Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Question 29.4, Problem 29.26
Discuss why radioactive (14,6)C will not undergo β+￼ decay, and must instead undergo β– decay. Explain your reasoning using the properties of nuclides and radioactive decay modes.
Solution and grading rubric:
Correct. Discusses β+ decay as converting protons into neutrons, and since carbon-14 has more neutrons than protons, this would not lead to a more stable nucleus, thus β– decay (which converts a neutron into a proton) would result in a more stable nucleus.
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
Nearly correct, but argument has conceptual errors, or is incomplete.
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some attempt at finding the number of neutrons and protons in carbon-14.
Implementation/application of ideas, but credit given for effort rather than merit.
Irrelevant discussion/effectively blank.
Exam code: finalsM0k
p: 20 students
r: 0 students
t: 0 students
v: 1 student
x: 2 students
y: 0 students
z: 1 student
A sample "p" response (from student 0524):
Another sample "p" response (from student 1413):