Unit 4:Applications of Nuclear Chemistry

Including Changes in the Nucleus

Changes in the Nucleus

• Nuclear Reaction- rxn that affects the nucleus of an atom.– Changes the composition of an atom’s nucleus

• 3 kind of radiation:1. Alpha particles 2+ charge2. Beta particles 1- charge3. Gamma rays have no charge

• Radioactivity- the spontaneous emission of radiation from an atom’s nucleus.

Nuclear Stability• If: protons have a positive charge, nucleus

is made of protons and neutrons, like charges repel; how does a nucleus stay together?

• Strong Nuclear Force- an attractive force STRONGER than the electric repulsion force btwn protons. Only exists btwn particles (protons) extremely close together.– The presence of neutrons adds a

net attractive force in the nucleus

Types of Radioactive Decay

α4

2He • Alpha radiation- has 2 protons

and 2 neutrons (same as a helium-4 nucleus).

– Do not have much penetrating power, can be stopped by paper or skin. Does not pose a health problem.

β

• Beta particle- mass=0 but has a charge -1. Essentially an electron.– Can penetrate paper and skin. Does present a

health hazard.

γ

• Gamma rays- extremely high energy ray or light.– High penetrating power. Very dangerous and

hazardous to your health.

Radioactive Decay• Radioactive Decay- when an atom emits any type

of radiation.– Results in a new nucleus. The original nucleus decays

(breaks apart) to form a new, smaller/lighter nucleus.

Nuclear Equation- rxn that affects the nucleus of an atom.

“In any radioactive decay, the sum of the mass #s and the atomic #s are the same before and after the reaction.” (on both sides of the arrow)

Try solving:

Applications of Nuclear Chemistry

Radioisotopes• Radioisotopes- an

isotope of an element which is unstable (radioactive).

Half-Life• All radioactive isotopes decay at different rates.• Half-Life- t½ , is the time required for half the atoms

of a radioactive nuclide to decay.– More stable nuclides decay slowly. Less stable nuclides

have shorter half-lives and decay much more quickly.

Half-life practice problems• Solve:– Nitrogen-13 has a half-life of 10 minutes. IF there are

2.00g of nitrogen-13 at the start, how many grams will exist after 3 half-lives?

– How long will it take 3.8 x 1024 atoms of 10047Ag to

disintegrate to 2.93 x 1023 atoms if the half life of 10047Ag is

24.6 seconds?– Radioactive copper, 64

29Cu, is found in quantities exceeding pollution standards in the sediments of a reservoir in a routine check on Monday. The standard allows up to 14 ppm/cubic meter of sediment. On Monday, 59ppm/cubic meter were measured. The half life of 64

29Cu is 12.7 hours. When will the pollution level return to 14ppm?

Nuclear Bombardment Reactions

• We can make stable nuclei by:– Nuclear Bombardment Rxns- an atom is

bombarded with a stream of particles like alpha particles.

– When the nucleus is hit, the particles and the nucleus combine to form a new, unstable, nucleus.

Atom Smashing!

Fermi National Accelerator Laboratory, Illinoiscyclotron

Stanford Linear Accelerator Center, California.

• Can also bombard with neutrons…– 1934, Enrico Fermi

figured out that we can make radioactive isotopes by smashing nuclei with neutrons.

Biological Effects of Radiation

• Units of Radiation:– SI unit: becquerel (Bq)– more common: the curie (Ci)- only measures

amount of radiation – Most often used: the rem (roentgen equivalent for man) –

measures amount of radiation & the sensitivity of the body• < 150 rem: not fatal but can cause serious damage• 150 – 1000 rem: Damaging and can be fatal• > 1000 rem: FATAL!

Measuring Doses & Detecting Radiation

Dose Amount• Dosimeter: small badge or

pen warn on the person.• Like a mini Geiger counter.• Used to monitor personal

radiation exposure.

• The film is developed after use, the darker the film the more exposure experienced.

Radiation Amount• Geiger Counter: most

common instrument used for detecting radiation.– As radiation passes through

it’s window, it ionizes gas in the cylinder. Ions strike a charged cylinder and wire which created an electric pulse…. Which clicks and is read on the counter.

Beneficial Uses of Radioisotopes

1. Radiotracers: used to follow a specific substance as it moves through a natural system. Ex- your body.

2. Cancer treatment: Fast growing cancer cells are more susceptible to radiation than healthy cells. The hope is, cancer cells will be damaged and die while healthy cells survive treatment.

3. Food Preservation: can prevent spoiling of food.

Harnessing the Nucleus:Fission vs. Fusion

• Besides nuclear decay and bombardment, there are 2 other types of nuclear reactions.1. Nuclear Fission & 2. Nuclear Fusion

Nuclear Fission• Enrico Fermi bombarded uranium-238

with neutron (s) which eventually becomes Neptunium- 239 (a heavier element).

• 1938 Otto Hahn & Fritz Strassman– Tried to replicate Fermi’s experiment but

they also got Barium (a lighter element).– Couldn’t figure out why. Wrote letter to

Meitner.

• Lise Meitner– Thought that the nucleus must become

unstable and BREAK APART to form the lighter atom.

Nuclear fission cont.

• Meitner was RIGHT! but Hahn got the

Nobel prize.• Nuclear Fission- a large nucleus

is split into 2 smaller nuclei of approximately equal mass.

Energy & “Missing” Mass

• There is so much nuclear energy in a very small amount of mass. – 4.5g of U-235 = 1 persons energy use for 1 year.– Compared to 15 tons of coal.

• Where does the energy come from?- the “missing” mass is matter that has been converted into energy via Einstein’s E=MC2.

Chain RXNs and The Atomic Bomb• Because, in a fission rxn, neutrons are released as the U

atom breaks apart, they can go and bombard other U atoms and cause them to break apart.

• Chain Reaction- a continuous series of fission rxns.

The atomic bomb relies on a runaway chain rxn.

http://www.youtube.com/watch?v=qT4mSoZsbzM

http://www.youtube.com/watch?v=RqyBzXYZPoM

Nuclear Reactors

• Nuclear power plants use the fission process to heat water into steam, that drives a generator. Turning nuclear reactions into electricity.

Three Mile Island, Pa

• Lost water, due to operator error, and the rising heat could cause a “meltdown”.

• Water was restored and a disaster was averted.

Chernobyl, Russia

• Used Graphite to absorb neutrons, graphite ignited and burned out of control. Burned for days, destroying the reactor and releasing huge amounts of radiation.

• Winds carried the radiation into Europe… many people developed cancers, malformed children, etc.

Nuclear Waste Disposal

• Radioactive fission products build-up on fuel rods. Eventually the fuel rods have to be replaced.

• Currently, waste stored at site. Best solution burial but no country has an underground site.

• Yucca Mountain- was designed to be the U.S.’s underground storage site.

Nuclear Fusion

• Nuclear Fusion- 2 small nuclei join to form a large nucleus.– Releases a considerable

amount of energy.• Down side- difficult to produce

and hard to control!Type of nuclear rxn that takes place on the sun.

The Hydrogen Bomb!

• http://www.youtube.com/watch?v=NNcQX033V_M

• Releases much more energy than an atomic bomb.

• Triggered by a small atomic blast.• Only tested, never used in a conflict.

Fusion Research

• Gram for Gram, fusion rxns releases more energy than fission rxns.

• Controlled fusions are difficult and require temps of 40 million K or more. (difficult!- no material can withstand that kind of temps.)

Cold Fusion??

• 1989- Pons & Fleishman @ the University of Utah.

• Claimed to achieve cold fusion by the electrolysis of heavy water (D2O).

• Didn’t work out as claimed.