Unstable Nuclei and Radioactive Decay Radioactivity – spontaneous emission of radiation Radiation – rays and particles emitted from a radioactive material Nuclear reaction – A reaction that involves a change in an atom’s nucleus Radioactive decay – a spontaneous process where unstable nuclei lose energy by emitting radiation

Types of Radiation Alpha radiation – radiation deflected toward a negatively charged plate (positive radiation) Alpha (α) particle – contains two protons and two neutrons; a helium nucleus Beta radiation – radiation deflected toward a positively charged plate (negative radiation) Beta (β) particle – an electron with a 1- charge Gamma (γ) ray – high-energy radiation with no mass; a high energy photon

Alpha, Beta, Gamma

Alpha is large and can be easily stopped Beta is smaller and is more difficult to stop Gamma is a photon and can pass through most things

Nuclear fission vs. fusion Nuclear fission – the splitting of a nucleus into smaller, more stable fragments, accompanied by a large release of energy – Splits the atom – e.g. atom bomb Nuclear fusion – the process of binding smaller atomic nuclei into a single, larger, and more stable nucleus – Fuses two atoms together – e.g. the Sun fuses hydrogen atoms into helium

Nuclear Fission

Nuclear Fusion

Half-life The time required for one-half of a radio- isotope’s nuclei to decay into its products Parent particle – the original radio-isotope Daughter particles – the products of radioactive decay

Formula for Half-Life Formula: N = N 0 (1/2) n – N is the remaining amount – N 0 is the initial amount – n is the number of half-lives that have passed. – n = t/T, where t is the amount of time passed and T is the half-life. Example (pg. 872) – You are given a known mass of a radioisotope with a known half-life. You must first determine the number of half-lives that passed during the 33-year period. Then use the exponential decay equation to calculate the amount of the sample remaining.

Example Initial amount. N 0 = mg Elapsed time. t = 33 years Half-life. T = 11 years First, solve for n = t/T. – 33 years / 11 years = 3. n = 3. N = N 0 (1/2) n N = (2.000)(1/2) 3 N = (2.000)(1/8) N = mg

Try for yourself Try pg. 872 #9 and #10. We will work on #11 together after you’ve tried these.