Type of Radiations Alpha ( α) particles > Helium Nucleus ( 4 2 He) > Positive Charge > high mass > a few centimeters range in air > slight deflection in electric/magnetic fields. > strong ionization > can be stopped by thin paper > Pure source: Americium (Am-241)
Type of Radiations Beta ( β) particles > High-energy electron ( 0 -1 e) > Negative Charge > low mass > a few meters range in air > great deflection in electric/magnetic f. > weak ionization > can be stopped by aluminium (5mm) > Pure source: Strontium (Sr-90)
Type of Radiations Gamma ( γ) rays > High-energy electromagnetic radiation > un-charge > zero mass > a few hundred meters range in air > none deflection in electric/magnetic field. > very weak ionization > can be stopped by thick lead or concrete > source: Cobalt (Co-60) covered by aluminium
Radioactive Decay After ejecting particles, a nucleus becomes the nucleus of a different element. It’s called radioactive decay. If the new element is also unstable, the process of decay will continue until there are atoms with stable nuclei.
18 Plutonium-238 (plutonium oxide). The plutonium glows in the dark as a result of nuclear fission reactions which release enough energy to increase the metal's temperature to red-heat. The heat produced by plutonium has been used as an energy source on spacecraft.
Sample Problems 19 1.A radioactive source has a half-life of 10 minutes. What fraction is left in 1 hour? 2.Carbon-14 has a half-life of 5700 years. A 10 g sample of wood cut recently from a living tree has an activity of 160 counts/minute. A piece of charcoal taken from a prehistoric campsite also weight 10 g but has an activity of 40 counts/minute. Estimate the age of the charcoal.
Sample Problems 20 3.The ratio of the number of atoms of argon-40 to potassium-40 in a sample of radioactive rock is 1 : 3. Assuming that there was no potassium in the rock originally and that argon-40 decays to potassium-40 with a half life of 1500 million years, estimate the age of the rock. 4. Radioactive Uranium-238 (U, proton number 92) decays to thorium (Th), emitting an alpha particle and gamma rays. Show this decay reaction as a nuclide equation