Measuring radon in residential propertiesWhat are the units for measuring radon?

Lesson4:What are the units for measuring radon?

Lesson overview

This lesson introducesthe units used to measure radon.

Lesson objectives

By the end of this lesson, the learners will be able to:

  • Identify three units used to measure radon and radon decay products in homes
  • List the EPA action levels for the three units used to measure radon and radon decay products in homes
  • Identify four factors that may affect measurements of radon decay products

Introduce the lesson.

In this lesson, we are going to talk about the units that we use to measure radon.

Show slide 4-1.

Explain picocuries.

First, we’ll talk briefly about measuring radioactivity, or the number of radioactive decays over a given period of time.

The important unit here is the picocurie, which equals

  • 0.037 decays per second
  • 1 decay every 27 seconds
  • 2.22 decays per minute

Show slide 4-2.

When we measure radon gas, we consider the activity (the number of decays per minute) for a given volume of air (one liter). A liter is a little larger than a quart.

So

1 pCi/L = 2.22 decays/minute/liter

Click to animate the slide.

Remember the EPA action level for radon: 4 pCi/L.

Ask.

What does the EPA action level represent in terms of radioactive decays per time and volume?

Give learners a moment to calculate.

Click to show correct answer:

EPA action level = 4 pCi/L = 8.88 decays/minute/liter.

Show slide 4-3.

Ask.

Assume that a client spent 10 hours/day (perhaps sleeping for 8 hours and watching TV for 2 hours) in a room that had a radon level of 4 pCi/L.

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

Click to show the answer.

5,328 days/day/liter.

Introduce becquerels.

Show slide 4-4.

This slide illustrates the average exposure to radiation in the United States. As you can see, radon accounts for more exposure than any other single source.

Show slide 4-5.

Another method of measuring radioactivity, often used outside the United States, uses units called becquerels. A becquerel equals 1 decay per second. Since a picocurie equals one decay every 27 seconds, one becquerel also equals 27 picocuries.

And since one picocurie equals 0.037 decays/second, one picocurie also equals 0.037 becquerels.

Like picocuries, becquerels measure activity. To measure radon gas, we use activity (becquerels)for a given volume of air (in this case, a cubic meter, not a liter). A cubic meter equals 1000 liters.

When we do the math, we find:

One picocurie per liter of radon equals 37 becquerels per cubic meter.

Ask.

Again, let’s consider the EPA action level for radon. How would you represent it in becquerels?

Give learners few moment to calculate.

Click to animate correct answer.

Correct answer:

EPA action level = 4 x 37 Bq/m3 = 148 Bq/m3

Introduce working levels.

Show slide 4-6.

So far, we’ve been talking about how to measure radon gas alone. However, earlier we explained that radon decay products (RDPs) also contribute to health risks. In fact, the term radonsometimes refers broadly to both radon and its decay products.

In particular, we measure the alpha radiation emitted bythe four short-lived radon decay products:

  • Polonium-218
  • Lead-214
  • Bismuth-214
  • Polonium-214

Show slide 4-7.

We measure the radiation from radon decay products differently. For RDPs, we generally use a unit called the working level (WL).

There are several ways to define the working level.

  • One WL is the concentration of RDPs produced from one liter of air that contains 100 pCi/L of radon.
  • One WL is the amount of short-lived radon progeny that exists at a single moment if a container is kept at a constant 100 pCi/L.

The equivalent of the EPA action level of 4 pCi/L is 0.02 WL.

Show slide 4-8.

In summary, we can express the EPA action level for radon in three forms:

  • 4 pCi/L
  • 148 Bq/m3
  • 0.02 WL

As a practical matter, the form we use most often is 4 pCi/L.

Show slide 4-9.

Ask.

Are there any questions so far?

Show slide 4-10.

Several factors can raise or lower the concentration of radon and RDPs that can be measured.

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

As we noted earlier, unlike radon gas, radon decay products are

  • Solid particles
  • Electrically charged
  • Chemically reactive

These characteristics determine how RDPs behave and how they are measured.

  • Some RDPs attach to (or plate outon) solid objects, such as walls, floors, ceilings, and furniture.
  • Plating out lowers their concentration in the air.
  • Plated-out RDPs cannot be measured.
  • Only the RDPs that remain in the air can be measured.
  • Therefore, factors that affect plating out also affect the measurement of RDPs.

Show slide 4-11.

Explain.

Among the factors that we need to consider are

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

Show slide 4-15.

Explain.

Let’s first consider air circulation (that is, moving around the air that is already within a room). For example, fans increase normal air circulation.

Ask.

How do you think air circulation would affect the concentration of RDPs?

Click to show correct answer:

  • Circulation, or moving air, may increase plating out, as RDP particles blow toward solid objects and attach to them.
  • When plating out increases, the concentration of RDPs in the air decreases.

