Radioactivity
Objectives:
 define radioactivity
 trace the discovery of radioactivity and isotopes
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Radioactivity refers to…unstable isotopes that spontaneously emit radiation in an
effort to become stable.
Wilhelm Roentgen (Rontgen) 1895- accidentally discovered X-rays when he developed
photographic plates that had been exposed to certain materials.
Henri Becquerel- accidentally discovered that phosphorescent uranium salts
produced emissions that darkened photographic plates even when not exposed
to light.
Marie Curie- coined the term radioactivity, discovered Polonium (Po), and
discovered Radium (Ra).
Identify all of the listed sources of radiation in everyday life:
Radon-222 in the earth, Tritium (heavy water) in water from cooling towers,
Americium in smoke detectors, UV radiation from sun exposure
T. O’Toole
Types of Radiation
Particle
Alpha (helium nucleus)
α
decreases atomic number and mass
Example: Radon-222
Beta (electron)
βconverts a neutron into a proton and an electron
Example: Carbon-14
Positron
β+
Gamma (high energy photon)
γ
# protons and neutrons in nucleus remain the same
Example: Cobalt-60
Symbol
Stopped by…
paper
Al foil or wood
Al foil or wood
concrete or Pb
Practice-write the decay reactions for the following
a. Uranium 238 emits an alpha particle
b. Iodine 131 emits a beta particle
c. Potassium 38 emits a positron
Minute Paper
T. O’Toole