Online reading assignment: radioactive decay modes

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 modes.

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.
"Protons and neutrons make up the nucleus. Greater than 83 protons, more protons than neutrons, or excess neutrons create instability. This can be stabalized in a few ways: alpha, beta minus, beta plus, and gamma decay."

"Contrails in a cloud chamber, produced by natural background radioactive decay particles passing through cold, alcohol-saturated air. Radioactive particles from natural background decays zing around all the time, whether or not the air just so happens to be cold and alcohol-saturated."

"We cannot count radio active atoms we can only count how many decayed atoms there are. Atoms decay randomly but we are able to give each isotope a half-life based on the number of daughters it produces during a period of time."

"The neutrons in the nucleus of an atom help to mitigate the repulsion forces the protons exert on themselves and helps keep the nucleus intact (strong force). A nucleus of an atom is stable only when the number of protons is slightly lower than or equal to the number of neutrons; if these conditions are not met, then the atom will undergo some sort of decay to stabilize the nucleus."

"What I was able to gather from the reading is that the 'backbone' of an atomic nuclei are the neutrons within the nucleus. As I learned in chemistry last semester (physics has made me question how much I can rely on what I learned) the number of protons in an atom is equal to the amount of neutrons (I say this reluctantly now). So even while protons repel from each other, the neutrons within the nucleus sort of balance out this repulsion so that the atomic nuclei itself can remain whole. Until there are 83 protons in which the amount of repulsion within the nuclei despite the amount of neutrons will subsequently result in an unstable nucleus. I know I'm talking about stuff that doesn't directly regard physics, however, I've been trying to dive into the chemistry we have been talking about because I'm realizing now that my chemistry class was even more basic than I had originally thought."

"What keeps together the nucleus in an atom is the attraction between the protons and the neutrons and the ratio of them is important (because neutrons turn into protons and vice versa WHAAAT!). When there are more than 83 protons than normal then alpha radiation occurs. When there are more protons in the ratio then beta minus occurs while a bunch more neutrons in the ratio causes beta plus radiation. After a nucleus returns from an excited state they still may have to much energy which they may release through gamma radiation."

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.
"It makes sense, but HOW. Magic repulsion and stickiness?"

"This presentation went very well. I really thought this presentation helped a lot, it even helped me understand whats going on in chemistry better thanks!"

"I am confused on how the electron capture is calculated. I don't know how to determine the number of protons or neutrons in the electron capture."

"What I found confusing about the reading is how the heck does a proton turn into a neutron and vice versa! More importantly how the heck is a neutron 'intrinsically' unstable!!! Physics is making me question the very little amount of things I know about chemistry."

"I'm mostly confused about the strong force that nucleons exert on each other that sticks them together. If a neutron has no charge...how can they possibly be attracted to anything? Or is this just something that isn't quite understood yet?"

"Nothing. I've got this chemistry on lock!"

Explain what a "nucleon number" is, and/or describe how to calculate it for a nucleus.
"The nucleon number denotes the total number of nucleons (protons and electrons), such that the number of neutrons is the difference between the nucleon number and atomic number."

"The total number of protons and neutrons. Z + N = A."

Identify the processes that increase, decrease, or do not change the number of protons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [80%]
β– decay: increase. [74%]
β+ decay: decrease. [66%]
electron capture: decrease. [34%]
γ decay: does not change. [71%]

Identify the processes that increase, decrease, or do not change the number of neutrons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [77%]
β– decay: decrease. [69%]
β+ decay: increase. [71%]
electron capture: increase. [26%]
γ decay: does not change. [74%]

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. [77%]
β– decay: n → p. [77%]
β+ decay: p → n. [74%]
electron capture: p → n. [29%]
γ decay: no p/n conversion. [80%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"This stuff is basically alchemy. That's so awesome!"

"This antimatter electron twin stuff is freaky. Somebody should have Antman jump into a positron annihalating an electron and see which universe he ends up in."

"I need to start showing up to class again. I'm losing patience with this semester. Thank God we have three weeks left."

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