Question

Background (Part 1):
We are continuously exposed to ionizing radiation from natural and artificial sources. All of us are exposed to radiation every day, from natural sources such as minerals in the ground and cosmic radiation to man-made sources such as medical x-rays. According to the National Council on Radiation Protection and Measurements (NCRP), the average annual radiation dose per person in the U.S. is 620 millirem. In this activity, you will use the interactive online dose calculator to estimate your yearly dose from the most common sources of ionizing radiation.

Part 1- Calculate Your Radiation Dose
Use the link below to estimate your yearly dose from the most significant sources of ionizing radiation. Estimates are given in millirem (mrem), the U.S. unit for effective dose. Before you start, do you expect to be above or below the national average? Effective dose is a measure of the amount of radiation absorbed by a person that accounts for the type of radiation received and the effects on particular organs.

Q1. What was your estimated total yearly dose (in mrem) ______________________________ (2 points)

Q2. How did your value compare to the average annual radiation dose per person in the U.S.? (2 points)

Q3. Identify three sources of radiation that have a significant effect on your own total exposure. How could you protect yourself against these sources? (2 points)

Q4. Consider the following scenarios:

⦁   John likes to watch TV, play video games on his computer, and go camping (where he uses a gas lantern). After realizing that these activities expose him to radiation, he gives up all three. How much has he reduced his annual radiation dose? (2 points)

⦁   Sam lives in a suburb of a large city. His house is 55 miles from a nuclear power plant and 20 miles from a coal-fired electrical plant. His family buys a house in another suburb on the other side of the same city. It is 20 miles from a nuclear power plant and 60 miles from a coal-fired electric plant. What is the change in his annual radiation exposure? (2 points)

Background (Part 2)
If two nuclei have different masses, but the same atomic number, those nuclei are considered to be isotopes. Isotopes have the same chemical properties, but different physical properties. An example of isotopes is carbon, which has three main isotopes: carbon-12, carbon-13 and carbon-14. All three isotopes have the same atomic number of 6, but have different numbers of neutrons. Carbon-14 has 2 more neutrons than carbon-12 and 1 more than carbon-13, both of which are stable. Carbon-14 is radioactive and undergoes radioactive decay.

Radioactive materials contain some nuclei that are stable and other nuclei that are unstable. Not all of the atoms of a radioactive isotope (radioisotope) decay at the same time. Rather, the atoms decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life. The half-life of a radioactive isotope refers to the amount of time required for half of a quantity of a radioactive isotope to decay. Carbon-14 has a half-life of 5,730 years, which means that if you take one gram of carbon-14, half of it will decay in 5,730 years. Different isotopes have different half-lives. The ratio of the amounts of carbon-12 to carbon-14 in a human is the same as in every other living thing. After death, the carbon-14 decays and is not replaced. The carbon-14 decays, with its half-life of 5,730 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing. Radiocarbon dates do not tell archaeologists exactly how old an artifact is, but they can date the sample within a few hundred years of the age.

Part 2 - Licorice Half-Life Activity
⦁   Label the horizontal axis of the graph paper “Time (seconds)” and the vertical axis “Radioactive Licorice (%)”. Calibrate the horizontal axes so that one block equals 5 seconds and two blocks equal 10 seconds. Mark the axis at 10-second intervals.
⦁   Start with one piece of licorice to place onto the graph paper. Stretch the full length of the licorice vertically over the time “zero” mark, which is the same as the vertical axis. Make a mark on the graph paper at the top of the licorice. This mark represents 100% of the radioactive material at time zero.
⦁   Have a friend or relative call out “GO” or “HALF-LIFE” at 10-second intervals up to 90 seconds. When this person says “GO” or “HALF-LIFE” you will have ten seconds to remove one-half of your licorice and set it aside. Place the remaining piece of licorice on the 10 seconds line and mark its current height. At 20 seconds, you should again remove half of the licorice and set it aside, then mark the height of the remaining portion on your graph at the 20-second line. Repeat this process until 90 seconds have gone by.      
⦁   Now, connect all the height marks with a “best fit” line, completing a graph of the “Half-Life of Licorice.” Submit a picture of your graph (2 points). NOTE: The original strip of licorice represents radioactive material. The portion which is “set aside” during the activity represents the material that has “decayed” and is no longer radioactive.

Q1. Describe the shape of the line on your graph? (1 point)

Q2. How would you describe what happens to the amount of licorice after each step? (1 point)

Q3. What is the half-life of your licorice? Report your answer in seconds. (2 points)

Q4. Using your graph from part 2, determine whether this statement is true or false. Explain your answer. Half-life means that half of a sample decays after one half-life and the rest of the sample decays after the next half-life. (2 points)

Q5. One reason it is important to know the half-life of a sample is to safely dispose of radioactive waste, which is usually stored for 10 half-lives. If you have 250 g of radioactive waste, how much of the sample would be left after 10 half-lives? (2 points)

Q6. Radioisotope A has a half-life of 2 minutes. Radioisotope B has a half-life of 2 hours. Which one would have a larger amount left after 5 hours has elapsed? Explain your answer. (2 points)

Concept Questions

Mo-88 decays via positron emission. Graph the following data and then use the graph to answer the questions below. Submit a picture of your graph (2 points).

           Time (min)       Mass of Mo-88 (grams)  
           0           1.00
           2.0           0.80
           4.0           0.68
           6.0           0.65
           8.0           0.45
           10.0           0.38
           12.0           0.30
           14.0           0.26
           16.0           0.21

Q1. What is the half-life of the decay? (2 points)

Q2. What is the rate constant for the decay in units of min-1? (2 points)

Q3. What percent of the original sample of Mo-88 remains after 12 minutes? (2 points)

Answer 1

1. average yearly radiation dose per person in the U.S. is 620 mrem.

2.The annual average dose per person from all natural and man-made sources is about 350 mrems

3.Naturally occurring radioactive materials are present in its crust, the floors and walls of our homes, schools, or offices and in the food we eat and drink. There are radioactive gases in the air we breathe. Our own bodies - muscles, bones, and tissue - contain naturally occurring radioactive elements.

Man has always been exposed to natural radiation arising from the earth as well as from outside the earth. The radiation we receive from outer space is called cosmic radiation or cosmic rays.

We also receive exposure from man-made radiation, such as X-rays, radiation used to diagnose diseases and for cancer therapy. Fallout from nuclear explosives testing, and small quantities of radioactive materials released to the environment from coal and nuclear power plants, are also sources of radiation exposure to man.

If you work around radioactive materials itʻs good to have a radiation detector. Things change from day to day. Other workers can forget to replace shielding around sources. X-ray machines can be be inadvertently activated. Things can get spilled. Itʻs good to review your environment on a regular basis.

Use a Respirator or Face Mask if You are exposed to airborne sources.

Be Aware of All Sources of Radiation Exposure. We are all exposed to radiation every day from natural sources, outer space, the earth, radon gas in our homes and businesses. We are also exposed inadvertently to sources that can include people undergoing medical procedures, radioactive antiques such as Fiestaware, and diagnostic medical procedures.

• John reduced (TV +1, video display terminal +1 = 2.0 mrem)
• Sam's change in his annual radiation exposure: First house (coal plant +0.03) Second house (nuclear plant +0.01) His annual exposure is REDUCED by 0.02 mrem.