extension beyond this point requires Management approval up to 4000 mrem/current year.Pregnant females limited to 500

mrem exposure during entire gestation period, also limited to 50 mrem/month.

Radiation Exposure Limits• General Public

– Plants must keep TEDE to individual members of the public below 100 mrem/yr

• Planned Special Exposures– Plant may authorize an adult worker to receive

doses in addition to the daily occupational dose– Worker cannot exceed annual limit (about 5 Rem

TEDE) as specified in 10CFR20 Worker cannot exceed 5x the annual limits during his/her lifetime (5 X 5 = 25 Rem) during the planned special exposure period.


Radiation25


Radiation Exposure Limits• Whole Body Radiation Exposure

– Head, trunk, extremities (hands, forearms, feet, and ankles), active blood forming organs, lens of the eyes, and gonads

– Total lifetime whole-body accumulated dose to one individual may not exceed 5N x 1000 mrem TEDE

• N = age of the individual in years– Whole-body accumulated dose must be determined

by the plant and recorded on Form NRC 4, “Occupational External Radiation Exposure History".

• Radiation exposure is always restricted to the lowest value of any applicable limits (ALARA)


Radiation26

Restricted Areas• Area to which access is limited by the plant for

purposes of protecting individuals from risks from exposure to radiation and radioactive materials

• Unrestricted Area: any area to which access is not controlled


Radiation27

Reactor Building Control

Building

TurbineBuilding

Restricted Area

UnrestrictedAreaIntermed.

BuildingAuxBldg

Fuel Bldg

Barrier Fence

Radiation/High Radiation Areas• Restricted areas subdivided into:1. Radiation Areas

– Any area in which radiation levels could result in an individual receiving 5 mREM in 1 hour, at a distance of 30 cm from the source

– Typically defined as an area with general area dose rates of 5 – 99 mRem/hr

2. High Radiation Areas– Any area in which radiation levels could result in an

individual receiving 100 mREM in 1 hour, at a distance of 30 cm from the source

– Typically defined as an area with general area dose rates of 100 – 999 mREM/hr

• 10CFR20 requires these areas to be marked with a radiation symbol plus identifying words– CAUTION: RADIATION AREA– CAUTION: HIGH RADIATION AREA– GRAVE DANGER: VERY HIGH RADIATION AREANET 130


28

Image source:

Wikimedia.org

(public domain)


Radiation29


Radiation30

Radiation/High Radiation Areas• 10CFR20: At any access point to a high

radiation area, the following conditions must exist:– Access door must be equipped with a visible or

audible alarm that will activate upon opening, warning the entrant

– Access door must be locked except when access is required, at which point positive control over each entrant must be maintained.

– Access point must be equipped with a control device (automatic shield) that will decrease the dose rate to < 100 mREM/hr upon entry


Radiation31

Personnel Monitoring Equipment

• Form NRC 5, “Current Occupational External Radiation Exposure“– Plant maintain records of individuals

requiring personnel monitoring– NRC 5 maintains the total lifetime

accumulated dose to the individual from various types of radiation

– Entries are made at least quarterly

• Devices worn or carried by workers to measure dose• Must be worn by:

– Anyone who enters a restricted area and receives, or is likely to receive in 1 year, a dose in excess of 10% of 10CFR limits

– Anyone who enters a high or very high radiation area


Radiation32

Image source: Wikipedia.org

(public domain)

Airborne Radioactive Material• Radioactive material that has been dispersed through

the atmosphere, in the form of either particles or gases

• Can be caused from radioactive particulates, iodine, noble gases, or tritium oxide

• Primary concern: potential for deposition inside the body– Ingestion: do not eat/drink inside Radiologically Controlled

Areas– Absorption and Cuts: use protective clothing– Inhalation: use engineering controls, cleanliness controls,

and respiratory equipment


Radiation33

10CFR20: Internal Exposure• To determine amount of radioactive material inside

your body and as a baseline to detect any internal contamination in the future, a whole body count is given prior to entry into the reactor containment area

