Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2019
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz07SGnD



Sections 30882, 30883 results

0- 6 :	* [low = 6]
7-12 :	****
13-18 :	***********
19-24 :	************* [mean = 20.3 +/- 5.9]
25-30 :	******* [high = 30]

Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz07NWst



Sections 30882, 30883 results

0- 6 :	***** [low = 3]
7-12 :	******
13-18 :	******** [mean = 16.2 +/- 7.7]
19-24 :	********
25-30 :	**** [high = 30]

Physics final exam question: valid or invalid Feynman diagram?

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

Discuss whether this Feynman diagram is valid or invalid. Explain your reasoning using the properties of Feynman diagrams, particles and antiparticles, and interactions.

Solution and grading rubric:

• p:
  Correct. Argues why this Feynman diagram is invalid by either one of two arguments:
  1. this process is not a proper permutation of a known weak interaction (as the nucleon changes into a lepton in the top path); or
  2. charge conservation is violated (zero charge of neutron does not equal the net positive charge of neutrino, positron, and proton out).
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete. May argue why this Feynman diagram is invalid as does not correspond to a known weak decay process (but discussion of the known weak decay process is garbled); or argues that this Feynman diagram is valid as the "one line in, one line out" vertex rule is obeyed by both vertices (although charge conservation is violated, and the nucleon and lepton paths are mixed).
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying properties of Feynman diagrams, particles and antiparticles, and interactions.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying properties of Feynman diagrams, particles and antiparticles, and interactions.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: finalmR3x
p: 3 students
r: 3 students
t: 18 students
v: 2 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 7117):

Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2017
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz07N4ci



Sections 30882, 30883 results

0- 6 :	**** [low = 0]
7-12 :	************** [mean = 10.5 +/- 6.1]
13-18 :	*****
19-24 :	*
25-30 :	* [high = 27]

Physics final exam question: invalid Feynman diagram

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

Discuss why this Feynman diagram is invalid. Explain your reasoning using the properties of Feynman diagrams, particles and antiparticles, and interactions.

Solution and grading rubric:

• p:
  Correct. Recognizes that the diagram is invalid by discussing:
  1. this was originally an electron capture process that has been rotated, but the proton path is reversed; or
  2. the "one line in, one line out" vertex rule is violated; or
  3. charge conservation is violated (net negative charge of electron and antineutrino in does not equal the net positive charge of neutron and proton out).
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying properties of Feynman diagrams.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: finalm4u1
p: 26 students
r: 7 students
t: 2 students
v: 3 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 2691):
Another sample "p" response (from student 3158):

Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2015
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz07d4wN


Sections 30882, 30883 results

0- 6 :	**** [low = 3]
7-12 :	******
13-18 :	*************
19-24 :	****** [mean = 18.4 +/- 7.8]
25-30 :	*********** [high = 30]

Physics final exam question: manipulating Feynman diagram paths

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

This (valid) Feynman diagram depicts electron capture. Demonstrate how the paths on this diagram can be manipulated to depict β⁺ decay. (Ignore the direction of the interaction particle, but all other particle paths must have the correct directions and labels.) Explain your reasoning using the properties of Feynman diagrams, particles and antiparticles, and interactions.

Solution and grading rubric:

• p:
  Correct. Demonstrates how left-to-right path of electron entering the vertex can be draw exiting the vertex, but with a right-to-left arrow direction, representing a positron (a "β⁺" particle) as a decay particle, along with a neutrino, as a proton converts into a neutron.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Error in keeping direction of electron/positron path consistent as it is flipped, making the vertex invalid, but understands that beta-plus decay process has only proton decaying into byproducts (as opposed to a proton-to-neutron conversion by antineutrino bombardment).
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete. At least some attempt at showing a positron-out process, despite drawing invalid Feynman diagrams and/or neutrino/antineutrino bombardment of a nucleon by path/direction manipulation of given electron capture Feynman diagram.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some use of Feynman diagrams or some other attempt, but no positron output.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: finalEL7a
p: 3 students
r: 3 students
t: 6 students
v: 16 students
x: 5 students
y: 1 student
z: 1 student

A sample "p" response (from student 1208):
A sample "r" response (from student 7810), with an invalid vertex due to the wrong electron path direction:
A sample "t" response (from student 6644), at least showing a valid Feynman diagram with an exiting positron path, but with an incoming antineutrino path, and a strange antineutron-to-antiproton conversion:
A sample "v" response (from student 5555):
Another sample "v" response (from student 0008):

Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2014
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz07bC4n



Sections 30882, 30883 results

0- 6 :
7-12 :	*** [low = 12]
13-18 :	****************
19-24 :	************ [mean = 20.4 +/- 5.4]
25-30 :	******* [high = 30]

Physics final exam question: incorrect Feynman diagram

Physics 205B final exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

The Feynman diagram (A) correctly shows an electron capture decay process, where a proton and an electron interact to convert into a neutron and a neutrino. Discuss why the other Feynman diagram (B) showing an antineutrino interacting with a proton to convert into a neutron and positron is incorrect. Explain your reasoning using the properties of Feynman diagrams, particles and antiparticles, and interactions.

Solution and grading rubric:

• p:
  Correct. Discusses (1) how the second Feynman diagram violates the in-out path vertex rule, and/or (2) draws a corrected Feynman diagram for an antineutrino and proton respectively turning into a positron and neutron after the interaction.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882
Exam code: finalpL3x
p: 16 students
r: 1 student
t: 5 students
v: 3 students
x: 2 students
y: 1 student
z: 2 students

A sample "p" response (from student 1408):
A sample "x" response (from student 8325), with at least some demonstration of understanding charge flow conservation:

Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2013
Cuesta College, San Luis Obispo, CA
Section 30882, version 1
Exam code: quiz07f3yN



Section 30882 results

0- 6 :	** [low = 0]
7-12 :	****
13-18 :	************* [mean = 18.4 +/- 7.2]
19-24 :	*****
25-30 :	******** [high = 30]