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Ch. 25- Nuclear Chemistry (originally ch. 18 from

old textbook)

Diablo Canyon Nuclear Power PlantSan Luis Obispo, CA(192 miles south of

Cupertino)

25.1 Nuclear Radiation

25.2 Nuclear Transformations

25.3 Fission and Fusion of Atomic Nuclei

25.4 Radiation in Your Life

Marvel Comics’ “The Incredible Hulk” was

created in 1962 by Stan Lee and artist Jack Kirby.

The Hulk’s powers began when nuclear scientist Dr. Bruce

Banner was accidentally bombarded with gamma

rays from a "gamma bomb" he had invented.

To properly view this presentation on the web, use the navigation arrows below andleft-click on each page to view any animations.

Chemical reaction vs. Nuclear reaction

Chemical reactions:• Atoms attain stable

isotopes by losing or sharing electrons

• Reactions affected by changes in temperature, pressure, or the presence of catalysts

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Nuclear reactions:* The nuclei of unstable isotopes gain stability by undergoing changes*The changes are accompanied by emission of large amounts of energy

Nuclear chemistry: the chemistry of radioactive substances; study of the atomic nucleus, including fission and fusion and their products

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Atomic Review

• Atomic number = – Every atom of an element has the same

atomic number because the # p defines the element.

sum of p+ & n• Mass number (or atomic mass) =

The # n may vary without changing the element.

# of p+

XMass #

Atomic # Symbol

• Atomic notation:

Ex: magnesium atom with 13 n =2512

Mg

4

Practice

Fill in the blanks:

52He 2 3

NameSymbol

# p # n

Hydrogen-1

Helium-5

Carbon-13

11H 1 0

136

C 6 7

11H

136

C

52He

5

Four Forces in the Nucleus

Repulsive:1. Electrostatic: between p+

(like charges repel)

Strong > electrostatic > weak > gravity

++

Attractive:

2. “Strong force”: between p+

3. “Weak force”: between p+ and n

4. Gravity: between all particles

25.1 Nuclear Radiation

Marie Curie was a Polish scientist whose research led to many discoveries about radiation and radioactive elements. In 1934 she died from leukemia caused by her long-term exposure to radiation. You will learn about the various types of radiation and their effects.

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Natural Radioactivity * Discovered in 1895 by Antoine Henri Becquerel, who

observed that a uranium salt produced an image on photographic film—thought the film had to be exposed to sunlight, but the plates fogged in a drawer.

* The term radioactivity was coined in 1898 by Marie Curie, a Polish physicist, who was doing research with her husband Pierre. (They did much of the initial work on radioactivity, and eventually died of radiation-related illnesses.)

Radioactivity: spontaneous emission of particles and/or energy from the nucleus of an atom

Radioactive decay: process in which a radioactive atom disintegrates into a different element

Radioactivity

How does an unstable nucleus release energy?•Marie Curie (1867-1934) and Pierre

Curie (1859-1906) were able to show that rays emitted by uranium atoms caused fogging in photographic plates.

–Marie Curie named the process by which materials give off such rays radioactivity.

–The penetrating rays and particles emitted by a radioactive source are called radiation.

Radioactivity

Nuclear reactions differ from chemical reactions in a number of important ways.•In chemical reactions, atoms tend to attain

stable electron configurations by losing or sharing electrons.

•In nuclear reactions, the nuclei of unstable isotopes, called radioisotopes, gain stability by undergoing changes.

•An unstable nucleus releases energy by emitting radiation during the process of radioactive decay.

25.1

Types of RadiationThe three main types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation.

25.1

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Types of Radioactive Decay

Type Consists of Stopped by

Interesting Fact

alpha

He nucleus:2 p & 2 n

Paper or skin

If ingested, is harmful to lungs

beta

High energy e- Clothing, glasses, or thin sheet of Al

Causes damage to sensitive tissues like eyes

gamma

Photon (particle of light)* Has essentially no mass (m < 5.81 x 10-72 g…it’s complicated!)

A few feet of dirt or concrete, or 6” of Pb

Causes severe damage to body tissues

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Alpha decay

Example:

U236

92+ He

4

2Pu

240

94

13

Alpha decay

Example:

U236

92+ He

4

2Pu

240

94

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Beta decay• Ex:

Ba137

56+ e

0

-1Cs

137

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p 1

1+ e

0

-1n

1

0

(One of Cs’s neutrons converts to a proton and electron.)

