The 1st quiz is posted at http://radchem.nevada.edu/classes/chem312/quizzes.html. You should be prepared to discuss the quiz during the class meeting on 24 September. Questions related to the quiz can be posted here. Responses to all questions will be posted on the blog.
Good Afternoon Professor,
ReplyDeleteI am having trouble with one of the question of the take home quiz. For question 3 where you ask about the decay mode and daughter isotope I can not find 241 Rf isotope. I have use the Chart of the Nuclides and all of the isotopes of Rf, Rutherfordium, start with A=253 and higher none have a mass of less than 253. I am not sure if I am misunderstanding the question or misinterpreting the chart.
Hello Angel
DeleteThat is a typo on my part. Lets do 261Rf rather than 241Rf.
Sorry for the mistake.
ken
I'm having a lot of trouble understanding questions 10. and 11. I am able to calculate the radius fro 56-Fe, but I am unsure of how to calculate the mass of the nuclear matter. I assumed that I needed to use the density of nuclear matter and convert the 1 mL to fm^3 to find the volume and solve for mass, but I couldn't find anything to support that method online or in the textbooks. For number 11, I was also unable to find anything about gamma decay intensities in the textbooks or online and I didn't recall hearing about it in the lectures.
ReplyDeleteQuestion 10 first.
Delete10. (10 Points) Calculate the mass of 1 mL of nuclear matter. Base the calculation on an 56Fe nucleus, with ro = 1.3 fm to determine the radius of 56Fe.
The radius can be found from R=roA^(1/3). This gives the radius in fm (10^-15 m). If you remember that 1 mL = 1 cm^3, you can convert the radius from fm to cm. Using the equation to determine volume, 4/3Pir^3 gives the volume in cm^3, hence mL. Pi is 3.14.
r=1.3(56^1/3)=4.97 fm =4.97E-15 m = 4.97E-13 cm
V=4/3Pi(4.97E-13 cm)^3=5.14E-37 cm3=5.14E-37 mL
Now we need the mass of the 56Fe nucleus. We will assume all the mass of 56Fe is in the nucleus. This is not completely correct as it added the electron masses to the nucleus but this is really a small error. The AMU for 56Fe is 56, so 56 grams of 56Fe is one mole. We use this to determine the mass of one atom.
1 atom x 1 mole/6.02E23 atom x 56 g/mole = 9.30E-23 g for 1 atom of 56 Fe.
Density =9.30E-23 g/5.14E-37 mL = 1.80E14 g/mL
Neutron star density is around 3E14 g/mL (http://en.wikipedia.org/wiki/Neutron_star), so this is a reasonable calculation.
I will get to question 11 later.
I understand number 10 now except for where the 1 mL of nuclear matter given in the question comes into play.
DeleteAaron
ReplyDeletePlease clarify your comment. I am not sure to which part of the quation your statement refers. If you are talking about the neutron star density, this is a good way to check your answer. I would not expect the estimate to be exact but I would expect it to be within an order of magnitude.
Comment on question 11
ReplyDeleteIn question 11 your were requested to find the gamma ray intensities for following isotopes and their corresponding gamma rays.
Isotope Gamma Energy (keV) %gamma
46Sc 1120.5
103Ru 497.1
198Au 411.8
241Am 59.1
152Eu 121.8
152Eu 1408.0
152Eu 344.3
This information is presented in lecture 1, slide 37. This discusses how to use the Table of the Isotopes to find the gamma ray intensities.
Lets use 46Sc as an example and use the Table of the Isotopes to find the gamma intensity.
Go to the Table of the Isotopes, click the Summary Scheme Index, and select A=46. From there click in 46Sc, this will bring you to the data on this isotope. Continue to scan past the 46Sc data to where you see gamma (46Ti) from 46Sc. This is on page 978 of the Chart of the Nuclides. There is data for gamma rays of 889 keV, 1120 keV, and 2010 keV. Above this data table is instructions to multiply the value by 1.0 to find the % gamma decay. For 1120 keV the value in parenthesis is 99.987. The 99.987 %. Repeat for the other isotopes.
More on question 11.
ReplyDeleteAnother route to finding the gamma yield is to go to: http://nucleardata.nuclear.lu.se/toi/radSearch.asp
In our example enter Sc for element and 46 for mass number. Click search and the data table for this isotope appears. For 1120 keV the gamma intensity is 99.987 %.
You can get an app for this data by downloading "nuclear data search" app for your phone.
Ok thanks for the help with question 11. For the previous question, though, it states that "10. Calculate the mass of 1 mL of nuclear matter. " I wasn't sure where you incorporated that into your explanation.
ReplyDeleteThis is just done by solving for density. If I calculate the mass of one atom in g, and I know the volume in mL, then I have the density (g/mL)
ReplyDelete