Monday, February 6, 2017

Spring 2017 CHEM 312: Exam 1

Exam 1
Assigned: 7-Feb-2017
Due:13-Feb-2017
2nd Due Date: 16-Feb-2016

Use the chart of the nuclides, table of the isotopes, and/or data from the web links to answer the following questions. Please feel free to contact me via the blog with questions. The quiz is due on 13-Feb-2017. The answers will be posted on 14-Feb-20176. Changes can be made to the quiz after reviewing the answers. You will need to provide your work for any changes in a separate document. All changed questions will be worth a maximum of 50 % of the point total. A skype meeting of the quiz will be held.  The exam covers:

Lecture 1: Introduction, Chart of the Nuclides
Lecture 2: Nuclear Properties
Lecture 3: Decay Kinetics

34 comments:

  1. For the ERG program use the local download link from lecture 3 of the course website.

    http://radchem.nevada.edu/classes/rfss/program/NToolsV2002.zip

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  2. Two corrections to the exam should be noted:
    Question 5.1 5X10^14 n cm^-2 sec^-1 instead of 5E1014.
    Question 7: 187Re instead of 187Rh

    An updated, corrected quiz will be posted.

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  3. This comment has been removed by the author.

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  4. I have a really simple units question. For number 5, if we keep the irradiation time, t, in minutes can we just leave the decay constant in min^-1? I just left everything in minutes but then I saw that the neutron flux units is in seconds. I'm not sure how the units cancel out just to get atoms....

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    Replies
    1. Since the flux is in seconds all the time units should match. The time and decay constant can cancel if both are in minutes. However the flux and decay constant will not cancel, since they are in different units.

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  5. For 10.1, I am confused on where the information of, "The same neutron flux as above for 10 hours," works into the calculation. So far I worked backwards. I got N from using N=A/lambda. In which I used the half-life of 198Au to find lambda. Then I converted the atoms Au to grams using Avogadro's number and the molecular weight. I then divided the answer by the total ore mass. Does this work? (I got that it is unsuitable because my answer is less than 1 ppm of gold for this ore.)

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    1. Questions 10.1 states An unknown potential Au ore is irradiated in
      the same neutron flux as above for 10 hours. The
      ore mass is 10 mg. At the end of the irradiation
      the 198Au activity is 11.5 Bq. Is this ore suitable
      for mining?.

      Route you uses does not include the 10 hour irradiation.

      Another way to solve this is using the data from the table you made in question 10. You have the 198Au activity at 10 hours from the table. This is the result from the activation of 1E-7 g of 197Au (0.1 g ore x 1E-6 g Au/g ore). From this you get a specific activity, 1E-7 g 197Au/ x Bq = specific activity. This provides the relationship between activity and mass at 10 hours. In question 10.1 the activity is provided, 11.5 Bq. From this you can find mass of 197Au in the 10 mg sample. From this you can see if the sample is above 1 ppm.

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  6. For Question 1 , I got the 2.04E14 g/mL for Ni, but I have no ideal for neutron star, can you give me a equation? Also, for Question 5, it should be use the equation A = N₀ σ ∅ (1-e^(-λt)) ? and the λ is calculated from the half life? how about Question 10, it is same as the Question 5?

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    1. I think for question 1, he wants us to go to the website link in the question and just take one of the values to compare to the answer we calculated.

      For question 5, in office hour, he said to use the equation: N1 = ((N₀σ∅)/λ1)(1-e^(-λ1t)

      And for 10, I solved it the way I solved for 5, bur I honestly have no idea if that's right....

      I hope this helped!

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    2. This is correct. You can find the density of a neutron star on the web, specifically in the link provided in the quiz.

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  7. But how to get λ1, and σ is from the element chat, right? Thanks

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    1. I think is λ1 = ln2/42m where 42m is the half-life of 227Ra.

      I took σ from the chart he put next to the question!

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    2. Correct. The decay constant is ln2/t 1/2, where t 1/2 is the half-life. Make sure all your time units are the same. There is a comment on this in the blog.

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  8. would a word doc be acceptable for describing the reasons for changes?

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    1. Yes a word document is acceptable. However it is only needed for the 2nd submission.

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  9. For question 10, I input the neutron flux into my calculator and it says "overflow system". Is the neutron flux really 2.5E10^10? If so, is there a way to get it into my calculator without it overflowing?

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    Replies
    1. That is an error. On 10 February there is a blog post (see above) that states:

      Two corrections to the exam should be noted:
      Question 5.1 5X10^14 n cm^-2 sec^-1 instead of 5E1014.
      Question 7: 187Re instead of 187Rh

      An updated, corrected quiz will be posted.

      The flux should be 2.5E10.

      Delete
  10. Test #1 Submitted. Many of my questions were already addressed in the blog. Thank you.

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  11. Exam 1 has been sent. Thanks, I learned a lot from office hours!

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  12. Are you taking off points even if our values slightly differentiate? For example, on #3, I originally got 291.5, so I rounded up to 292, but you have 291. Will I lose points for that? Also, on #4 you marked that nuclear matter is compressible, but in lecture 2 slide 12, it states that nuclear matter is incompressible. Lastly, are you giving partial credit, or if part of the answer is incorrect, all of it is?

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    Replies
    1. You are correct on my error. Nuclear matter in NOT compressible. For calculations such as the one in question 3 I will NOT deduct points for rounding. The main point of the question is to understand the equation and how to use it. An answer of 291 or 292 years demonstrates one can utilize the equation.

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  13. can you double check the question 4:" Nuclear matter in incompressible" the answer should be right?

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    1. Yes, you are correct regarding question 4. An updated version of the answers will be posted.

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  14. Oops, I forgot to comment here. I submitted the exam yesterday. The office hours were helpful; thanks for organizing that.

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  15. Hi,
    I was wondering if you could clarify on #4 why nucleons are not in shells? On slide 15 of lecture 2 it says that there is a concept of closed shells in nuclei. Is it because the liquid drop model doesn't rely on this concept?
    Thanks!

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    Replies
    1. Correct, the liquid drop model does not consider nucleons in shells. Evaluation of differences between measured and calculated binding energy using the liquid drop model show strong deviations by the magic numbers. This pointed to the need for an updated nuclear model.

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  16. thanks for the comments and submissions.

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  17. This comment has been removed by the author.

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  18. I have already sent the quiz for the 2nd submission. Thank you.

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  19. I wasn't certain if I was supposed to comment on these quizzes, so I figured I would go back and comment just in case. I submitted my quiz and quiz correction to you via email. Thanks!

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