Chapter 21: Nuclear ChemistryChapter 21: Nuclear Chemistry

• This unit looks at the nature of radiation,

• Types of radiation and decay products,

• Radiation Units and exposure precautions

• Nuclear fission and fusion reactions

• Applications of Nuclear Chemistry

What does a Geiger Counter measure?

• Radiation that can cause atoms to lose or gain electrons and become ionsions.

• This type of radiation is called ionizing radiation.

• There are two causes of background radiation:

• Outer Space- Cosmic rays• Natural decay from isotopes in the earth’s

crust/core

Historical Perspectives• 1895: Wilhelm Roentgen discovers X-rays and their 1895: Wilhelm Roentgen discovers X-rays and their

effects.effects.• 1896: Henri Becquerel discovers radioactive 1896: Henri Becquerel discovers radioactive

Uranium.Uranium.• 1898: Pierre and Marie Curie discover two new 1898: Pierre and Marie Curie discover two new

elements, polonium and radium.elements, polonium and radium.• 1905: Albert Einstein theory of relativity and mass 1905: Albert Einstein theory of relativity and mass

defect.defect.• 1908: Hans Geiger creates an instrument to measure 1908: Hans Geiger creates an instrument to measure

ionizing radiation.ionizing radiation.• 1934: Enrico Fermi proposes ‘transuranes” elements 1934: Enrico Fermi proposes ‘transuranes” elements

beyond uranium.beyond uranium.• 1939: Lise Meitner , Otto Hahn and Fritz Stassman 1939: Lise Meitner , Otto Hahn and Fritz Stassman

explain nuclear fission. explain nuclear fission.

Nuclear Composition• Nucleons are any particles found in the nucleus, Nucleons are any particles found in the nucleus,

commonly they are protons and neutrons.commonly they are protons and neutrons.

• We would expect, the total mass of the electrons, We would expect, the total mass of the electrons, protons, and neutrons would be the mass of the protons, and neutrons would be the mass of the atom, it is not, but rather it is a smaller value.atom, it is not, but rather it is a smaller value.

• Mass defectMass defect is the difference between the mass is the difference between the mass of an atom and the sum of the masses of its of an atom and the sum of the masses of its protons, neutrons and electrons.protons, neutrons and electrons.

• Einstein explained this loss of mass as the result Einstein explained this loss of mass as the result of the nucleus formation. Energy is given off of the nucleus formation. Energy is given off from the conversion of matter to energy (E=mcfrom the conversion of matter to energy (E=mc22 ). ).

• This loss of mass from it’s conversion to energy This loss of mass from it’s conversion to energy provides nuclear stability.provides nuclear stability.

Nuclear Binding EnergyNuclear Binding Energy• The energy released when a nucleus is formed The energy released when a nucleus is formed

from nucleons is called the from nucleons is called the nuclear binding nuclear binding energyenergy..

• This can be thought of the amount of energy to This can be thought of the amount of energy to break a nucleus apart.break a nucleus apart.

• The higher the nuclear binding energy of a The higher the nuclear binding energy of a nuclide. the greater the nuclide stability.nuclide. the greater the nuclide stability.

• The The binding energy per nucleonbinding energy per nucleon is the binding is the binding energy of the nucleus divided by the number of energy of the nucleus divided by the number of nucleons(mass number) it contains.nucleons(mass number) it contains.

• Elements with intermediate atomic masses (iron Elements with intermediate atomic masses (iron through lead) have the greatest binding energies through lead) have the greatest binding energies (stability).(stability).

Nuclear StabilityNuclear Stability• The neutron/proton ratio can be used to The neutron/proton ratio can be used to

predict nuclear stability.predict nuclear stability.• For elements with low atomic numbers (1-30) For elements with low atomic numbers (1-30)

the nucleus is stable when there is a 1:1 ratio.the nucleus is stable when there is a 1:1 ratio.• For elements with a high atomic number (up For elements with a high atomic number (up

to element 83), the nucleus is stable when the to element 83), the nucleus is stable when the ratio is 1.5:1.ratio is 1.5:1.

• Elements having an atomic number greater Elements having an atomic number greater than 83 are unstable or radioactive.than 83 are unstable or radioactive.

• Stable nuclei tend to have even numbers of Stable nuclei tend to have even numbers of nucleons in their nucleus. nucleons in their nucleus.

Nuclear Shell ModelNuclear Shell Model• Stable nuclei tend to have even numbers of Stable nuclei tend to have even numbers of

nucleons in their nucleus. (protons, neutrons or nucleons in their nucleus. (protons, neutrons or total nucleons) total nucleons)

• The most stable atoms have 2, 8, 20, 28, 50, 82 The most stable atoms have 2, 8, 20, 28, 50, 82 or 126 protons, neutrons, or total nucleons.or 126 protons, neutrons, or total nucleons.