• Additional whole body counts are given:– Annually– Anytime internal contamination is expected– Termination of employment

• 10CFR20 appendices give specific limits regarding sources of internal exposure– Appendix B, Tables 1, 2, and 3– Appendix C


Radiation34

10CFR 20, Appendix B, Table 1• Occupational values for radionuclide concentration limits• Determine internal dose due to ingestion and inhalation

– Col 1: ALI for oral ingestion– Col 2: ALI for inhalation– Col 3: DAC values

• Classes– D: t½ < 10 days

– W: t½ = 10 to 100 days

– Y: t½ > 100 days


Radiation35Source: NRC.gov (public domain)

Annual Limit of Intake (ALI)• Max allowable limit for amount of radioactive material taken into the

body of an adult worker by inhalation OR ingestion in a year 1 ALI = 5 Rem CEDE (whole body) 1 ALI = 50 Rem CDE (individual organ or tissue)

• Example: Thorium-228

– This means that if a worker swallows Th-228 of activity 6E0 = 6 Ci OR inhales Th-228 of activity 1E-2 = 0.01 Ci, he/she has received 1 ALI and cannot be allowed to risk further internal exposure.

– Worker would be subject to 5 Rem whole-body equivalent exposure, or 50 Rem local exposure to the specific tissues in contact with the ingested material.


Radiation36

Source: NRC.gov

(public domain)

Derived Air Concentration (DAC)• Concentration of a given radionuclide in air which, if breathed for a

working year of 2000 hours, results in an intake of one ALI• DAC = Nuclide activity (µCi/ml) ÷ DAC limit from table (µCi/ml)• DAC-hrs = DAC x time (in hours)

2000 DAC-hrs = 1 ALI = 5 Rem CEDE = 50 Rem CDE1 DAC-hr = 0.0025 Rem = 2.5 mRem = 0.0005 ALI

• Example: Th-228

– This means that if a worker breathes air contaminated with Th-228 of activity 4E-12 Ci per mL of air, he/she has received 1 DAC.

– If this occurred over a period of one working year (~2000 hrs), the worker has received 1 ALI and cannot be allowed to risk further internal exposure.


Radiation37

Source: NRC.gov

(public domain)

• Radionuclide concentration limits (µCi/ml ) for airborne and liquid effluents released to environment (unrestricted areas)

• Col 1: air• Col 2: water• Activity limits are such that continuous inhalation or ingestion

over 365 days would result in TEDE of 50 mRem


Radiation38

10CFR 20, Appendix B, Table 2

Source: NRC.gov (public domain)

• Monthly radionuclide concentration limits (µCi/ml) for releases to sanitary sewer systems


Radiation39

10CFR 20, Appendix B, Table 3


• Lists activity values of specified radionuclides in units of microcuries (µCi)

• An area containing any radioactive material in excess of 10X the listed activity value must have a sign posted:

Caution Radioactive Materials• Exceptions

1. Material is stored less than 8 hours2. Area is attended by an individual assuming control to prevent exposure to

others


Radiation40

10CFR 20, Appendix C


10CFR20: Notifying the NRC• Certain radiation events must be reported to the

NRC within a certain timeframe– Reports of exposure to individuals– Loss of licensed material or other radioactive materials of

certain amounts designated below– Etc..

• Depending on the specific risk posed by the event, the notification might have to be:– Immediate (call)– Within 24 hours (call)– Within 30 days (written report)


Radiation41

External Exposure Control: Time• 3 basic mechanisms of external exposure control:

– Time– Distance– Shielding

• Dose Rate: Dose per unit time (e.g., mR/hr)

• Example:– Compare the total dose received by a person in a 100 mR/hr field for

15 minutes and one who remained there for 45 minutes.


