Half Life Half Life Chart for Carbon14 Half
Half Life
Half- Life Chart for Carbon-14 Half -Life Years Fraction Left Percent Left 0 0 1/1 100% 1 5730 1/2 50% 2 11460 1/4 25% 3 17190 1/8 12. 5%
Detecting Radiation Geiger Counter Alpha Gas or beta particles hit the tube in the tube becomes charged Creates electrical pulse and makes a “click” sound
Geiger Counter Ionization of fill gas takes place along track of radiation (-) (+) Speaker gives “click” for each particle Metal tube (negatively charged) Window + e- e+ + + ee- Ionizing radiation path Atoms or molecules of fill gas Wilbraham, Staley, Matta, Waterman, Chemistry, 2002, page 857 Central wire electrode (positively charged) Free e- are attracted to (+) electrode, completing the circuit and generating a current. The Geiger counter then translates the current reading into a measure of radioactivity.
Geiger-Muller Counter Zumdahl, De. Coste, World of Chemistry 2002, page 614
Scintillation Counter Fluoresces when exposed to radiation The intensity of light can measure the amount of radiation Radon in basements can be detected with this. Radon gas builds up from uranium decaying in soil.
Half Life the time it takes for one half of a sample of a radioisotope to decay Every radioisotope has a different half-life length The longer a half life is the longer it takes to decay
Half-Life 20 g 10 g 5 g Start after 1 half-life Dorin, Demmin, Gabel, Chemistry The Study of Matter 3 rd Edition, page 757 after 2 half-lives 2. 5 g after 3 half-lives
b emissions 131 53 I 89. 9% 7. 3% 131 54 Half-Life g emissions 131 54 0. 500 mg 131 53 I 131 54 0. 750 mg Xe 0. 875 mg 0. 500 mg 131 53 0. 00 days I 0. 250 mg 8. 02 days 131 I 53 Dorin, Demmin, Gabel, Chemistry The Study of Matter 3 rd Edition, page 757 131 Xe 54 0. 125 mg 24. 06 days 16. 04 days + Xe* 0 b -1 + g Xe
Half-life of Radiation Radioisotope remaining (%) Initial amount of radioisotope 100 After 1 half-life After 2 half-lives 50 After 3 half-lives t 1/2 25 t 1/ 12. 5 2 0 t 1/2 1 2 3 Number of half-lives 4
Half-Life Plot Amount of Iodine-131 (g) 20 Half-life of iodine-131 is 8 days 15 1 half-life 10 2 half-lives 5 3 half-lives 4 half-lives etc… 0 0 Timberlake, Chemistry 7 th Edition, page 104 8 16 24 Time (days) 32 40 48 56
The half life of C-14 is 5730 years. If a sample originally contained 3. 36 g of C-14 how much is present after 22, 920 years?
The half life of C-14 is 5730 years. If a sample originally contained 3. 36 g of C-14 how much is present after 22, 920 years? Half -Life Time years sample 0 0 3. 36 g 1 5730 2 11460 3 17190 4 22920
algebra ln no nf 0. 693 t t 1/2 ln = natural log no = mass original sample nf= final sample mass t = total time t 1/2 = half life time
There are 3. 29 g of Iodine-126 remaining in the sample originally containing 26. 3 g of I-126. The half life of Iodine- 126 is 13 days. How old is the sample? Half -Life Time (days) sample 0 0 26. 3 1 13 days 2 3 4 3. 29
Lets try the same problem with the algebra formula. There are 3. 29 g of Iodine-126 remaining in the sample originally containing 26. 3 g of I-126. The half life of Iodine- 126 is 13 days. How old is the sample? Ln 26. 3 = 0. 693 (x) 3. 29 2. 078 * 13 =. 693 ln (7. 99) =. 693 x 13 days x = 38. 98 days This is a more exact method. 13
Gold-191 has a half life of 12. 4 hours. After one day and 13. 2 hours, 10. 6 g of Au-191 remains in a sample. How much Au-191 was originally present? Half -Life Time hours 0 0 1 12. 4 sample 2 3 4 37. 2 10. 6 g
Gold-191 has a half life of 12. 4 hours. After one day and 13. 2 hours, 10. 6 g of Au-191 remains in a sample. How much Au-191 was originally present? Half -Life Time hours sample 0 0 84. 8 g 1 12. 4 42. 4 2 3 4 21. 2 37. 2 10. 6 g
Algebraic Gold-191 has a half life of 12. 4 hours. After one day and 13. 2 hours, 10. 6 g of Au-191 remains in a sample. How much Au-191 was originally present? Ln x = 0. 693(37. 2 hr) 10. 6 g x = 12. 4 hr 2 nd ln(2. 079) 10. 6 x = 7. 996 x = 84. 76 grams 10. 6 This is a more exact method. so take the antilog
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