1. Atomic: Nuclear Reactions 2018
Unit 4:
Physical Science , 4
Geo Ch

2. Nuclear Chemistry
Nuclear Decay
Nuclear Reactions
Alpha Decay
Beta Decay
Gamma Decay
Fission
Fusion

3. Golden Ratio: Stable and Unstable Nuclei
Smaller elements neutron to proton ratio is 1:1 to be stable isotopes
Example: Helium, Nitrogen, Oxygen
Heavier elements neutron to proton ratio is 3:2 to be stable isotopes
Example: Iron, Nickel, Copper, Zinc
Larger nuclei tend to be unstable – all nuclei containing more than 83 protons are radioactive
All elements with more than 92 protons are synthetic and decay soon after they are created (UNSTABLE)
Nuclei of any isotopes that differ much from these ratios are unstable, whether heavy or light

4. Physics - Radioactivity: The Discovery of Radioactivity
Radiation
When a nucleus becomes unstable, it is said to be radioactive. It decays releasing particles and energy called nuclear radiation
Some radiation is more powerful than others
There are four types of nuclear radiation –
alpha (α) – made of 2 p+ and 2 n0
beta (β- and β+)
n0 decays into p+ and e- (beta minus)
p+ decays into n0 and e+ (beta plus)
gamma (γ) – no mass or charge, just energy
Types of Radioactive Decay (great resource comparing/contrasting)

5. What kind of decay will occur?

6. 4 Types of Radiation, cont
Particle Type
Alpha
Beta
Gamma
Symbol
Mass
Charge
Penetration
Stopped by thin layer of material
Stopped by thick materials
Only stopped by very thick materials
2 4 He or α β γ 4
0.0005 +2
-1, +1

7. Prior Knowledge
Isotope Notation

8. Alpha Decay Alpha radiation is made of alpha particles
Alpha particles are made of two protons and two neutrons (a Helium atom!)
They are represented by: α
Properties:
Large size
Cannot pierce deep into matter – easily stopped by a thin layer of material
When alpha decay occurs, the nucleus loses 2p+ and 2n0
Atomic number is 2 less
Mass is 4 less

9. Beta Decay (+ or -) Beta radiation is made of beta particles
Beta particles are made of a high energy electron
They are represented by: β+ or β-
Properties:
Small and light
Move fast
Can only be stopped by thick materials, like stacked sheets of metal, blocks of wood or heaving clothing
When Beta + decay: a proton turns into a neutron and a β+ is emitted
Atomic number is 1 less
Mass number is same
When Beta - decay occurs, a neutron changes into a proton and a β- is emitted
Atomic number is 1 more
Beta plus (positron, which is a positively charged electron) and Beta minus (electron)

10. Gamma Decay Gamma radiation is made of gamma rays
Gamma rays are a high-energy form of electromagnetic radiation
They are represented by: γ
Properties:
No mass or charge
Can pass through most types of materials – need a material thicker than blocks of concrete
When gamma radiation occurs, only energy is given off
Usually occurs along with another type of decay
Atomic number is same
Mass number is same

11. Half-Life Spontaneous: you cannot predict when each atom will decay
Random: you cannot predict which atom will decay
But, each radioisotope has a predictable half-life
Half-life: amount of time it takes for half of the nuclei in a radioactive isotope to decay
Original, unstable substance = parent
New, (stable or unstable) substance = daughter
After 1 half-life 50% of parent isotope has decayed into a daughter isotope
Overall rate of decay is constant
This allows you to predict when a given fraction of the sample will have decayed
Reference penny lab. I cannot predict which round the penny will flip. I cannot predict which penny will flip this round. But I know that each round, about half of the pennies will have flipped.

12. Half-Life Values and Graph

13. Half-Life Values and Graph
½ or 1:1 ratio
¼ or 1:3 ratio
1/8 or 1:7 ratio

14. Carbon 14-Dating radiocarbon dating
Carbon-14 is widely used to determine the ages of fossils
All organisms take in carbon during lifetime
Most of this carbon is the isotope carbon-12
1 in every million is the radioisotope carbon-14
When an organism dies, carbon is no longer being taken in
The amount of carbon-14 slowly decreases
the half-life of carbon-14 is short compared to ages of many fossils and geological formations
Objects more than 60,000 years old cannot be dated using carbon-14
radiocarbon dating

15. Check for Understanding
What fraction of the parent isotope is left after 9 half-lives?
What is the half-life of the element below?

