12/3/98 Illinois Department of Nuclear Safety 1

RADON MEASUREMENT OPERATORS PROFICIENCY

COURSE

IN CONCERT WITH UNIVERSITY OF ILLINOIS AT CHICAGO AND

ILLINOIS DEPARTMENT OF NUCLEAR SAFETY

12/3/98 Illinois Department of Nuclear Safety 2

Physics ofRadon and its Decay

Products

12/3/98 Illinois Department of Nuclear Safety 3

Introduction to Radon andRadioactivity

4

Radon Characteristics

Colorless gas

Odorless gas

Tasteless gas

Naturally Occurring

Radioactive

Inert, does not chemically react (Noble Gas)

5

Atom comprised of:Atom comprised of:

NucleusNucleus Protons (+)Protons (+)

Neutrons (neutral)Neutrons (neutral)

Electrons (-)Electrons (-)

Simple Model of an Atom

6

The Nucleus Made up of positively charged protons and neutral

neutrons. The number of protons and neutrons combined is

called the “mass number” (or atomic mass). The number of neutrons is generally more than the

number of protons. The number of protons is the atomic number (which

identifies the element). The number of electrons is normally equal to the

number of protons, so that the total atom has no net charge.

7

Isotopes

An isotope is any atom with the same number of protons as another atom, but a different number of neutrons.

Radon-220 (thoron) is an isotope of Radon-222, since it also has 86 protons, but it has 134 rather than 136 neutrons.

8

Isotope Example

1P1P 1P, 1N1P, 1N 1P, 2N1P, 2N

Atomic # ?Atomic # ?Atomic Mass?Atomic Mass?

9

A Radon - 222 Nucleus

Protons Neutrons Atomic Mass Atomic Number This isotope of radon

is further identified by its mass number, hence the name radon-222

= 222= 222= 136= 136= 86= 86

= 86= 86

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Periodic Table of the Elements

Rn86222

11

Occurs spontaneouslyOccurs spontaneously An atom changes An atom changes

identity due to change identity due to change

in number of protons. in number of protons.

(-2)(-2) Radiation is released in Radiation is released in

the process. the process.

Radioactive Decay

Radon-222Radon-222

Alpha RadiationAlpha Radiation

GammaGammaRadiationRadiation

Polonium 218Polonium 218

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Radon Entry

Uranium

Radium

Radon

13

Abbreviated Uranium-238Decay Series

Uranium decays to Radium and then to Radon.

Uranium and Radium as solids are trapped in soil, but radon gas can move.

The decay rate is expressed by “half life”.

Uranium-238 (solid)Uranium-238 (solid)4.47 billion years4.47 billion years

Radium-226 (solid)Radium-226 (solid)1,620 years1,620 years

Radon-222 (gas)Radon-222 (gas)3.8 days3.8 days

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The Meaning of Half Life

Half Life is the

time required for

half of the atoms

to decay.

It is not the time

for all of the

atoms to decay.

100

50

25

12.56.25 3.125

0102030405060708090

100

0 1 2 3 4 5

Number of Half Lives

Per

cent

Rem

aini

ng

15

Uranium 238Uranium 238Decay SeriesDecay SeriesRadium-226Radium-226

Thorium-230Thorium-230

Uranium-234Uranium-234

Protactinium-234Protactinium-234

Thorium-234Thorium-234

Uranium-238Uranium-238

Lead-206Lead-206(Stable)(Stable)

Polonium-210Polonium-210

Lead-210Lead-210

Polonium-214Polonium-214

Bismuth-214Bismuth-214

Lead-214Lead-214

Polonium-218Polonium-218

Radon-222Radon-222 Bismuth-210Bismuth-210

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Radon Decay Product Characteristics

Source of cell damage in lungs

Short-lived decay products most significant

Have static charges

Chemically reactive

Solid particles

Heavy Metals

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Fate of Indoor Radon

Plated OutPlated Out Non-BreathableNon-Breathable Non-MeasurableNon-Measurable

AirborneAirborne BreathableBreathable MeasurableMeasurable

Radon-222Radon-222 Radon DecayRadon DecayProductsProducts

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Alpha Radiation ()

Alpha radiation is a particle released when the nucleus kicks out 2 neutrons and 2 protons (mass number changes by 4 and atomic number changes by 2).

