## 20180425

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.

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 atomic number represents the total amount of protons. The nucleon number represents the combined number of protons and neutrons. The number of neutrons can be determined by having the nucleon number minus the atomic number."

"The different decays all achieve stability through different means. Some expel particles while other transform particles into other ones."

"The key to stability is being able to keep the protons in the nucleus together. Alpha decay is how a nucleus with excess protons achieves a more stable configuration. Beta-minus decay is how a nucleus with excess neutrons achieves a more stable configuration. Beta-plus decay is how a nucleus that is neutron deficient achieves a more stable configuration. Gamma decay is how a nucleus achieves a more stable configuration, but not because it has too many protons, or the wrong ratio of protons to neutrons."

"For all atomic nuclei the key to stability is being able to keep the protons in the nucleus together. Also, having a certain number of neutrons in the nucleus will decrease the proton-proton repulsion."

"For all atomic nuclei, to have stability they have to keep the protons in the nucleus together, in spite of them all repelling each other. They need to have the proper ratio of neutrons, approximately equal to or slightly greater than the number of protons. More than 83 protons would automatically make the nucleus unstable."

"Stability conditions. A nucleus with more than 83 protons will always be unstable. Neutrons help to balance out proton to proton repulsion so it's necessary to have more neutrons than protons in a nucleus in order to be stabilized. The different decay processes we are learning about are used by nuclei to help them reach stable conditions depending on what makes them unstable to begin with."

"Radioactive decay occurs in four ways. If a nucleus has more than 83 protons, it will emit He to decrease p and n equally (alpha particles). If protons are significantly less than neutrons, neutrons will be converted to protons, releasing antineutrinos and electrons (Β particles). If protons are more numerous than neutrons, protons will be converted to neutrons, releasing positrons (Β+ particles) and neutrinos. Nuclei become excited after decay and will release photons to 'calm down' (gamma particles)."

"This is pretty basic chemistry stuff, it doesn't seem to be a problem."

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--from a problem-solving perspective it would just be nice to see some different examples going through how to sort each type of decay."

"Most of this was a good refresher on decay and specifically all of the types of it that I learned in the tail-end of my general chemistry series last year."

"I don't understand the difference between a nucleus that is stable or unstable."

"Electron capture and the 'swallowing' thing. And also a bit of gamma decay."

"I am having a harder time with gamma (γ) decay. I will do more research to clarify the topic but for right now I'm not grasping it."

"I feel like electron capture was passed over too quickly, I don't really understand what happens."

"What is a neutrino and can it be positive or negative?"

"Outside of confusing the different decay processes this is thankfully review from other classes. "

Explain what a "nucleon number" is, and/or describe how to calculate it for a nucleus.
"It is the total number of protons and neutrons inside the atomic nucleus."

"The nucleon number is the total number of nucleons (protons and electrons), such that the number of neutrons is the difference between the nucleon number and atomic number."

"Not there yet."

Identify the processes that increase, decrease, or do not change the number of protons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [77%]
β– decay: increase. [77%]
β+ decay: decrease. [77%]
electron capture: decrease. [38%]
γ decay: does not change. [69%]

Identify the processes that increase, decrease, or do not change the number of neutrons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [69%]
β– decay: decrease. [65%]
β+ decay: increase. [65%]
electron capture: increase. [19%]
γ decay: does not change. [65%]

Identify the processes that change a proton to a neutron, or change a neutron to a proton in the nucleus.
(Only correct responses shown.)
α decay: no p/n conversion. [62%]
β– decay: n → p. [73%]
β+ decay: p → n. [69%]
electron capture: p → n. [35%]
γ decay: no p/n conversion. [69%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Quiz 6 is going to be awful...I have such a hard time with the right-hand rules and flux laws."

"This seems like it is going to be the most interesting section to date!"

"I think I'll like this chapter a lot better than the previous ones!"

"Could we go over electron capture?"