Unstable Nuclei and Radioactive Decay

Radiation Scientists began to notice that some elements spontaneously emitted energy and particles. These emissions became known as radiation. Elements that give off radiation are said to be radioactive. Radioactive elements are elements which change into other elements after emitting radiation.

Radioactive Decay Some nuclei are unstable and gain stability by emitting radiation. This process is called radioactive decay.

Types of Radiation There are three basic types of radiation given off during radioactive decay. Alpha radiation Beta radiation Gamma radiation

particle: (contain 2p+ and 2n0) Alpha Radiation In this type of radiation alpha particles (a particles) are ejected from the nucleus. An a particle is equivalent to a helium-4 nucleus, a nucleus with 2 protons and 2 neutrons. Alpha particles have a 2+ charge. particle:     (contain 2p+ and 2n0) Protection required: a sheet of paper

b particle: (high energy e-) Beta Radiation This type of radiation consists of high- energy electrons called beta particles (b particles). b particle: (high energy e-) Remember, that beta particles emitted by the atom’s nucleus increase the elements atomic number by 1+. Protection required: sheet of aluminum foil

Gamma Radiation Gamma (g)radiation consists of high-energy electromagnetic radiation. This type of radiation is usually emitted along with a particles and b particles. Protection required: thick sheet of lead

Practice Write the balanced nuclear equation for the alpha decay of each of the following. a. gold-185 b. protactinium-225 c. francium-221 Write the balanced nuclear equation for the beta decay of each of the following. a. krypton-87 b. actinium-228 c. nickel-63 3. What is the missing particle in this equation? 2713Al + 42He ---> 3015P + ?

Radioactive Decay Rates Radioactive decay rates are measured in half- lives. A half-life is the time requires for one half of an elements nuclei to decay. Each radioisotope has a different half-life.

Amount remaining = (initial amount)(1/2)n where n = the number of half-lives that has passed Amount remaining = (initial amount)(1/2)(t/T) where t= elapsed time and T = duration of the half-life Half-Life Equations

Use Table 25-2 on page 818 of your textbook to answer the following questions. How much of a 2.00 x 103 mg sample of polonium- 214 will remain after 1637 microseconds? How much of a 50.0 g sample of tritium will remain after 37 years? How much of a 20.0 g sample of carbon-14 will remain after one half-life? After 190 years? Practice

Answers 1.953 mg 6.3 g 10.0 g; 2.5 g