4.4 Unstable Nuclei and Radioactive Decay

Types of Radiation and Unstable Nuclei I. Chemical and Nuclear Reactions Chemical reactions only involve an atoms electrons Nuclear reactions involve changing an atoms nucleus Nuclear reactions release a million times more energy than chemical reactions Unlike chemical reaction, nuclear reactions are not affected by temperature, pressure, or a catalyst. II. Nuclear Vocabulary Radioactivity the process of emitting radiation. Radiation - rays and particles emitted by a

radioactive source. Radioisotopes isotopes of atoms with unstable nuclei and emit radiation to obtain a more stable nuclei Radioactive decay - Unstable nuclei losing energy by emitting radiation in a spontaneous process. Nucleon refers to both protons and neutrons III. Which Isotopes are Radioactive? Small Nuclei - Atoms which contain up to 20 protons (up to Calcium) are usually stable. Large Nuclei - Larger nuclei tend to be radioactive. All nuclei with 84 or more protons (Polonium and up) are radioactive. For example, all

isotopes of Uranium are radioactive. Atoms with more neutrons than protons - There are radioactive nuclei that have less than 84 protons. These nuclei have more neutrons than protons. For example, Carbon-12 (6 protons and 6 neutrons) is stable, while Carbon-14 (6 protons and 8 neutrons) is radioactive. IV. Why Does an Atom Undergo Radioactive Decay? Radioactive atoms emit radiation because their nuclei are unstable. The stability of the nucleus

depends on the neutron to proton ratio Neutrons vs. protons graph stable nuclei found in a region called the band of stability. V. Types of Radiation Alpha Radiation Alpha radiation are attracted to the negatively charged plate Alpha particles contain two protons and two neutrons (A helium nucleus) Blocked by paper Least penetrating form of radiation (only travels a

few centimeter in the air) Carry +2 charge 4 4 Symbolized by 2 He or 2 VI. Types of Radiation Beta Radiation Beta radiation attracted to the positively charged plate Carry 1 charge Beta particles are fast moving electrons Blocked by metal foil or wood Medium penetration power (travels a few

meters in the air) Symbolized by -10 e or -10 VII. Types of Radiation Gamma rays Gamma rays are high energy radiation that possess no mass. Possess no electrical charge and are not deflected by magnetic or electrical fields. Not completely blocked by lead or concrete The most penetrating and damaging type of radiation Carry no charge0 Symbolized by

0 IX. Electrostatic Force Electrostatic force is when like charges repel and opposite charges attract. X. Strong Nuclear Force The strong nuclear force or nuclear force is an attractive force that acts between all nuclear particles that are extremely close together. It keeps the nucleus together.

Remember Mass Number and Atomic Number Mass number Atomic number 14 6 C XI. Writing and Balancing Nuclear Equations In a balanced nuclear equation, mass numbers

and atomic numbers are conserved. Example 226 4 230 90 Th 88 Ra + 2 He Notice the mass numbers and atomic numbers add up to the same on both sides of the equation VIII. Electron Capture Electron capture occurs when a nucleus of an atom draws in an electron.

81 37 Rb + - 01 e 81 36 Kr Also known as Beta capture

Practice 1. 97 40 2. 218 84 Zr 0

-1 Po 4 2 3. ? 4. 47 20 5.

244 96 222 86 e + ? Ca Cm 4 2

Nb 214 82 Pb He 226 88 Ra

e + ? 47 21 Sc 240 94 Pu He + ?

Rn + 0 -1 97 41 4 2 He + ?

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