section 3: radioactive decay and half-life. the spontaneous emission of rays or particles from...
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UNIT 14: NUCLEAR
CHEMISTRYSection 3: Radioactive Decay and
Half-Life
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RADIOACTIVE DECAY The spontaneous emission of rays or
particles from certain nuclei as they “decay,” such as Uranium.These rays or particles are called nuclear radiation.
They come in three types: Alpha Radiation: Helium nucleus; 2+ Charge;
Low power (0.05 mm body tissue) Beta Radiation: electron; 1- Charge;
Moderate power (4 mm body tissue) Gamma Radiation: electromagnetic wave;
neutral charge; High Power (penetrates entire body easily)
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ALPHA DECAY OF URANIUM
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HALF-LIFE While the process is spontaneous, it is not instantaneous… it takes time!
The time required for HALF of the atoms of a radioactive substance to decay is called a half-life.
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CARBON-DATING!! C-14
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EXAMPLE: FLUORINE-18 Fluorine 18 ( F) has a half-life of 110 seconds. This material is used extensively in medicine. The hospital laboratory begins the day with 10 grams of F…
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1 half-life = 110 seconds
660 seconds110 seconds
= 6 half-lives
HOW MANY HALF-LIVES OF F-18 OCCUR IN 11 MINUTES (660 SEC)?
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6 half-lives = 10 divided in half, 6 times1) 10/2 = 5 grams2) 5/2 = 2.5 grams3) 2.5/2 = 1.25 grams4) 1.25/2 = 0.625 grams5) 0.625/2 = 0.3125 grams6) 0.3125/2 = 0.15625 grams
After 11 minutes, only 0.16 g of the 10 g sample remain!!!!!!
HOW MUCH OF THE 10-GRAM SAMPLE WOULD BE LEFT AFTER 11 MINUTES?