Today, AP Physics 2 students completed their last unit exam of the year! Time to start reviewing for the AP exam….

## Day 144: Stochastic Nature of Radiation

Today, students explored the stochastic nature of radiation my measuring the beta decay from samples of Tl-204. The lab doesn’t require a great deal of interaction; so, we discussed other topics while gathering data. I like to share the story of the assassination of former KGB agent Alexander Litvinenko with polonium-210. This gives us the opportunity to compare and contrast beta decay and alpha decay.

The original version of the lab came from a colleague at our sister high school. The analysis and discussion questions have students calculate the full-width at half-max for the histogram. Is this a common statistical measure for this type of data? I’m not familiar with it in this context and not sure why calculating the standard deviation wouldn’t suffice. Any ideas?

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## Day 143: Engaging Nuclear Physics Problems

Today I was off campus writing the curriculum for our new NGSS-aligned physics course. While I was gone, students whiteboarded three very engaging problems from Knight’s College Physics text. One (Chapter 30; Problem 33) was how radioactive iodine from the Chernobyl accident was ingested by cows and contaminated the milk. Farmers couldn’t see the milk and used it to make cheese. The problem is to solve for how long it takes for the concentration of radioactive iodine isotope to fall to 1% of its original concentration. The second problem was a typic Carbon-14 dating problem, but still interesting for students to work through. The third problem (Chapter 30; Problem 65) had students solve for how long ago the supernova occurred that produced the very heavy atoms found in the earth based on their current concentrations of uranium isotopes. Great problems!

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## Day 142: Nuclear Decay, Fission, and Fusion

Today, we I introduced nuclear decay, fission, and fusion. I always feel bad that nuclear physics is such a rich topic and we rush through it at the end of the semester. We did answer a very important question today which is why do elements such as Radon exist if they have such short half lives? I’m not sure where I found this chart, but it clearly answers this question.

I also shared the story of SCRAM “safety control rod axe man” and the role of that person during the development of the nuclear reaction at the University of Chicago. Potentially apocryphal, but a great piece of local history!

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## Day 141: Half-Life Plots

Today, groups whiteboarded one of the three graphs that they prepared last night for homework. They presented how they used it to find the half-life of the sample and we compared and contrasted different approaches and different graphs by different groups. The aggregated data from two classes was great:

One group realized that the area under the plot of number of “nuclei” decayed in a given roll vs. time was the total number of nuclei decayed. They integrated the function that fit the graph to find the half life.

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## Day 140: Half-Life Lab

This year, we used our new collection of dice to perform the half life lab instead of M&Ms. Over the two classes, we aggregated over 1100 rolls. For homework, students will plot the aggregated data in three ways: number of “nuclei” remaining vs. time, number of “nuclei” decayed in a given roll vs. time, and ln(number of “nuclei” remaining vs. time). They then will use each graph in some manner to determine the half-life of the sample.

The Chromebook once again demonstrates its flexibility:

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