NUCLEAR CHEMISTRY Chapter 21: The Nucleus: A Chemist’s View

Nuclear chemistry is one of my favorite topics to teach and unfortunately, because of our time

limitations, this is the best we can do. So let’s go. I’m going to highlight the topics I feel are

important or like to talk (write) about and you need to follow along with graphs and problems

in your book (the white heavy thing…).

As the graph on page 906 shows there is a band of stability for elemental nuclides (general name for the nucleus

of an atom). If the proton-neutron ratio does not fall in this band, the nucleus experiences radioactive decay, to

achieve the correct ratio for stability. Many elements contain radioactive isotopes.

What is radiation??

Energy or particles emitted from a source and travel through a medium or space.

A. Ionizing-powerful enough to produce ions out of molecules (x-rays)

B. Nonionizing-radio waves, light waves

BACKGROUND RADIATION: Radiation is all around us, we get it from all kinds of sources: outer space,

cosmic radiation, the Earth, food (potatoes have a lot), building materials, human body minerals, TV (this is

why you should sit 10 ft away), computer screens (uh oh), and especially cell phones…

FDA recommendation for radiation exposure is <500 millirems per year. Check

out page 923 for the rem definition. The average exposure is 100 millirems

annually but of course, some people get more exposure by nature of their

occupation or habits. People who live in high altitudes receive more radiation as

do people who work in the airline industry because they are closer to cosmic

sources. For example a chest x-ray = 50 mrems while your set of dental x-rays =

20mrems. I’ve included a little exercise to figure your personal radiation does…try it. Oh yeah, all you

smokers…2 packs a day = 10,000 mrems per year. Also, some detectors have Am-

241…if you laid 20cm underneath one for one year you would get an additional 2

mrems/year. The original cellular phones contained a radioactive isotope until the

main tester got a brain tumor right above his right ear…coincidence?? What about

M. Curie…how did she die?? And those terrible things the dentist’s put in and say,

“hold here”…well they used to hold them until they started losing fingers, really

black, dead tissue. And did you know they always leave to hide behind a wall of

lead!! The people who take your x-rays have to wear a name tag or ring to monitor

the amount of radiation they are exposed to and astronauts have a short career, too

much radiation exposure.

What are the effects of radiation?

*human DNA seems to be the most sensitive to ionizing radiation, exposure changes

the DNA resulting in cell death or uncontrolled growth AKA cancer. Most sensitive areas

are bone marrow, reproductive organs, and intestinal linings.

Did you know the only organisms we know of that will live through nuclear destruction and is unaffected by

radiation… the cockroach and the moth. Moths can survive a greater amount of radiation, thank you Myth

buster’s. Check out this link http://www.youtube.com/watch?v=S-6cIy_s8pQ

Effects of Short-term Exposures:

0-25 rems No visible effect

25-50 rems White blood cell count drops slightly

100-300 rems Nausea, fatigue, vomiting, hair loss

300-500 rems White blood cell count drops to zero,

hemorrhages & ulcers develop

>500 rems Fatal to 50% of population within 30 days

THREE TYPES OF RADIOACTIVE DECAY:

1) Alpha-particle production—common mode of decay for heavy nuclides. The nucleus releases an alpha

particle which is 2 protons & 2 neutrons. It is written as an helium nucleus and is symbolized by the

letter α.

Animated version http://library.thinkquest.org/27954/dequ.htm

Uranium is the parent nuclide, and thorium is the daughter nuclide (sorry no sons).

Did you know?

α radiation is the weakest and can be stopped by a sheet of paper

2) Beta-particle production—common for nuclides that lie above the stability zone because it decreases the

neutron/proton ratio). It is a production of an electron from the nucleus. Where are the electrons in the

nucleus??? Think of a neutron as a proton and an electron (actually protons and neutrons are made of

smaller matter called quarks. These guys can exist as particles and energy. Also, a positron is the

antimatter of the electron. When they collide, annihilation happens and energy is released…star trekkies

beware.) And remember an electron has negligible mass.

http://library.thinkquest.org/27954/dequ.htm

Who’s the parent here?