• The nuclear shell theory states that nucleons The nuclear shell theory states that nucleons exists in different energy levels, or shells, in the exists in different energy levels, or shells, in the nucleus. Completed nuclear energy levels are nucleus. Completed nuclear energy levels are those with 2, 8, 20, 28, 50, 82 and 126.nucleons.those with 2, 8, 20, 28, 50, 82 and 126.nucleons.

• These numbers are sometimes called the These numbers are sometimes called the ““magic numbers”magic numbers” for nuclear stability. for nuclear stability.

Nuclear Reactions and terms:Nuclear Reactions and terms:4 types of Nuclear Reactions:4 types of Nuclear Reactions:

1.1. Radioactive decayRadioactive decay refers to the emission of refers to the emission of an alpha particle, a beta particle, or gamma an alpha particle, a beta particle, or gamma ray and the formation of a slightly lighter and ray and the formation of a slightly lighter and more stable nucleus.more stable nucleus.

2.2. Nuclear disintegration Nuclear disintegration is when an unstable is when an unstable nuclei from nuclear bombardment emits a nuclei from nuclear bombardment emits a proton or neutron and becomes more stable.proton or neutron and becomes more stable.

3.3. FissionFission refers to the process in which a very refers to the process in which a very heavy nucleus splits to form two or more heavy nucleus splits to form two or more medium-mass nuclei.medium-mass nuclei.

4.4. FusionFusion refers to the process in which refers to the process in which lightweight nuclei combine to form heavier lightweight nuclei combine to form heavier more stable nuclei. more stable nuclei.

Nuclear Terms:Nuclear Terms:• Transmutation Transmutation is the changeis the change in the identity of a in the identity of a

nucleus as a result of a change in the number of nucleus as a result of a change in the number of protons.protons.

• Radioactive decay Radioactive decay is spontaneous is spontaneous disintegration of a nucleus into slightly lighter and disintegration of a nucleus into slightly lighter and more stable nucleus, accompanied by the emission more stable nucleus, accompanied by the emission of particles, electromagnetic radiation or both.of particles, electromagnetic radiation or both.

• RadiationRadiation- the process of emitting or releasing - the process of emitting or releasing waves of energy, such as light, x-rays, or other types waves of energy, such as light, x-rays, or other types of electromagnetic waves.of electromagnetic waves.

• RadioactivityRadioactivity is the property of some elements to is the property of some elements to spontaneously emit alpha or beta particles with spontaneously emit alpha or beta particles with gamma rays by the disintegration of the nuclei.gamma rays by the disintegration of the nuclei.

Properties of Radioactive Properties of Radioactive Nuclides:Nuclides:

• They expose light sensitive emulsions. They expose light sensitive emulsions. (Roentgen, 1895)(Roentgen, 1895)

• They fluoresce or glow with certain compounds. They fluoresce or glow with certain compounds. (Curie, 1898)(Curie, 1898)

• They produce “charged” or ionized gas particles. They produce “charged” or ionized gas particles. (Geiger, 1908)(Geiger, 1908)

• Exposure to radio-nuclides can cause harmful Exposure to radio-nuclides can cause harmful physiological effects leading to death.physiological effects leading to death.

• They undergo radioactive decay and have a half-They undergo radioactive decay and have a half-life.life.

Half-Life of a Radioisotope

Half-lifeHalf-life is the time it required for half the atoms of is the time it required for half the atoms of a radioactive nuclide to decay. It can be measured a radioactive nuclide to decay. It can be measured in seconds, minutes, days, or years.in seconds, minutes, days, or years.

IsotopeIsotope Half lifeHalf lifeC-15C-15 2.4 sec2.4 secRa-224Ra-224 3.6 days3.6 daysRa-223Ra-223 12 days12 daysI-125I-125 60 days60 daysC-14C-14 5700 years5700 yearsU-235U-235 710 000 000 years710 000 000 years

Decay SeriesDecay Series

• A A decay seriesdecay series is a series of radioactive is a series of radioactive nuclides produced by successive radioactive nuclides produced by successive radioactive decay until a stable nuclide is reached.decay until a stable nuclide is reached.

• The heaviest nuclide in a decay series is The heaviest nuclide in a decay series is called the called the parent nuclide.parent nuclide.

• The particles in a decay series that are The particles in a decay series that are produced from parent nuclides are called produced from parent nuclides are called daughter nuclides.daughter nuclides.

