HalfLife Calculating HalfLife Every radioisotope has a characteristic

Half-Life Calculating

Half-Life • Every radioisotope has a characteristic rate of decay measured by its half-life • Half-life is the time required for one-half of the nuclei of a sample to decay

Half-Life # of ½ lives 0 1 2 % Remaining 100% 50% 25% 3 4 12. 5% 6. 25%

Half-Life • For example, suppose you have 10. 0 grams of strontium-90, which has a half life of 29 years……. . # of ½ lives Time Amount (Years) Remaining How much (g) will be remaining 0 0 10 after 3 half-lives have passed? 1 29 5 Use a table like this (or an equation) Equation: time in total time of decay = # half lives x 1 half life 2 3 4 58 87 116 2. 5 1. 25 0. 625 4

Half life by ratios…. After 1 half life - - - 1/2 of sample remains After 2 half lives - - -1/4 of sample remains After 3 half lives - - - 1/8 of sample remains After 4 half lives - - - 1/16 of sample remains and so on…… • Equation: time in total time of decay = # half lives x 1 half life • •

Half-life How do I find out how many half-lives have passed? final sample original sample = 25 g 1 EXAMPLE: 100 g = 4 = 2 2 half lives have passed

Half-Life • Example: If 100 grams of Carbon-14 decays to only 25 g of Carbon-14 after 11, 460 years, what is the half-life of Carbon 14? amt of time • total time of decay = # half lives x 1 half life amt. of time total time of decay 1 half life = number of half lives final sample 25 g 1 original sample = 100 g = 4 = 2 half lives passed 11, 460 yrs 2 half lives = 5, 730 yrs for one half life