Dosimetric Quantities and Uni

10/25/10
Contents

IntroductionExposureAbsorbed DoseKermaDose Equivalent

Committed Dose EquivalentEffective Dose Equivalent

Total Effective Dose Equivalent (TEDE)Total Organ Dose Equivalent (TODE)Summary
INTRODUCTION
International Commission on Radiation U

Measurements (ICRU)The group formally charged with defining the quantunits employed in radiation protection. Key Reports:Fundamental Quantities and Units for Ionizing RadiICRU Report 60 (1998).Quantities and Units in Radiation Protection Dosim

Report 51 (1993).
International Commission on Radiologica

Protection (ICRP)Make recommendations regarding radiation protectUsually employ ICRU terminology, but sometimes gin defining radiological quantities and units.Key Publications: Recommendations of the International Commission Radiological Protection. ICRP Publication 26 (1977)Recommendations of the International Commission Radiological Protection. ICRP Publication 60 (1990)Recommendations of the International Commission Radiological Protection. ICRP Publication 103 (2008
U.S. Regulatory Agencies

Almost all U.S. regulatory agencies employ the quaunits of ICRP 26.The exception is the Department of Energy which eterminology of ICRP 60.
Four Dosimetric Quantities

• Exposure (X)

– Units: roentgen (R), coulombs/kilogram (C/kg)

• Absorbed Dose (D)

– Units: rad, gray(Gy), joules/kilogram (J/kg)

• Kerma (K)

– Units: rad, gray(Gy), joules/kilogram (J/kg)

• Dose Equivalent , aka Equivalent Dose 

(H or DE)

– Units: rem, sievert (Sv)
Exposure (X) 

and

Exposure Rate (X) 
Exposure (X)

Quantity: Exposure (X)Units: roentgen (R)

coulombs/kilogram

Unit conversions: 1 R = 2.58 x 10-4 C/kg

The quantity exposure reflects the intensity of gamx-rays and the duration of the exposure.More specifically, it is a measure of the charge on tone sign (negative or positive) resulting from the ingamma ray and x-ray photons in a specified mass 
Exposure (X)

Current Definition of the Roentgen

1 R = 2.58 x 10-4 C/kg

Original Definition of the Roentgen

The quantity of x-ray or gamma ray photons that pThe quantity of x-ray or gamma ray photons that p

charge of one sign, either positive or negative, of (electrostatic unit) per 1 cc of air at STP (0.001293 
PE Gamma ray or 1 kg of air x-ray photons Exposure (X)

CS

PP
Exposure Rate (X)

Quantity: Exposure Rate (X)Units: roentgen/hour (R hr -1

)

coulombs/kilogram/second (C kg-1

Unit conversions: 1 R/hr = 71.7 x 10-8 C kg-1

s-1

The quantity exposure reflects the intensity of gamx-rays.
Exposure (X) and Exposure Rate (X

General CommentsThe quantity is only defined for photons (e.g., gamand x-rays). Instruments measuring exposure rate mR/hr) should not respond to charged particles (e.The quantity is only defined in air. The exposure omaterials (e.g., tissue) should not be expressed in exposure rate (e.g., mR/hr). The quantity is considered unnecessary and is somreplaced by the absorbed dose rate or kerma rate 
Exposure Rate (X)

Important Equation

X is the exposure rate (e g R/hr)X is the exposure rate (e.g., R/hr)A is the source activity (e.g., Ci)' is the specific gamma ray constant (e.g., R m

2 hr

d is the distance from the source (e.g., m) 
Exposure (X)

Important Equation

X is the exposure (e g R)X is the exposure (e.g., R)A is the source activity (e.g., Ci)' is the specific gamma ray constant (e.g., R m2 hr

d is the distance from the source (e.g., m)t is the duration of the exposure (e.g., hr) 
Exposure Rate (X)

Important Equation

d is the distance from the source at which a given 

rate will occur
General Comments about the Equation

It calculates the exposure rate for a point source. 

