Online reading assignment: radioactive decay modes

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 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.
"A nucleus must have just the right ratio of protons to neutrons or the atom becomes unstable."

"Nucleus, protons, neutrons, electrons...yeah I got this"

"Did not get to it"

"I understood that when there is not the correct ratios of protons to neutrons that the atom will turn a proton into a neutron or vice versa. There are a few different types of decay: alpha, beta (+), beta (–), and gamma."

"Decay occurs as a nucleus attempts to become more stable. A proper balance of protons and neutrons is necessary for stability. If balance is not maintained, protons may be transformed into neutrons (or vice versa), or proton/neutron couples can be released."

"The reason nuclei are unstable are due to the unfavorable ratio of protons to neutrons. The charges and forces protons carry are too much for the nuclei too handle if out of proportion."

"A nucleus containing more than 83 protons is unstable. If there are more neutrons than protons or the same amount then there is stability."

"Greater than 83 protons means unstable nuclei no matter how many neutrons. Having approximately the same number of protons as neutrons will make the nucleus stable."

"I have covered some of this in chemistry, so I know some of it but not well."

"The nucleus of an atom is composed of nucleons, that is, protons and neutrons. Radioactive decay occurs to lower the nucleus' energy state through a shift in the configuration/numbers of nucleons or when rays are released. There are five different types of radioactive decay: alpha, beta-positive, beta-negative, electron capture, and gamma."

"I understand the composition of an atom as well as the various types of decay because I have learned it before in my physics class. Alpha and gamma decay is very solid in my mind."

"I understand that alpha particles are decay that are equivalent to a helium atom flying off, thus changing the element overall to two less protons and two less neutrons. A beta particle or decay is where the radioactive material becomes a different element by gaining or losing a proton."BR>
"There are different ways for radioactive material to decay. I never knew protons could be emitted or change to neutrons and back"

"Nuclear instability is the result of an improper ratio of neutrons to protons in a nucleus. The nucleus will then emit several different types of particles in order to achieve a more stable state, depending on the number of each to begin with. The three types of decay are: alpha decay (He nucleus) Beta minus (n->p + e–) beta plus (p->n + e+) and gamma (decay->photon)."

"I understand that nuclei stable or unstable have a set of positive charged protons and neutrally charged neutrons and that from chemistry, the periodic table and how to read a specific element from the table. I also understand now that as a radioactive decay process occurs, a nucleus with an unstable configuration always seeks a more stable configuration."

"For all atomic nuclei, big and small, the key to stability is being able to keep the protons in the nucleus together. A nucleus containing more than 83 protons will always be unstable, no matter how many neutrons there are."

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.
"Mixing up the different kinds of decay. As in which are alpha, beta, and so on."

"On the homework problems for the half-life and exponential problems those were a tiny bit confusing because it wasn't clear to me that R0 is the original rate of decay. So, doing those problems shed some light on that."

"he strong force. I understand how it is applied in the class notes for neutron balance, but what makes it different from electromagnetic force?"

"I don't really find it confusing, but I found it I retesting that neutrons and protons switch back and forth into each other inside a nucleus. I always thought they were the same 100% of the time."

"How the ratio of protons to neutrons effects the stability of the nucleus."

"I didn't understand either of the beta decays."

"Beta positive versus beta negative decay. I could benefit from some examples in class of that and also when the nucleus swallows an neutron."

"I do not understand how the neutrons hold the protons together in a nuclide in almost a 1:1 ratio up until 20 protons and then start having to dramatically increase the number of neutrons per proton."

"That protons can be turned into neutrons; I thought the protons were what made a particular element a particular element."

"Electron capture."

"Parts about different processes that unstable nuclei can undergo to achieve stable configurations. This material is very interesting, but a little difficult to understand in terms of how they all apply in a physics sense."

"I understand how you tell if a nucleus is stable or unstable, but could use a little help in determining what it would take to make it stable."

"Trying to identify the processes that increase or decrease or do not change protons into neutrons."

"Not much."


Explain what a "nucleon number" is, and/or describe how to calculate it for a nucleus.
"The nucleon number is also the 'mass number,' and it can be found in the top left corner of each elements box on the periodic table. It is the number of protons and neutron in an atom."

"The total number of protons and electrons."

"Nucleon number is noted as 'A', neutrons = AZ(atomic number, or the number of protons)."

Identify the processes that increase, decrease, or do not change the number of protons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [87%]
β– decay: increase. [65%]
β+ decay: decrease. [70%]
electron capture: decrease. [17%]
γ decay: does not change. [78%]

Identify the processes that increase, decrease, or do not change the number of neutrons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [57%]
β– decay: decrease. [83%]
β+ decay: increase. [78%]
electron capture: increase. [22%]
γ decay: does not change. [83%]

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. [70%]
β– decay: n → p. [87%]
β+ decay: p → n. [70%]
electron capture: p → n. [26%]
γ decay: no p/n conversion. [83%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Is my smoke detector giving off harmful radiation?" (Only if you crack it open.)

"What causes the emission of positrons or electrons when protons or neutrons transform into each other?" (Charge and mass must be conserved. Also a neutron is just a proton with an electron added to it. Weird, huh?)

"A neutron walked into a bar and asked, 'how much for a gin and tonic?' the bartender said, For you, no charge.'" (#rimshot)

"Wouldn't electron capture simply balance the charge of the entire atom, and not affect the nucleus?" (It might make the atom ionized, as it would lose an electron, and definitely affect the nucleus it turning a proton into a neutron.)

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