Online reading assignment: radioactive decay rates

Physics 205B, spring semester 2019
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on radioactive decay rates.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"That a half-life is the amount of time it takes for half the atoms in a sample to decay."

"I learned rates of decay and radioactive dating in a biology class that I took before so most of this is familiar to me."

"Melting rocks and measuring gaseous daughter atoms release which are trapped within the sample help determine the age using radioactive atoms. Also M&Ms® make a great model for radioactivity based off of how many land 'm' side up."

"Radioactive decay is exponential and that after a molten sample solidifies, it starts (over) with radioactive atoms that don't have daughter atoms."

"I understand the concepts of radioactive decay pretty well. So far it is making sense."

"Radioactive atoms decay into daughter atoms."

"Older samples have more daughter atoms."

"How does radioactivity become hazardous? Why is radioactivity seen as eminently dangerous?"

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I'm confused about the relationship between half-life and the time constant."

"I don't understand radioactive dating."

"I am a little confused about how to implement these equations in a problem."

"The only thing that really confused me was the resetting of half life by melting. I have never heard of this and don't understand how that works."

"I think it will be fine to understand once there is an example to use the equations."

"I don't understand the relation of daughter atoms to radioactive atoms. I cannot tell the difference between the two and which one is the original."

State the SI units for activity (radioactive decays per time).

"The units for radioactive decay are becquerels, decays per second."

"The becquerel (Bq), equal to one reciprocal second."

For a radioactive decay process, the time constant τ ("average lifetime") is __________ half-life T_1/2.

less than.	***** [5]
equal to.	********* [9]
greater than.	************** [14]
(Unsure/guessing/lost/help!)	****** [6]

Two samples are each comprised of 800 unstable atoms that will undergo radioactive decay. The remainder of one sample is 200 inert, stable atoms not involved in a radioactive decay process. The remainder of the other sample is 200 daughter atoms of the radioactive decay process.
(Only correct responses shown.)

Sample with more activity (decays/time): (there is a tie). [15%]
Sample with older solidification age: radioactive sample with daughter atoms. [56%]

Describe what changes in a sample when it melted and then solidified that resets its solidification age as determined by radioactive dating.

"There are gaseous daughter atoms trapped inside and are released when melted and can be compared to the amount of radioactive atoms left in the molten sample to determine how long ago the sample started with radioactive atoms with no daughter atoms."

"When a sample melts, the gaseous daughter atoms are released and when the sample cools it resets because it no longer has any daughter atoms."

"The gaseous daughter atoms evaporated to leave only inert or unstable atoms, 'reseting' the age by removal of the daughter atoms."

"Gaseous daughter atoms are released and can be compared to the amount of radioactive atoms remaining in the molten sample in order to determine how long it has been since the sample had radioactive atoms with no daughter atoms."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"If an atom is stable why it doesn't decay? In other words, what makes an atom radioactive versus inactive?" (As we'll see in the next lecture, a stable atom has an optimal ratio of protons-to-neutrons in the nucleus, while an unstable radioactive atom would have too many protons or too few protons compared to the number of neutrons.)

"I am a little confused, I am starting to kind of get the idea, but it needs to be clarified a bit."

"I am really trying to make every class, listen, understand, and identify where I need to ask questions."

Online reading assignment: radioactive decay rates

Physics 205B, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on radioactive decay rates.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"Exponential and half life decay are both covered well in general chemistry so it's somewhat of a review. But the M&Ms® example is still helpful."

"I understood the introduction to radioactive decay and half-lives. I feel like most of this is from previous biology and chemistry classes."

"Thankfully, this presentation was a bit of a refresher from my other physical science classes. Radioactive dating helps us determine how long the radioactive substance has been around, assuming that there are no daughter atoms to begin with."

"I understand that older substances have more daughter atoms in them. Different elements have different half-lives."

"When there are more daughter atoms the sample is older. The daughter are released when the sample that is being melted, which will then determine the age of the material/sample."

"Radioactive decay can be used to determine the age of an unknown material. This is done using half-lives to measure the time these radioactive materials decay in the unknown material."

"Gaseous daughter atoms can be compared to the amount of radioactive atoms left in a sample to determine how long ago the sample started. After a molten sample solidifies, it will start anew with having radioactive atoms with no daughter atoms."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I actually feel okay with this stuff thanks to chemistry and other classes I've taken that have dealt with radioactive decay. Going through the slides one more time will help me understand things more."

