Supplemental Questions

Pav 2012

This work will now be due two days before your next test to allow enough time evaluation and return

1. One of the most fascinating experiments that led to a better understanding the electron was conducted by Robert Millikan.

a. Briefly describe his experiment and give it a try using the simulator found on the following website: http://www.montereymotiongraphics.com/example1.swf

Millikan determined the charge on an electron in his amazing oil drop experiment. In this experiment, he suspended droplets of oil in a chamber against gravity by varying the strength of an applied electric field.

b. Using Thomson’s charge to mass ratio of the electron (1g = 1.76 x 108 Coulombs) and Millikan’s charge on the electron (1.5924 x 10-19 Coulombs), calculate the mass of a single electron. Use factor-label pleaseJ

2. James Chadwick was responsible for the discovery of the neutron. Prior to Chadwick’s discovery, the atom was only thought to contain protons and electrons. Interestingly enough, the mass of the atom was known, but something just didn’t add up: namely, the mass of all the protons and electrons in an atom did not add but to be equal to the mass of the atom.

a. The mass of a proton is 1.0073amu. The mass of a neutron is 1.0086amu. Determine the mass of carbon-12 (in amu) based on these values.

6 x 1.0073amu = 6.0438amu

6 x 1.0086amu = 6.0516amu

12.0954amu

b. The actual mass of carbon-12 is 12amu. Go to http://www.colorado.edu/physics/2000/periodic_table/amu.html and read about “mass defect”. At the bottom of the page, click on the “binding energy” link and read about binding energy.

Explain why the mass of carbon-12 does not equal the sum of its parts in terms of mass defect and binding energy.

When particles in the nucleus fuse, some of the mass is converted to energy (binding energy), therefore, the mass of all the individual particles is always more than the mass of the nucleus they form. This is the mass defect.

3. Go to http://www.periodictable.com/index.html to answer the following questions.

a. Locate element #60, neodymium on the periodic table. What period does it reside in?

Period 6

b. Click on neodymium, at the top of the neodymium page click on “neodymium isotope data”. How many different isotopes of neodymium are there?

c. Which isotopes account for the atomic mass of neodymium?

Nd-142, Nd-143, Nd-144, Nd-145, Nd-146, Nd-148,

d. Why don’t the other isotopes contribute to the atomic mass of neodymium?

They have zero abundance. Note: they may be more stable than the remaining isotopes, but some of them are unstable and undergo radioactive decay.

e. Calculate the neutron to proton ratio for each of these isotopes.

Nd-142 = 82/60=1.37:1 Nd-143 = 83/60=1.38:1 Nd-144 = 84/60=1.40:1

Nd-145 = 85/60=1.42:1 Nd-146 = 86/60=1.43:1 Nd-148 = 88/60=1.47:1

f. Plot the approximate location of Nd-124, Nd-145, and Nd-161 on the band of stability graph below.

g. Unstable isotopes will often undergo a series of decay reactions until a stable isotope is formed. Write the first reaction in the decay series for both Nd-124 and Nd-161, showing the parent nuclide and the reaction products.

If you didn’t look at the actual decay series on-line, you would predict either positron emission or electron capture for Nd-124. It is actually positron emission.

h. Based on the half-life of Nd-124, how long would it take for 128g of the isotope to decay leaving only 16g to remain.

This would require using the ln function. However, 16/128 = 1/8 which is a multiple of ½. So…..n=3 and TE=n x t1/2

TE = 3 x 0.5s = 1.5s

4. How long would it take for a 235 g sample of Bi-186 to decay to 18g if the half life of this isotope is 14.8ms. Report your answer in microseconds. (see power point slide on the use of natural logs for help)

5. Using the figure to the right, list each type of decay

that uranium-238 goes through to become lead-206.

The decay of uranium-238 consists of a total of 14 reactions.

1. Alpha

2. Beta

3. Beta

4. Alpha

5. Alpha

6. Alpha

7. Alpha

8. Alpha

9. Beta

10. Beta

11. Alpha

12. Beta

13. Beta

14. Alpha

6. Thorium-238 undergoes radioactive decay until a stable isotope is reached. Write the reactions for the decay of Th-238. There are eleven steps beginning with Alpha decay with each product becoming the reactant of the next decay. Circle the final Stable isotope.

• Alpha:

• Beta:

• Alpha:

• Beta:

• Alpha:

• Beta: ______

7. One of the elusive quests of ancient alchemists was to “manufacture” gold. Although we have the ability to induce transmutation of elements, the cost of producing gold in this way would far outweigh the value of the gold itself. However, this should not keep you from experiencing some “funstration” as you attempt to solve the following theoretical problems.

Gold can currently be manufactured in a nuclear reactor by irradiation either of platinum or mercury. Since platinum is more expensive than gold, platinum is economically unsuitable as a raw material. Only the mercury isotope Hg-196, which occurs with a frequency of 0.15% in natural mercury, can be converted to gold by neutron capture, forming Hg-197 which naturally decays to Au-197.

a. Write the transmutation reaction of Hg-196 into Au-197, with the decay of Hg-197 as an intermediary step.

b. What mass of natural mercury would be required to produce 1 x 109 Au-197 atoms? (1Hg-196 atom = 3.25x10-22g)

To do this, you must recognize that for every one Hg-196 atom, one atom of Au-197 is produced. This relationship should be used as a conversion factor to solve this problem.

c. How much would this amount of mercury cost if 1L of mercury costs $2000.00 and the density of mercury is 5.43g/cm3?

You must first find the volume of mercury given the mass and the density (V=M/D). Once the volume is converted to Liters then the cost can be determined.

8. Using the internet as a resource, research a treatment for a medical condition that uses radioactive isotopes. Briefly state the isotopes used and the process by which they work to treat the condition.

There are so many medical uses of radioactive isotopes. The idea was to independently learn about the connection between some of the content in chapter 25 and the real world. This was a no brainer, look it up and write it down.