External Dosimetry

Professional Training Programs

Oak Ridge Associated Universities
Objectives

 Review the dose quantities used in externa

dosimetry.

 Discuss dosimeter types and wearing locat

workers in various situationsworkers in various situations.

 Review the regulations about monitoring w Review the essential elements of an extern

dosimetry program.

 Discuss frequently encountered problems i

dosimetry programs.
Dose Equivalent

External doses are evaluated at variodepths depending on where the tissuis located. 
Dose Quantities

 NRC defines the whole body as 

head, neck, trunk of the body, aabove the elbows, and legs abovk

nee.

 The extremities are the hands, e

arms below the elbow, and feetlegs below the knee. 
Dose Quantities

 DOE defines the whole body as 

head, trunk of the body, arms aand including the elbows, and le

b d ld h k

a

bove an

d inclu

din

g t

he 

knee.

 The extremities are the hands, a

below the elbow, feet, and legs the knee.
Dose Quantities

 The total risk of radiation exposure i

the risks from both external and inteexposures.

 The total effective dose equivalent (T

the sum of the internal dose (CEDE) external dose (DDE).

 TEDE = CEDE + DDE
Dose Quantities

 Similarly, the total organ dose 

equivalent (TODE) is the sum of committed dose equivalent (CDEcommitted dose equivalent (CDE

organ or tissue and the DDE to organ or tissue.

 TODE = CDE + DDE
Dose Limits
External Dose 

 An individual's external dose is infe

from:

 dosimeter results. radiation survey results. both.

 The dosimeter provides a represent

dose to the individual in most situa
External Dose

The following variables affect exdose:

 radiation type and energy

radiation type and energy

 dose rate duration of exposure exposure geometry tissue composition and depth
Types of Dosimeters

The types of dosimeters used to measure individual dose are:

 Film Dosimeters

Film Dosimeters

 Thermoluminescent Dosimeters (TLDs) Optically Stimulated Luminescence Dosi

(OSLDs)

 Pocket Ionization Chambers Electronic Dosimeters
Film

 The film dosimeter, or film badg

consists of one or more dental radiographic film(s) wrapped in 

f

proo wrappers.

 The film wrapper is placed in a p

holder which is clipped to the individual's clothing. 
Film
Film

 Metal foils of Al, 

and/or Pb are pthe badge holdedifferentially abphotons of diffephotons of diffeenergies.

 The approximat

of the photons ethe individual cadetermined by cthe density of thunder the meta
Film

 The sensitivity of the film is ene

dependent below about 300 keV

 This means that the film absorb

radiation than tissue does.
Film

 The energy dependence of film 

from the silver content of the fil(silver has a higher atomic num(silver has a higher atomic num

tissue).

 Above about 300 keV the film is 

energy independent.
Film

 A window in the film holder allows b

to be determined for all but the weabetas. 

 After exposure the film is processed.  Strict quality control during processin

required to ensure that the measuredensity is produced by ionizing radianot poor processing.
Thermoluminescent 

Dosimeters (TLDs)

 Radiation exposure of 

thermoluminescent materials leasome electrons in excited statessome electrons in excited states

 This stored energy is released in 

form of light upon heating.
TLDs

 The light emitted is measured, a

proportional to the radiation absby the TLD.by the TLD.

 Most TLDs are LiF crystals.
TLDs

LiF is nearly air/tissue

equivalent, so it is energy independent from 10 keV to 10 MeV.
TLDs

Dose resplinear from μGy (10 mμGy (10 m

approximaGy (1,000 
TLDs

Other Li compounds and applications 

 Li2B4O7:Cu for measuring skin dose equ Li2B4O7:Cu for measuring skin dose equ Li2B4O7:Cu with plastic shield for measu

dose equivalent

 CaSO4:Tm for measuring low doses, e.g

checks
TLDs

 Like film, TLDs are sent to a pro

who reads the TLDs and reports results.

 TLDs are usually exchanged on 

quarterly basis instead of monthfilm badges.
Optically Stimulated 

Luminescence Dosimeters (

 This dosimeter is a crystalline so

the TLDthe TLD.

 When exposed to radiation, it st

energy in the same manner as Tmaterial. 
OSLD

 The stored energy in the TLD is 

released by heat.

 The stored energy in the OSLD 

released by exposing it to laser 
OSLD

 The principal advantage of the 

OSLD over film and TLD is the sensitivity.

 The OSLD can measure down to 

about 0.01 mSv (1 mrem).

