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Content Benchmark P.12.C.4
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Physical Science
Matter
Force and Motion
Energy
  P.12.C.1
  P.12.C.2
  P.12.C.3
  P.12.C.4
  P.12.C.5
  P.12.C.6
Content Areas
Nature of Science (NOS)
Life Science
Earth Science
Physical Science

Students know characteristics, applications and impacts of radioactivity. E/S

Since the Big Bang, radioactivity has been a part of the universe. Star formation and destruction generate new elements, many with unstable nuclei. On Earth, many elements have unstable isotopes whose nuclei spew particles and energy through a decay process.
These emitted particles and energy constitute what is called radioactivity. Radioactivity was first identified in the late 1800’s. The three common components of radioactivity are alpha particles, beta particles, and gamma radiation. Collectively, they are referred to as nuclear radiation.

Nuclear radiation is ionizing radiation. The radioactive rays have very high energy, and when molecules are struck by nuclear radiation, the energy is transferred to the electrons that bind the atoms. This process causes the electrons to be ejected from the molecule generating charged molecular fragments, which in living organisms can be very disruptive. High frequency ultraviolet light, X-rays, gamma-rays, high speed electrons (and positrons) and alpha particles are ionizing.

Non-ionizing radiation has a lower energy and does not cause molecular disruptions. The energy transferred causes molecules to vibrate or electrons to jump to higher energy levels. Low frequency ultraviolet light, visible light, infrared radiation, microwaves, and radio are examples of non-ionizing radiation

Radioactivity is a spontaneous process. We do not have a clear idea of why some atoms decay in a short period of time while others decay over billions of years. We do know how to precisely predict when an individual nucleus will emit radioactivity, but we can precisely calculate radioactive decay when trillions of nuclei are involved and this has proved very useful in a variety of applications. Many elements have isotopes (atoms that have different numbers of neutrons in their nuclei) which are radioactive.

The time required for half of the atoms in any given quantity of a radioactive isotope to decay is the half-life of that isotope. The concept of half life is discussed in more detail at http://www.lbl.gov/abc/Basic.html#Half.

For example, if a 10 gram sample of radioactive material has a half-life of 7 days, then in that amount of time roughly 5 grams of the material will have decayed into a more stable substance. At the end of 14 days, 2.5 grams will remain.

Figure 1. Chart showing the decrease (decay) in radioactivity over time for Sodium-24, a concept called radioactive half-life. (from http://gcse.com/radio/images/halflife.gif)

Ernest Rutherford demonstrated in 1899 that radioactivity consisted of at least two types of particles that he called alpha and beta rays. Later, a third type of ray was found and named gamma rays.

Upon analysis, alpha particles were determined to be a positively charged helium nucleus with two neutrons in its nucleus. Beta particles were determined to be high speed electrons and gamma rays were very high frequency photons (higher in frequency than X-rays). Of the three, gamma rays have no mass, traveled the fastest (the speed of light), and were able to pass through most materials, except very dense lead. Beta particles were the second fastest of the three particles. Because beta particles are electrons, they have a very low mass and are negatively charged. Beta particles can pass through many materials, but are stopped by aluminum foil. Alpha particles, which are helium nuclei, are the heaviest of the three particles, stopped by most materials such a piece of paper, and travel the slowest.

For more information please see
http://www.accessexcellence.org/AE/AEC/CC/radio_slides.html.

Figure 2. Penetrative characteristics of radioactive particles.
(from http://www.ocrwm.doe.gov/factsheets/images/
ymp0403graphics.htm
)

All unstable atomic nuclei undergo transformations that eventually stabilize their nuclei. These transformations involve radioactive decay and emission of alpha, beta, and/or gamma radiation. Most unstable nuclei require several decays in order to form a stable nucleus. Uranium is a good example of a multi-step decay series.

Figure 3. The decay of naturally occurring uranium (U-238) to lead. (from http://earthguide.ucsd.edu/virtualmuseum
/images/Uranium238.html
)

Radiometric dating is one very important application of radioactivity. Carbon dating is used to determine the relative age of ancient artifacts. The radiocarbon method is based on the rate of decay of the radioactive or unstable carbon isotope 14 (14C), which is formed in the upper atmosphere through the effect of cosmic ray neutrons upon nitrogen 14.

