Nuclear ChemistryUnit 10

RadioactivityThe spontaneous emission of

radiation by an unstable atomic nucleus.

DiscoveryHenri Becquerel-1896Worked with phosphorescent uranium

(thought to be x-rays)Marie and Pierre Curie were the one’s

to actually name the process as radioactivity

Nuclear Notation

Radioactive DecayAlpha Decay (α)Alpha particles are helium nuclei

consisting of 2 protons and 2 neutrons

Does not penetrate deeply into matter.

Loss of 2p and 2n results in the daughter atom being two elements before the parent atom.

Example:

Radioactive DecayBeta Decay (β)Beta particles are high energy

electrons with a -1 charge. Represented by e.

Pass through matter easier than alpha.The electron is produced when a

neutron turns into a proton and electron. Daughter atom has atomic number 1 greater than parent atom.

Example:

Radioactive DecayGamma Decay (γ)Gamma ray is a high energy form

of electromagnetic radiation without a mass or charge.

Need thick blocks of lead or concrete to stop.

Normally does not occur alone but accompanies other forms of decay.

PracticeDecay of U-238 to Pb-206: a,b,b,a,a,a,a,a,b,b,a,b,b,a

Detecting RadioactivityDetects ionizing radiation

Radioisotope DatingHalf-life – the time it takes for half of a given amount of a radioactive isotope to undergo decay.

Carbon-14 dating1 in a million carbon atoms Decays to nitrogen-14 after deathHalf life is 5,730 yearsOther isotopes used for datingPotassium-40 (half life = 1.25 billion years)Uranium-238 (4.5 billion years)Rubidium-87 (48 billion years)

Einstein and EnergyFirst scientist to realize the amount of potential energy available in matter.

E=mc2

E=Energy m = massc= speed of light (671,000,000 mph)

Nuclear FissionThe splitting of an atomic nucleus into two or more smaller fragments, accompanied by a large release of energy.

Uranium nuclei are split by bombarding with a neutron.

Nuclear FissionSubcritical mass – If there is not enough fissionable material present to sustain a chain reaction

(super)critical mass – If there is enough fissionable material to sustain a chain reaction. (exponential and dangerous if not controlled)

Nuclear Reactor

Elements UsedUranium-235 is the main radioactive element used in a fission reactor.

Plutonium-239 can also be usedBreeder reactionFission Bombs

Nuclear FusionProcess of combining two or more nuclei to form a larger nucleus.

Process that produces energy in stars.

Most typical fusion reaction is when hydrogen atoms fuse to make helium.

Fusion processDeuterium (D) – A hydrogen atom with a mass number of 2.Tritium (T) – A hydrogen atom with a mass of 3.

Radioisotopes and HealthTracers – used in the body to find abnormalities.Act like normal isotopesRadiation can be detected

Iron-59Used to show circulatory system

EnvironmentSulfur-35 used to trace pesticides from field

to streams

Sources of RadiationBackground radiation- caused by radioactive elements in rocks, fabrics, food, etc.

Health ProblemsRadiation can knock electrons

creating ions.Damages cell processesDividing cells pass down

damaged DNAWaste can take thousands of

years to decay

Measuring RadiationGray – equal to the

transfer of 1 joule of energy in the form of radiation to 1 kg of living cells.

Sievert (Sv)- equal to 1 gray multiplied by a factor that take tissue absorption into account.

Radon and the HomeRadon-222 can cause lung cancer.changes into isotopes of polonium and

lead.Po and Pb isotopes attach to dust

particles and enter lungs.Emit alpha particles which damage

cells.Radon is dense and normally

accumulates in basementsExhaust fan and sealing large cracks