 Film and TLD cannot measure 

less than about 0.1 mSv (10 mrem).
Dosimeter Processing

 Dosimeter processors must be accredited by th

National Voluntary Laboratory Accreditation Program, or NVLAP, which is currently not volu

 The accreditation program 

ensures that the processors meet specific standards and that dosimeter results are reliable.
Secondary Dosimeters

The film badges, TLDs , and OSaccepted by the regulatory agenaccepted by the regulatory agen

primary dosimeters, or the dosimthat will be used to measure the worker's dose of record.
Secondary Dosimeters

 There are times when secondary 

supplemental dosimeters are appropriate.

 Secondary dosimeters are not u

measure the dose of record, but provide additional information.
Pocket Dosimeters

 Pocket ionization chambers

(pocket dosimeters) are compact, easy-to-carry devices that indicate an individual's accumulated dose immediately, eliminating the delay of dosimeter processing.

 Pocket dosimeters should be worn on the up

part of the body close to the primary dosime
Pocket Dosimeters

For example, they are often issued temergency workers during emergencemergency drills.
Electronic Dosimeters

 Electronic do

(EDs) are usesecondary domany facilitieparticularly aparticularly a

power plants

 EDs, like th

dosimeter, an immediaof accumuladose.
Electronic Dosimeters

 Audible alarms for accumulated 

and dose rate.

 Stable readout that is not affect

physical activity (drift).

 Wide range of accumulated dose

dose rates.
Electronic Dosimeters

 Real time dose 

monitoring using radiotelemetry.

 Electronic storag

daily dose in a dbase.
Electronic Dosimeters

In spite of these advantages, eledosimeters are not currently accby regulatory agencies in the U.by regulatory agencies in the U.

primary dosimeters.
External Dosimetry Issue

 Where should a dosimeter be w

Are there situations where a wo

 Are there situations where

a wo

may need to wear more than ondosimeter?
Where to Wear?

 NRC regulations require that dos

be worn on the part of the body to receive the highest dose.to receive the highest dose.

 Usually this will be on the front 

body, but will depend on the sit
More Than One?

 When only one dosimeter is issu

worker, it is usually a whole boddosimeter.

 Additional dosimeters may be ne

when parts of the body could remore exposure than the whole bdosimeter indicates.
More Than One?

For example, extremity dosimeteissued to radiopharmacists or radiochemists who frequently haradiochemists who frequently ha

and prepare large amounts of radioactivity.
More Than One?

The most common extremity

dosimeter TLD finge
More Than One?

The flat portiring (which cTLD) must be facing the pafacing the pa

of the dominawhichever orwill measure greatest dose
More Than One?

 High dose tasks could require a num

dosimeters located on various parts body, e.g. front and back, head, nec

d/ h d

and/or 

han

ds.

 Pregnant workers may be issued a s

dosimeter for assessment of the dosthe embryo/fetus. (usually worn at tabdomen)
Lead Aprons and Dosime

 Usually, the dosimeter should no

shielded.

 However, some situations requir

knowledge of the dose for a shiepart of the body in addition to thoutside of a shield (location of hdose).
Lead Aprons and Dosime

 The classic example of this is oc

diagnostic radiology department

 Many diagnostic radiology proce

require the worker to wear a leaapron.
Lead Aprons and Dosime

 The primary dosimeter should be worn at the 

collar outside the apron, the location of the highest whole body dose.whole body dose.

 On the other hand, the 

result of this dosimeter may not be representative of the dose to the rest of the whole body, shielded by the apron.
Lead Aprons and Dosime

 Two dosimeters may be worn by wo

wearing lead aprons:

 one at the collar outside the apron. one on the trunk under the apron.

 The vendors can color-code the dosi

so that workers can wear them cons(e.g. red neck and yellow belly).
Weighting

 If two dosimeters are worn, wh

dosimeter result becomes the drecord?

 The answer is: It depends on t

state where you work !
Weighting

 Some facilities are weighting dosime

results to reasonably estimate the efwhole body dose when a lead apron 

 Several formulae are reported, but th

Webster formula is very common:

 EDE = 1.5 HW + 0.04 HC

 HW is the result of the waist dosimeter (under t HC is the result of the collar dosimeter (outside 
Weighting

 NRC has issued several summar

address this topic.

 Some states allow dose weightin

diagnostic and interventional radprocedures. 
Weighting

NCRP Report #122 Use of PersoMonitors to Estimate Effective DMonitors to Estimate Effective D

Equivalent and Effective Dose to Workers for External Exposure tLet Radiation (1995) discusses tin more detail.
Summary

 Use film, TLD, and OSL dosimet

primary dosimeters.