"There wasn't anything too confusing from the presentation preview. I have learned about radioactive decay in other classes before."

"I don't understand the equation for half-life decay, or radioactive dating."

"I would like to go over problems to get more familiar with the equations."

"I'm confused with the section on radioactive dating, or carbon dating. How exactly is the age of something determined?"

"I don't understand the process to calculate the half life of a material or why melting an object affects its half-life."

"How is the clock reset when matter is solidified after melting if gaseous daughter particles escape?"

"I am struggling with the melting and solidification ages."

"At the moment I am not sure what I find confusing. Most of the lecture made sense to me as far as I am concerned."

State the SI units for activity (radioactive decays per time).

"Decays/s."

"s^–1."

"Bq, or becquerel."

"Curies?"

"Lambda?"

"Not sure."

For a radioactive decay process, the time constant τ ("average lifetime") is __________ half-life T_1/2.

less than.	** [2]
equal to.	***** [6]
greater than.	******************* [19]
(Unsure/guessing/lost/help!)	** [2]

Two samples are each comprised of 800 unstable atoms that will undergo radioactive decay. The remainder of one sample is 200 inert, stable atoms not involved in a radioactive decay process. The remainder of the other sample is 200 daughter atoms of the radioactive decay process.
(Only correct responses shown.)

Sample with more activity (decays/time): (there is a tie). [24%]
Sample with older solidification age: radioactive sample with daughter atoms. [45%]

Describe what changes in a sample when it melted and then solidified that resets its solidification age as determined by radioactive dating.

"Daughter atoms are released and are compared to the radioactive atoms that are left in the sample. Melting it resets its solidification age."

"Since daughter atoms (which are used to date the substance) are gaseous, when the substance is melted they are released. Therefore, they are no longer in the substance effectively resetting the age of the substance."

"There are technically no radioactive atoms or daughter atoms in the sample anymore, so it can reset its solidification age."

"Gaseous daughter atoms are released. This tells us how long ago the sample started with radioactive atoms with no daughter atoms."

"When a substance is liquified the once solidified daughter atoms are released into the air. When the substance is allowed to cool back into a solid the daughter atoms to not solidify back into the original state. This makes its a less reliable in radioactive dating."

"Not sure."

"Hmm..."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I really still think I need help with Lenz's law and Faraday's law."

"The semester after spring break is harder than I thought. But I think I will be able to catch up for the final."

"I need to play Half-Life again."

"I'm excited to eat M&Ms®!!!" (Wait for it--we'll get to do this in the last lab.)

Online reading assignment: radioactive decay rates

Physics 205B, spring semester 2017
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on radioactive decay rates.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"Radioactive decay is exponential."

"Honestly, not much. This whole concept is very foreign to me."

"Half-life is the time for one-half of a statistically large sample to decay. Half-life is proportional to the time constant and the decay constant."

"I totally understand how half lives work because I have learned it before in other classes like chemistry and geology. Those classes really helped with this lecture!"

"I understand half-life and radioactive decay as I have had it in math."

"When there are more daughter atoms the sample is older. The daughter are released when the sample that is being melted, which will then determine the age of the material/sample."

"After a molten sample solidifies, it will start anew with having radioactive atoms with no daughter atoms. Melting a sample 'resets' its solidification age."

"Radiation is hella bad for you."

"Haven't got to it yet."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I would like more practice in obtaining the half-life given the time constant. Also, I want to know how equations look for radioactive dating or if you just count up the ratio of daughter atoms to radioactive atoms."

"What solidification age is and how was supposed to know which had an older solidification age."

"The concepts seem pretty easy to understand. Doing some problems to see how the different constants work would be great!"

"Very confused as to what is going on and am having trouble understanding activity (half-life decay) and half life equations."

"It all is pretty confusing, but it should clear up after lecture."

"Not sure yet."

"I'm good."

State the SI units for activity (radioactive decays per time).

"Becquerel."

"Bq."

"I believe that it is Bq = 1 decay/second."

"A becquerel, Bq, is the unit for one disintegration per second."