All living organisms contain radioactive carbon-14. When an organism dies, it no longer takes in any carbon at all. The amounts of carbon-14 slowly begin to decrease as the decay series begins. Using the half-life information about carbon-14 and its amount in the environment, the age of the organic material can be dated. The half-life of carbon-14 is 5730 years. The decay equation is as follows:

Carbon-14 → Nitrogen-14 + ß

It can be seen that carbon-14 decays back to nitrogen releasing a beta particle in the process. There is a quantitative relationship between the decay of carbon and the production of the beta particle. From this relationship the age of the artifact can be determined.

For further information about carbon dating, go to http://www.c14dating.com/int.html.

About 56% of the ionizing radiation we are exposed to comes from natural sources, with the two primary sources being cosmic rays and Earth minerals. Cosmic rays are comprised mostly of high speed protons emanating from space. When these protons interact with the atmospheric molecules, they can create secondary alpha, beta, and gamma radiation. Earth minerals contain many naturally occurring radioactive elements, such as radon (a radioactive element produced as naturally-occurring uranium decays). Almost all other human exposure (42%) ionizing radiation is caused by mental and dental X-rays.

To learn more about human exposures to ionizing radiation, go to
http://www.atsdr.cdc.gov/tfacts149.html

Even though ionizing radiation is dangerous, it does benefit humans in many ways, such as diagnosing and fighting diseases. For example, cancer cells are destroyed by ionizing radiation, and food and water supplies are disinfected from disease-causing bacteria by using ionizing radiation.

For more about the beneficial uses of radioactivity in medicine and other fields, go to
http://www.pbs.org/newshour/forum/november96/nuclear_power.html.

Wastes results from human uses of radioactivity. Understanding that radioactivity can be contained (e.g., alpha particles are stopped by paper, beta particles are stopped by aluminum, and gamma rays by lead or reinforced concrete) allows engineers to design canisters and other systems to effectively contain radioactive waste, preventing release into the environment. The repository at Yucca Mountain is a barrier system in which the radioactive spent nuclear fuel pellets (solids) are placed in steel canisters, which are in turn backfilled by bentonite clay, which are turn placed 300 m underground and 300 m above the water table.

For more information about the Yucca Mountain Project, go to
http://www.ocrwm.doe.gov/factsheets/doeymp0026.shtml.

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Content Benchmark P.12.C.4

Students know characteristics, applications and impacts of radioactivity. E/S

Common misconceptions associated with this benchmark:

1. Students are confused about radioactive half-life, and incorrectly think that mass is reduced, the process is influenced externally, and/or decay rate can be controlled.

These misconceptions may stem just from the term itself. There is also confusion with the word “decay” because students associate decay with “rotting” and “loss.” During the decay process, radioactive nuclei do not disappear but rather decay into more stable nuclei. Although some of the parent mass is converted to energy in the release of radioactivity, this amount is very small (i.e., not half). Also, while the parent material is converted to progeny material, the sum of the masses of parent and progeny are almost the same as the original mass.

Also, external effects, such as environmental conditions or external energy sources do not increase or decrease the half-life of a substance. For example, radioactive decay of carbon-14 does not depend on the temperature of the material. External energy sources can result in nuclear fission or fusion reactions, which may release large quantities of radioactive material. However, the half-life of the materials created during fission and fusion reactions is independent of the external energy added.

Finally, students can confuse chemical reactions, which involve electrons, and nuclear reactions, which involve the neutrons and protons. Because of this confusion, students may incorrectly think that half-life and radioactivity is a result of chemical reactions, rather than the correctly identifying them with nuclear.

To learn more about half-life and other radioactivity misconceptions, go to http://www.jal.cc.il.us/~mikolajsawicki/ex_radio.html.