β radiation can be stopped by aluminum foil.

Similar to beta decay is positron emission. A particle with the same mass as the electron but opposite in charge

(quarks at work here, can you hear them?). Occurs for nuclides below the zone of stability.

Positron emmission topography is used as a medical diagnostic

test. (Heard of a PET scan?)

Electron capture happens when one of the inner-orbital electrons is captured by the nucleus.

3) Gamma Radiation—a release of energy often accompaning alpha or beta decay. It does not cause a

change in atomic or mass number. Penetrating power: several cm of Pb

Look above for its release in the electron capture equation.

NUCLEAR TRANSFORMATIONS:

The change of one element into another, first observed by Lord Rutherford in 1919

Particle accelerators used to add particles to the nucleus. Transuranium elements (Z>93) have been

synthesized since 1940. All are radioactive and decay at different rates.

Fermilab in Chicago is a nationally known SSC.

(superconducting supercollider) It has a 6.3 km

circumference, is underground and accelerates the

bombarding particle with magnetic oscillations to a speed

of 250,000 cycles per second. Then the particle has

enough potential energy to be added to the nucleus of

another atom. And Fermilab is not the most recent or the

largest. Learn more about Fermilab!

http://www.fnal.gov/faw/fermilab_at_work.html

T1/2 = radioactive nuclei are considered dangerous for 10 half lives. Check out the variance on pg.

918. For example Polonium-214 has a half life of 0.0002 seconds while Neodymium-144 has a half life of 5 x

1015

years.

Radioactive decay makes the same graph as integrated first-order rate laws.

T1/2 = 0.693/k

Example: T1/2 of Fluorine-21 is 5 seconds.

a) What fraction of the original nuclei would remain after 1 min?

b) Given 21 grams of fluorine, how many grams would remain?

60 sec / 5 sec = 12 half-lives have passed

(1/2)n where n = # of elapsed half-lives; (1/2)

12 = 1/4096

21 grams x 1/4096 = 0.0051 grams remain

Radioactive isotopes are used in diagnostic

medical testing daily. They are used as

radioactive tracers. Check out table 21.12 on pg.

919. Keep in mind one would not want to use a

tracer that had a very long half-life, because it

remains harmful for 10 half-lives. The longest

tracer in this list would be negligible after 451

days (still pretty long for my taste). A commonly

used tracer is Iodine-131 for thyroid detection.

DATING BY RADIOACTIVITY

The process of dating fossils by geologists requires the knowledge of radioactivity and the use of an instrument

to measure high-energy particulate decay. The most common device is

called a Geiger counter. Your book gives you a little bit of background on

how it operates. Unfortunately a rather large sample must be burned to

analyze for present level of radioactive carbon. Or the more recent use of

the mass spectrometer allows much smaller samples to be analyzed.

To date organic remains, the decay of Carbon-14 is measured. As you

know, anything that has been alive must contain carbon and once an

organism dies the rate of decay of carbon-14 steadily decreases. Therefore by measuring the present amount of

decays/minute/gram one can estimate the approximate time the organism died and be able to “date” the fossil.

Using the integrated first-order rate law, estimation can be made of the fossils age. Radiation half-lives are first

order rate because in an allotted amount of time half of the reactions, in this case half of the nuclei have

decayed. And for first order reactions, the half-life does not depend on initial concentration, which is

appropriate for radioactive decay. Check out sample exercises 21.7 & 21.8 on pg. 913-914.

Remember that radioactivity is only harmful or, in carbon-14 case, detectable for ten half-lives or 57,300 years.

Do we have older fossils? How do we date these?? Most often older fossils are dated indirectly. This means

they are dated by the layer of rock they are found in assuming that the layer of sediments within that layer

occurred at the same time period.