For a radioactive decay process, the time constant τ ("average lifetime") is __________ half-life T_1/2.

less than.	*** [3]
equal to.	************ [12]
greater than.	******** [8]
(Unsure/guessing/lost/help!)	* [1]

Two samples are each comprised of 800 unstable atoms that will undergo radioactive decay. The remainder of one sample is 200 inert, stable atoms not involved in a radioactive decay process. The remainder of the other sample is 200 daughter atoms of the radioactive decay process.
(Only correct responses shown.)

Sample with more activity (decays/time): (there is a tie). [21%]
Sample with older solidification age: adioactive sample with daughter atoms. [75%]

Describe what changes in a sample when it melted and then solidified that resets its solidification age as determined by radioactive dating.

"Gaseous daughter atoms are released. This tells us how long ago the sample started with radioactive atoms with no daughter atoms."

"After a molten sample solidifies, it will start over with having radioactive atoms with no daughter atoms. Melting a sample restarts its solidification age."

"Not sure what is meant by 'solidification age.'"

"Uhh...what?"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Not sure what the relationship between half-life and the time constant is." (As long as you realize they're not the same thing, but can be converted from one to the other (by a factor of ln(2)).)

"Is exponential decay just an overview and half-life is more specific?" (They're related to each other mathematically, as are the exponential decay and half-life decay equations. Both either will give you the same results computationally.)"

"I have always associated half-life with chemistry. It is interesting to explore this concept from a physics standpoint."

"Do you prefer Rockstar or Monster energy drinks?" (RockStar sugar-free tastes much better than Monster sugar-free.)

Online reading assignment: radioactive decay rates

Physics 205B, spring semester 2016
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on radioactive decay rates.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"The 'activity' is the number of atoms that decay during a time interval. Half-life is the time it take for one-half of a sample to decay. The decay constant is the likelihood that a particular atom will decay in certain time interval. Finally, the time constant is the average lifespan of an atom in a sample."

"I understand quite a bit about half-life and radioactive decay. I've taken chemistry courses about the purposes behind radioactive dating and how to use the half life equations. That's essentially all it is, is understanding how to use the half life equations in certain situations to solve the problems. But i guess that's all what physics is. It is knowing which equation to use for each particular situation."

"Not much."

"I thought it was really interesting to find out how the older a substance is, the more daughter atoms it has. Also finding the age of the material was really interesting. It all has to do with the daughter atoms, something I didn't even know existed."

"Not sure what I do know."

"That radioactivity is a relation of atoms the are stablizing slowly or rapidly and give off energy as a result. I get that different elements will have different half-lives."

"Decay is exponential."

"In order to determine the rate at which radioactive nuclei disintegrate within an object is like taking me back to stats class; you basically have to collect data for a given amount of time until one can come up with a relative decay/activity rate that he/she is confident in. After this collection of data has been made then one can come up with a relative decay/activity constant which they can later reference."

"Radioactive decay counts the number of disintegrations per half-life. Each half life theoretically activates one-half of an isotope."

"In this case, R₀ is the initial rate of decays per second at t = 0. We can use a Wolfram Mathematica template with our M&M™ data to find an expression for the decay constant λ, which for a statistically large sample is the probability that a given single M&M™ will decay in a given time interval. "

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"The different types of decay such as exponential and activity? I have no idea what is going on with the equations or constants. Help!"

"Nothing really confuses me in this section."

"What does e stand for in the decay equation?"

"I'm so lost I don't know what to ask"

"I feel I just need to reread the chapter a couple of more times, and I will really get it. It wasn't that difficult when I really sat down to it. All I need to do is practice more."

"I actually understand this stuff because of chemistry. :) Yay!"

"I thought that everything with the half life seemed pretty straight forward. Im still really confused by all of the hand rules and fields and stuff so I'm really trying to wrap my mind around that first before the quiz/midterm."

State the SI units for activity (radioactive decays per time).

"R(t)."

"Curies?"

"Lambda?"

"It is decays/sec."

"The SI unit for radioactivity is the becquerel (Bq)."

"The becquerel (Bq), one of which is one disintegration per second."

For a radioactive decay process, the time constant τ ("average lifetime") is __________ half-life T_1/2.

less than.	*** [3]
equal to.	******** [8]
greater than.	********************** [22]
(Unsure/guessing/lost/help!)	**** [4]

Two samples are each comprised of 800 unstable atoms that will undergo radioactive decay. The remainder of one sample is 200 inert, stable atoms not involved in a radioactive decay process. The remainder of the other sample is 200 daughter atoms of the radioactive decay process.
(Only correct responses shown.)

