Nuclear Energy SI

A. What does radioactive mean? 1. Radioactive materials have unstable nuclei, which go through changes by emitting particles or releasing energy to become stable a. Call this nuclear decay

B. Types of Radiation 1. Background Radiation: radiation that the general population is exposed to (ex. the sun, water, plants) 2. Nuclear Radiation: the particles that are released from the nucleus during radioactive decay

Background Radiation

3. Alpha Particle: a positively charged atom that consists of two protons and two neutrons a. Do not travel far through materials (cannot pass through a piece of paper) b. Symbol: 4 2 He

4. Beta Particle: a negatively charged electron emitted during radioactive decay a. Fast-moving b. Can penetrate sheet of paper, but stopped by piece of aluminum c. Symbol: 0 -1 e

d. A neutron turns into a proton and an electron. The electron gets emitted from the nucleus.

5. Gamma Rays: high-energy radiation emitted during radioactive decay and nuclear fission a. Gamma rays are a form of electromagnetic energy b. Not stopped by clothing or most building materials, so are much more dangerous c. Symbol: γ

d) Atom goes from an excited state to a less excited state. The nucleus does not change and a gamma ray (unit of energy) is emitted from the nucleus.

C. Decay Rates 1. Half-life: time required for half of a sample of radioactive substance to decay 2. Use these decay rates to tell the age of rocks and fossils ( radiometric dating) a. Carbon-14 is common isotope used in radiometric dating

D. What makes a substance radioactive?  Substances with too many or too few neutrons  Substances with equal amounts of protons and neutrons are stable  Which isotope is more stable?  C-14 or C-12

E. What happens during nuclear decay?  The parent element (starting substance) decays into the daughter element (new substance) and emits radiation  The daughter element can be an entirely new element or an isotope of the parent element

II.) Nuclear Reactions A) Nuclear Fission: t he process by which a nucleus splits into two or more smaller atoms and releases neutrons and energy 1. In nuclear fission, tremendous amounts of energy can be produced from very small amounts of mass

2. Converting Mass into Energy a. Albert Einstein introduced the mass-energy equation: E = mc 2 b. According to the law of conservation of mass and energy, the total amount of mass and energy remains constant

3. Triggering a Chain Reaction a. Nuclear fission follows a pattern of a chain reaction b. Chain reaction: a continuous series of nuclear fission reactions [Fig 8 p.296]

c. Nuclear weapons are designed to have an uncontrolled chain reactions d. In controlled chain reactions, heat from the reaction can be used to generate electrical energy e. Critical Mass: the minimum amount of a substance that can undergo a fission reaction and can also sustain a chain reaction.

4. Nuclear Energy From Fission a. Nuclear power plants generate about 20% of electricity in the U.S. b. Controlled fission of uranium- 235 in a fission reactor c. Don ’ t emit air pollutants, but have other safety concerns d. 1986: meltdown of reactor at Chernobyl nuclear power plant in Ukraine

B. Fusion: the process in which smaller nuclei fuse together at high temperatures and release energy 1. In nuclear fusion, tremendous amounts of energy can be produced from very small amounts of mass 2. Releases more energy than nuclear fission

3. Requires extremely high temperatures—i.e. Sun reaches temp of 10,000,000 o C 4. Fusion may someday provide clean and efficient source of electricity

5. Two problems creating a fusion reactor: a. Need very high temperatures to start reaction b. Must contain plasma