Rocks can be dated by the ratio of Uranium-238 to Lead-206 composition. Because lead-206 is the daughter

nuclide or uranium-238, the ratio can lead to the relative number of half-lives that have elapsed. The half-life of

uranium-238 is 4.5 billion years and of course, this number is estimated from the rate of decay measured during

a unit of time. Remember, we have no way of altering the decay rate or half-life of radioisotopes… if we did

nuclear power would be the answer to all of our energy crisis concerns.

ENERGY & MASS IN NUCLEAR REACTIONS

Our buddy, Albert Einstein, developed the concept that the measurable mass

that was lost in nuclear reactions was somehow related to the large release of

energy. This is where the famous equation

E = mc2 We have used this equation in our studies of thermodynamics…remember?

Example:

One mole of Hg-200 nuclei is produced through alpha decay. If the mass of the

particles before is 201.6228g, find the energy released if its final mass is

199.9244g.

1. Write the equation.

204Pb

200Hg +

4He

2. Determine change in mass (final – initial).

199.9244g – 201.6228g = -1.6984g

3. Convert to kg. -1.6984 x 10-3

kg

4. Plug into Einstein’s equation to solve for energy.

E = (-1.6984 x 10-3

kg) (3.00 x 108)2 = -1.53 x 10

14 Joules

This means that there was a release in energy, show by the negative energy value. Your text goes on to put the

units into million electronvolts. Also, the components of a nucleus weigh more separately than they do collect

together as a given nucleus. This difference in mass is called the mass defect and could be plugged into

Einstein’s equation to find the amount of energy needed to decompose that nucleus into its component

nucleons. This is called the binding energy. Sample exercise 21.9 on pg. 917 show the manipulation commonly

used with this information.

NUCLEAR REACTIONS FOR ENERGY

A) FISSION: Fission reactions are nuclear chain reactions that are started by bombarding a nucleus

with high speed neutrons. This causes a domino effect by causing further splitting of the nuclei until

stable nuclides are obtained. As a result of this rather quick chain reaction, a large amount of energy is

released. This is the nuclear reaction that fuels the nuclear energy power plants, like in San Onofre, and

the Atom Bomb dropped in WWII.

*You are too young to really know about the “Back to the Future” movies but check out this clip of an

alternate outcome to the use of plutonium to power the time machine. http://youtu.be/MmOnhjO8cwU

Do you know the name of his dog?

Nuclear power plants have harnessed this energy by controlling the rate of neutron bombardment. Read

pg. 920-925 to get a general idea how they operate. Consider the following pros for nuclear energy:

1) For every 1 kg of lost mass in a nuclear reaction enough energy is released that would take

3,000,000,000 kg of coal to duplicate.

2) For the fission of 1 mole of Uranium-235 where only 0.22g is lost, a whopping 2.0 x 1010

kJ of

energy is released.

3) Our coal and fossil fuel supplies are nonrenewable energy sources.

Consider the cons.

1) The fuel is the isotope of uranium that is only present in nature at 0.3% occurrence and as a

result is rather costly.

2) Once initiated reaction can only be controlled but not halted at any time.

3) A great deal of toxic waste has been made that will be “hot” for thousands of years.

4) Reactor safety has been shown to be a problem. Can you say tsunami in Japanese? March 2011

http://youtu.be/BsRd7WQuBHc

B) FUSION: this nuclear reaction in what fuels the stars.

3H + 2H 4He + 1n

Two hydrogen nuclei “fuse” together to form helium nucleus and release a

lot of energy.

Consider the pros:

1) The fuel is inexpensive and abundant. We would only need

10-13

% of hydrogen isotopes in sea water to meet the energy needs of the entire world for one

year.

2) The products, helium and neutrons, are nonreactive…no toxic waste .

3) The reaction can be stopped at any time, simply by decreasing the temperature.

4) Source of inexhaustible energy…too good to be true?

5) Fission of 1 kg of uranium = 2 million kg of coal while fusion 1 kg of hydrogen = 40 million kg

of coal.