Radiation42

TIME STAYx RATE DOSE DOSE TOTAL

mRhr

hr

mRDosePerson

mRhr

hr

mRDosePerson

75min60

1min45

100:2#

25min60

1min15

100:1#

Exposure vs. Exposure Rate

• EXPOSURE: total amount• EXPOSURE RATE: amount per unit time


Radiation43

1 HOUR

2 HOURS

4 HOURS

8 HOURS

100 mR

200 mR

400 mR

800 mR

100 mR

HR

Stay Time Exposure

Expo- sure Rate

External Exposure Control: Distance• 3 basic mechanisms of external exposure control:


• Distance– Radiation beam spreads wider as distance from source increases– Thus penetrating radiation decreases in intensity as distance from source

increases– Exposure minimized by maintaining the maximum feasible distance from

source– Decrease is function of source’s geometry. Four types:

• Point source (simplest)• Line source• Plane source• Tank source


Radiation44


Radiation45

DISTANCE vs. EXPOSURE

Radiation Source

5 ft

2 ft1 ft

4 mR

25 mR100 mR

DISTANCE

EXPOSURE


Radiation46

Dose Rate Formulas, in terms of Distance• Point Source: Small concentrated source

I1d12 = I2d2

2 (inverse square law) I = radiation intensity in mR/hr d = distance from source

• Line Source: e.g., a pipeI1d1

= I2d2 Applies only up to d = ½L, where L= length of line source Beyond that, Inverse Square Law is used

Point Source Example• Calculate the dose rate at 20 feet if a reading

taken at 5 inches is 100 R/hr from a point source.


Radiation47

I d I d

II d

d

R hr in

ft

ft

in

mR hr

1 12

2 22

21 1

2

22

2

2

2

2

100 5

20 12

43

( / ) ( )

( ) ( )

/

Line Source Example• Calculate the dose rate at 10 and 15 feet from a 20

foot pipe if the measured dose rate at five feet is 150 mR/hr.


Radiation48

II d

d

mR hr ft

ft

mR hr

105 5

10

150 5

10

75

/

/

II d

d

mR hr ft

ft

mR hr

1510 10

2

152

2

2

75 10

15

33

/

/

External Exposure Control: Shielding• 3 basic mechanisms of external exposure control:


• Shield– A material that is placed between a source of radiation and

personnel in order to protect individuals from excessive exposure

– Used if time and distance are not sufficient or practical– Material type and thickness required is function of type and

energy of radiation


Radiation49


Radiation50


Radiation51


Radiation52

External Exposure Control: Shielding• Alpha particles

– Very low penetrating power– Shielded by most materials, even one sheet of paper– Incapable of penetrating further than first layers of skin– Internal hazard only, usually ignored as an external exposure

hazard• Beta particles

– More penetrating than alpha radiation, but still not considered in shielding calculations

– Any material used to shield gamma radiation will usually also attenuate beta particles

– Special care must be taken to protect the lens of the eyes from beta

– Protective glasses must be worn whenever the possibility of beta exposure exists


Radiation53

External Exposure Control: Shielding• Fast and thermal neutrons and gamma radiation

– Of most concern in shielding– Greater penetrating power: can affect the whole

body– Material’s ability to shield neutrons is function of its

total absorption cross section– As neutron energy decreases, scattering and

absorption cross sections increase– For shielding thermal neutrons, any material with a

high absorption cross section (e.g. boron) is effective


Radiation54


Radiation55

Radiation Shielding

Paper Plastic Lead Image source:

Wikimedia.org

(public domain)

Shielding: Neutron Radiation• Recall for neutron radiation:

• Where:• I = remaining number of neutrons• Io = original number of neutrons

• T = total macro cross section (cm-1)• x = target material thickness (cm)


Radiation56

xo

TeII

Shielding: Half and Tenth-Thickness• Half-thickness for shielding

– Thickness of material needed to reduce the radiation level to 1/2 original intensity (aka “half-value layer”)