Sample with more activity (decays/time): (there is a tie). [24%]
Sample with older solidification age: adioactive sample with daughter atoms. [57%]

Describe what changes in a sample when it melted and then solidified that resets its solidification age as determined by radioactive dating.

"The radioactivity is what changes here."

"Can't say I know =/"

"Not sure sounds cool."

"Gaseous daughter atoms are trapped within a sample over time. When this sample is melted, then these gaseous daughter atoms are released and are compared to it's original non-daughter atom state. By melting the object, you are transforming the daughter atoms into a gaseous state and releasing them from the object they are trapped in. Once resolidified, there will not be any daughter atoms within the object."

"After a molten sample solidifies, it will start of again having radioactive atoms with no daughter atoms. So, melting a sample 'resets' its solidification age."

"When it is melted then solidified then the gaseous daughters are released. Because of this it resets the solidification age."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I assume it's no coincidence that this class and my chemistry class are almost always covering the same topic at the same time?" (But physics class will make it more fun.)

"Radioactive decay? I think I recall covering this in chemistry class. But that was ages ago."

"Honestly , I'm just ready for school to be over. I am so done with life!"

"When a sample is melted to restart the timer is that melting the daughter element/compound? Will the daughter atoms always be released in a gaseous form? If not, then would you not be able to date the material?" (Typically, the daughter elements are either helium or radon gas, which would bubble out and be released from the sample before it cools and hardens. These gases do not naturally occur inside of rocks unless they were produced by radioactive decays, so they can be used for radioactive dating. Other elements used for radioactive dating that aren't gaseous must specifically be daughter elements that would not naturally occur inside of a sample.)

"I understand we may get to eat some M&M™s in class? Other than that I am lost."

"I have a problem with eating M&M™s since I do not like chocolate." (#wut)

"I was really confused on what the solidification age of a substance tells us? I don't really get it." (It tells you how long it has been since that sample cooled and hardened. Geologists always want to know how long a sample has been solidified, as it reveals when a volcano last erupted, etc.)

"How did physicists/chemists before us determined the half-life of specific substances? I understand that they can collect data and perform a decay rate test, but how accurate are all of the tests done across the board?" (You don't even need to know how many radioactive atoms you have in your sample, you just need to record how the decay rate changes over time to find out the half-life of that atom. We'll do this with M&M™s, where we don't know their half-life, but we'll observe how they "decay" over time to do an exponential curve-fit to empirically find out the decay constant and their half-life. The larger your sample, the more accurate your half-life will be)

"Currently traveling at 36 m/s so I'm unable to complete this assignment at the moment." (80 mph? #wut)

Online reading assignment: radioactive decay rates

Physics 205B, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on radioactive decay rates.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"What equations to use to determine radioactive decay, and what half-life is and how it could be use to find the 'age' of a material."

"How the nucleus of certain elements is unstable and cannot hold together. The idea that this happens at a half-life rate is an idea that I am familiar with. That is about it, I want to know more."

"The older the sample, the more daughter atoms it has. Releasing the daughter atoms when the sample is melted is how you determine the age of the material."

"We are finding the probability of decay over time. The decay of nuclei are indepenant of one another. If we use a short time then we can assume that N (nuclei) is constant. Rate decays also do so exponentially."

"From taking a lot of biology classes and pre calculus I have already been 'exposed' to radioactive decay and have worked out different problems relating to radioactive decay before. I also already understand the idea of it tho the equations seem a bit different compared to how I have solved for decay before."

"I havent gotten to the reading just yet."

"M&Ms® make friends."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I did not find anything particularly confusing."

"I need to read this more throughly in order to understand this section."

"The whole melting reset thing."
"I do not understand the clock diagram included in the blog presentation. I'm confused as to what happens when the number of daughter atoms dwindles in relation to the clock example."

"How are daughter atoms trapped as gas inside the sample instead of released into the air?"

"Nothing seems too confusing about this chapter. I didn't know about the reseting the solidification age and why it worked but now I do so that was pretty cool."

"I found some of the equations for activity confusing. If you could go over exactly how to use those equations in class it would be helpful."

"I haven't gotten to the reading just yet."

"I think I have it just fine."

State the SI units for activity (radioactive decays per time).

