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Transcript

Radioactivity Topic Many atoms have an unstable nucleus. Such atoms are said to be radioactive and will undergo decay. All radioactive isotopes (radioisotopes) will turn into stable atoms by decaying, but as they do so they give out radiation. Radiation consists of 3 types of particles: Summary table Particle Description How it affects the atom Alpha A Helium When an nucleus alpha Symbol 4 particle He is lost the 2 atoms Contains: mass no. 2 protons decreases 2 neutrons by 4 and the atomic no. decreases by 2. What stops it Skin or paper It has little penetrating power. Beta This is a fast moving electron. Just like an electron it has no mass but a charge of -1 When a beta symbol particle is lost the atoms mass stays the same. The atomic no. increases by 1. Gamma High energy A gamma rays rays has symbol no affect on mass or atomic no. Examples of Radioactive equations: ALPHA DECAY Thin sheets of aluminium metal (mm) thick Travels several metres. Only stopped by thick sheets of lead or concrete. 241 Am + Alpha particle 95 Complete the equation: 241 Am 95 237 Np + 93 4 He 2 NOTE: THE ATOMIC NO. DECREASES BY 2 AND MASS NO. DECRESES BY 4. # Note both sides of the equation are equal: mass numbers and atomic numbers add up. BETA DECAY 14 C 6 + Beta particle Therefore: 14 C 6 14 N + 7 0 e -1 NOTE: THE ATOMIC NUMBER INCRESES BY 1 Complete the following: What is formed when an alpha particle is given off from? 239 Pu 94 238 U 92 232 Th 90 What is formed when a beta particle is given off from? 234 Th 90 212 Pb 82 131 I 53 Complete questions 1-3 page 209 Half Life Definition: This is the time taken for a radioactive substance to decay to half its original value. Example: If the half life for A is 24 days. How long will it take to decay to 6.25 % 100% A 50% A 25% A 12.5% A There are 4 half life values to get from 100%- 6.25% 6.25% A 4 X 24 days = 96 days Questions: 1. Find the time taken for B to decay to 12.5% if the half life is 27 hours? 2. What is the half life if the time taken to decay to 1/16th of its orginal value is 128 years? Summaries radiation What is nuclear fission the uses of ionising