Katarzyna Chmielewska-Folek

Teaching the Concept of Nuclear Reactions: Half-Life - Summary

Background Information

Nuclear reactions are a broad topic area. If we think about them, usually the first words that come to mind are nuclear energy, nuclear medicine and nuclear technology. However, there is one significant application of radioactive isotopes that was not mentioned yet. It is half-life. In physics, half-life refers to “the average length of time it takes a radioactive material to decay to half of its original mass “ (Physics 11, textbook). Half-lives can vary, as isotopes decay with different speeds. Some of the radioactive isotopes have useful applications due to their particular half-lives. One of the most important applications of half-life is carbon dating. Carbon-14 is a radioactive isotope that allows scientists to establish the age of fossils they examine, as well as many archeological artifacts. In order to make a practical application of the material that is taught in Grade 11 Physics, to real life, one of the activities students will be doing during learning about half-life is radioactive dating activity concentrated on discovering the age of fossils.

Advance Preparation/ Teaching Ideas/ Materials Needed

Before students start to acquire knowledge on nuclear reactions, they should have an understanding of the structure of an atom, Bohr-Rutherford Model of an atom and isotopes. They should also know how to use periodic table and determine the atomic structure of an element. As a consequence of the first lesson of nuclear reactions, they should also have knowledge about strong nuclear force, stable and unstable isotopes, radioactive decay, as well as parent and daughter atoms. Students should be able to recognize the following nuclear reactions: alpha, beta and gamma decay. These concepts are indispensable to fully understand the lesson on half- life and the subsequent lessons.

Teaching Strategy 1 – Inquiry Based Learning

The first activity that students do during a lesson on half-life is a virtual lab. Therefore, a teacher needs an access to a computer room and the Internet. It is a good idea to put the website address on a whiteboard/ blackboard or to provide students with a worksheet where the website address is written. First task that students need to do is to watch a short video explaining the structure of an atom. Then students read background information about radioactive decay (review) and watch a simulation of radioactive decay. Based on the simulation they need to observe, collect and record data for 4 hypothetical radioactive elements (table), and, finally, based on their observations and analysis, make connections, draw conclusions and answer 5 questions in their worksheets. When the virtual laboratory is finished, a teacher asks students what the meaning of half-life is. After a short discussion, 2 slides of Power Point are shown explaining the concept of half-life. Teaching Strategy 2- Demonstration

Materials needed: pennies (as many as students in the classroom)

Students will participate in a demonstration that visually illustrates the concept of half-life. All students need to stand up and while standing, each of students will be flipping a penny. Each time they flip a penny, one half-life is passed. If a penny lands on heads, the student is regarded as radioactive, has decayed, and needs to sit. If a students’ penny lands on tails, the student has not decayed and needs to remain standing. After each half-life, a teacher should count students who stand and plot data on the overhead. Students will be asked to predict what will happen to the numbers of remaining parent isotopes. When the discussion is finished, students are going to watch two videos.

Teaching Strategy 3: Videos and Discussion

In order to show two short videos on Carbon Dating and Carbon-14 Decay, a teacher needs an access to a computer, the Internet, projector and an overhead screen. The videos discuss how and why scientists use Carbon- 14 as a useful isotope for dating fossils and archaeological objects. After watching these videos, students are asked to discuss (in small groups) why they have seen and what the importance of using C-14 is. It is an introduction to their last activity during their lesson on half-life.

Teaching Strategy 4: Radiometric dating activity

Materials needed: 5 numbered plastic bags –representing fossils; beads of different colors – they represent atoms that make the fossils up. In each bag put a specific number of parent (one color) and daughter (second color) isotopes plus other random color of beads. Prepare a worksheet with the following data table: fossil number, number of parent isotope atoms, number of daughter isotope atoms, number of half –lives and age of fossil.

A teacher needs to prepare 5 plastic bags that include different number of beads and put them into 5 different locations around the classroom. The locations should be numbered. The teacher also should make sure that all desks and chairs are removed from places were students will be circulating. During this hands-on activity students have a chance to gain a better understanding of how scientists use isotopes to establish the age of fossils and archeological objects. They will be asked to count the number of parent and daughter isotope atoms in each bag. Then they should figure out how many half-lives the isotope has gone through, and finally establish the age of the fossil. Discussion on radiometric dating will closed this activity.

Curriculum Expectations Addressed ( SPH3U Physics Grade 11)

Curriculum Expectations for Energy and Society Unit

Overall: D3. demonstrate an understanding of work, efficiency, power, gravitational potential energy, kinetic energy, nuclear energy, and thermal energy and its transfer (heat).

