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Objective: Build student’s ability to read and interpret information on the worksheet. Develop understanding of natural background radiation vs. man-made radiation. Facilitate discussion of how we assess what is acceptable radiation exposure.
As you review answers to these questions and discuss the Estimate Your Personal Radiation Dose worksheet, point out to students that:
How does this compare to the average annual dose?
(It is only a fraction of the average annual dose. Remember the average annual dose for most people in the U.S. is about 620 mrem, so this is about 2/620 = 1/360 th of the average annual dose OR less than 0.3 % of the average.)
Do you think this is a significant amount?
(Answers will vary. Remind students that the average annual dose for most people in the U.S. is about 620 mrem.The change is much less than 1 mrem, so the change is less than 1/620 th of the average. It is actually, 0.02 mrem/620 mrem = 0.003%)
How did this radiation compare to her average annual dose?
(The radiation from medical exams accounted for more than the average annual dose, which is about 620 mrem.)
Why is this acceptable?
(Answers may vary. Several points are worth noting: (1) the benefits obtained from the medical diagnostics may outweigh the perceived risk, (2) people who work with or around radioactive material are allowed up to 5,000 mrems per year according to accepted standards, (3) some people who have been seriously injured or ill have required many x-rays, been exposed to fairly large quantities of radiation, and still lived long lives.)
Objective: Students learn that many units can be used for measuring radiation. Students learn how to convert mrems to mSv.
Present the following information to students, using whatever concrete examples are available (12 inch rulers, meter sticks, yard sticks, measures for liquid volume, etc.)
Variety of Units. More than one type of unit is used for measuring most things. The choice of measurement units depends upon many factors, including:
Most people in the U.S. are accustomed to measuring distance in inches, feet, yards, or miles depending on the circumstance. They also use fractions of an inch [½, 1/4, 1/8/ 1/16, or thousandths of an inch (0.001 inch), in some applications such as making precision machinery]. However, people in most parts of the world are accustomed to measuring distance using the basic unit of distance for the metric system, the meter. They also use kilometers (1000 meters), centimeters (1/100 meter) and millimeters (1/1000 meter).
It is possible to convert measurements from one unit of measurement to another using known equivalents, such as:
1 inch = 2.54 centimeters 1 kilometer = 0.62138 mile 1 meter = 39.37 inches 1 yard = 36 inches
Units for Radiation. Radiation, too, is measured in a variety of units (Curie, bequerel, rad, rem, sieverts, etc.)
In the U.S., it is common to measure radiation dose in rems or millirems (mrem). In certain scientific disciplines and in other parts of the world, it is common to measure radiation dose in sieverts (Sv) or millisieverts (mSv) or even microsieverts (μSv).
Measurements of radiation doses can be converted from one measuring unit to another using conversion factors, such as:
1 rem = 1000 mrem 1 sievert (Sv) = 1000 millisieverts (mSv) 1 Sv = 10,000 microSv (μSv)
1 rem = 1/100 Sv 1 rem = 10 mSv 1000 mrem = 10 mSv
1 mrem = 0.01 mSv 1 mrem = 10 μSv
Classroom Activity: Converting Radiation Dose Estimates from one unit to another
You can help students be aware of commonly-used units and integrate a bit of math into your science content by teaching them how to convert mrem to mSv. You could apply one of two approaches:
1) Using a conversion formula x mrem x 0.01 mSv/mrem =
For example, an average annual dose of 620 mrem 620 mrem x 0.01 mSv/mrem = 6.2 mSv
2) Using ratios
1000 mrem known mrem
____________ = ____________
10 mSv ? mSv
You can provide students with a variety of radiation doses and have them convert them to other units, including mSv and Sv. OR, you could have them convert numbers from the worksheet (exposure from TV, exposure from smoke detector, etc.) into other units (Sv and mSv).
Question for Discussion:
What is one reason we might choose mSv instead of Sv as a unit for expressing a person’s average annual radiation dose?
(For most people, the average annual dose is relatively small. If you measure in Sv, the value will be a decimal value. Sometimes people get confused by decimals. For example, which is a greater amount of radiation, 0.02 mSv or 0.0006 mSv? At first glance, the value with the “6″ looks greater. But, because it has more decimal places, 0.006 mSv is actually a smaller radiation dose.)
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