Alpha particle– relatively massive– relatively slow– total charge of +2

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Beta Radiation (

Beta Radiation is a particle which is released when the nucleus changes a neutron into a proton and a beta particle (atomic mass number remains unchanged).

Beta particle– Relatively small mass– Relatively fast moving– Total charge of -1

P+N

20

Radon & Short-Lived Decay Products

Pb Bi Po At

-2 P-2 P-2N-2N

-2 P-2 P-2N-2N

+1P+1P+1P+1P

Rn868482 83 85

21

Gamma Radiation ()

Gamma radiation is pure energy. It is released from the nucleus whenever an alpha or a beta is emitted.

Gamma ray– No mass– Moves at the speed of light– No charge

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Relative Penetrating Power

AlphaAlpha

BetaBeta

GammaGamma

PaperPaperConcreteConcrete

23

Alpha Particles Are Strong Enough To Pit Plastic

Plastic chip from

passive radon test

(alpha track).

Magnified only 100

times.

3 months at EPA to

Action Level of 4

pCi/L.

24

Ionization Caused by Radiationcan occur with a , , or

Before CollisionBefore Collision After CollisionAfter Collision

Atom in airAtom in air Ion in air (net charge +1)Ion in air (net charge +1)

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Ion

Normally, the number of electrons orbiting the

nucleus is equal to the number of protons inside

the nucleus, so that the net charge of the atom is

zero.

An ion is an atom that has either lost or gained

electrons. It has a net positive or negative charge.

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Impact of IonizationCaused by Radiation

Measuring ionization allows one to detect the

presence of radiation:

– Pulsed ion chambers, Electret ion chambers, Geiger

counters

Ionization also contributes to overall health

effects.

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Radon Measurement Units

One picocurie per liter (pCi/L) is 2.22 disintegration's per minute within a liter

– This comes from the fact that one Curie is 37 billion disintegration's per second (dps) and:

One picocurie is one trillionth of a Curie, or .037 decays per second

There are 60 seconds in a minute 60 x .037=2.22, or 1 pCi/L is 2.22 dpm

28

International Radon Unit:The Becquerel

One Becquerel per cubic meter (Bq/m3) is one disintegration per second within a cubic meter

Becquerel = 1 disintegration per second

1 pCi/L = 37 Bq/m3

In other words:– pCi/L x 37 = Bq/m3, or– (Bq/M3)/37 = pCi/L– 4pCi/l = 148Bq/m3

29

Radon Decay Product Units:The Working Level (WL)

1 Working Level is the total amount of energy which would be eventually released by the alpha particles coming from the short- lived RDPs.

1 WL is created by 100 pCi/L of radon 1 Working Level is the amount of short-lived

radon decay products within one liter that would ultimately come from the complete disintegration of 100 pCi/L of radon (assuming all RDPs that are produced are measured).

30

Radon Decay Product Units:A More Practical Definition

1 Working Level is the amount of short-lived radon decay products that exist at any one moment within one liter if a room, or container, is constantly maintained at 100 pCi/L (assuming all RDPs that are produced are measured.)

Radon

Radon100 pCi/L100 pCi/L

1 WL1 WL

31

Secular Equilibrium

The condition where the short-lived Radon Decay

Products (RDPs) have each reached the same

radioactivity ( in picocuries per liter) as the radon

forming them.

It takes 4 hours for this to occur.

32

A Water Flow Experiment

33

At EquilibriumWater Flows are Equal

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At EquilibriumWater Flows are Equal

The waterfalls would be measured in gallons/minute.

Replace waterfalls with radioactive decay in decays/minute, or picocuries.

The volume of water in the buckets is analogous to the number of atoms of each isotope with the short lived isotopes having the least number of atoms at any one time.