2. Students incorrectly believe that all radiation is harmful.

Humans are continuously exposed to radiation both ionizing and non-ionizing. Much of this radiation is in the form of electromagnetic waves, which are commonly referred to as electromagnetic radiation (EMR). The Sun emits all frequencies of EMR, but most of this radiation is in the form of visible light.

Ionizing radiation is most harmful to humans because it can damage interior cell structure, which in turn causes diseases such as cancer. Non-ionizing radiation, such as visible light, is typically not harmful.

To learn more about EMR and naturally occurring radiation, go to
http://www.ocrwm.doe.gov/factsheets/doeymp0403.shtml

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Content Benchmark P.12.C.4

Students know characteristics, applications and impacts of radioactivity. E/S

Sample Test Questions

1st Item Specification: Identify the difference between ionizing and non-ionizing radiation.

Depth of Knowledge Level 1

  1. Ionizing radiation is different from non-ionizing because ionizing radiation
    1. causes electrons to be ejected from the atom or molecule.
    2. changes the way atoms bond with other atoms in a molecule.
    3. causes molecules to vibrate at low energies releasing light.
    4. causes electrons to jump from one energy level to another.
  1. Non-ionizing radiation is different from ionizing radiation because
    non-ionizing radiation
    1. is very high in energy and causes molecular disruptions.
    2. causes atomic nuclei to eject high speed beta particles.
    3. causes atomic nuclei to rearrange its nucleons.
    4. is low energy and does not cause molecular disruptions.
  1. The difference between ionizing and non-ionizing radiation is that ionizing radiation is located in which range of the electromagnetic spectrum?
    1. Visible and lesser frequencies
    2. Microwave frequencies only
    3. Ultraviolet and greater frequencies
    4. Radio frequencies only
  1. The difference between ionizing and non-ionizing radiation is that non-ionizing radiation is located in which range of the electromagnetic spectrum?
    1. Ultraviolet and greater frequencies
    2. Visible and lesser frequencies
    3. Microwave frequencies only
    4. X-ray frequencies only

Depth of Knowledge Level 2

  1. A student reads that slamming the door on a microwave can cause radiation to be released and she incorrectly assumes that she will get radiation poisoning. Which of the following would be the BEST explanation to give to her?
    1. Microwaves can damage the DNA of cells and she should stand at least 2 meters away from her microwave.
    2. Microwaves are non-ionizing radiation and cannot cause cancer, but the door should be repaired to prevent burns.
    3. High energy X-rays are also emitted by microwave ovens and can cause cancer.
    4. Radio waves are also emitted by microwave ovens and will also cause cancer.
  1. Non-ionizing radiation such as infrared radiation can cause burns, but is different from ionizing radiation because
    1. infrared radiation exposure can lead to lung cancer.
    2. radiowave exposure can lead to mutations in skin cells.
    3. DNA disruption by ionizing X-ray result in mutations.
    4. non-ionizing radiation does not change the DNA of a cell.

2nd Item Specification: Identify characteristics of radioactivity, including differences between alpha, beta, and gamma rays.

Depth of Knowledge Level 1

  1. One characteristic of radioactivity is it
    1. spontaneously releases particles or waves.
    2. has low energy and low frequency.
    3. is detected by radio towers on Earth.
    4. is often found in the infrared range.
  1. Alpha particles are different from beta particles because
    1. alpha particles are low mass and energy.
    2. beta particles are charged helium nuclei.
    3. beta particles are high speed electrons and alpha particles are charged helium nuclei.
    4. alpha particles are high speed waves and beta particles are high speed hydrogen nuclei.
  1. One significant difference between gamma radiation and alpha radiation is
    1. that alpha particles can penetrate lead shields.
    2. gamma radiation can penetrate concrete blocks.
    3. alpha particles have negative charges.
    4. gamma radiation carries positive charges.

Depth of Knowledge Level 2

  1. Use the following table to answer the question below.
Type of Radiation Alpha Beta Gamma
Symbol α β γ
Relative Mass 4 1/2000 0
Relative Charge +2 -1 0
Relative Speed slow fast ligt speed
Penetrating power low medium high
Stopped by paper aluminum lead

If a source is emitting all three types of radiation, what type of container should be used to protect people from the radiation?