• Tenth-thickness for shielding– Thickness of material needed to reduce the radiation level

to one-tenth of its original intensity (aka “tenth-value layer”)

• Neutron: 10 inches of water• Gamma:

– 2 inches of lead– 4 inches of steel– 12 inches of concrete– 24 inches of water


Radiation57

xo

TeII

r

x

)1.0ln(

101

r

x

)5.0ln(

21

Neutron Shielding Example• Calculate the half and tenth thicknesses of water for fast

neutrons


Radiation58

in8.8 cm22.4 x

103.0

)1.0ln(

103.0)1.0ln(

1.0

1.0

10

1

103.0

101

110

1

101

1

103.0

00

0

1,0

101

1

101

cmx

xcm

e

eII

II

cmeII

xcm

x

waterrx

r

r

in2.65 cm6.73 x

103.0

)5.0ln(

103.0)5.0ln(

5.0

5.0

2

1

21

12

1

21

1

103.0

00

0

21

1

21

cmx

xcm

e

eII

II

xcm

xr


Radiation59

Shielding: Attenuation of E.R.• Recall for attenuation of photons (gamma and x-

rays)

I = remaining number of photonsIo = original number of photons

= total linear attenuation coefficient (cm-1)x = target material thickness (cm)= target material density (gm/cm3)m.a.c. = mass attenuation coefficient (cm2/gm)

xoeII

... cam

)5.0ln(2

1x

)1.0ln(

101x


Table of Mass Attenuation Coefficients (cm2/gm)0.1 0.15 0.2 0.3 0.4 0.5 0.6 0.8 1.0 1.25 1.5 2 3 4 5 6 8 10

H .295 .265 .243 .212 .189 .173 .160 .140 .126 .113 .103 .0876 .0691 .0579 .0502 .0446 .0371 .0321Be .132 .119 .109 .0945 .0847 .0773 .0715 .0628 .0565 .0504 .0459 .0394 .0313 .0266 .0234 .0211 .0180 .0161C .149 .134 .122 .106 .0953 .0870 .0805 .0707 .0636 .0568 .0518 .0444 .0356 .0304 .0270 .0245 .0213 .0194N .150 .134 .123 .106 .0955 .0869 .0805 .0707 .0636 .0568 .0517 .0445 .0357 .0306 .0273 .0249 .0218 .0200O .151 .134 .123 .107 .0953 .0870 .0806 .0708 .0636 .0568 .0518 .0445 .0359 .0309 .0276 .0254 .0224 .0206

Na .151 .130 .118 .102 .0912 .0833 .0770 .0676 .0608 .0546 .0496 .0427 .0348 .0303 .0274 .0254 .0229 .0215Mg .160 .135 .122 .106 .0944 .0860 .0795 .0699 .0627 .0560 .0512 .0442 .0360 0315 .0286 .0266 .0242 .0228Al .161 .134 .120 .103 .0922 0840 .0777 .0683 .0614 .0548 .0500 .0432 .0353 .0310 .0282 .0264 .0241 .0229Si .172 .139 .125 .107 .0954 .0869 .0802 .0706 .0635 .0567 .0517 .0447 .0367 .0323 .0296 .0277 .0254 .0243P .174 .137 .122 .104 .0928 .0846 .0780 .0685 .0617 .0551 .0502 .0436 .0358 .0316 .0290 .0273 .0252 .0242Si .188 .144 .127 .108 .0958 .0874 .0806 .0707 .0635 .0568 .0519 .0448 .0371 .0328 .0302 .0284 .0266 .0255Ar .188 .135 .117 .0977 .0867 .0790 .0730 .0638 .0573 .0512 .0468 .0407 .0338 .0301 .0279 .0266 .0248 .0241K .215 .149 .127 .106 .0938 .0852 .0786 .0689 .0618 .0552 .0505 .0438 .0365 .0327 .0305 .0289 .0274 .0267