Specific:

D1.2 assess, on the basis of research, how technologies related to nuclear, thermal, or geothermal energy affect society and the environment (e.g., thermal regulating units, radiopharmaceuticals, dry-steam power plants, ground-source heat pumps) [IP, PR, AI, C]

D2.1 use appropriate terminology related to energy transformations, including, but not limited to: mechanical energy, gravitational potential energy, kinetic energy, work, power, fission, fusion, heat, heat capacity, temperature, and latent heat [C]

D2.7 compare and contrast the input energy, useful output energy, and per cent efficiency of selected energy generation methods (e.g., hydroelectric, thermal, geothermal, nuclear fission, nuclear fusion, wind, solar) [AI, C]

D2.8 investigate the relationship between the concepts of conservation of mass and conservation of energy, and solve problems using the mass– energy equivalence [PR, AI]

D3.6 describe and compare nuclear fission and nuclear fusion

D3.9 identify and describe the structure of common nuclear isotopes (e.g., hydrogen, deuterium, tritium)

D3.10 compare the characteristics of (e.g., mass, charge, speed, penetrating power, ionizing ability) and safety precautions related to alpha particles, beta particles, and gamma rays

D3.12 explain the energy transformations that occur within a nuclear power plant, with reference to the laws of thermodynamics (e.g., nuclear fission results in the liberation of energy, which is converted into thermal energy; the thermal energy is converted into electrical energy and waste heat, using a steam turbine)

Specific Curriculum expectations for the Half-Life lesson ( SPH3U Physics Grade 11)

• D3.11 explain radioactive half-life for a given radioisotope, and describe its applications and their consequences

Lesson Sequence

Nuclear reactions are a part of Energy and Society Unit in Grade 11 Physics Curriculum. As this is a complex topic, the following outline gives an idea how the material has been planned to be delivered:

Lesson 1: Radioactive Decay

 Bohr-Rutherford model of atom, isotopes – review  Alpha, Beta and Gamma Decay Lesson 2: Measuring the rate of Radioactive Decay Process

 Half-Life  Application of Half-Life: Carbon Dating Lesson 3: Nuclear Fission and Nuclear Power Generation

 Mass Energy Equivalence  Nuclear Fuel  Chain Reactions Lesson 4: Nuclear Fusion

 Nucelar Stability  Stellar Fusion  Magnetic Confinement Fusion Lesson 5: Applications of Nuclear Technology

 Candu Reactors, Waste disposal  Medical applications of Radioisotopes Lesson 6: Nuclear Energy: Benefits and Hazards

Potential Student Difficulties and Possible Solutions

As nuclear reactions and topics related to nuclear energy and technology may be difficult for students to understand, it is expected then that students may face the following difficulties:

 Confuse understanding of the concept that radioactive decay is a spontaneous process that involves irreversible transformation of one element into another

One of the possible solutions to this problem is showing students a demonstration with popping popcorn. Reference to a known process, should allow students to understand the idea. While presenting the demonstration to students, a teacher should explain that when kernels are poured into a popper, it is impossible to predict which of the kernels pops first. This can be compared to the spontaneity of radioactive decay. However, if we take into account that as a consequence of nuclear reactions a new element is formed, we can compare it to a kernel that was transformed into popcorn.

 Confuse the difference between radioactivity and radioactive decay

In order to help students to realize the difference between these two notions, it is a good strategy to prepare a poster/ Power Point presentation including definitions of both processes supported by visual explanation – a picture or drawing. Show students the poster/ Power Point presentation and explain, using pictures, what the difference between radioactivity and radioactive decay is. Emphasize that radioactivity refers to particles that are emitted from nuclei, while radioactive decay results in a formation of a new element.

 Do not understand that nuclei do not disappear when they decay

A great teaching strategy to explain the concept is using a visual tool. Show students an animation that clearly explains the concept: http://www.youtube.com/watch?v=o-9yt7OAYmE  Interpret half-life as half the time for the radioactivity to disappear

One way to help students to comprehend this concept is showing them a demonstration using coins or M&M’s as it was explained in the teaching strategies section of this summary. Then, present the results of these demonstrations as a curve of an exponential decay function. Analyze with student the shape and changes in number of isotopes.

