Early Pioneers in Radioactivity
Roentgen:
Discoverer of X-rays 1895
Becquerel:
Discoverer of Radioactivity
1896
The Curies:
Discoverers of Radium and
Polonium 1900-1908
Rutherford:
Discoverer Alpha and Beta
rays 1897
Radioactive Bands
• The Firm- “Radioactive” circa 1985
• Imagine Dragons- “Radioactive” circa 2012
What do we mean by Radioactivity?
Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.
There are numerous types of radioactive decay. The general idea:
An unstable nucleus releases energy to become more
stableDecay continues until a stable, non-radioactive product is formed
Reason for Radioactivity
• The number of Neutrons in the nucleus affects the stability of the atom
• In some cases all the isotopes are unstable
Isotopes….a review-mass of the atom depends on the number of protons and neutrons in the element
-isotopes are forms of the same element have different #s of neutrons but same # of protons (atomic number)
ex. 12C, 13C, 14C 6 6 6
-many isotopes have unstable nuclei and they release radiation (are radioactive)
What are the Sources of Radioactivity?
• Naturally Occurring Sources:– Radon from the decay of Uranium and Thorium– Potassium -40 – found in minerals and in plants– Carbon 14 – Found in Plants and Animal tissue
• Manmade Sources:– Medical use of Radioactive Isotopes– Certain Consumer products –(eg Smoke detectors)– Fallout from nuclear testing– Emissions from Nuclear Power plants
Products of Radioactive Decay• When the unstable element (Parent
Isotope) decays it makes:– a new element (Daughter Element) – Gives off radiation 238
92U 42He + 234
90Th
Parent radiation Daughter
Three Common Types of Radioactive Emissions
Alpha
Beta
Gamma
• Half-life- time it takes for half of the atoms in a radioactive isotope to decay
• Each isotope has its own HL• HL cannot be altered by temperature
or pressure• Decay continues until a stable, non-radioactive product is formed • Decay of an individual atom is
random
Half life – exponential decayHalf life – exponential decay
Carbon Dating
• When a plant dies, it stops the intake of carbon
• Since the 14C decays, after 5730 years, half of it will be gone
• We can just weigh a piece of dead wood, calculate how much 14C it originally had and measure to how much it has now to get the age
Uranium Dating
• We know the half -life of 238U and 235U• They have series that end in 206Pb and
207Pb• Compare how much U vs. special lead
and calculate the age of the rock!!• Carbon dating only good for about 50,000
years• Uranium rock dating good for millions of
years
Telling time by absolute ageTelling time by absolute age
Carbon-14Carbon-14 to Nitrogen 14 in ~5700 years found to Nitrogen 14 in ~5700 years found in any living thingin any living thing
Uranium-235Uranium-235 to lead 207 in 700 million years to lead 207 in 700 million years
Potassium-40Potassium-40 to Argon-40 in 1.3 billion years to Argon-40 in 1.3 billion years found in the mineral feldsparfound in the mineral feldspar
Uranium-238Uranium-238 to lead 206 in 4.5 billion years to lead 206 in 4.5 billion years
Thorium 232Thorium 232 to Lead 208 in 14 billion years. to Lead 208 in 14 billion years.
Rubidium 87Rubidium 87 Strontium 87 in 48.6 billion years Strontium 87 in 48.6 billion years
Transmutations
• The changing of one element to another is called transmutation
• This occurs whenever there is an alpha decay or a beta decay
Two Main Types of Nuclear Reactions
• Fusion - two light nuclei are combined to form a heavier, more stable nucleus– This occurs in stars to
produce energy
(electromagnetic radiation)• Fission - a heavy nucleus is
split into two nuclei with smaller
mass numbers– This occurs in nuclear power
plants
Nuclear Power PlantFission of Uranium in the reactor creates large amounts of energy to
heat water, spin a turbine and generate electricity