Ca .238 .158 .132 .109 .0965 .0876 .0809 .0708 .0634 .0566 .0518 .0451 .0376 .0338 .0316 .0302 .0285 .0280Fe .344 .183 .138 .106 .0919 .0828 .0762 .0664 .0595 .0531 .0485 .0424 .0361 .0330 .0313 .0304 .0295 .0294Cu .427 .206 .147 .108 .0916 .0820 .0751 .0654 .0585 .0521 .0476 .0418 .0357 .0330 .0316 .0309 .0303 .0305Mo 1.03 .389 .225 .130 .0998 .0851 .0761 .0648 .0575 .0510 .0467 .0414 .0365 .0349 .0344 .0344 .0349 .0359Sn 1.58 .563 .303 .153 .109 .0886 .0776 .0647 .0568 .0501 .0459 .0408 .0367 .0355 .0355 .0358 .0368 .0383I 1.83 .648 .339 .165 .114 .0913 .0792 .0653 .0571 .0502 .0460 .0409 .0370 .0360 .0361 .0365 .0377 .0394

W 4.21 1.44 .708 .293 .174 .125 .101 .0763 .0640 .0544 .0492 .0437 .0405 .0402 .0409 .0418 .0438 .0465Pt 4.75 1.64 .795 .324 .191 .135 .107 .0800 .0659 .0554 .0501 .0445 .0414 .0411 .0418 .0427 .0448 .0477Tl 5.16 1.80 .866 .346 .204 .143 .112 .0824 .0675 .0563 .0508 .0452 .0420 .0416 .0423 .0433 .0454 .0484Pb 5.29 1.84 .896 .356 .208 .145 .114 .0836 .0684 .0569 .0512 .0457 .0421 .0420 .0426 .0436 .0459 .0489U 10.60 2.42 1.17 .452 .259 .176 .136 .0952 .0757 .0615 .0548 .0484 .0445 .0440 .0446 .0455 .0479 .0511

Air .151 .134 .123 .106 .0953 .0868 .0804 .0706 .0636 .0567 .0517 .0445 .0357 .0307 .0274 .0250 .0220 .0202Nal 1.57 .568 .305 .155 .111 .0901 .0789 .0657 .0577 .0508 .0465 .0412 .0367 .0351 .0347 .0347 .0354 .0366H2O .167 .149 .136 .118 .106 .0966 .0896 .0786 .0706 .0630 .0575 .0493 .0396 .0339 .0301 .0275 .0240 .0219

Concrete .169 .139 .124 .107 .0954 .0870 .0804 .0706 .0635 .0567 .0517 .0445 .0363 .0317 .0287 .0268 .0243 .0229Tissue .163 .144 .132 .115 .100 .0936 .0867 .0761 .0683 .0600 .0556 .0478 .0384 .0329 .0292 .0267 .0233 .0212

Gamma-Ray Energy, MeVMat'l


Radiation61

ER Shielding Example• Calculate the 1/2 and 1/10 copper shield thickness

required for a 3 MeV gamma beam (Cu = 8.96 g/cm3)

cmxcmx

cmx

cmx

xx

cmcmgmgmcm

gmcmMeV

20.717.2

32.0

)10.0ln(

32.0

)5.0ln(

)10.0ln()5.0ln(

32.0)/96.8()/0357(.

/0357.3@

101

21

110

112

1

101

21

132

2

Example

It is desired to reduce a beam of 7 rays to 1/16 of its initial intensity. The gammas have an energy of 1 MeV and lead will be used as the shielding material. How many half value layers are required? How many m of lead are required?

Solution:

(a)

Io/I = 16 = 2n,

In 16 = n In 2, or

n=(In16/ln2)= 2.773/0.693=4

Therefore, 4 half value layers are required.