Differentiated Assessment

Students will be assessed on an ongoing basis thorough the unit, keeping in mind assessment for, as and of learning. In order to provide an equal opportunity for all types of multiple intelligences an effort will be made to organize an assessment to meet all students’ learning styles. Students then will have a chance to participate in classroom and virtual laboratories and write laboratory reports. Students will take written tests and quizzes. Learners will be given an opportunity to present their knowledge orally. They will also have a chance to participate in classroom discussions. Students will watch videos and share their opinions and observations in small groups. An opportunity will be given to solve numerical and non-numerical problems. At the end of the unit a research project on applications of nuclear technology will be provided. Student will have a chance to choose a topic of their interests and a method they would like to prepare the concept: poster, newspaper article, song, Power Point Presentation, debate, drama, podcast, game, photo journal, demonstration, and jigsaw. At the end of each lesson exit tickets will be taken to check students’ understanding of delivered material, as well as plan and develop strategies for the next lesson.

Practical Applications

While teaching a concept of nuclear reactions, an emphasis is placed on how this topic relates to practical applications in real life. Consequently, students will gain knowledge about medical applications of radioisotopes. They will learn about diagnostic medical imaging (X-ray images, SPECT, PET, MRI), as well as a radionuclide therapy (RNT) - bombarding harmful cells with radiation. They will also gain an understanding of how scientists use C-14 for dating of geological specimens and archeological artifacts. They will have a chance to extend their awareness of nuclear energy production and its impact on our lives. They will explore benefits and hazards of nuclear energy. At the end of the unit, they will prepare a research project on application of nuclear technology.

Annotated References and Internet Addresses

Carleton College (2008). Radiometric Dating Activity. Retrieved July 15, 2012, from http://www.acad.carleton.edu/curricular/BIOL/classes/bio302/pages/half-life.html

This website was used to design a teaching strategy 4 and a radiometric activity for students. Carbon Dating (2008). Retrieved July 17, 2012, from http://www.youtube.com/watch? v=31P9pcPStg&feature=related

Carbon 14 Decay (2008). Retrieved July 17, 2012, from http://www.youtube.com/watch?v=81dWTeregEA

These videos serve as a tool helping students to comprehend why scientists use C-14 when dating fossils.

DiGiuseppe M., Howes Ch. , Speijer J., Stewart Ch., Bemmel H. , Vucic R., Wraight V. Nelson Thompson Learning. (2011). Physics 11. Toronto, Nelson Education Ltd.

This textbook was used to establish a lesson sequence for Energy and Society Unit. It was also used to plan and organize ideas while preparing activities for Half-life lesson. All scientific definitions of half-life used in PP presentation come from this source.

Explaining Radioactivity animation (2010). Retrieved July 15, 2012, from http://www.youtube.com/watch?v=o- 9yt7OAYmE This video would serve as a tool helping students to comprehend that nuclei do not disappear when they decay.

McgGaw Hill Higer Education. How can you stimulate the radioactive half-life of an element? Retrieved July 15, 2012, from http://glencoe.mcgraw-hill.com/sites/dl/free/0078693896/280405/E18.html

This website is where students complete their virtual lab on half-life. First, students watch a short video explaining the structure of an atom. Then students will see a simulation, read background information about radioactive decay, collect and record data for 4 hypothetical radioactive elements (table), and, finally, based on their observations and analysis, make connections, draw conclusions and answer 5 questions in their journals. This site provides students with a better understanding of radioactive decay and half-life.

Misconceptions about radioactivity. Retrieved July 15, 2012, from http://www.furryelephant.com/content/radioactivity/teaching-learning/radioactivity-misconceptions/

This website was used when describing common problems that students face regarding misconceptions about nuclear reactions. This is a website designed for teachers and students. It includes many simulations and animations that simply explain scientific topics.

Ontario Science Curriculum Grades 11-12( 2008). Retrieved July 15, 2012, from http://www.edu.gov.on.ca/eng/curriculum/secondary/2009science11_12.pdf

This document provides overall and specific expectations for all teachable subjects in Science grades 11-12. Wenner, J. (2012). Demonstration of radioactive decay using pennies. The Science Education Resource Centre at Carleton College. Retrieved July 15, 2012, from http://serc.carleton.edu/quantskills/activities/PennyDecay.html

This website was used as a source for a teaching strategy number 2: demonstration.

Wenner, J. (2012).How Does Radioactive Decay Work? The Science Education Resource Centre at Carleton College. Retrieved July 15, 2012, from http://serc.carleton.edu/quantskills/methods/quantlit/RadDecay.html

This website was used as a source for teaching ideas on half-life.

Werner J. (2012). Using Popcorn to Simulate Radioactive Decay. The Science Education Resource Centre at Carleton College. Retrieved July 15, 2012, from http://serc.carleton.edu/quantskills/activities/popcorn.html This website was used as a source for creating a solution on how to explain spontaneity of radioactive decay to students .