Exposure Rate (X)

It works reasonably well for other source geometrithe distance (d) is greater than five times the maxdimension of the source.It does not include the background exposure rate.It does not consider the contribution to the exposumade by scattered photons.
Exposure (X) and Exposure Rate (X

Specific Gamma Ray Constant (

'

)

Each gamma emitting radionuclide has its own unispecific gamma ray constant.The specific gamma ray constant is the exposure rspecified distance from a specified activity of the nThese constants are usually looked up in tables, bcan be calculated if necessary.For look up tables, see PTP’s Rad Health Handbooat page 69.
Specific Gamma Ray Constant (

'

)

The exposure rate constant for Co-60 is 1.32 R m

2 

This means that the exposure rate at one meter frocurie Co-60 source is 1.32 R/hr. 

Exposure (X) and Exposure Rate (X

This is equivalent to 13.2 R/hr at one cm per mCi 

(13.2 R cm

2 hr-1 mCi-1) 
Calculating the Specific Gamma Ray Constant 

To determine the specific gamma ray constant for a radionuclide, individual constants are calculated fothe radionuclide's gamma rays and x-rays and then individual constants are summed. The formula for constant is 

Exposure (X) and Exposure Rate (X

' is the constant in R m2 

h-1 Ci-1

E is the gamma energy in MeVI is the gamma intensity (gammas/disintegration)uen

/

D is the mass energy absorption coefficient in 
Exposure Rate (X) - example calcu

What is the exposure rate at one foot from a 30 cu192 source? 
Rule of Thumb Regarding Radium-226

The exposure rate at one meter from a one curie source is approximately 1 R/hr.As such, the exposure rate at one meter from one Ra 226 is approximately 1 mR/hr

Exposure Rate (X)

-226 is approximately

1 mR/hr.

Similarly, the exposure rate at one meter from one Ra-226 is approximately 1 uR/hr above backgrouFinally, the exposure rate at one foot from one uCis approximately 10 uR/hr above background.
Absorbed Dose (D)

and

Absorbed Dose Rate (D)
Absorbed Dose (D) and Absorbed Dose 

Quantity: Absorbed Dose (D)Units: rad

gray (Gy)

joules/kilogram

Unit conversions: 1 Gy = 1 J/kg = 100 rads
The quantity absorbed Dose (D) is a measure of th

of radiation energy absorbed per unit mass (e.g., joules/kilogram or ergs/gram).It applies to all types of radiation, e.g., x-rays, gambetas, al

phas, neutrons

Absorbed Dose (D) and Absorbed Dose 

,p ,

The absorbed dose can be calculated for any mateair, water, tissue, lead
General Comments

The absorbed dose reflects the energy deposited mass, not the total energy: 

A 100 kg person absorbing 100 joules of energabsorbed dose of 1 Gy (100 rads)

Absorbed Dose (D) and Absorbed Dose 

absorbed dose of 1 Gy (100 rads). 

A 50 kg person absorbing the same energy haabsorbed dose of 2 Gy (200 rads).

The absorbed dose is material specific, e.g., the adose to human tissue from gamma rays or x-rays greater than the absorbed dose to air in the same 
Absorbed Dose or Dose Rate to Air (gammas, x

By definition 1 roentgen (R) = 2.58 x 10-4 C/kg

Since the charge on a single ion (e.g., electron) is 1

coulombs, an ex

posure of 1 roent

gen results in the 

Absorbed Dose (D) and Absorbed Dose R

,p g

of 1.6125 x 1015 ion pairs/kg in air. 

Since the average energy absorbed in air per ion pproduced is 34 eV (or so), an exposure of one roenequates to the absorption in air of 5.48 x 1016 eV/k
Absorbed Dose or Dose Rate to Air

Since 1 eV equals 1.6 x 10-19 joules, an exposure o

roentgen equates to an absorbed dose in air of 0.00.0088 gray.

