Auburn High School Nuclear Chemistry The study of nuclear change. Some elements undergo chemical changes in their nucleus that alters their number of protons or neutrons. (yes, before we said that protons can’t be changed but this is newer technology and discovery. If you change the number of protons, you change the element)

Nucleus nucleus contains nucleons atomic mass, a.k.a. mass number p+ and n0 atomic mass, a.k.a. mass number protons + neutrons atomic number # protons identifies the element

Isotopic notation Symbol Mass Atomic number

Same number of protons but different number of neutrons

An element is considered radioactive because it releases Energy Transmutation Sometimes the changes in the nucleus are such that an element is transformed into a different element change in atomic number An element is considered radioactive because it releases Energy during transmutation

Artificial Natural Transmutation Transmutation Change in nucleus occurs when bombarded by an alpha particle or neutron 2 in reactant 2713Al + 42He 3015P + 10n Change in nucleus occurs spontaneously ONLY one reactant is the atom undergoing transmutation 23994Pu 23592U + 42He

Remember- you always need to conserve Notice the atomic mass and atomic numbers on both sides are equal 2713Al + 42He 3015P + 10n 23994Pu 23592U + 42He

FUSION Two elements JOIN to become one new element EXTREMELY Large quantities of E are released when smaller nuclei are combined to form larger nuclei Occurs at very high temperatures Power of the sun and stars

Fusion Look for: Two small elements combine to make a larger element

Hydrogen becomes helium Deuterium Tritium

Nuclear Fission Splitting an atom – one element goes to Two or more elements

The energy produced in a times greater than the E fission reaction is 1,000,000 times greater than the E produced in a chemical reaction

Splitting one atom doesn’t provide a lot of energy but if . . . Chain Reaction

Fission Look for: One heavy element and a neutron collide to create 2 smaller elements and 3 neutrons

Nuclear Power Plants Nuclear power plants UO2 pellets as fuel uses 3% U-235 A controlled chain reaction occurs in the fuel rods to create E To slow and control a reaction- cool it Weapons grade U is 90% U-235 Uncontrolled chain reaction

Reactor= holds control rods filled with uranium Reactor= holds control rods filled with uranium. Has cold water circulating to control reaction Condensor=Creates steam to turn the turbine which creates elecricity from spinning magnets around copper with Pump = cold water cools the condensor and water around the reactor Containment shell- Thick concrete to shiel the environment from radiation

Stability of Nuclei Most nuclei are stable some elements have unstable isotopes Radioisotopes- have more neutrons than they should Ex. C-12 stable and won’t transmutate C-14 unstable and will transmutate

What causes instability? As atoms increase in size the ratio of neutrons to protons also increases the larger the ratio of Neutrons to Protons the more unstable the atom (more neutrons = unstable) All nuclei with atomic numbers > 83 are unstable and radioactive

Types of Radiation Types of radiation emitted from the nucleus during transmutation THESE ARE ON TABLE O and N

alpha particles Alpha particle – A Helium atom WEAK form of radiation with very little penetrating power. Often cannot penetrate through your skin. alpha particles 42 He or

Beta particles Beta particles – the nucleus ejects an electron a neutron breaks apart into a proton and an electron. The electron is emitted from the nucleus Beta decay

e Positron Radiation +1 ß+ +1 Positron Radiation ß+ Positron – a positive electron is emitted from the nucleus X = 3718Ar isotope

Neutrons= 10n Protons = 11 H ( H+ Ion)

Gamma Radiation energy usually released as a result of a nuclear decay. It has the STRONGEST penetrating power of all the radiation types

Radiation Penetration

Radiation risks Can cause mutations High exposure can lead to serious illness or injury. Spent fuel rods from power plants are still radioactive for thousands of years. Thermal pollution from water dumped into streams or lakes by power plant. if there is a meltdown and radiation is released (ex Chernobyl in the Ukraine in 1986.) Farmland is unusable for generations, unsafe for people to live in the area. Nuclear weapons destroy everything

Severe low WBC / lesions Dose (rem) Effects 0 - 25 No observable effects 25 - 50 Decreased WBC count 50 - 100 Severe low WBC / lesions 100 - 200 Radiation burns 200 - 300 Internal bleeding 300 - 500 50% death in few weeks > 700 DEATH

Effects of radiation from the Chernobyl nuclear accident

Hiroshima

People burned into the landscape

Radiation burns and clothing patterns burned onto skin

Those cells that undergo rapid mitosis (cell division) are more sensitive to radiation. Bone marrow:Cells that make blood cells “Pre” sperm & egg cells Lung tissue Digestive lining eyes

Benefits of radiation Radioisotopes are used in diagnosing and treating cancer I-131 diagnose thyroid disorders Co-60 treat cancer Short half lives decay quickly

Produce LOTS of elecritcity Smoke detectors Am- 241 24195Am Carbon – 14 dating to determine age of ancient materials U-238 date the earth

In 1991 the Iceman was discovered In 1991 the Iceman was discovered. Less than 50% of the C-14 atoms had decayed. T = 5730 y the age of the Iceman was determined to be approximately 5300 years old. Carbon Dating

C-14 is NOT used to date the Earth. WHY? C-14 has too short of a half life Found in organic materials U-238 date the age of the earth T = 4.5x109 y Found in rocks

1/2 life Time it takes for 1/2 of the atoms in a sample to decay.

Table N 1/2 lives are always constant 1/2 lives are different for different radioisotopes (nuclides) An atom with a short half-life decays faster than an atom with a long half life

C-14 U-238 Time in 5730 year intervals Can’t tell when an individual atom will decay BUT 50% of the atoms will decay in one half life Time in 4.5 billion year intervals U-238 Time in 5730 year intervals C-14

Applications of 1/2 life Radioactive Dating C-14 Used to date organic materials aged up to 60,000 years.

Radioactive Decay Formulas Table N 1/2 lives of radioisotopes Radioactive Decay Formulas 1 2 Number of 1/2 life periods Fraction of sample remaining = Number of 1/2 life periods = Time elapsed (t) 1/2 life (T)

Easier way than formula 100 = 1 whole 50 = 1/2 25 = ¼ 12.5 = 1/8 6.25 = 1/16 3.125 = 1/32 1.5625 = 1/64 1 half life 2 half life Determine how many half life the element has gone through and divide by 2 that many times 3 half life 4 half life 5 half life 6 half life

The End