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At Secular Equilibrium the Decay Rates of RDPs and Radon are Equal

Radon 222 - 3.8 daysRadon 222 - 3.8 days

Po 218 - 3 min.Po 218 - 3 min.Pb 214 - 27 min.Pb 214 - 27 min.

Bi 214 - 19.7 min.Bi 214 - 19.7 min.Po 214 - .000164 sec.Po 214 - .000164 sec.

Pb 210 - 19.7 yearsPb 210 - 19.7 years

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Equilibrium Ratio (ER)

The equilibrium ratio The equilibrium ratio

describes the fraction of describes the fraction of

RDPs that are suspended RDPs that are suspended

in the air, and therefore in the air, and therefore

measurable, to the total measurable, to the total

RDPs created.RDPs created. ER =ER =

Plated outPlated outRDPsRDPs

SuspendedSuspendedRDPsRDPs Measured RDPsMeasured RDPs

Total RDPsTotal RDPs

37

Equilibrium Ratio Example

Assume that you measured the RDPs suspended in the room with a working level meter and determined there were 0.5 WL in the room.

Assume that you measured the radon and determined that there was enough radon (i.e... 100 pCi/L) to create 1 WL of RDPs.

Therefore E.R. = = 0.50.5 WL0.5 WL1.0 WL1.0 WL

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Another Equilibrium Ratio Equation

Since the total RDPs can be found by measuring the radon, the total RDPs part of the equilibrium ratio equation can be replaced by:

Total RDPs = Radon (in pCi/L) 100 pCi/L per WL

This provides a more useful equation:ER = Measured RDPs (in WL)

Radon (in pCi/L) 100 pCi/L per WL

39

Equilibrium Ratio Equation

Canceling units and moving the “100” gives:

RDPs (in WL) x 100 Radon ( in pCi/L)

This equation allows one to determine an equilibrium ratio, and to convert from Radon to Working Levels, or vice versa.

ER =ER =

40

Equilibrium Ratio Calculation Example

Simultaneous measurements of radon and radon decay products indicate 4.0 pCi/L and .02 WL respectively. What is the equilibrium ratio?

This could also be expressed as a percent byThis could also be expressed as a percent bymultiplying by 100, or 0.5 x 100 = 50%multiplying by 100, or 0.5 x 100 = 50%

ER = = = 0.5ER = = = 0.5.02 x 100.02 x 100 2244 44

41

Factors AffectingEquilibrium Ratio

Air circulation– Increases plate-out, thereby decreasing ER

Electronic air filters– Decreases RDPs attached to dust particles, thereby

decreasing ER Suspended dust, smoke

– Increases sites for RDPs so fewer plate-out Recent ventilation

– Inadequate time for RDPs to have been formed 0.3 < ER < 0.7 in homes.

42

The Equilibrium Ratio Assumption

EPA and IDNS often assumes that, if nothing else is known about the home, an ER of 0.5 (50%) is a reasonable assumption.

Remember that the ER can be different, not only from house to house, but also within the same house.

Equilibrium ratios in homes range from 0.3 to 0.7

43

Other Versions of theEquilibrium Equation

ER =ER =

pCi/L =pCi/L =

WL =WL =

WL x 100WL x 100

ERER pCi/LpCi/L

WL x 100WL x 100pCi/LpCi/L

WL x 100WL x 100ERER

ER x pCi/LER x pCi/L100100

44

Dynamic Equilibrium

Once the radon entry Once the radon entry rate into a building has rate into a building has been altered, time is been altered, time is needed for radon and needed for radon and RDP levels to stabilize.RDP levels to stabilize.

12 hours is normally 12 hours is normally sufficient for dynamic sufficient for dynamic equilibrium to occur in equilibrium to occur in a home.a home.

12 Hours12 Hours

House ClosedHouse ClosedHouseHouseOpenOpen

TimeTime

RnRn

WLWL

Mea

sura

ble

Rad

ioac

tivi

tyM

easu

rabl

e R

adio

acti

vity