Absorbed Dose (D) and Absorbed Dose R

Since one gray equals 100 rads, an exposure of 1 requates to an absorbed dose 0.88 rads in air
Absorbed Dose or Dose Rate to Air

The absorbed dose or dose rate to air from photons rays and x-rays) is related to the exposure as follow

Dair = 0.88 X

Absorbed Dose (D) and Absorbed Dose R

Dair is the dose or dose rate to air (e.g., rads or 

X is the exposure or exposure rate (e.g., R or R
Important Equation

The absorbed dose or dose rate to any material cacalculated from the exposure or exposure rate as 

Absorbed Dose (D) and Absorbed Dose 

Dmaterial is the dose or dose rate to the specified ma

(e.g., rads, rads/hr) due to photons.X is the exposure or exposure rate (e.g., R or R/hr

(:en/D)material is the mass energy absorption coefficie

specified material at the photon energy of interest
Absorbed Dose or Dose Rate to Tissue due to P

The absorbed dose or dose rate to human tissue dphotons can be calculated by using the following e

Absorbed Dose (D) and Absorbed Dose 
Absorbed Dose or Dose Rate to Tissue due to P

The photon energy must be specified in order to demass energy absorption coefficients (

:en

/

D).

The energy selected is not very important because the absorption coefficients for two materials tends 

Absorbed Dose (D) and Absorbed Dose 

constant as a function of energy. For the purpose example, we will use 1 MeV photons.The mass energy absorption coefficient at 1 Mev f3.074 x 10-2 cm

2/g

The mass energy absorption coefficient at 1 MeV 2.789 x 10-2 cm

2/g 
Absorbed Dose or Dose Rate to Tissue due to 

Absorbed Dose (D) and Absorbed Dose 

In other words, the absorbed dose to human tissapproximately 1 rad if the exposure in air is 1 R.If the exposure rate at a point is 1 R/hr, then the adose rate to tissue at that point is approximately 
KERMA (K)
Kerma

Quantity: Kerma (K)Units: rad

gray (Gy)

joules/kilogram

Unit conversions: 1 Gy = 1 J/kg = 100 radsKerma is similar to absorbed dose except that it is of the energy released (lost) by the radiation ratheenergy absorbed by a material.
• Kerma is the energy transferred to charged partic

unit mass of material by indirectly ionizing radiatiogamma rays, neutrons. It is not defined for chargeradiation (e.g., alphas, betas).

• Kerma is “

kinetic 

energy 

released in matter”

Kerma

• Kerma can be useful for explaining certain pheno

near the interface of two materials, e.g., the lack damage to skin from high energy photons (e.g., Cmulti MV x-rays).

• The concept of kerma is most widely employed in 

radiology
• Gamma rays or x-rays

In many, but not all, situations, the absorbed dos

the kerma: 

For Air: Exposure Absorbed Dose Ke

1 roentgen 0.88 rad 0.8

Kerma

Air kerma (rads) is sometimes used instead of e(R) to describe the intensity of photons.

• Neutrons

In almost all situations, the absorbed dose equakerma because the range of the charged particshort and there is no radiative loss (bremsstrahl
Kerma and dose as a function of depth in a mater

Dose

Kerma

Depth in material

Kerma

Attenuation
Dose Equivalent (H)
Quantity: Dose Equivalent (H or DE). 

Also referred to as Equivalent Dose.Units: rem

Dose Equivalent (Equivalent Dose)

sievert (Sv)joules/kilogram

Unit conversions: 1 Sv = 1 J/kg = 100 rems
• The quantity dose equivalent is an administrative 

employed for the purpose of radiation protection.

• It attempts to be a measure of the long term biolo

conse

quences for humans of a 

given ex

posure to 

General

Dose Equivalent (Equivalent Dose)

q gp

This is why the regulatory limits are expressed as equivalent rather than exposure or absorbed dos

• It “is defined for routine radiation protection applic

should not be used in the numerical assessment level exposures” (ICRU 51).
• The dose equivalent should only be applied to hu

Nevertheless, it is sometimes applied to other ma

• It can be calculated for any type of radiation.

General

Dose Equivalent (Equivalent Dose)
• The dose equivalent is calculated as follows:

H = D Q

H is the dose equivalent (e.g., rems, sieverts)

General

Dose Equivalent (Equivalent Dose)

D is the absorbed dose to human tissue (e.g., rad

Q is the quality factor

Internationally, the quality factor (Q) has been replac

radiation weighting factor w

R:

H = D w

R
• The value assigned the quality factor is based on 

stopping power of the charged particles in water, energy lost per unit distance travelled. The chargparticles being referred to are those which transfet th ti

Quality Factor (Q) and Stopping Power

Dose Equivalent (Equivalent Dose)

to the tissue.