Beta decay animation: http://ie.lbl.gov/education/glossary/AnimatedDecays/Beta-Decay.html

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Gamma ray emission• Ex: Pu* (energized) → Pu (stable)

Types of RadiationGamma Radiation

A high-energy photon emitted by a radioisotope is called a gamma ray. The high-energy photons are electromagnetic radiation.

25.1

Radium

Types of Radiation25.1

25.1 Section Quiz.

1. Certain elements are radioactive because their atoms have a) more neutrons than electrons.b) an unstable nucleus.c) a large nucleus.d) more neutrons than protons.

25.1 Section Quiz.

2. An unstable nucleus releases energy bya) emitting radiation.b) thermal vibrations.c) a chemical reaction.d) giving off heat.

25.1 Section Quiz.

3. Which property does NOT describe an alpha particle? a) 2+ chargeb) a relatively large massc) a negative charged) low penetrating power

25.1 Section Quiz.

4. When a radioactive nucleus releases a high-speed electron, the process can be described as a) oxidation.b) alpha emission.c) beta emission.d) gamma radiation.

25.2 Nuclear Transformations

Radon-222 is a radioactive isotope that is present naturally in the soil in some areas. It has a constant rate of decay. You will learn about decay rates of radioactive substances.

Nuclear Stability and Decay

What determines the type of decay a radioisotope undergoes?

– The nuclear force is an attractive force that acts between all nuclear particles that are extremely close together, such as protons and neutrons in a nucleus

– At these short distances, the nuclear force dominates over electromagnetic repulsions and hold the nucleus together.

– More than 1,500 different nuclei are known. Of those, only 264 are stable and do not decay or change with time. These nuclei are in a region called the band of stability.

Nuclear Stability and Decay

• The neutron-to-proton ratio determines the type of decay that occurs.

• A positron is a particle with the mass of an electron but a positive charge. During positron emission, a proton changes to a neutron.

• Positron emission is a byproduct of a type of radioactive decay known as beta plus decay. In the process of beta plus decay, an unstable balance of neutrons and protons in the nucleus of an atom triggers the conversion of an excess proton into a neutron.

25.2

Wisegeek.com

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Unstable Atoms• If # of neutrons is

too high or too low, the nucleus becomes unstable and emits energy.

* Stable, naturally occurring isotopes

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*Transmutation• Conversion of one element into another that is the result of

radioactive decay.Artificial transmutation:• First accomplished by Rutherford in 1919, even though

alchemists tried for hundreds of years.• Transmutation of lead into gold was achieved by Glenn

Seaborg, who succeeded in transmuting a small quantity of lead in 1980. He also first isolated plutonium for the atomic bomb and discovered/”created” many elements. (NY Times, Feb 1999)

• There is an earlier report (1972) in which Soviet physicists at a nuclear research facility in Siberia accidentally discovered a reaction for turning lead into gold when they found the lead shielding of an experimental reactor had changed to gold.

• Accomplished with particle accelerators

Transmutation Reactions

What are two ways that transmutation can occur?

The conversion of an atom of one element to an atom of another element is called transmutation.

– Transmutation can occur by radioactive decay. Transmutation can also occur when particles bombard the nucleus of an atom.

Transmutation Reactions

The first artificial transmutation reaction involved bombarding nitrogen gas with alpha particles.

Transmutation Reactions

The elements in the periodic table with atomic numbers above 92, the atomic number of uranium, are called the transuranium elements.

– All transuranium elements undergo transmutation.

– None of the transuranium elements occur in nature, and all of them are radioactive.

Transuranium elements are synthesized in nuclear reactors and nuclear accelerators.

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*Disintegration Series • “Heavy” atoms (greater than Bismuth, #83) naturally

decay to smaller atoms along a consistent path, or series, of decays.

Radioactive U-238 → Th-234 + Th-234 → Pa-234 + Pa-234→ U-234 + U-234→ Th-230 + Th-230 → Ra-226 + Ra-226 → Rn-222 + Rn-222 → Po-218 + Po-218 → Pb-214 + Pb-214 → Bi-214 + Bi-214 → Po-214 + Po-214 → Pb-210 + Pb-210 → Bi-210 + Bi-210→ Po-210 + Po-210 → Stable Pb-206 +

Mass

Nu

mb

er

Atomic Number & Symbol

Source: http://www.frontiernet.net/~jlkeefer/uranium.html

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*Radiocarbon (C-14) dating

Basic assumptions:• CO2 in the atmosphere contains about 0.00000000010%

C-14; this level is held constant through the decay of N-14 to form C-14 which happens in the upper atmosphere.

