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7.2 Half-Life What will we learn?
-What are daughter isotopes?-What is the decay curve?-What is half-life?-What are parent isotopes?-What is radiocarbon dating?
Half-Life is the time it takes for half of the mass of a substance to decay.Shows the rate of radioactive decay for different isotopes.Short half-life = Fast decay rateKnowing the half-life of an isotope allows radioisotope dating to be possible
7.2 Half-Life
A decay curve shows the decay rate for radioisotopesGraphing any isotope’s decay rate will produce the same curve, the only difference is how long the half-life is
Decay Curve
The parent isotope = isotope that undergoes radioactive decayThe daughter isotope = stable product of radioactive decayIt may take several decays for a parent isotope to produce stable daughter isotopesThe most common of these parent/daughter pairs are shown in the Common Isotope Pairs ChartThese isotopes can all be used in radioisotope dating, for various dating ranges
Parent & Daughter Isotopes
This is the method used to date organic materialUses the isotope carbon-14, which has a half-life of 5730 years, and decays into nitrogen-14Can date material up to 50000 years old
Radiocarbon Dating
7.2 Quiz1. How much of a sample of 100g of Carbon-14 will be
left after 22920 years?a) 50g b) 25g c) 12.5g d) 6.25g
2. What is the daughter isotope of Uranium-235 when it decays?
a) nitrogen-14 b) lead-207c) argon-40 d) lead-206
7.2 Answers1. How much of a sample of 100g of Carbon-14 will be
left after 22920 years?a) 50g b) 25g c) 12.5g d) 6.25g
2. What is the daughter isotope of Uranium-235 when it decays?
a) nitrogen-14 b) lead-207c) argon-40 d) lead-206
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7.3 Nuclear Reactions What will we learn?
-What is a chain reaction?-What is fission?-What is fusion?-What is a nuclear equation?-What is a nuclear reaction?
Nuclear FissionThe splitting of a nuclei into two smaller nuclei, subatomic particles and energyHeavy nuclei are unstable because of protons’ repulsive forcesMay split into smaller atoms to become stableAll nuclear power generation comes from nuclear fissionNuclear waste must be stored away for hundreds of thousands of years
Nuclear FusionThe joining of two nuclei to form a larger nucleiHappens in the core of starsRequires high pressure and temperatureIn our Sun, hydrogen-2 and hydrogen-3 fuse into helium-4Currently not a feasible way of generating electricity
Nuclear ReactionA reaction that changes the nucleus of an atomGains or releases particles or energyCan release electrons, protons, neutrons, or gamma raysSmall change of mass = Large change of energy
Chain ReactionOne reaction starts the next reactionReaction continues on its ownReleases a large amount of energy, possibly leading to an explosion if not controlledCan be controlled by materials that absorb neutrons, such as cadmium
Nuclear EquationSum of mass numbers on both sides of the equation must be equalSum of charges/atomic numbers on both sides of the equation must be equal
Equation for nuclear fission of uranium-235:
Equation for nuclear fusion of hydrogen-2 and hydrogen-3:
7.3 Quiz1. What is the missing atomic mass?a) 6 b) 7 c) 14 d) 15
2. What is the missing atomic number?a) 92 b) 90 c) 93 d) 234
3. What type of radiation caused Bruce Banner to turn into the Hulk?
a) Alpha b) Beta c) Gamma d) Neutron
7.3 Answers1. What is the missing atomic mass?a) 6 b) 7 c) 14 d) 15
2. What is the missing atomic number?a) 92 b) 90 c) 93 d) 234
3. What type of radiation caused Bruce Banner to turn into the Hulk?
a) Alpha b) Beta c) Gamma d) Neutron
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