• In the case of gamma ray or x-rays, the charged 

are electrons.

• In the case of neutrons, a mix of charged particle

involved: electrons, protons, carbon nuclei, etc. 
Standard Quality Factors (Q or w

R

)

The quality factor depends on the energy of the radbut the dependence is minimal for beta particles, aparticles and photons. 

I l t ll th f ll i lit f t ( 

Dose Equivalent (Equivalent Dose)

In almos

t all cases, the 

f

ollowing quality 

fac

tors 

(ra

weighting factors) are employed 

Radiation Q or w

R

Beta Particles (electrons) 1

Gamma rays and X-rays 1

Alpha particles 20
• Unlike the quality factors for beta particles, gamm

rays and alpha particles, the quality factor for ne

very dependent on neutron energy. Neverthelessare often assigned a “default” quality factor of 10

Quality Factor for Neutrons

Dose Equivalent (Equivalent Dose)

• Different regulatory agencies use different neutro

factors . The NRC uses those of ICRP 26. DOE uhigher quality factors recommended by ICRP 60

• An accurate determination of the dose equivalen

neutrons requires that the neutron spectrum mus- the neutron spectrum is rarely known
ctor (Q)

10

QualityFactor

Quality Factor for Neutrons (ca. those of ICRP 26

Dose Equivalent (Equivalent Dose)

Neutron Energy (MeV)

Quality Fac

05

0.001 0.01 0.1 1 10 

FissioSpect
Quality Factor for 

Neutrons (10 CFR 20)Dose Equivalent (Equivalent Dose)

If the average neutron energy is known, it is tempting to apply the quality (radiationquality (radiation

weighting) factor for that energy. It’s not the correct way to do the calculation, but it might be good enough.
Example Calculation

If the absorbed dose to a nuclear worker were 0.1 neutrons of unknown energy and 0.3 rads from gamrays, the worker’s dose equivalent (equivalent dosbe:

Dose Equivalent (Equivalent Dose)

H = (D Q)neutron + (D Q)gamma

= (0.1 x 10) + ( 0.3 x 1)= 1.3 rems or 0.013 Sv
Versions of the Dose Equivalent 

(Equivalent Dose) 

It is an unfortunate fact of life that the ICRU, ICRP

defined a large number of dose equivalent quantitof these include:• Committed dose equivalent (committed equivale

• Effective dose equivalent (effective dose)• Committed effective dose equivalent (committed 

effective dose)

• Collective dose equivalent (collective equivalen• Ambient dose equivalent• Directional dose equivalent
Committed Dose Equivale

(H50 or CDE)

or CDE)
Committed Dose Equivalent 

(Committed Equivalent Dose)The Committed Dose Equivalent (H50 or CDE) is 

calculated for internal exposures. In other words eresulting from inhalation, ingestion, absorption throskin, or injection.

It i th t t l (i t t d) d i l t th It is the 

t

o

t

al (i

n

tegra

t

ed)

dose equivalen

t over the 

following the intake of the radionuclide. The committed dose is attributed to the year of the In a manner of speaking, it is the dose that you are committed to over the course of your life as a resuintake in a given year.
Committed Dose Equivalent 

(Committed Equivalent Dose)For short-lived nuclides (e.g., I-131), or radionuclidcleared from the body (e.g., H-3), the committed dequivalent is the same as the dose equivalent deliduring the year of the intake.F l li d lid th t i i th b d thFor long-live

d nuclides th

a

t remain in the 

b

o

dy, the 

committed dose equivalent is much greater than thequivalent during the year of intake.The concept simplifies bookkeeping. In a given ye2009) an employer only has to deal with the dose from intakes during that year. They don’t have to cthe doses that result from intakes in previous year
Effective Dose Equivalen

(H

E or EDE)

or EDE)
Effective Dose Equivalent 

(Effective Dose)For the most part, the Effective Dose Equivalent (

EDE) is only calculated for internal exposures. In owords, exposures resulting from radionuclides getthe body via inhalation, ingestion, absorption throuskin, or injection.