• Plants consume CO2 during photosynthesis and animals eat the plants, so they contain the same C-14:C-12 ratio as long as they are alive.

• When an organism dies, the amount of C-12 does not change, but the C-14 content diminishes as it decays. The half-life of C-14 is 5668 years.

• By comparing the C-14:C-12 ratio in an artifact to the same ratio in living plants, the age of the artifact can be estimated.

• Discovered at University of Chicago in 1949 by Dr. W.F. Libby and his colleagues.

• The accuracy of the method has been validated by comparison testing of artifacts with independently known ages, such as those of ancient Egypt and old redwood trees.

Limitations:• C-14 dating has a limit of about 70,000 years. Beyond that,

the % of C-14 remaining is too small to accurately calculate the age.

• However, other radiometric dating methods exist, including:Rb-87 : Strontium 87 (half-life of 48.8 billion years)Th-232 : Pb-208 (half-life of 14.0 billion years)U-238 : Pb-206 (half-life of 4.5 billion years)K-40 : Ar-40 (half-life of 1.3 billion years)

• The formation of our solar system (and thus the Earth) has been estimated at 4.5 - 5.0 billion years.

• It is also estimated that our universe is between 15-20 billion years old.

Sources: http://www.geology.sdsu.edu/visualgeology/geology101/lab6time.htmhttp://www.dc.peachnet.edu/~pgore/geology/geo102/radio.htmhttp://superstringtheory.com/cosmo/cosmo1.html

Half-Life

After each half-life, half of the existing radioactive atoms have decayed into atoms of a new element.

A half-life (t1/2) is the time required for one-half of the nuclei of a

radioisotope sample to decay to products.

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Half Life

Ex:

• Phosphorus-32 radioactively decays to form Sulfur-32

• Half life 32P = 14 days

Half-Life

The ratio of Carbon-14 to stable carbon in the remains of an

organism changes in a predictable way that enables the archaeologist

to obtain an estimate of its age.

25.2 Section Quiz.

1. During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is a) a positron.b) an alpha particle.c) a neutron.d) a proton.

25.2 Section Quiz.

2. When potassium-40 (atomic number 19) decays into calcium-40 (atomic number 20), the process can be described as a) positron emission.b) alpha emission.c) beta emission.d) electron capture.

25.2 Section Quiz.

3. If there were 128 grams of radioactive material initially, what mass remains after four half-lives? a) 4 gramsb) 32 gramsc) 16 gramsd) 8 grams

25.2 Section Quiz.

4. When transmutation occurs, the ________ always changes. a) number of electronsb) mass numberc) atomic numberd) number of neutrons

25.2 Section Quiz

5. Transmutation occurs by radioactive decay and also bya) extreme heating.b) chemical reaction.c) high intensity electrical discharge.d) particle bombardment of the nucleus.

25.3 Fission and Fusion of Atomic Nuclei

The sun is not actually burning. If the energy given off by the sun were the product of a combustion reaction, the sun would have burned out approximately 2000 years after it was formed, long before today. You will learn how energy is produced in the sun.

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Nuclear Fission

• Fission: process in which the nucleus of a large, radioactive atom splits into 2 or more smaller nuclei– Caused by a collision with an energetic neutron.

• *A neutron is absorbed by a U-235 nucleus. The nucleus is now less stable than before. It then splits into 2 parts and energy is released. Several neutrons are also produced; they may go on to strike the nuclei of other atoms causing further fissions in a process called supercriticality.Fission animation: http://www.howstuffworks.com/nuclear-bomb3.htm

Ba +13956 Kr +94

36 3 n + energy10 U235

92n + 10

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• *The process of neutron capture and nucleus splitting happens very quickly (takes about 1 x 10-12 seconds).

• An incredible amount of energy is released:– As heat and gamma radiation– Because the product atoms and neutrons

weigh less than the original U-235 atom; the “missing mass“ has been converted to energy by E=mc2

Nuclear Fission

What happens in a nuclear chain reaction?When the nuclei of certain isotopes are bombarded with

neutrons, they undergo fission, the splitting of a nucleus into smaller fragments.

In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more neutrons which react with still more fissionable atoms.

25.3

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Mass-Energy Relationship• Einstein's theory of relativity states that energy

and mass are related by the speed of light (c) squared.