Example (cont’d)

Solution (con’t)(b)

The value of (µ en /ƍ) Pb is obtained from the energy absorption coefficient versus energy curve (see next slide, or slide 60; Note: to convert m2/kg to cm2/g, multiply m2/kg by 10)

(µ en /ƍ) Pb= 0.0038 m2/kg

1 half value layer = 0.693/(µ en ) Pb = 0.693/43.1 m-1

4 half value layers = 4x(0.693/43.1) = 64.3 mm of lead

Gamma/X Shielding: Point Source• For gamma or X radiation from a point source:

C = activity in CiE = total energy emitted in MeVD = distance from source in ft


Radiation65

2

6

d

CEhr

RadRateDose

Example: Point Source Gamma• Calculate the dose rate from a 1 Ci cobalt 60

point source at a distance of 5 ft. Two gammas are emitted in the decay of cobalt 60 of energy 1.33 and 1.17 MeV.


Radiation66

hrRad

hrRadratedose

ftd

MeVE

CiCd

CEhrRad

/6.0

)5(

)50.2()1(6/

5

50.217.133.1

1

6/

2

2

Buildup factor• Any of the common gamma interaction processes

may result in secondary photons that have a finite probability of reaching the dose point.

• The extent to which such secondary photons add to the fluence or dose at the dose point is usually described through the use of an appropriate buildup factor.

• Buildup factors may refer to various quantities of interest, such as photon fluence, photon energy fluence, exposure, or dose, and the values among all are somewhat different.

Buildup factor

• The dose buildup factor is a dimensionless quantity that represents the ratio of total dose (including the dose from secondary photons) at the dose point to primary photon dose at the same point.

• The primary photon dose naturally comes from original photons that have penetrated the shielding material without interacting.

• Magnitudes of buildup factors vary widely, ranging from a minimum of 1.0 to very large values, depending on source and shield characteristics.

Buildup factor

• The ratio of the total photons at a point to the number arriving there without being scattered

• In the passage of radiation through a medium, the ratio of the total value of a specified radiation quantity at any point to the contribution to that value from radiation reaching the point without having undergone a collision.

Internal Exposure Control• Time/distance/shielding are ineffective if radioactive

materials enter the body• Internal exposures to power plant workers are

typically very low• Control methods: prevent radionuclides from

entering the body in the first place– Eating, drinking, smoking prohibited in radiation areas– If airborne radioactivity exists, protective breathing

apparatus is used– Maximum permissible concentrations (MPCs) for airborne

radionuclides• Internal dose approximated by evaluating the time

spent in areas with airborne contamination and the type of radiation present.


Radiation70

Internal Exposure: Half-Lives• Both radiological (t½, rad ) and biological half life (t½, bio ) must be

considered• t½, rad = amount of time required for sample to decay to 1/2 its

original activity• t½, bio = amount of time required for half the mass of a sample that

has entered the body to be removed through natural biological processes

• Combination of both these factors: Effective half life (t‑ ½, eff )


Radiation71

biorad

biorad

biorad

eff tt

tt

tt

t,2

1,21

,21,2

1

,21,2

1

,21

11

1

Use of respirators

• ALARA analysis – use of respiratory protection

Decision on respirator use: – optimal sum of external and internal doses– internal exposure must be evaluated against

• the increased external exposure and • related stresses caused by the use of respirators:

– Heat stress, reduced visibility, and reduced communication associated


Internal Exposure Example• Calculate the effective half life for iodine 131.

Radionuclide: 131IHalf-Life, Biological: 138 db

Half-Life, Radiological: 8.05 d


Radiation73

days

tt

ttt

dayst

dayst

biorad

biorad

eff

bio

rad

6.7

1388

1388

138

8

)(21)(2

1

)(21)(2

1

)(21

)(21

)(21

10CFR20: Federal Exposure Limits

• Adult Occupational Exposure Limits:5 REM / yr TEDE15 REM / yr LDE (Lens Dose Equivalent: exposure to

the lens of the eye)50 REM / yr CDE50 REM / yr SDE50 mREM / mo ; 500 mREM total during entire

pregnancy (Declared Pregnant Female)


Radiation74

10CFR20: Federal Exposure Limits


Radiation75

• Minor Occupational Exposure Limits (10% of adult limits):500 mREM / yr TEDE1.5 REM / yr LDE (Lens Dose Equivalent:

exposure to the lens of the eye)5 REM / yr CDE5 REM / yr SDE

• General Public Exposure Limits:No more than 100 mREM / yr TEDENo more than 2 mREM in any one hour in

unrestricted areas.

