Nuclear Chemistry Ch. 28

Nuclear Radiation 28-1

Radioactivity Radioactivity = spontaneous emission of radiation by an unstable atomic nucleus. –Some elements give off radiation naturally, without an input of energy!! –In chemical reactions the number of electrons changes, in nuclear reactions the number of protons + neutrons changes! –If the proton number changes a new element is made!

6 Nuclear Notation Nuclear Notation – Indicates mass number and atomic number, allowing isotopes to be differentiated U – can also be written as Uranium-238 Superscript: Mass # = # of protons plus neutrons Subscript: Atomic # = # of protons Isotopes have same # of protons but different # of neutrons

Ex: Isotopes of Hydrogen

Radioactive Decay Radioactive Decay = release of radiation by radioactive isotopes, or radioisotopes, to become more stable. Nuclei of radioisotopes are unstable, give off varying degrees and different types of nuclear radiation. Three types of nuclear radiation: 1) Alpha particles 2) Beta particles 3) Gamma rays

Alpha Decay Alpha particle: helium nuclei consisting of 2 protons and 2 neutrons (+2 charge!) –Symbol: 4 2 He or α –Affect: large in size, do not penetrate into matter easily, stopped by thin layer of material (paper, skin) Alpha decay: nucleus releases an alpha particle, becoming a different element –Decreases mass of original nucleus by 4 and the new element has an atomic number 2 less than original

As uranium decays it becomes multiple elements releasing multiple types of radiation! Transmutation = when a nucleus releases either an alpha or beta particle the atomic # changes becoming a different element!

Beta Decay Beta particle = a high energy electron with a charge of -1. –Symbol: 0 -1 e or ß - –Affect: smaller, lighter, can be stopped only by thicker materials (aluminum foil or wood). Beta decay = decaying nucleus turns into new element with atomic number + 1 but with same mass.

Gamma Decay Gamma ray = high energy form of electromagnetic radiation without mass or charge. –Symbol: γ or 0 0 γ –Affect: Very hard to stop, only thick layers of lead or thick concrete. Causes great harm to living cells  Gamma Decay = only energy is given off, usually occurs simultaneously with other types of decay, often omitted from equations.

Overview Draw! Type of Radiation SymbolAtomic mass Atomic # Affect Alpha Beta Gamma

Type of Radiation SymbolAtomic mass Atomic #Affect Alpha 4 2 He αDecrease by 4 Decrease by 2 Stopped by thin layer Beta 0 -1 e ß - sameAdd 1 Stopped by thick material Gamma γ00γγ00γsame Only stopped by thick concrete, or lead

Explain why the 3 types of radiation moved in the following directions!

Nuclear Transformations 28-2

Radioactive Dating Unlike chemical reactions affected by temperature, pressure, and concentration, the rate of nuclear decay cannot be changed! Able to predict amount of decay that has occurred. Half-life = time it takes for half the given amount of a radioisotope to decay. “Is that what atoms do when they’re single?!”

Half-life Calculation: –M O = 2 x M r –Where M O = original mass, x = # of half-lives, M r = mass remaining Example: 2.00 g of nitrogen-13 emits beta radiation with a half-life of 10 minutes. –Write a nuclear equation N  13 8 O e –How long is 3 half-lives? 10 minutes x 3 half-lives = 30 minutes –How many grams of oxygen-13 will be present at the end of 3 half-lives? M O = 2 x M r 2.00g = 2 3 M r M r = 0.250g of oxygen-13

What is the half-life (time) of this radioactive sample?

Commonly used Radioisotopes for Radioactive Dating Carbon-14 used to date artifacts made of organic material Uranium-238 used to date rocks as old as solar system Radon-222 and Thorium-234 used in nuclear medicine IsotopeHalf-lifeRadiation emitted Carbon x 10 3 yearsβ Uranium x 10 9 yearsα Radon daysα

Nuclear Reactions and Energy 28-3

Nuclear Fission Nuclear Fission = an atomic nucleus is split into two or more large fragments Ex: Uranium is bombarded with a neutron forming two lighter elements: krypton and barium, 3 neutrons, and a large amount of energy! U n  Ba Kr n If the reaction takes place too quickly an explosion will occur (atom bomb), if it is controlled to release heat slowly it can be used to heat water and do other useful work! = nuclear reactor

San Onofre Nuclear Power Plant (Fission of Uranium!)

Nuclear Fission as a source of energy! Pros: –>100 nuclear reactors in U.S. –Provide ~20% of electricity used –Do not release pollutants to air Cons: –Form highly radioactive waste –Can cause serious accidents –Limited supply of fissionable material –Higher cost than fossil fuels

Nuclear Accidents Chernobyl, Ukraine, 1986Fukushima, Japan, 2011

Nuclear Fusion Nuclear Fusion = two or more nuclei combine to form a larger nucleus. Fusion is the process that produces energy in stars, sun (2 H nuclei form He) 2 1 H H  4 2 He n deuterium + tritium  helium + neutron The fusion of hydrogen produces 20 times the energy produced by fission of uranium but can only take place at very high temperatures! (40 million °C)

Nuclear Fusion as a source of energy! Pros: –Fusion done successfully in laboratories –Deuterium, a fuel in fusion, abundant on Earth –No radioactive products produced –Easier to control than fission Cons: –Requires large input of energy, 200 million K heat required!!! –Only known source of this amount of thermal energy is an atom bomb, thus must be used to start reaction! –Material to contain reaction melts –Tokamak = uses electromagnets to contain nuclei, radio waves initiate fusion, but no net energy produced

The Large Hadron Collider at CERN, Switzerland 17 mile circumference, 574 ft below the surface. World’s largest particle accelerator

Artificial Transmutation: can occur by applying an outside force.  Requires lots of energy!!  High speed neutrons act as “bullets” to hit nuclei = Particle accelerators  Neptunium and Plutonium were discovered in lab (synthetic elements), as were all elements with atomic #’s greater than 92 on periodic table = transuranium elements. Fermilab, Illinois Shutdown in 2011

Comparison (DRAW!)