E = mc2

• Can be used to calculate the energy liberated when the “missing mass” (between reactants & products) is known.

• * The energy that can be released from 2 kg of highly enriched U-235 (as used in a nuclear bomb) is roughly equal to the combustion of a million gallons of gasoline. 2 kg of U-235 is smaller than a baseball; a million gallons of gasoline would fill approximately 220 tanker trucks.

Nuclear Fission

A Nuclear Power Plant

Neutron moderation is a process that slows down neutrons so the reactor

fuel (uranium-235 or plutonium-239) captures

them to continue the chain reaction.

Neutron absorption is a process that decreases

the number of slow-moving neutrons. Control rods, made of a material

such a cadmium, are used to absorb neutrons.

Check out: http://science.howstuffworks.com/nuclear-power1.htm• Nuclear power plants utilize the energy released in a controlled

fission reaction in the core to heat water in one pipe.• The heat then vaporizes water in another pipe.• The steam drives a turbine and generates electricity.

*Harnessing Fission: A nuclear power plant

• The steam is in a closed circuit that is never exposed any radiation.

•The speed of the fission chain reaction is regulated using carbon control rods which can absorb extra neutrons.

Nuclear Waste

Why are spent fuel rods from a nuclear reaction stored in water?

– Water cools the spent rods, and also acts as a radiation shield to reduce the radiation levels.

25.3

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*Nuclear Power• The United States currently imports over

58% of its oil supply. There is a need to develop alternative energy sources, such as nuclear, wind, geothermal, solar, …

• By 2020 it is expected to be 67%.

• At present about 20% of the electrical energy used in the U.S. is generated from power plants using uranium. In France the percentage is 75% .

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*Nuclear Reactor OperationHazards1. Radioactive waste from normal operations.2. Reactor coolant has tritium 1H3 which is radioactive

with a half-life of 12.3 years.3. Used fuel cells are radioactive and have half-lifes in the

millions of years.4. Miscellaneous equipment can be contaminated with

radioactive material.

Accidents: loss of coolant, coolant flow, or pressure, control rod drive mechanism failure

• Fuel cell meltdown then liquid uranium pools into a supercritical mass then explosion then radioactive waste is ejected around the planet

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The Atomic Bomb• Uses an unregulated fission reaction in a

very fast chain reaction that releases a tremendous amount of energy.

*Critical mass: the minimum amount of radioactive, fissionable material needed to create a sustainable fission chain reaction

* Site of fission reaches temperatures believed to be about 10,000,000°C.

• Produces shock waves and , , , x-rays, and UV radiation.

*A Fission Chain Reaction

*US Army aerial photograph from 80 km away, taken about 1 hour after detonation over Nagasaki, Japan, August 9, 1945.

*The classic “mushroom cloud” is a result of dust and debris lifted into the air as a result of the

detonation.

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Nuclear FusionFusion: process in which 2 nuclei of small elements are

united to form one heavier nucleus• * Requires temperatures on the order of tens of

millions of degrees for initiation.• * The mass difference between the small atoms and

the heavier product atom is liberated in the form of energy.

• Responsible for the tremendous energy output of stars (like our sun) and the devastating power of the hydrogen bomb.

H + 31

H

21

He +42

n10

+ energy

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*Stars & the Hydrogen Bomb• The first thermonuclear bomb was exploded in 1952 in

the Marshall islands by the United States; the second was exploded by Russia (then the USSR) in 1953.

• “H bombs” utilize a fission bomb to ignite a fusion reaction.

Nuclear FusionFusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei and two positrons.

•Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split.•The use of controlled fusion as an energy source on Earth is appealing.•The potential fuels are inexpensive and readily available.•The problems with fusion lie in achieving the high temperatures necessary to start the reaction and in containing the reaction once it has started.

25.3 Section Quiz.

1. One of the control mechanisms for a sustainable nuclear chain reactor involves slowing down the released neutrons so they may be captured by other nuclei. This is done using a) moderators.b) shielding.c) absorbers.d) control rods.

25.3 Section Quiz.

2. Spent fuel rods are stored in a) lead-lined containers.b) deep pools of water.c) thick concrete bunkers.d) cadmium or graphite containers.

