Lesson 4

What are the units for measuring

radon?

Slide 4-2

Radioactivity unitsPicocuries (pCi)

Measures • Activity (radioactive decays/second)• 1 picocurie (pCi)

= 0.037 decays/second = 1 decay/27 seconds= 2.22 decays/minute

Slide 4-3

Radon unitsPicocuries/liter (pCi/L)

Measures • Activity (decays/minute) per volume (one

liter of air)• 1 pCi/L

= 2.22 decays per minute per liter of air

What is the EPA action level in terms of decays per minute per liter of air?

Slide 4-4

EPA action levelPicocuries/liter

4 pCi/L = 4 x 2.22 decays/minute/liter= 8.88 decays/minute/liter

QuestionAssume that a client spent 10 hours/day in a room with a radon level of 4 pCi/L.

How many decays/liter would the client be exposed to each day?

Answer5,328 decays/day/liter

Slide 4-5

International System (SI)Radioactivity units

1 becquerel (Bq)= 1 decay/second= 27 pCi

1 pCi = 0.037 decays/second

= 0.037 Bq

Henri Becquerel, discovered radioactivity in 1896

Slide 4-6

International System (SI)Radon units

1 pCi/L = 37 Bq/m3

Slide 4-7

EPA action level International System (SI)

4 pCi/L = 4 x 37 Bq/m3

= 148 Bq/m3

Slide 4-8

Measuring radon decay products (RDPs)

Measure alpha radiation emitted by short-lived RDPs

Polonium-218

Bismuth-214

Polonium-214

Lead-214

Slide 4-9

Measuring RDPsWorking level (WL)

1 WL = Concentration of RDPs produced from

one liter of air that contains 100 pCi/L of radon

= Amount of short-lived RDPs that exists at a single moment if a container is kept at a constant 100 pCi/L

Slide 4-10

Working levelEPA action level

4 pCi/L = 0.02 WL

Slide 4-11

EPA action level Summary

• 4 pCi/L• 148 Bq/m3

• 0.02 WL

Slide 4-12

Questions?

Slide 4-13

Characteristics of radon decay products (RDPs)

• Solid particles• Electrically charged• React chemically

Slide 4-14

Factors that affect radon and RDP concentrations

• Some radon gas and RDPs escape as air flows out of home

• Some RDPs attach to (plate out on) solid objects, such as– Walls– Floors– Ceilings– Furniture

Plating out• Lowers RDP

concentration in air• Plated out RDPs

cannot be measured• Only RDPs in air can

be measured• Factors that affect

plating out also affect measurement of RDPs

Slide 4-15

Factors that affect radon and RDP concentrations

• Air circulation – Air moving within a

room• Ventilation

– Fresh air entering a room

• Air filters• Particles

suspended in the air – Dust– Smoke– Aerosols

Some RDPs plated out

Slide 4-16

Air circulation

• Circulation = moving around air already in a room

• How would air circulation affect concentration of RDPs?

• May increase plating out, as RDP particles blow toward solid objects and attach to them

• As plating out increases, concentration of RDPs in the air decreases

Fans increase normal air circulation

Slide 4-17

Ventilation

• Ventilation = supply of fresh air

• How would ventilation affect concentration of RFDs?

• Ventilation likely to lower concentration of RFDs• May also reduce radon concentration, as gas

escapes from home

Open windows and doors increase

ventilation

Slide 4-18

Air filter

• How would air filters affect concentration of RFDs?

• Air filters may remove some RDPs, which– Are particles– Have electrical

charge– React chemically

ExampleFurnace air filter

• Air filters will not remove radon, which– Is a gas– Has no electrical

charge– Does not readily

react chemically

Slide 4-19

Particles suspended in air

• Examples– Dust– Smoke– Aerosols

• How would particles affect concentration of RDPs?

• RDPs are more likely to attach to particles• RDP concentration in air decreases

Slide 4-20

Factors may affect radon measurement

• Air circulation• Ventilation• Air filters• Particles in the air

Slide 4-21

Secular (eventual) equilibrium

Radon

Radon decay products

Radon

• In closed home, concentration of RDPs increases until secular equilibrium is reached– Means RDPs have same

level of radioactivity as radon itself

– Takes 3-4 hours– Measure home after it has

reached secular equilibrium

• At secular equilibrium, 1 WL = 100 pCi/L

Slide 4-22

A home inspector’s lament and pledge

Picocuries and becquerels; secular equilibrium.

Radon decaying has made my brain cells go numb.

But I do understand: breathing radon’s not healthy,

So I’ll master these concepts, though they won’t make me wealthy.

Convert all these measurements? Curse that uranium!

I’m working at levels that hurt my poor cranium.

I’ll learn proper techniques, use the right protocol,

To help prevent cancer: that’s the goal of my role.

Slide 4-23

SummaryEPA action level

4 pCi/L = 148 Bq/m3 = 0.02 WL

4 4 pCi/L = 148 Bq/m3 = 0.02 WL

See handout 4-1

Slide 4-24

SummaryFactors affecting measurement

• Air circulation• Ventilation• Air filters• Particles in the air

ImportanceFactors affect conditions for testing a

home

Slide 4-25

Questions?

Slide 4-26

Checkyour comprehension

• See handout 4-2

Slide 4-27

Checkyour understanding

• See handout 4-