The concept is intended to deal with non-uniform rexposures. Although the doses to the different tissues/organs of the body are pretty much the saexternal exposures, the different tissues/organs oreceive very different doses for internal exposures
Effective Dose Equivalent 

(Effective Dose)The effective dose equivalent concept equates nointernal exposures to external uniform exposures considering the risk.This allows external exposures to be added to inte

i d t l l t t t l d ( t

exposures in or

der 

to calcula

te a 

t

o

t

al dose 

(e.g., t

TEDE). 

Total Dose = External Exposure + Internal Ex
Effective Dose Equivalent (effective dos

for a Specific TissueThe effective dose (HE,T) for a given tissue is the p

the dose equivalent for that tissue (H

T) and the tiss

weighting factor for that tissue (w

T) :

HE T

=

H

T

w

T

H

E,T

H

T

w

T

The w

T reflects the risk of dying of cancer per unit 

equivalent to that tissue. The value assigned to thtissues in the body has changed over time as the estimates have been refined. 
If the dose equivalent to the tissue is a committed d

equivalent (and it almost always is), we calculate a committed effective dose equivalent rather than an dose equivalent. 

CEDE

= CDE x w

T

Effective Dose Equivalent (effective dosfor a Specific Tissue

CEDE CDE

x

w

T

The NRC uses the weighting factors (w

T) of ICRP 2

DOE uses those of ICRP 60. As yet, no one uses the weighting factors recommeICRP 103.
Tissue Weighting Factors

Tissue/Organ ICRP 26 ICRP 60 ICRP 

Gonads 0.25 0.20 0

Breast 0.15 0.05 0

Red Bone Marrow 0.12 0.12 0

Lung 0.12 0.12 0

Thyroid 0.03 0.05 0

Bone Surfaces 0.03 0.01 0

Colon 0.12 0

Stomach 0.12 0

Bladder 0.05 0

Liver 0.05 0

Esophagus 0.05 0

Skin 0.01 0

Salivary Glands 0

Brain 0

Remainder 0.30 0.05 0

Total 1.00 1.00 1
As an example, the ICRP 26 tissue weighting fact

thyroid is 0.03. This can be interpreted in several 

• 3% of the deaths due to uniform whole body 

exposures are due to thyroid cancer.

Effective Dose Equivalent (effective dosfor a Specific Tissue - Meaning of the TiWeighting Factor

p y

• The risk due to a specific dose (e.g., 1 rad) j

thyroid is 3% of the risk that would result if twere delivered to the entire body.

• 100 rems just to the thyroid carries the same 

3 rems uniform exposure to the whole body.
The sum of the weighting factors for all the tissues 

body is 1.Effective Dose Equivalent (effective dosfor a Specific Tissue - Meaning of the TiWeighting Factor
Effective Dose Equivalent (effective dos

for the Whole Body

The effective dose (H

E) for the whole body is the su

effective dose equivalents for the individual tissues:

H

E = 

Σ

H

T

w

T

Example: The next slide shows the committed dose equivalenvarious tissues of the body when an individual ingesmCi of I-131. These committed doses are multiplied by the approICRP 26 weighting factors to get the effective dose equivalents for these tissues. Finally, these are sumget the effective dose equivalent for the whole body
Tissue/Organ WT HT (rem) HE,T (re

Gonads 0.25 0.02 0.00

Breast 0.15 - -

Red Bone Marrow 0.12 0.03 0.00

Lung 0 12

Effective Dose Equivalent (effective dosfor the Whole Body

0.12 - -

Thyroid 0.03 130 3.90

Bone Surfaces 0.03 0.03 0.00

Small Intestine (remainder) 0.06 0.10 0.00

Stomach (remainder) 0.06 0.14 0.00

Bladder (remainder) 0.06 0.24 0.01

Liver (remainder) 0.06 0.04 0.00

HE = Σ HT wT 3.94
Committed Effective Dose 

Equivalent (HE 50 or CEDEEquivalent (H

E,50 or CEDE
Committed Effective Dose Equivalent 

(Committed Effective Dose)There is not much to say about the committed effedose equivalent (HE,50 or CEDE). 