 Use pocket chambers, electronic 

dosimeters, and additional film, OSL dosimeters for secondary dosimeters.
Summary

 In most cases, a single whole bo

dosimeter is adequate for inferrrepresentative dose to the wholrepresentative dose to the whol

 Some situations may require add

dosimeters to obtain realistic doestimates.
NRC Monitoring Requirem

DDE SDE LDE

Adults > 5 mSv/yr 

(500 mrem/yr)

> 15 mSv/yr (1500 mrem/yr)

> 5(50

Mi >1 S / >15 S / >5 

nors

>

1 m

S

v/yr 

(100 mrem/yr)

>

1.5 m

S

v/yr

(150 mrem/yr)

>

5 

(50

Declared pregnant women: DDE > 1 mSv/gestation (1mrem/gestation).Individuals entering a high radiation area.Individuals entering a very high radiation area.Individuals who may have received radiation doses duwhile employed elsewhere.
Who Should Be Monitore

 The workers who should be monitore

more difficult group to identify, becathe phrase “likely to receive” in the regulations

.

 In the past, facilities monitored just 

everyone under the rationale that it only way to know if monitoring was required, and because monitoring prdegree of reassurance to workers.
Who Should Be Monitore

 Today, as a result of ALARA requirem

(including cost factors), most facilitieunnecessary issuance of dosimeters, on other means of determining the lon other means of determining the l

of exposure and providing reassuran

 In a survey of research or academic 

institutions, the percentage of radiatworkers assigned whole body dosimevaried widely, from 6%-100%.

1
Exchange Procedures

 The exchange procedures shoul

part of the dosimetry program procedures.

 The vendor will supply a shippin

with a new batch of dosimeters, should be checked for accuracy. 
Exchange Procedures

 The exposed dosimeters are exc

with the new ones as soon as po

 Problems can arise from:

 Lost or forgotten dosimeters. Damaged dosimeters (laundered b

mistake, etc.).
Exchange Procedures

 Unusual situations should be docume The shipment to the vendor should b

The shipment to the vendor should b

as soon as most of the dosimeters acollected.

 A shipment should not be detained v

waiting for individual dosimeters to breturned. 
The Control Dosimeter

 Each new shipment of dosimete

contains a control dosimeter. 

 The purpose of the control dosim

to measure background (dose dtransit and storage).
Control Dosimeter

 The control dosimeter should be 

back with the same batch of dosin which it arrived.in which it arrived.

 Any accumulated dose on the co

dosimeter is subtracted from inddosimeter results in that batch.
Control Dosimeter

 The control dosimeter must not 

any dose other than background the deployment period, or individ l b fdosimeter results may 

be si

gni

fi

underestimated.

 The purpose of the control dosim

frequently misunderstood.
Control Dosimeter

 For example, the control dosimeter shou

NOT be mounted in a central location frequently occupied by the monitored 

k

wor ers.

 The control dosimeter should be carefu

stored in a shielded location until it is dube shipped back with the batch of dosimin which it arrived.
Training

A badged workers responsibilities includ

 Wearing the dosimeter at the assigned place. Wearing the dosimeter at all work times.

Wearing the dosimeter at all work times.

 Handling it properly when it is not being worn (no la

no trunk of the car, etc.).

 Not let others wear his/her dosimeter. Exchanging the dosimeter promptly. Notifying the RSO if there is an occupational exposu

outside of work (part-time jobs, etc.) or previous exduring the year with another employer.

 Not deliberately exposing, destroying, contaminating

falsifying or tampering with his/her own or another's dosimeter.
Reports

 Prior to January 3, 2008, NRC regulations (10 CFR 

that workers be notified of dosimeter results on at annual basis in writing.

 Currently, licensees must provide an annual report 

i di id l it d f th d i d i th t individual monitored, of the dose received in that m

year if:

 the individual’s occupational dose exceeds 1 millisiev

millirem (mrem)) TEDE, or

 1 mSv (100mrem) to any individual organ or tissue, o the individual requests his or her annual dose report

 Workers have a right to review their dosimeter resu

time (in addition to the annual report). 
References

 O’Brien, S.L. et al., Howard Hughes Medica

Dose Assessment Survey. Health Physics 7

969;1996.

 NCRP Report #122 Use of Personal Monito

Estimate Effective Dose Equivalent and EffDose to Workers for External Exposure to LRadiation (1995).

 Webster, E.W. EDE for exposure with prote

aprons. Health Physics 56: 568-569, 1989.