  1. A container that is made of concrete.
  2. Using a lead container will be sufficient.
  3. No container will prevent the radiation from leaking.
  4. Multiple layers of concrete and steel are needed.
  1. Use the following table to answer the question below.
Type of Radiation Alpha Beta Gamma
Symbol α β γ
Relative Mass 4 1/2000 0
Relative Charge +2 -1 0
Relative Speed slow fast ligt speed
Penetrating power low medium high
Stopped by paper aluminum lead

The reason that alpha particles are stopped by paper and have low penetrating ability is due to

  1. relatively high mass compared to the other radiation.
  2. relatively low mass compared to beta particles.
  3. small atomic size compared to the other radiation.
  4. low charge compared with gamma rays.

3rd Item Specification: Recognize applications of radioactivity from examples.

Depth of Knowledge Level 1

  1. Which of the following is an application of Cobalt-60 gamma radiation?
    1. Radio-dating of ancient artifacts.
    2. Generation of energy in nuclear power plants.
    3. Irradiation of food to extend shelf life.
    4. Radio-tracing of sensitive documents.
  1. Which of the following is an application of Uranium-235?
    1. Generation of energy in nuclear power plants.
    2. Dating of ancient artifacts.
    3. Detection of cancer tumors.
    4. Irradiation of equipment for sterilization.

Depth of Knowledge Level 2

  1. Carbon -14 is used to date artifacts. The half-life of Carbon-14 is about 6000 years. After 12,000 years, about how much Carbon-14 would remain in a sample?
    1. None
    2. One quarter
    3. One half
    4. Three quarters
  1. Which of the following uses radiometric techniques?
    1. Combustion engines
    2. Climate change models
    3. Dating artifacts less than a year old
    4. Developing packaging for food items

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Content Benchmark P.12.C.4

Students know characteristics, applications and impacts of radioactivity. E/S

Answers to Sample Test Questions

  1. A, DOK Level 1
  2. D, DOK Level 1
  3. C, DOK Level 1
  4. B, DOK Level 1
  5. B, DOK Level 2
  6. D, DOK Level 2
  7. A, DOK Level 1
  8. C, DOK Level 1
  9. B, DOK Level 1
  10. B, DOK Level 2
  11. A, DOK Level 2
  12. C, DOK Level 1
  13. A, DOK Level 1
  14. B, DOK Level 2
  15. B, DOK Level 2

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Content Benchmark P.12.C.4

Students know characteristics, applications and impacts of radioactivity. E/S

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. Radioactivity Background Information
This site provides the student and the teacher with solid background information on radioactivity and can be found at http://www.darvill.clara.net/nucrad/.

2. Nuclear Medicine Information Sheet
Radioactivity, Isotopes and Radioisotopes from Nature, Nuclear Reactors and Cyclotrons for use in Nuclear Medicine are discussed in this Web site maintained by the Australian government.

To access this site, go to http://www.ansto.gov.au/info/reports/radboyd.html

3. Radioactive Decay Lesson
Science NetLinks, a site created by the American Association for the Advancement of Science, has science content lessons that link to the Project 2061 Benchmarks. One lesson at this site concerns radioactive decay. This lesson is very popular with students because it involves the use of candy.

To get this lesson, go to http://www.sciencenetlinks.com/lessons.cfm?
BenchmarkID=4&DocID=178

4. Half Life Simulation
The 7Stones Web site contains many lessons, activities, and simulations covering physics and chemistry. If computer access is available in the classroom, the site has an excellent simulation of radioactive decay.

The simulation can be accessed at http://www.7stones.com/Homepage/
Publisher/halfLife.html

5. Access Excellence Health Museum Information and Activities
This site and its companion sites feature the contributions and research of four different scientists as they tried to understand the phenomenon of radioactivity. Background readings for student research are provided at the site.

To access the site, go to http://www.accessexcellence.org/AE/AEC/CC/historical_background.html

This website has an excellent student activity and simulation for teaching half-lives that can be found at http://www.accessexcellence.org/AE/AEPC/WWC/1995/teach_rad.html.

 

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