Almost inevitably, when an effective dose equivalecalculated, it is the committed effective dose equiv

th d l t l d l ith th CED

other wor

ds, we almos

t always 

deal with the CED

EDE is rarely calculated.An exception: situations when the effective dose eis calculated for a non-uniform external exposure. case, it would simply be an effective dose equivalecommitted “concept” only applies to internal expos
Committed Effective Dose Equivalent 

(Committed Effective Dose)To obtain the committed effective dose equivalent specific tissue, the committed dose equivalent to tdue to an internal exposure is multiplied by the tissweighting factor:

CEDE CDECEDE = CDE x w

T

HE,T,50 = HT,50 x w

T
Total Effective Dose Equiva

(TEDE) 
TEDE

The NRC currently limits a worker’s total effective dequivalent (TEDE) to 5 rems in a year.This is intended to minimize the possibility of stochaeffects (e.g., cancer).TEDE is pronounced “teddy”TEDE is pronounced teddyIt is the sum of the external exposure and the internexposures:TEDE = External dose equivalent + Internal dose 
TEDE - external exposure

The external dose equivalent is measured with a doOnly dosimeters accepted by the regulatory agency “dosimeter of record” can be used (e.g., TLDs, OSLThe analysis of the dosimeter typically results in threquivalents being reported :

Deep dose equivalent (DDE)Shallow dose equivalent (SDE)Dose to the lens of the eye (LDE)

Of these, the deep dose equivalent is used as the mthe external exposure.
TEDE – internal exposure

The internal exposure is sometimes assumed to be However, if the internal dose equivalent is expected sufficiently large, it must be accounted for.To calculate the internal exposure, the person’s intapCi Bq) via ingestion inhalation injection or absorpCi, Bq) via ingestion, inhalation, injection or absor

be known. The intake might be estimated on the basis of a whcount, urine analysis, etc.Once the intake is known, the committed effective dequivalent (CEDE) can be determined from lookup (e.g., Federal Guidance Report 11.
TEDE – internal exposure

Such lookup tables are fine for the chemical form oradioactive material normally present in the workplaHowever, these tables should not be used to determCEDE due to the intake of the radiopharmaceuticalemployed in nuclear medicine. Determining the CEDE from the intake of radiopharmaceuticals involves the MIRD methodoloThe RADAR website is an excellent place to find outhis.

http://www.doseinfo-radar.com
TEDE – internal exposure

For the purpose of calculating the TEDE, the commeffective dose equivalent (CEDE) serves as the inteexposure.TEDE = External dose equivalent + Internal dose 

TEDE = DDE + CEDETEDE

= DDE

+ CEDE
TEDE

The external exposure component of the TEDE is texposure for a specified year, e.g., 2009. The internal component of the TEDE (the CEDE) is equivalent accumulated over the 50 years following (e.g., 2009-2060) that year.It might seem odd to do it this way, but that is how i
Total Organ Dose Equivale

(TODE) 
TODE

The NRC currently limits a worker’s total organ dos(TODE) to 50 rems in a year.The exception is the lens of the eye which is only arems in a year.The limit on the TODE is intended to eliminate (not The limit on the TODE is intended to eliminate (not 

the possibility of deterministic (non-stochastic) effeccataracts.The TODE is the sum of the external exposure and exposures:TODE = External dose equivalent + Internal dose 
TODE

For most organs/tissues, the deep dose equivalent with a dosimeter serves as the external exposure.For the lens of the eye, the eye dose equivalent is uexternal exposure.As was true for the TEDE the external exposure coAs was true for the TEDE, the external exposure co

the TODE is the actual exposure for a specified yea2009. On the other hand, the internal component of exposure (the CDE) is the dose equivalent accumuthe 50 years (e.g., 2009-2060) following the intake 2009).
TODE

Depending on its magnitude, the internal dose mighnot be calculated. If it must be calculated, the persoestimated via a whole body count, urine analysis, eFor the purpose of calculating the TODE, the commequivalent (CDE) serves as the internal exposure.TODE = External dose equivalent + Internal dose 