6) Even “Back to the Future” updated the use of plutonium with fusion, look for the title on the

food processor: http://youtu.be/7EXOxilOi7Y

Consider the cons:

1) We can’t get it to work. Huge amount of energy is needed to initiate the reaction. 200 million

Kelvin to sustain reaction. Where would we keep this reaction??

2) There is some research using fusion reactors called TOKAMAK reactors.

http://youtu.be/PvISgdwMGRs To my knowledge, the best we can do, with magnetic fields, is to

reach the break-even point. In other words we get back the same amount of energy we put

in…care to invest?

3) There was a claim to have successfully harness cold fusion. Watch the original news report from

1989 http://youtu.be/mgZw1zC1F3Q The science community could not replicate the results

which exiled the scientists from mainstream research. Where is cold fusion today? Underground

mostly http://youtu.be/5W9cDgGWTVM

NUCLEAR WARFARE

Of particular interest to students are the nuclear weapons that have been developed and used, especially at the

close of WWII. Atom bombs are generally fission bombs. In all bombs like this you have a central core fuel,

usually uranium or plutonium that is surrounded by TNT and a detonator is embedded in the

apparatus. The two bombs dropped over Hiroshima & Nagasaki were fission bombs. A lot

of controversy still surrounds the decision to drop the second bomb. Critics point to the fact

that the second bomb, “Fat Man”, (first bomb = “little boy”) was a differently constructed

bomb. Some say it was a type of experiment and little time was given for the people of

Japan to respond to the first bombing. Everyone has their own opinion. My problem is the

fallout and the years of radiation that resulted from this action. Theoretically the next

generation was effected, unborn children and all.

Fusion bombs or Hydrogen bombs are also referred to as thermonuclear

devices. And, they too, release nuclear fallout. Don’t be confused by this, even

though the main fuel is hydrogen, a fission explosion must happen to reach the

high temperatures needed to initiate the fusion reaction. So, these are double

explosions, first the TNT detonation of the fission explosion then the heat

released allows the fusion bomb to go. Ivy Mike, the first H-Bomb

http://youtu.be/NNcQX033V_M

Also existing are neutron bombs. These are interesting. They do not damage buildings because their detonation

is negligible. What causes the damage is the massive release of neutrons which imbed themselves in tissue,

usually targeted humans, and cause death, yet the buildings are okay.

“Lost” Bombs From the Cold War At least 11 of our nuclear bombs from the Cold War era are still “lost”, despite the Pentagon’s best efforts to

retrieve them. Five are in the US.

A powerful thermonuclear bomb is buried at the mouth of Georgia’s Savannah River, dropped by

accident from a B-47 on Feb. 5, 1958.

Two bombs lie on the ocean floor off Cape May, N.J., dropped by a cargo plane that developed

engine trouble on the way to Europe in July 1957.

A nuclear weapon disappeared in Washington’s Puget Sound when a Navy plane crashed on a

training mission in September 1958.

Part of a bomb is buried near Eureka, N.C., from a B-52 accident in 1961.

Documents confirming these and other nuclear mishaps since 1940 were discovered by Stephen I. Schwartz

while preparing his book “Atomic Audit”, published by The Brookings Institution. Schwartz stresses that the

bombs are all “unarmed” (unassembled for a nuclear explosion), and there’s no evidence of any radiation leaks.

In fact, he tells us that moving the bombs-if found now-may be more dangerous than letting them lie.

NUCLEAR WASTE

I think this is the most important topic, and appropriate to your life.

You will be voting on the use of nuclear power in the future, this I

am certain. What do we do with the waste since fusion reactors are

still a thing of science fiction. We presently pour the waste into

molten glass and allow this to solidify into rods. We pack the rods

into canisters and bury them. Cool, who wants a canister in their

backyard. Turns out not many Americans but the terrorists would

like to play. Originally power plants were designed to recycle the

fuel yet it proved economically unfeasible. Today, if these rods

were placed end to end…they would more than circle the Earth.