• U-238 the parent nuclide decays to Pb-206, U-238 the parent nuclide decays to Pb-206, which is stable and non-radioactive.which is stable and non-radioactive.

Types of Radioactive DecayTypes of Radioactive Decay

• Alpha EmissionAlpha Emission

• Beta EmissionBeta Emission

• Positron EmissionPositron Emission

• Electron CaptureElectron Capture

• Gamma EmissionGamma Emission

Alpha EmissionAlpha Emission• consists of a Helium nucleus with no consists of a Helium nucleus with no

electrons.electrons.

• has 2 protons and 2 neutrons.has 2 protons and 2 neutrons.

• has a +2 chargehas a +2 charge

• has an atomic mass of 4has an atomic mass of 4

• has a speed that is 1/10 the speed of light.has a speed that is 1/10 the speed of light.

• can be stopped by a piece of paper, cloth, or can be stopped by a piece of paper, cloth, or skin.skin.

• The symbol is the Greek letter alphaThe symbol is the Greek letter alpha

particle or particle or 4 4

2 2 HeHe

Beta EmissionBeta Emission• is a stream of negatively charged electrons.is a stream of negatively charged electrons.

• has a very light mass of an electronhas a very light mass of an electron

• has a -1 chargehas a -1 charge

• can be stopped by a piece of aluminumcan be stopped by a piece of aluminum

• has a speed that is 90% of the speed of has a speed that is 90% of the speed of light.light.

• can ionize air and other particles.can ionize air and other particles.

• The symbol is the Greek letter, betaThe symbol is the Greek letter, beta

• particle or 0particle or 0

-1 -1 ee

Positron EmissionPositron Emission• is a stream of positively charged electrons.is a stream of positively charged electrons.

• has a very light mass of an electronhas a very light mass of an electron

• has a +1 chargehas a +1 charge

• can be stopped by a piece of aluminumcan be stopped by a piece of aluminum

• has a speed that is 90% of the speed of has a speed that is 90% of the speed of light.light.

• can ionize air and other particles.can ionize air and other particles.

• The symbol is the Greek letter, betaThe symbol is the Greek letter, beta

• particle or 0particle or 0

+1 +1 ee

Electron CaptureElectron Capture

• is a capture of an inner orbital electron by is a capture of an inner orbital electron by the nucleus.the nucleus.

• has a very light mass of an electron.has a very light mass of an electron.• has a -1 charge.has a -1 charge.• results in a combination of an electron and results in a combination of an electron and

a proton to form a neutron.a proton to form a neutron.

• The symbol on the reaction side of a The symbol on the reaction side of a nuclear reaction is nuclear reaction is 0 0

-1 -1 ee

Gamma EmissionGamma Emission• is form of energy or electromagnetic radiation.is form of energy or electromagnetic radiation.

• has an extremely short wavelength.has an extremely short wavelength.

• has no mass since it is energy.has no mass since it is energy.

• travel at the speed of light.travel at the speed of light.

• can cause air and most materials to become can cause air and most materials to become ionized or charged.ionized or charged.

• can only be stopped by using 2 to 4 inches of can only be stopped by using 2 to 4 inches of lead or many feet of concrete.lead or many feet of concrete.

• do not change the identity of the radio-nuclide.do not change the identity of the radio-nuclide.

• The symbol is the Greek letter, gammaThe symbol is the Greek letter, gamma

Units of Radioactivity:Units of Radioactivity:• Roentgen:Roentgen: the amount of gamma or x-rays the amount of gamma or x-rays

required to produce one unit of electrical required to produce one unit of electrical charge per cubic centimeter from charge per cubic centimeter from ionization of air. (1 roentgen = 86 ergs per ionization of air. (1 roentgen = 86 ergs per gram)gram)

• REP:REP: (roentgen equivalent units) the (roentgen equivalent units) the amount of radiation to produce an harmful amount of radiation to produce an harmful effect on living tissue.effect on living tissue.

• REM:REM: (roentgen equivalent man) the (roentgen equivalent man) the amount of radiation that produces the amount of radiation that produces the same biological damage in man resulting same biological damage in man resulting from the absorption of 1 REP of radiation. from the absorption of 1 REP of radiation.

Additional Units of Additional Units of Radioactivity Radioactivity

• Curie:Curie: the number of nuclear disintegrations the number of nuclear disintegrations that occur in one second. Commonly used in that occur in one second. Commonly used in medical laboratory diagnostic procedures. medical laboratory diagnostic procedures. One cure is 3.7 x 10One cure is 3.7 x 101010 nuclear disintegrations. nuclear disintegrations.