TODE = DDE + CDE

= LDE + CDE
TODE

In a previous example, an individual ingested 0.1 mCi of I-131following table indicated the committed dose equivalent (HT) t

tissue, the committed effective dose equivalent for each tissu

the summed whole body committed effective dose equivalent

Tissue/Organ WT HT (rem) HE,T (re

Gonads 0.25 0.02 0.005

Breast 0.15 - -

Red Bone Marrow 0 12 0 03 0 004Red Bone Marrow 0.12 0.03 0.004

Lung 0.12 - -

Thyroid 0.03 130 3.900

Bone Surfaces 0.03 0.03 0.001

Small Intestine (remainder) 0.06 0.10 0.006

Stomach (remainder) 0.06 0.14 0.008

Bladder (remainder) 0.06 0.24 0.014

Liver (remainder) 0.06 0.04 0.002

HE = Σ HT wT 3.940
TODE

If the individual’s external deep dose equivalent (as by a dosimeter) was 1 rem, the TEDE is just below limit:

TEDE = DDE + CEDE 

= 1 rem + 3.94 rems 

= 4.94 rems

However, the TODE for the thyroid would exceed tlimit!

TODE = DDE + CDE 

= 1 rem + 130 rems = 131 rems
Inverse Square Law
Inverse Square Law

As the distance from a source changes, the intensitradiation changes with the square of the distance:

I2 is the intensity of the radiation at distance 2 (d

2

I2 is the intensity of the radiation at distance

2 (d

2

rads/hr, rems/hr, n/cm

2/s, etc

I1 is the intensity of the radiation at distance 1 (d1

I

I1

d1

I2

d

2
Inverse Square Law

The above equation gives the distance (d

2) at which 

intensity of the radiation will be I

2 if the intensity of 

intensity of the radiation will be I2 if the intensity of 

radiation (I1) is known at another distance (d1)

I

I1

d1

I2

d

2
Summary
Quantity Symbol Units

Radiation Type (from 

what?)

Exposure X roentgens

C/kg

gamma and x-rays 

The quantity exposure is a measure of the intensity of gamma rays anMore specifically, it is a measure of the charge on the ions produced in 

Absorbed 

Dose

D rad

gray (Gy)

J/kg

any type 

The quantity absorbed dose is the radiation energy absorbed per unit The quantity absorbed dose is the radiation energy absorbed per unit 

Kerma K rad

gray (Gy)

J/kg

uncharged

(photons, neutrons)

The quantity kerma is the energy released by uncharged particles (phoneutrons) per unit mass of material through which the particles travel

Dose 

Equivalent

H rem

sievert (Sv)

J/kg

Any type h

The dose equivalent is an administrative concept used for the purpose protection. It is related to the risk of dying of cancer due to an exposur

to apply in the low dose range of the regulatory limits
Summary

As an approximation:

1 roentgen . 1 rad . 1 rad . 1 r

(photons in air) (absorbed dose to tissue) (kerma in tissue) (dose equiv

1 roentgen . 0.88 rad . 0.88 rad

g

(photons in air) (absorbed dose to air) (air kerma)
Summary

Key Equations:
Summary

TEDE = External Exposure + Internal Exposu

(DDE) (CEDE)

TODE = External Exposure + Internal Exposu

(DDE or LDE) (CDE)
APPENDIX

Additional Dose Equivalent QuanAdditional Dose Equivalent Quan
Collective Dose Equivalent

The collective dose equivalent is simply the averaequivalent to a population multiplied by the numbindividuals in that population.The units of the collective dose equivalent are theperson rems (or person sieverts)

-rems (or person

-sieverts).
Ambient Dose Equivalent

The ambient dose equivalent, symbolized H*(10), operational quantity intended for environmental mIt is defined for penetrating radiation (photons and at a depth of 10 mm.The ambient dose equivalent, symbolized H*(0.07operational quantity intended for environmental mIt is defined for weakly penetrating radiation (betasdepth of 0.07 mm.Directional Dose Equivalent
Individual Dose Equivalent, Penetrating

The individual dose equivalent penetrating, symboH(10), is an operational quantity intended for persIt is defined for penetrating radiation (photons and at a depth of 10 mm.The individual dose equivalent superficial, symboH(0.07), is an operational quantity intended for pemonitoring. It is defined for weakly penetrating radiation (betasdepth of 0.07 mm.Individual Dose Equivalent, Superficial