radioactivity nuclear chemistry. discovery of radioactivity wilhelm roentgen discovered x-rays in...
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Discovery of RadioactivityWilhelm Roentgen discovered x-rays in 1895.Henri Becquerel discovered that uranium salts produced similar emissions.Marie and Pierre Curie isolated the source on the emissions in Becquerel's sampleuranium.Marie Curie named the process of emitting raysradiation.
Changes in the NucleusA change in the nucleus of an atom is called a nuclear reaction.These reactions are associated with radioactivity the emission of radiation in the form of rays and particles.Nuclear reactions occur because of nuclei that are unstable.Unstable isotopes are referred to as radioisotopes.
When is a nucleus stable?The strong nuclear force holds the protons and neutrons together in the nucleus of an atom. The electrostatic charge of the protons is repulsive, but the presence of the neutrons adds a stronger attractive force.To be stable, a nucleus must have from 1 to 1.5 neutrons for each proton. Atoms with more protons need the higher number of neutrons.
TransmutationThe changes in the nucleus can sometimes transform an element into a different element The result = change in atomic numberAn element is considered radioactive because it releases Energyduring transmutation
Artificial TransmutationChange in nucleus occurs when bombarded by an alpha particle or neutronNatural TransmutationChange in nucleus occurs spontaneouslyThe ONLY reactant is the atom undergoing transmutationU-238 Th-234 +
Stability of NucleiMost nuclei are stable ex. C-12As atoms increase in size the ratio of neutrons to protons increases the larger the ratio the more unstable the atom ex. C-14
All nuclei with atomic numbers > 83 are unstable and radioactive
Unstable nuclei will spontaneously decay in order to form a stable nucleus
Types of Radiation
NameSymbolMass (amu)ChargeDescription Alpha42+a helium nucleusBeta1/18401-electronsGamma00short wavelength electromagnetic waves
Alpha Particles or Hehelium nucleus
HeaviestTravels slowest & least amount of distancePoor penetrating power MOST DAMAGING42
Alpha DecayA type of radioactive decay where an atomic nucleus emits (releases) an alpha particle (2 p+ and 2 no).The atom reduces its atomic number by 2 and its mass number by 4. This transforms the atom into a different element.
Alpha DecayAlpha Particle is one productmass and charge must be conserved
travel near the speed of lightmoderate penetrating powercan be stopped by aluminum
Beta DecayA type of radioactive decay where a beta particle (electron or positron) is emitted.This causes a neutron to be turned into a proton.
Gamma RadiationNo mass no chargesimilar to x-rays Fastest type of radiationStrongest penetrating powernot very dangerous
Uranium DecayAtoms of U-238 go through a series of decays to make Thorium Th Radon Rn Radium Ra Lead PbExample of natural decay
Radioactive Decay RatesOver time, radioisotopes will decay into stable atoms. The time this takes is measured in half-lives.A half-life is the time it takes one-half of radioisotope to turn into stable atoms.
Radioactive Decay Rates (contd)Example: 20 g of the strontium-90 will decay into 10 g over 29 years.
Amount remaining = (Initial amount)()t/T
t = total timeT = half-life
Half-life of Radiation