Surface Contamination• Radioactive Contamination

– Deposition of radioactive material in any place where it is not desired, particularly in any place where it may be harmful to personnel

– Two types: Surface and Airborne

• Surface Contamination– Dirt that contains radioactive materials– Sources: spills, leaks, or residue from mechanical

grinding– Co 60 is isotope of most concern


Radiation76

Surface Contamination• Fixed contamination

– Surface contamination that cannot be easily removed– Removed by filing, grinding, or other heavy-duty method

• Loose contamination– Surface contamination that is relatively easy to remove– Spreads easily– Greatest surface contamination hazard– Detected by using smears

• Filter paper is wiped over the surface• Paper is placed in a counting apparatus to determine the amount of

radioactivity picked up


Radiation77

Airborne Contamination• Particulate airborne contamination

– Radioactive material either suspended as small particles or entrained as suspended mist in the atmosphere

– Can be removed by fine filters

• Gaseous airborne contamination– Primary importance: tritium, krypton, xenon, iodine, and

argon– Cannot be removed by filtration– Gaseous fission products formed in the fuel elements during

power operation– Possible for these gases to be released into the primary

coolant– When coolant is vented, gases come out of solution and pass

to the atmosphereNET 130


78

Decontamination• Material with contaminated surface: Radionuclides are

removable• Material that has been irradiated:

– Material has been made radioactive due to exposure to radiation– Radionuclides are NOT removable

• Decontamination– Removal of contamination from undesirable location to more acceptable

location– Does not eliminate radioactivity, just moves it to where it can be

controlled safely or immobilized and ultimately disposed of– May be required for plant components, tools, equipment, areas of

compartments, clothing, or personnel– Alternatives:

• Storage for decay• Disposal without decontamination• Restricted use without complete decontamination


Radiation79

Decontamination: Surface Contamination• Generally loose radioactive material dropped on a

surface or spread around by hands or feet• Usually decontaminated by normal cleaning• Cleaning is done from less to more contaminated areas• Isolate area• Contamination carefully and completely removed to

avoid spreading• Loose contamination

– Blotting– Taping– Washing with sudless detergent and citric acid solutions– If solvents don’t work, strong chemicals or mechanical means

may be required


Radiation80

Decontamination: Tools• Contaminated tools and equipment

– May be used again in contaminated areas– May be temporarily stored in a designated area without decontamination

• If tools are reserved for contaminated area use only, must be distinctively marked to indicate they are always considered contaminated

• Some cases: taping tool prior to use and stripping off the contaminated tape after use eliminates need for decontamination

• Large tools are often wrapped in plastic instead of tape.

• Decontamination– Wipe with cloths soaked in detergent– Ultrasonic cleaning (good for irregular or recessed surfaces)– Mechanical decontamination methods (e.g. abrasives) (remove some of the tool's

surface)

• Cost factor: sometimes cheaper to dispose as radioactive waste and replace


Radiation81

Anti-Contamination Clothing• Prevent personnel from inadvertently spreading

radioactive contamination outside of controlled areas Also keeps the wearer free from contamination

• Full set: Designed to protect the worker’s head, neck, body, and extremities

• Totally protects skin from alpha particles and partially protects it from low energy beta

• Not meant to be a shield against penetrating radiation

• Only protects against direct skin contact with radioactive materials

• Either laundered or discarded


Radiation82

acads (08-006) covered keywords contamination, decontamination, dose equivalent, effective dose,...

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