Nuclear Chemistry

Only one element has unique names for its isotopes … Deuterium and tritium are used in nuclear reactors and fusion research.

Some isotopes are radioactive Radioactive isotopes are called radioisotopes. Radioisotopes can emit alpha, beta or gamma radiation as they decay.

Man-made Isotopes Cobalt-59 occurs naturally. When a neutron “sticks” to the nucleus, cobalt-60 is formed. Man-made isotopes are usually made by bombarding atoms with protons or neutrons.

Uses for Isotopes Radioisotopes are used as tracers in chemical reactions. Radioisotopes are used in “imaging” living and nonliving systems. Radioisotopes are used to kill cancer cells. (Co-60, Bi-212)

Properties of alpha, beta and gamma radiation

Subatomic particles H 1 1 e 0 n 1 0 proton neutron electron What do the numbers represent?

Mass number /Atomic number U Mass number Symbol of Element Atomic number protons + neutrons Protons in nucleus Mass number

Alpha (  ) particles are the nuclei of helium atoms and have the symbol 2 He 4. What is the atomic number of an  particle? 2 He 4

Alpha (  ) particles are the nuclei of helium atoms and have the symbol 2 He 4. How many times heavier is an alpha particle than a hydrogen atom? 4

Beta (  ) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1 e 0. What is the mass number of a  particle? -1 e 0

Beta (  ) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1 e 0. No protons or neutrons in an electron. -1 e 0

Beta (  ) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1 e 0. None What is the difference between a  particle and a “regular” electron?

Beta (  ) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1 e 0. Location What is the difference between a  particle and a “regular” electron?

Gamma (  ) rays are high energy electromagnetic waves, not particles. No protons, neutrons or electrons. Gamma rays have short wavelengths and high energies and travel at the speed of light.

Gamma rays have short wavelengths … and high energies. Increasing energy

Alpha, Beta, Gamma Radioactive Source Electric field from electrically charged plates What is the effect of an electric field on 

Alpha, Beta, Gamma Radioactive Source    Electric field from electrically charged plates

Alpha, Beta, Gamma Radioactive Source    Are ,  and  rays deflected by magnetic fields? Electric field from electrically charged plates

Radioactive Source  Paper Aluminum foil Lead Alpha, Beta, Gamma

Radioactive Source   Paper Aluminum foil Lead Alpha, Beta, Gamma

Radioactive Source    Paper Aluminum foil Lead Alpha, Beta, Gamma

Radiation Project Create a table listing information for each of the three kinds of radiation: Alpha, beta and gamma

Properties to include in your table: (1)Greek letter (2)symbol (3)actually is (4)atomic number (5)mass number (6) relative mass (7) relative. charge (8) penetrating ability (9) shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter Symbol Actually is… Atomic number Mass number Relative mass Relative charge Penetrating Shielding Stop! Complete the chart on notebook paper, then continue.

Nuclear Properties Table Property AlphaBetaGamma Greek Letter Symbol Actually is… Atomic number Mass number Relative mass Relative charge Penetrating Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol Actually is… Atomic number Mass number Relative mass Relative charge Penetrating Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol 2 He 4 -1 e 0 NA Actually is… Atomic number Mass number Relative mass Relative charge Penetrating Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol 2 He 4 -1 e 0 NA Actually is… He nucleuselectronEM energy Atomic number Mass number Relative mass Relative charge Penetrating Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol 2 He 4 -1 e 0 NA Actually is… He nucleuselectronEM energy Atomic number 2NA Mass number Relative mass Relative charge Penetrating Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol 2 He 4 -1 e 0 NA Actually is… He nucleuselectronEM energy Atomic number 2NA Mass number 40NA Relative mass Relative charge Penetrating Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol 2 He 4 -1 e 0 NA Actually is… He nucleuselectronEM energy Atomic number 2NA Mass number 40NA Relative mass 4 1 / 1837 NA Relative charge Penetrating Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol 2 He 4 -1 e 0 NA Actually is… He nucleuselectronEM energy Atomic number 2NA Mass number 40NA Relative mass 4 1 / 1837 NA Relative charge +2NA Penetrating Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol 2 He 4 -1 e 0 NA Actually is… He nucleuselectronEM energy Atomic number 2NA Mass number 40NA Relative mass 4 1 / 1837 NA Relative charge +2NA Penetrating LowMediumHigh Shielding

Nuclear Properties Table Property AlphaBetaGamma Greek Letter  Symbol 2 He 4 -1 e 0 NA Actually is… He nucleuselectronEM energy Atomic number 2NA Mass number 40NA Relative mass 4 1 / 1837 NA Relative charge +2NA Penetrating LowMediumHigh Shielding 2.5 cm of air; anything else Metal, plastic or wood Lead or concrete

Protection from radiation 1.Shielding2. Distance How do you protect yourself from … Alpha Beta Gamma 2.5 cm of air, paper, skin aluminum, lead, other metals, wood, plastic, etc. up to a foot or two of lead, many feet of concrete

There are some kinds of radiation you can not protect your self from.

Gamma rays and high energy cosmic particles from space. But there is one kind of radiation hazard that you can protect against. Radiation

That hazard comes from the uranium beneath your feet. Uranium in the ground decays according to …

Uranium-238 decays through many steps to make stable lead-206 The uranium decay series

The uranium decay series Radon is the only gas in the series.

Hazards from radon Since radon is the only gas in the decay series of uranium … …it can work its way up through the ground and into your basements and crawl spaces. You breathe radon into your lungs.

Hazards from radon And when radon is in your lungs… …it can decay and release an alpha particle … …which travels only a short distance before it is absorbed by your lungs, and transfers its energy.