• RAD:RAD: (radiation absorbed dose) similar to a (radiation absorbed dose) similar to a REM, and is used in monitoring dosimeter REM, and is used in monitoring dosimeter measurements for X-ray personnel.measurements for X-ray personnel.

• Sievert(Sv)- SI derived unit of dose and reflects Sievert(Sv)- SI derived unit of dose and reflects the biological effects of radiation that is the biological effects of radiation that is absorbed (in gray units).absorbed (in gray units).

• REMS, and RADS are the two most common REMS, and RADS are the two most common units for measuring radiation exposure.units for measuring radiation exposure.

Exposure Limits:Exposure Limits:• Average citizen:Average citizen:

No more than 500 millirems per year. No more than 500 millirems per year. X-rays can cause exposures of 100 millirem per X-rays can cause exposures of 100 millirem per procedure.procedure.

• Radiation or Nuclear medicine workers:Radiation or Nuclear medicine workers:No more than 5 rems per year.No more than 5 rems per year.

• Physiological effects:Physiological effects:Acute Radiation sickness: 100-400 remsAcute Radiation sickness: 100-400 remsLD-50 (lethal dose 50%):LD-50 (lethal dose 50%): 400 rems 400 remsDeath: Death: over 1000 over 1000

remsrems

Protection from RadiationProtection from Radiation•Three factors toThree factors to protect radiation workers areprotect radiation workers are

S-S-ShieldingShielding; ; the use of lead and orthe use of lead and or concrete in high concrete in high

radiation areas.radiation areas.T-T-TimeTime; ; limit the amount oflimit the amount of

time in high time in high radiation areas.radiation areas.

D-D-DistanceDistance; ; the farther away from the farther away from a high radiation areaa high radiation areathe lower the exposure.the lower the exposure.

Nuclear FissionNuclear Fission• When a nucleus fissions, it splits into several When a nucleus fissions, it splits into several

smaller fragments or atoms. smaller fragments or atoms. • These fragments, or fission products, are about These fragments, or fission products, are about

equal to half the original mass. equal to half the original mass. • Two or three neutrons can also be emitted. Two or three neutrons can also be emitted. • The sum of the masses of these fragments is less The sum of the masses of these fragments is less

than the original mass. This 'missing' mass (about than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been 0.1 percent of the original mass) has been converted into energy according to Einstein's converted into energy according to Einstein's equation.equation.

• Fission can occur when a nucleus of a heavy atom Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen captures a neutron, or it can happen spontaneously.spontaneously.

Fission ReactorsFission Reactors• The heat from a fission reactor is used to heat The heat from a fission reactor is used to heat

water to steam, which turns turbines to water to steam, which turns turbines to generate electricity.generate electricity.

• Fuels rods made of aluminum hold the Fuels rods made of aluminum hold the Uranium-235 which is the most common Uranium-235 which is the most common nuclide used in fission reactors.nuclide used in fission reactors.

• Control rods made of neutron-absorbing steel Control rods made of neutron-absorbing steel are used to limit the number of free neutrons. are used to limit the number of free neutrons.

• Graphite(carbon) is used to slow down fast Graphite(carbon) is used to slow down fast neutrons produced from fission. neutrons produced from fission.

• Control rods allow for a limited self-sustaining Control rods allow for a limited self-sustaining reaction.reaction.

Nuclear FusionNuclear Fusion• Nuclear energy can also be released by Nuclear energy can also be released by

fusion of two light elements (elements with fusion of two light elements (elements with low atomic numbers).low atomic numbers).

• The power that fuels the sun and the stars is The power that fuels the sun and the stars is nuclear fusion. nuclear fusion.

• In a hydrogen bomb, two isotopes of In a hydrogen bomb, two isotopes of hydrogen, deuterium and tritium are fused to hydrogen, deuterium and tritium are fused to form a nucleus of helium and a neutron. form a nucleus of helium and a neutron.

• Unlike nuclear fission, there is no limit on the Unlike nuclear fission, there is no limit on the amount of the fusion that can occur.amount of the fusion that can occur.

Applications of Nuclear Applications of Nuclear ChemistryChemistry

• Radioactive Dating using C-14Radioactive Dating using C-14• Treatment of Cancer (Phosphorous and Treatment of Cancer (Phosphorous and

Cobalt)Cobalt)• NMR and CAT scans in RadiologyNMR and CAT scans in Radiology• Sterilization of foodsSterilization of foods• Radioactive tracers (cardiology)Radioactive tracers (cardiology)• Fission reactors for Electrical Power Fission reactors for Electrical Power • Medical Laboratory proceduresMedical Laboratory procedures• Defensive and Offensive WeaponsDefensive and Offensive Weapons