Yikes.

ASSIGNMENTS:

1. Totally RAD: Flying Salesman and Twins Compete Activity

http://www.nrc.gov/about-nrc/radiation/around-us/calculator.html (useful website for this activity)

Chernobyl vs Japan

http://www.nytimes.com/packages/flash/newsgraphics/2011/0311-japan-earthquake-map/index.html

1. On a map of the Ukraine label the location of Chernobyl and the nuclear plant. Also label the surrounding

countries.

2. On a map of Europe color in the area affected by the nuclear radiation that was spread by the wind after

the explosion in Chernobyl.

3. Go on the BBC web site (or any site you feel is reputable) and research what happened to cause the

explosion. Take notes that include the date, location and the facts of the explosion.

4. Still using the BBC site locate the section about how the radiation spread and what the reaction was. Find

information about the effects of the radiation and what scientists think will happen to this area in the

future. Be sure to include information about the people, the animals, and the land.

5. Compare the Chernobyl disaster to the tsunami/nuclear accident from April 2011. Post a discussion

summary of your research results and make a statement on the severity of Japan compared to Chernobyl.

Discussion posts(Turnitin.com): 1. In Turnitin.com complete an original (something not already posted) discussion post summarizing the

results of your research and a personal statement about what you have learned about nuclear energy and

how it impacts your life. Due by Friday, the day after Thanksgiving!

2. On another day, respond to 2 other posts. Ask them to clarify something in their post or pose another

question that requires a response. Make your discussion thoughtful and meaningful. Due by December 5th.

AP Problems #1

The carbon isotope of mass 12 is stable. The carbon isotopes of mass 11 and mass 14 are unstable. However,

the type of radioactivity decay is different for these two isotopes. Carbon-12 is not produced in either case.

(a) Identify a type of decay expected for carbon-11 and write the balanced nuclear reaction for that decay

process.

(b) Identify the type of decay expected for carbon-14 and write the balanced nuclear reaction for that decay

process.

(c) Gamma rays are observed during the radioactive decay of carbon-11. Why is it unnecessary to include the

gamma rays in the radioactive decay equation of (a)?

(d) Explain how the amount of carbon-14 in a piece of wood can be used to determine when the tree died.

#2

Explain each of the following in terms of nuclear models.

(a) The mass of an atom of 4He is less than the sum of the masses of 2 protons, 2 neutrons, and 2 electrons.

(b) Alpha radiation penetrates a much shorter distance into a piece of material than does beta radiation of the

same energy.

(c) Products from a nuclear fission of a uranium atom such as 90Sr and 137Ce are highly radioactive and decay

by emission of beta particles.

(d) Nuclear fusion requires large amounts of energy and to get started, whereas nuclear fission can occur

spontaneously, although both processes release energy.

#3

Answer each of the following questions regarding radioactivity.

(a) Write the nuclear equation for decay of 23494Pu by alpha emission.

(b) Account for the fact that the total mass of the products of the reaction in part (a) is slightly less than that of

the original a(234, 94)Pu.

(c) Describe how , , and rays each behave when they pass through an electric field. Use the diagram below

to illustrate your answer.

(d) Why is it not possible to eliminate the hazard of nuclear waste by the process of incineration?

Watch Iron Man 2, pay special attention to scene 13

(you can get all the science needed from this scene but the whole movie

is great!). List the topics/inventions in the movie that follow the science

in nuclear chemistry. Make a table of these topics, take a poll of ten

people (not from AP chemistry students) asking people if they believe

these are possible. Research the science behind the show. Report your

findings in the Iron Man 2 discussion board.

Discussion posts (Turnitin.com): 1. Post your survey findings summarizing the results of your research

and a personal statement about this process. Address either the

results of your survey or the research of the science behind Iron Man

2 THAT IS ORIGINAL (not posted yet). Due by Monday, December 1st!

3. On another day, respond to 2 other posts. Ask them to clarify

something in their post or pose another question that requires a

response. Make your discussion thoughtful and meaningful. Due by December 5th.