16. Practice Example Problem:
228 Ac has a half life of 6.0 hours. How much of a 5.0 mg sample would remain after one day (24 hours)?
The first step is to determine the number of half lives that have elapsed.
number of half lives = total time / half-life
= 24 hours/6.0 hours = 4.0 half lives
For each half life, the total amount of the isotope is reduced by half.
Amount remaining = Original amount x half-life %
= 5.0 mg x 6.25% = 0.31 mg

17. Practice
Americium-242 has a half-life of 6.0 hours. If you started with 24 g and you now have 1.5 g, how much time has passed?
24 g  12 g  6.0 g  3.0 g  1.5 g st ½ nd ½ rd ½ th ½ 4.0 ½ lives x 6.0 hrs = 24 hrs
The half-life of cobalt-60 is 5.0 years. If you have 10. grams of Co-60, how much do you have after 15 years?
15 years ÷ 5.0 years = 3.0 half lives
10. g  5.0 g  2.5 g  1.25 g 1st ½ 2nd ½ 3rd ½

18. KEY TERMS: Ch 10.4 Nuclear Reactions
Nuclear Fission – the process of splitting a nucleus into two nuclei with smaller masses
Chain reaction – ongoing series of fission reactions
Critical mass – the amount of fissionable material required so that each fission reaction produce approximately one more fission reaction
Nuclear Fusion – two nuclei with low masses are combined to form one nucleus of larger mass
Fission and Fusion Video (~4 minutes)
KEY TERMS: Ch 10.4 Nuclear Reactions

20. Nuclear Fission Fission means “to divide”
The process of splitting a nucleus into two nuclei with smaller masses
This occurs when a neutron hits the nucleus of an atom
Only large nuclei can undergo fission reactions
Two uses from book: generate electricity, nuclear weapons
The total mass of the products is slightly less than the mass of the original nuclear and the neutrons that break free
The missing mass is converted into large amounts of energy

21. Nuclear Fission Lighter element Neutrons + Energy Neutron
Uranium - 235
Lighter element

22. Nuclear Fission
Chain reactions are continuing series of reactions in which each produces a product that can react again
If chain reaction occurs too quickly, explosions occur, releasing a lot of energy all at once
energy
energy
energy
energy
energy
energy

23. Fission of Uranium-238

24. Nuclear Fusion Fusion = combine
Nuclear Fusion is when two or more nuclei combine to form a larger nucleus (requires very high temps to overcome the repulsive forces)
The sun uses this process to produce energy
It fuses hydrogen into helium
The problem lies in the energy involved to start fusion
Most nuclei that can undergo fusion are fairly unreactive
Energy given off (output) does not outweigh the energy needed (input)
Hydrogen Bomb
Just like in fission, a small amount of mass is converted into a large amount of energy

25. Fusion of Hydrogen into helium

26. Nuclear Fusion
positron
energy
neutrino
positron
energy
neutrino

27. Energy to Mass Conversions
Think back to the law of conservation of energy
We need to include mass in this law when talking about fission and fusions reactions
This relationship is shown by Einstein’s theory of relativity
This states that energy and mass are equivalent and can be converted using the equation E=mc2

28. Extra Practice What type of nuclear reaction shown below?
Write an equation for the reaction. You only need to include the symbol and mass number.
What type of nuclear reaction is shown below?

29. Extra Practice
Gold-198 has a half-life of 2.7 days. How much of a 96 g sample of gold-198 will be left after 8.1 days?
What is the half-life of a g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 20.0 s? (Hint: 12.5 is 12.5% of 100.0, so figure out what fraction that is!)
The half-life of Zn-71 is 2.4 minutes. If one had g at the beginning, how many grams would be left after 7.2 minutes has elapsed?

30. Review: Types of Radioactive Decay and Nuclear Equations
Videos:
Types of Radioactive Decay and their effects on the Nucleus
Balancing Nuclear Equations and Predicting Products of Nuclear Reactions