25.3 Section Quiz.

3. Choose the correct words for the spaces. In solar fusion, _______ nuclei fuse to form _______ nuclei. a) helium, hydrogenb) hydrogen-1, hydrogen-2c) hydrogen, heliumd) hydrogen-1, hydrogen-3

25.4 Radiation in Your Life

In a smoke detector, radiation from the Americum nuclei ionizes the nitrogen and oxygen in smoke-free air, allowing a current to flow. When smoke particles get in the way, a drop in current is detected by an electronic circuit, causing it to sound an alarm. You will learn about some of the other practical uses of radiation.

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*Measurement of Radioactivity

Ionizing radiation:• When radiation from radioactive sources

strikes an atom or a molecule, one or more electrons are knocked off and an ion is created.

• Measured with a Geiger counter, a film badge or a scintillation counter.

Units:• Curie: measures radioactivity emitted by a

radionuclide.• Roentgen or rad: measures exposure to

gamma rays or X-rays• Rem: accounts for degree of biological effect

caused by the type of radiation exposure.

Detecting Radiation

What are three devices used to detect radiation?• Ionizing radiation is radiation with enough energy

to knock electrons off some atoms of the bombarded substance to produce ions.

– Devices such as Geiger counters, scintillation counters, and film badges are commonly used to detect radiation.

Radiation can produce ions, which can then be

detected, or it can expose a photographic plate and

produce images.

Detecting Radiation

A Geiger counter uses a gas-filled metal tube to detect radiation.

25.4

A scintillation counter uses a phosphor-coated surface to detect

radiation.

A film badge consists of several layers of

photographic film covered with black lightproof paper, all encased in a plastic or

metal holder.

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*Biological Effects of RadiationAcute:• High level radiation (gamma ray & x–ray) can cause death.• Damage is centered in nuclei of cells; cells undergoing rapid cell

division are most susceptible.• Gamma rays from a Co-60 source are often used to treat cancer

(since cancer cells multiply rapidly).

Long term:• Can weaken organism and lead to onset of malignant tumors, even

after fairly long time delays.• Largest source: X–rays• Sr-90 isotopes are present in fallout from atmospheric testing of

nuclear weapons.• Contaminated foods can increase incidence of leukemia and bone

cancers.

Using RadiationHow are radioisotopes used in medicine?

•Neutron activation analysis is a procedure used to detect trace amounts of elements in samples.

• Neutron activation analysis is used by museums to detect art forgeries, and by crime laboratories to analyze gunpowder residues.

• Radioisotopes can be used to diagnose medical problems and, in some cases, to treat diseases.

25.4

Using RadiationThis scanned image of a thyroid gland shows where radioactive iodine-131 has been absorbed

25.4

25.4 Section Quiz.

1. Ionizing radiation can remove _______ from atoms.a) protonsb) neutronsc) positronsd) electrons.

25.4 Section Quiz.

2. Which of the following is NOT a device used to detect radiation?a) geiger counterb) scintillation counterc) film badged) radioisotope

25.4 Section Quiz.

3. Choose the correct words for the space. When a tumor is treated by radiation, more cancer cells than normal cells are killed because cancer cells ____________ than normal cells.

a) are more susceptible to damage because they grow faster

b) absorb more radiation because they are larger

c) grow slower

d) are smaller

25.4 Section Quiz.

4. How do scientists detect thyroid problems?a) with teletherapyb) by neutron activation analysisc) using an iodine-131 tracerd) using a radioisotope sealed in a gold tube

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Practice problems

1. Using the examples above, write the reaction of bismuth-214 emitting an alpha particle

2. Write the reaction of silicon-27 emitting a beta particle

HeTlBi 42

21081

21483

ePSi 01

2715

2714

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for Sample Problem 25.1

Time amount

0 hours 1.0 mg

2.6 hours 0.5 mg

5.2 hours 0.25 mg

7.8 hours 0.125 mg

10.4 hours 0.0625 mg (6.25x10-5 g)

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Study Guide:• 25.1

Becquerel, Curieradioactivity, radioisotopesalpha, beta, gamma particles/decay

• 25.2neutron-to-proton ratio determines the type of decay that occurshalf-lifetransmutation, transuranium elements

• 25.3fission, nuclear reactorfusion, sun/hydrogen bomb

• 25.4 health uses/detection• Presentation information!; homework problems;

lab

Research Presentations—what do you want to know?

• What is chemotherapy? What is radiation therapy?

• What other types of things involve fission and fusion?

• What type of radiation is good? Bad? (such as food irradiation, MRI’s, dyes,…)

• How is solar radiation nuclear?• Is solar power an answer to our limited supply

of coal? Why or why not?

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