Nuclear Packet 95 pts.

Chapter 21-BLB

1. Radiation 21.5; 21.9 Totally RAD Activity /15 pts

2. Decay 21.1-21.3 Snowman Activity /15

3. Half-Life 21.4 Probs p. 932 #18,24,28,30 /5

4. Carbon Dating 21.4 Probs p. 932 #34,36,38,40 /5

5. E=mc2 21.6 Probs p. 933 #6,12,14,46,48a /5

6. Fusion/fission 21.7-21.8 Mapping Chernobyl /10

Discussion responses /15

7. AP Problems /5

_____8. Iron Man 2 Discussion responses /15

Monday Tuesday Wednesday Thursday Friday

17 18 19 20 21

Demise of Frosty

the Snowman

Activity

24

Nuclear Packet

Happy

25

Nuclear Packet

Thanks-

26

Nuclear Packet

giving

27

28

1st Discussion

post due

1

2nd Discussion

post due

2 3 4 5

Two responses to

both discussion

posts due

FROSTY THE

SNOWMAN MEETS

HIS DEMISE: AN

ANALOGY TO

CARBON DATING

PURPOSE

To develop the idea that carbon dating is based on gathering evidence in the present and extrapolating it to the past. Students will use a simple graph to extrapolate data to its starting point.

INTRODUCTION

Frosty the Snowman lies melting in the funnels at your lab station. There were no eyewitnesses, but there are several suspects. All the suspects have holes in their alibis. You need to determine the exact time at which Frosty was put into the funnels to melt away, leaving no trace.

PROCEDURE

On a separate sheet of paper, immediately record the volume of Frosty’s melted remains (water) in your graduated cylinder and note the time on the clock. Make a data table and at regular intervals (you decide how long) record the time on the clock and the volume of water in the graduated cylinder. Stop after about 30 minutes, unless Frosty has completely melted earlier.

Analysis: 1. What are the units for the rate at which Frosty melted?

2. Think about making a graph from your data. To determine which axis you will use for volume and which axis for time, recall that slope is rise (y-axis) over run (x-axis). Look at which units you decided to use for the rate of melting. Y-axis________________________________________ X-axis________________________________________

3. What volume will you start with at the origin of your graph? Why did you choose that number?

4. Estimate when you think Frosty met his demise. Explain how you got your estimate.

5. Using your answers to questions 1 through 4, set up your graph and graph your data.

6. Using your graph, find the exact time Frosty start to melt. How close is this time to the time you estimated in question 4?

7. Describe the shape of your graph.

8. What does your graph tell you about the rate at which Frosty melted and the rate of radioactive decay?

9. Write the equation for the beta decay of carbon-14.

10. If you started with a sample of 600 radioactive nuclei, how many would remain undecayed after three half-lives?

11. If 175 undecayed nuclei remained from a sample of 2800 nuclei, how many half-lives have passed? 12.. Is the quantity of a radioactive isotope ever equal to exactly zero? Be careful, this is a common sense question, not just math! 13. How many half-lives would it take for 6.02 x 10

23 nuclei to decay to 6.25% (0.376 x 10

23) of the original number of

nuclei?

14. Strontium-90 has a half-life of 28.8 years. If you start with a 10-gram sample of strontium-90, how much will be left after 115.2 years? Justify your answer. 15. The half-life of iodine-125 is 60 days. The half-life of iodine-131 is 8.05 days. Often radioactive isotopes are used as tracers in diagnostic medical tests. Radioactive iodine is used to help identify diseases of the thyroid gland. Which of these two isotopes do you think would be the best to use in this application? Explain.

16. One of the controversies surrounding the use of nuclear power is the storage of nuclear waste. Explain how the

concept of half-life is an important consideration in this debate.