Hazards from radon This ionizing radiation in your lungs can cause lung cancer. Smoking cigarettes and breathing radon really increases your chances of getting lung cancer.

Protecting against radon Get a test kit to see if there is a problem. Charcoal canisters, which are sent off for analysis. Abatement: Seal places where gas gets in. Ventilation – bring in fresh air.

Half life

What is half life? Half life is the time needed for one half of a radioisotope to decay. Suppose you start with grams of a radioisotope that has a half life of exactly 1 year.

What is half life? How much will be left after 1 year? Suppose you start with grams of a radioisotope that has a half life of exactly 1 year.

What is half life? After one year there will be 50.0 g left. Suppose you start with grams of a radioisotope that has a half life of exactly 1 year. After a second year there will be 25.0 g left.

What is half life? After a third year there will be 12.5 grams left. After one year there will be 50.0 g left. After a second year there will be 25.0 g left. After a fourth year there will be 6.25 grams left.

Half life project 1.Pick a mass between 10g and 50g. 2.Decide on a half life – any time. 3.Scale your graph – mass on y-axis and at least six (6) half-lives on the x-axis. 4.Plot the masses after intervals of one half-life.

Half life project 5.What shape is the graph? 6.When will the mass of the radioisotope fall to zero? 7.When is the radioactivity no longer a problem? 8.What mathematical function describes radioactive decay?

Half life project mass time t 1/2

Half life project mass time 2.5 t 1/2 10 5

Half life project Activity (counts/min) Time (min) t 1/2 Exponential decay A = A 0 e -kt

Half life project Time (min) t 1/2 Activity (counts/min) background Radiation is “not a problem” when it falls below background level. 200

Half life project Questions: 1. A radioisotope has a half-life of 100 years. How long will it take for the radiation to decrease to 1/16 of its original value? 400 years

Half life project Questions: 2. A radioisotope has an activity of 560 counts per minute. After 16 hours the count rate has dropped to 35 counts per minute. What is the half life of the radioisotope? 4 hours

Decay equations

Alpha decay In alpha decay, an alpha particle ( 2 He 4 ) is released from the nucleus. The alpha particle carries away two protons and two neutrons.

Alpha decay 92 U 238  2 He Th 234 alpha particle decay product

Alpha decay 92 U 238  2 He Th 234 The atomic number decreases by 2. The mass number decreases by 4.

Alpha decay These must add up to 238 These must add up to U 238  2 He Th 234

Alpha decay 86 Rn 220  2 He 4 + ??? Radon-220 decays by alpha emission. What is the decay product? 84 Po 216

Alpha decay Write the alpha decay equations for: Am 241  Po 216  Ra 226  2 He Np He Pb He Rn 222

Beta decay Neutrons are a little more massive than protons; neutrons are neutral. What does this suggest about the composition of neutrons? Beta decay occurs because of the instability of a neutron.

Beta decay Scientists used to think that neutrons might be a combination of a proton and an electron. We know that neutrons decay into protons, which stay in the nucleus, and electrons, which are ejected from the nucleus as beta particles.

Beta decay 0 n 1  1 H e 0 neutronprotonelectron The electron ejected from the nucleus is a beta particle. Decay of a neutron:

Beta decay 0 n 1  1 H e neutronprotonelectron Technically, the decay of a neutron also involves a neutrino. anti- neutrino

Beta decay 0 n 1  1 H e neutronprotonelectron Actually, an anti-neutrino. anti- neutrino The word “neutrino” comes from Enrico Fermi, meaning “little neutral one” in Italian.

Beta decay 0 n 1  1 H e neutronprotonelectron A neutrino is a particle with no charge and almost no mass. anti- neutrino

Beta decay 0 n 1  1 H e neutronprotonelectron A neutrino carries off some of the energy in the decay of the neutron. anti- neutrino

Beta decay 0 n 1  1 H e neutronprotonelectron When predicting the products of beta decay we will ignore neutrinos. anti- neutrino

Beta decay Start with a Li atom with 3 protons and 4 neutrons. Suddenly a neutron decays! Now there are 4 protons and 3 neutrons. A beta particle goes zipping out of the nucleus.

Beta decay The number of neutrons The number of protons The mass number The atomic number A neutron decays to make a proton. decreases by 1 increases by 1 stays the same. increases by 1

Beta decay 6 C 14  7 N e 0 beta particle decay product

Beta decay 6 C 14  7 N e 0 The atomic number increases by 1. The mass number stays the same.

Beta decay 6 C 14  7 N e 0 Notice that these add up to 6 These add up to 14

Beta decay Zn-69 decays by beta emission. What is the decay product? 30 Zn 69  -1 e 0 + ??? 31 Ga 69

Beta decay Write the beta decay equations for: Pb 214  Co 62  -1 e Bi e Ni ???  -1 e Cd Ag 113

Review: decay equations Alpha: Go down two on periodic table Atomic number decreases by 2 Mass number decreases by 4 Beta: Go up one on periodic table Atomic number increases by 1 Mass number stays the same

Nuclear energy All have enough energy to ionize atoms. Gamma rays are electromagnetic energy. Alpha and beta particles have high kinetic energies. All nuclear decay is accompanied by a release of energy.

Nuclear energy This can result in damage to your body. Ionization occurs when electrons are removed from atoms by  or  radiation. An ion is a “charged atom” or group of atoms. cancer

Nuclear energy Forms of ionizing radiation are: Alpha Beta Gamma X-rays Cosmic rays Ultraviolet light (UV) can cause cancer, but it is not ionizing radiation. Neutrons Positrons