Chapter 10: Radioactivity and Nuclear Processes

1. Chapter 10:Radioactivity and Nuclear Processes

2. RADIOACTIVE NUCLEI Radioactive nuclei are nuclei that undergo spontaneous changes and emit energy in the form of radiation. The emission of radiation by radioactive nuclei is often called radioactive decay. The intensity of radiation is unaffected by factors that normally influence the rates of chemical reactions: the temperature, pressure, and type of uranium compound used.

3. Radiation emitted by uranium, and by other radioactive elements, can be separated into three types by an electrical or magnetic field. The three types had different electrical charges: One was positive (alpha rays), one was negative (beta rays), and one carried no charge (gamma rays).

4. ALPHA RADIATION Alpha radiation consists alpha particles. Alpha particles are identical to helium-4 nuclei; they consist of two protons and two neutrons. Alpha radiation occurs when the nucleus is too large (atomic # > 83) and sheds particles to decrease in size BETA RADIATION Beta radiation consists of beta particles that are identical to electrons. Beta radiation occurs when a nucleus has too many neutrons and not enough protons. In this process a neutron splits to form a proton and an electron. GAMMA RADIATION Gamma radiation consists of energetic rays similar to X rays, but with a higher energy. Gamma radiation occurs when the particles in the nucleus are “stacked” in an unstable way and shift around to achieve stability.

5. CHARACTERISTICS OF NUCLEAR RADIATION The characteristics of the common types of radiation along with the symbols used to represent them are summarized in the following table:

6. EQUATIONS FOR NUCLEAR REACTIONS All particles involved in nuclear reactions are designated by the notation , where X is the symbol for the particle, A is the particle mass number, and Z is the particle atomic number. The equation for a nuclear reaction is balanced when the sum of the atomic numbers of the particles on the left side of the equation equals the sum of the atomic numbers of the particles on the right side, and the sum of the mass numbers on the left side equals the sum of the mass numbers on the right side. The products of radioactive decay processes are known as daughters.

7. EXAMPLES OF NUCLEAR REACTIONS Example 1: Bromine-84 decays by emitting a beta particle. What is the symbol for the daughter produced? Solution: The symbol for bromine-84 is . A beta particle has a mass number (the upper number) of 0, and a charge (the lower number) of -1. Thus, the daughter must have a mass number of 84 and an atomic number of 36. The element with an atomic number of 36 is krypton with a symbol of . The balanced equation is:

8. Example 2: When samarium-148 undergoes radioactive decay, the daughter produced is neodymium-144. What kind of radiation is emitted during the decay? Solution: The daughter has a mass number of 144, so the emitted radiation must have a mass number of 4. The difference between the atomic numbers is 2. Therefore, it is an alpha particle. The balanced equation is:

9. ISOTOPE HALF-LIFE The half-life of an isotope is the time required for one-half of a sample of the isotope to undergo radioactive decay. The half-life of an isotope is used to indicate stability. The longer the half-life, the more stable the isotope is and the slower the rate of radiation release. EXAMPLES OF HALF-LIVES

10. HALF-LIFE CALCULATIONS Half-lives can be determined by measuring the number of times a sample of radioactive material is reduced by 1/2 in a measured amount of time. N = # of half lives that have passed

11. Example 1: Iodine-132 decays by beta emission and forms krypton gas. A 100 mg sample of solid iodine-132 has a mass of 12.5 mg after decaying for 6.9 hours. Assume the krypton gas formed by the decay all escapes into the air, and determine the half-life of iodine-132. Solution: After one half-life passed, the sample would weigh 50 mg. After another half-life passes, the 50 mg would have become 25 mg, and after a third half-life had passed, the 25 mg would have become 12.5 mg. Thus, 3 half-lives passed in 6.9 hours, so one half-life is equal to 6.9hr/3 or 2.3 hours.

12. THE HEALTH EFFECTS OF RADIATION The greatest danger to living organisms of exposure to long-term, low-level radiation is the ability of high-energy or ionizing radiation to dislodge electrons from molecules and generate highly reactive particles called radicals or free radicals. Free radicals are very reactive and may cause reactions to occur among stable materials in the cells of organisms such as genes and chromosomes. Such reactions might lead to genetic mutations, cancer, or other serious conditions. Short-term exposure to intense radiation results in tissue destruction in the exposed area and causes the symptoms of acute radiation syndrome.

13. PROTECTION AGAINST RADIATION EXPOSURE The use of shielding or distance are effective ways to prevent or minimize the exposure of individuals to harmful radiation. Shielding involves the placement of dense absorbing materials such as lead or concrete between the radiation source and individuals.