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
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)
ALPHA DECAY OF URANIUM
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.
CARBON-DATING!! C-14
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)?
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?