1. 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?
2. 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 rate
Knowing the half-life of an isotope allows
radioisotope dating to be possible
7.2 Half-Life
3. A decay curve shows the decay rate for
radioisotopes
Graphing any isotope’s decay rate will produce the
same curve, the only difference is how long the
half-life is
Decay Curve
4. The parent isotope = isotope that undergoes radioactive decay
The daughter isotope = stable product of radioactive decay
It may take several decays for a parent isotope to produce stable
daughter isotopes
The most common of these parent/daughter pairs are shown in the
Common Isotope Pairs Chart
These isotopes can all be used in radioisotope dating, for various
dating ranges
Parent & Daughter Isotopes
5. This is the method used to date organic material
Uses the isotope carbon-14, which has a half-life
of 5730 years, and decays into nitrogen-14
Can date material up to 50000 years old
Radiocarbon Dating
6. 7.2 Quiz
1. 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-207
c) argon-40 d) lead-206
7. 7.2 Answers
1. 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-207
c) argon-40 d) lead-206
9. 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?
10. Nuclear Fission
The splitting of a nuclei into two smaller nuclei,
subatomic particles and energy
Heavy nuclei are unstable because of protons’ repulsive
forces
May split into smaller atoms to become stable
All nuclear power generation comes from nuclear fission
Nuclear waste must be stored away for hundreds of
thousands of years
11. Nuclear Fusion
The joining of two nuclei to form a larger nuclei
Happens in the core of stars
Requires high pressure and temperature
In our Sun, hydrogen-2 and hydrogen-3 fuse into
helium-4
Currently not a feasible way of generating
electricity
12. Nuclear Reaction
A reaction that changes the nucleus of an atom
Gains or releases particles or energy
Can release electrons, protons, neutrons, or
gamma rays
Small change of mass = Large change of energy
13. Chain Reaction
One reaction starts the next reaction
Reaction continues on its own
Releases a large amount of energy, possibly
leading to an explosion if not controlled
Can be controlled by materials that absorb
neutrons, such as cadmium
14. Nuclear Equation
Sum of mass numbers on both sides of the
equation must be equal
Sum 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:
15. 7.3 Quiz
1. 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
16. 7.3 Answers
1. 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