Show slide 4-13.

Explain.

We said that circulation refers to moving around air that is already in the space. In contrast, ventilation refers to a supply of fresh air. Open windows and doors increase ventilation.

Ask.

What effect do you think ventilation would have on the concentration of RDPs?

Click to show correct answer:

Again, ventilation is likely to lower the concentration of RDPs.

It may also reduce the concentration of radon, as the gas escapes from the home.

Show slide 4-14.

Explain.

Another factor that affects the concentration of RDPs is an air filter—in a furnace, for example.

Ask.

How do you think an air filter would affect the concentration of RDPs?

Click to show correct answer:

A filter might remove some RDPs, which are charged particles that are chemically active.

A filter would not remove radon gas itself, which has no electrical charge and is not chemically active. Thus, a filter would lower the concentration of RDPs.

Show slide 4-15.

Ask.

What effect do you think particles suspended in the air (such as dust, smoke, and aerosols) might have?

Click to show correct answer:

When there are particles in the air, RDPs are more likely to attach to these particles. Thus the RDP concentration in the air is likely to decrease.

Debrief the questions.

Show slide 4-16.

As you see, air circulation, ventilation, air filters, and particles in the air can all affect radon measurement. We’ll see the importance of these factors again when we discuss the conditions that are needed to measure radon during short-term tests.

Show slide 4-17.

Explain secular equilibrium

Earlier, when we described radon, we said that over time, radon decays into various short-lived radon decay products.

In a closed system, like a closed home, the concentration of RDPs in the house increases until a situation called secularequilibrium is reached. (In this term, secular means eventual.)

Secular equilibrium occurs when the radon decay products have the same level of radioactivity as the radon itself.In other words, the rate of decay of each short-lived RDP will equal the rate of decay of the radon itself.

Achieving secular equilibrium takes about 3 to 4 hours. You will need to measure radon in a home after it has reached secular equilibrium. When we talk about the necessary conditions for short-term testing, you’ll see that these conditions reflect the time needed to achieve secular equilibrium.

Show slide 4-18.

This slide is intended as a little light relief and as a reminder of why the information in this section is important. You may use it if you think it appropriate for your learners or you may skip it.

Unlike the other slides, this one is intended to be read aloud. However, the rhythm is a little tricky and the rhymes are not perfect, so practice it beforehand.

Note that this slide is animated. You must keep clicking to show the stanzas in order.

Distribute handout 4-1.

Handout 4-1 summarizes this section on the units we use to measure radon and its decay products.

Summarize the lesson.

Show slide 4-22. Note that the slide is animated. Show the fill-in-the-blank part first.

Let’s review the units for measuring radon and radon decay products:

  • Picocuries/liter
  • Becquerels/cubic meter
  • Working levels

Ask.

What are the EPA action levels for these methods of measurement?

Allow learners to answer.

Click to show the correct numbers:

  • 4 pCi/l
  • 148 Bq/m3
  • 0.02 WL

Show slide 4-23.

We also talked about factors that affect the measurement of radon and radon decay products, including

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

These factors are important when we consider the conditions necessary for testing a home.

Show slide 4-24.

Ask.

Do you have any questions about the units for measuring radon?

Show slide 4-25.

Check comprehension.Distribute handout 4-2A.

Learners may answer the questions individually, in pairs, or in small groups. This comprehension check is not graded.

Now you’re going to see whether you remember the main points that we’ve discussed in this lesson. Please answer the questions on handout 4-2A. When you all finish, we’ll review the answers together.

Review the answers. Distribute handout 4-2B, the answer key.

Resources

U.S. Environmental Protection Agency. 1996. Radon Proficiency Program (RPP) Handbook. Residential Measurement and Mitigation Proficiency. EPA 402-R-95-013. July. Accessed January 23, 2006.

------. EPA Assessment of risks from radon in homes.2003. United States Air and Radiation (6608J). EPA 402-R-03-003. June.

Lesson4-1

Measuring radon in residential propertiesWhat are the units for measuring radon?