"Decays/s."

"τ."

"Bq = 1 decay/second."

"Curie (Ci)."

"Didn't read yet."

For a radioactive decay process, the time constant τ ("average lifetime") is __________ half-life T_1/2.

less than.	******* [7]
equal to.	************ [12]
greater than.	****************** [18]
(Unsure/guessing/lost/help!)	**** [4]

Two samples are each comprised of 800 unstable atoms that will undergo radioactive decay. The remainder of one sample is 200 inert, stable atoms not involved in a radioactive decay process. The remainder of the other sample is 200 daughter atoms of the radioactive decay process.
(Only correct responses shown.)

Sample with more activity (decays/time): (there is a tie). [15%]
Sample with older solidification age: adioactive sample with daughter atoms. [28%]

Describe what changes in a sample when it melted and then solidified that resets its solidification age as determined by radioactive dating.

"The gaseous daughter atoms are released while the radioactive atoms are left in the sample."

"I am unsure."

"All the radioactive daughter atoms are released when the substance is melted. Once it solidifies, the substance starts out again with no daughter atoms."

"Its structure."

"The radioactive atoms change into a gaseous form."

"you date things by measuring the gases trapped in a melted. If it is melted then all the gas will escape and leave the melting, reseting it to just non decayed atoms."

"We are concerned with daughter atom counts. A resolidified material has no daughter atoms and is thus considered 'reset' in terms of radioactive dating."

"When a sample is melted all the daughter cells that are trapped in the sample in gaseous form are released and the age of the sample can be determined by the material that is left. The sample is reset without any daughter cells in the sample and sort of resets the age of the sample due to the lack of daughter cells."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Can you explain the concept of solidification?"

"I would not have guessed that radioactivity involves physics." (Damn straight it does.)

"I'm not sure if I really believe in the accuracy of carbon dating, seeing that decay is really a random event." (Yes, on an individual atom-by-atom basis, the event of a decay is randomized, but with a large enough statistical ensemble, the decays that occur match up well with the expected probability.)

"Trying to finish this semester strong and stay motivated in physics." (#livestrong #finishstrong)

Online reading assignment: radioactive decay rates

Physics 205B, spring semester 2014
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on radioactive decay rates.

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"I do vaguely remember the radioactive decay equation from pre-calculus. I get that the more atoms there are the older the object being tested."

"Radioactive atoms decay into daughter atoms. In one half-life, half of the radioactive atoms in a sample decay into their daughter atoms."

"You can reset the solidification age of a radioactive material if you melt it. This means it will have no daughter atoms when it resolidifies."

I liked the M&M's™ example. It really showed me how much probability plays into decay."

"I understand the average lifetime before decay and the half life and how they relate to one another."

"Didn't get much done over break."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"Nothing."

"The toy model of a radioactive substance was a little confusing. Also I couldn't really wrap my mind around a time constant and how it could be equal to approximately the average lifetime of a single M&M™ before it decays."

"The equations will confuse me as soon as I try to use them."

"Why are the equations so different than from an exponential decay problem from calculus?"

"I don't know why the M&M's™ don't have a 0.50 half-life."

"It seems confusing to find the radioactive age of a substance. I understand the explanation but I would benefit from practice."

State the SI units for activity (radioactive decays per time).

"Probability/ second."

"Lambda."

"SI unit for activity is the becquerel. 1 becquerel (abbreviated 'Bq') is 1 disintegration per second."

Explain what the Greek letter τ ("tau") refers to when used in radioactive decay calculations.

"Tau is the time constant, which is 1/λ. It is the average time that a nucleus survives before decaying."

What is the mathematical relationship between τ and half-life for radioactive decays?

"They are inverses of each other."

"T_1/2 = τ·ln(2)."

"I'm not sure. I'm confused on this."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I'm radioactive, radioactive." (Is this what you kids listen to these days? Or did you mean this video?)

"Yes...M&M's™. Nom nom nom."

"What did you do for spring break?" (I managed to both impress Mrs. P-dog and avoid killing myself...USING PHYSICS.)

"I think after I see some sample problems I will be okay with this section."

"What is decay referring to? When a nucleus decomposes and splits?" (That sounds like fission. A decay is just a conversion of a nucleus to a slightly more stable form, usually by converting or ejecting protons and/or neutrons, as we'll see in the next class.)