Handout 4-1:Units for measuring radon and its decay products

Radon gas

U.S. system

Measuring activity (number of radioactive decays per unit of time)

1 picocurie (pCi)

= one trillionth of curie (1Ci x 10-12)

= 0.037 decays/second (dps)

= 0.037 Bq

= 2.22 decays/minute (dpm)

= 1 decay/27 seconds

Measuring radon (number of decays per unit of time per volume)

1 picocurie/liter of air (pCi/L)

= 2.22 decays/minute/liter

EPA action level

4 pCi/L

International system

Measuring activity (number of radioactive decays per unit of time)

1 becquerel (Bq)

= 1 decay/second

= 27 pCi

Measuring radon (number of decays per unit of time per volume)

1 becquerel/cubic meter of air (Bq/m3)

= 1 decay/second/m3

Radon decay products

Working level (WL)

Measuring concentration of radon decay products in volume of air

= Any combination of short-lived radon decay products that will produce

1.3 x 105 million electron volts of alpha energy per liter of air

Conversions

If you have
picocuries/
liter
(pCi/L) / And you want
becquerels/
cubic meter[1]
(Bq/m3) / If you have
becquerels/
cubic meter*
(Bq/m3) / And you want
picocuries/
liter
(pCi/L)
Method / Multiply pCi/L by 37 / Multiply Bq/m3 by 0.027
Example:
EPA action level / 4 pCi/L x 37 = 148 Bq/m3 / 148 Bq/m3 x 0.027 = 4 pCi/L
Equation / 1 pCi/L = 37 Bq/m3 / 1 Bq/m3 = 0.027 pCi/L

Working levels

If you have
picocuries/
liter
(pCi/L) / And you want
working levels
(WL) / If you have
working levels (WL) / And you want
picocuries/
liter
(pCi/L)
Method / Multiply pCi/L by the equilibrium ratio (ER)(usually assumed to be 0.5)
and divide by 100 / Multiply WL by 100
and divide by equilibrium ratio (ER)(usuallyassumed to be 0.5)
Example:
EPA action level / WL =4 x 0.5 = 0.02
100 / pCi/L = 0.02 x 100= 4
0.5
Equation / WL=pCi/L x ER
100 / pCi/L= WL x 100
ER

Handout 4-2A: Check your understanding

Select the best answer from the choices below. Circle the correct answer.

Lesson4-1

Measuring radon in residential propertiesWhat are the units for measuring radon?

  1. Radon activity means
  2. How many radon atoms enter a home within a given period of time
  3. How many radon atoms spread through a home within a given period of time
  4. The number of radioactive decays in a given period of time for a given volume of air
  5. The number of radon atoms moving within a given volume of air
  1. We usually measure radon activity in
  2. Curies/cubic meter of air
  3. Picocuries/liter of air
  4. Picocuries/cubic meter of air
  5. Liters of radon gas/picocurie
  1. Using the units above (from question 2), the EPA action level for radon is
  2. 0.02
  3. 0.4
  4. 4.0
  5. 37
  1. In units used in the International System, the EPA action level for radon is
  2. 37 Becquerels/cubic meter
  3. 148 Becquerels/cubic meter
  4. 73 mackerels/liter
  5. 148 working levels/cubic meter
  1. The units we use to measure radon decay products are
  2. Microcuries/liter of air and acting levels
  3. Picocuries/liter of air and working levels
  4. Secular equilibrium ratios
  5. Functional levels
  1. The length of time to achieve secular equilibrium is about
  2. 7 days
  3. 3-7 minutes
  4. 3-4 days
  5. 3-4 hours
  1. Which of the following factors probably will not affect radon measurement
  1. Open windows
  2. Attic fans
  3. Dust in the air
  4. Furniture placement

Lesson4-1

Measuring radon in residential propertiesWhat are the units for measuring radon?

Handout 4-2B:Check your understanding

Answer key

The correct answers are shown in bold.

Lesson4-1

Measuring radon in residential propertiesWhat are the units for measuring radon?

  1. Radon activity means
  1. How many radon atoms enter a home within a given period of time
  2. How many radon atoms spread through a home within a given period of time
  3. The number of radioactive decays in a given period of time for a given volume of air
  4. The number of radon atoms moving within a given volume of air
  1. We usually measure radon activity in
  1. Curies/cubic meter of air
  2. Picocuries/liter of air
  3. Picocuries/cubic meter of air
  4. Liters of radon gas/picocurie
  1. Using the units above (from question 2), the EPA action level for radon is
  1. 0.02
  2. 0.4
  3. 4.0
  4. 37
  1. In units used in the International system, the EPA action level for radon is
  1. 37 Becquerels/cubic meter
  2. 148 Becquerels/cubic meter
  3. 73 mackerels/liter of water
  4. 148 working levels/cubic meter
  1. The units we use to measure radon decay products are
  1. Microcuries/liter of air and acting levels
  2. Picocuries/liter of air and working levels
  3. Secular equilibrium ratios
  4. Functional levels
  1. The length of time to achieve secular equilibrium is about
  1. 7 days
  2. 3-7 minutes
  3. 3-4 days
  4. 3-4 hours
  1. Which of the following factors probably will not affect radon measurement
  1. Open windows
  2. Attic fans
  3. Dust in the air
  4. Furniture placement

Lesson4-1

[1] 1 cubic meter (1 m3) = 1000 liters (1000 L)