1. Chapter 18 Nuclear Reactions

2. Chemical Reactions Occur in the outer electron energy level
Valance electrons

3. Nuclear Reactions Occur in the nucleus of the atom
Involve the NUCLEONS
Nucleons = protons & neutrons

4. Strong Nuclear Force
Protons are positively charged and repel each other
←+ +→
Strong Nuclear Force = the force that causes the protons and neutrons in the nucleus to stick together and holds the nucleus tightly together.

5. Radioactivity
When the strong force of an atom is not strong enough to hold the nucleus together, then the atom tends to decay
The atoms are considered unstable, or radioactive
The process of decay is called radioactivity and in the process particles and energy are released and the atom is changed into another type of atom

6. ISOTOPES
Atoms of the same element with a different number of neutrons.
Ex: carbon-12 & carbon-14
Carbon-12
6 protons
6 neutrons
6 electrons
Carbon-14
8 neutrons
Carbon 12 is a stable isotope of carbon. Carbon-14 is unstable or radioactive because the addition of the two neutrons have disrupted the strong force and made the nucleus start to decay, or break apart.

7. 3 Types of Radioactivity Radioactive Decay
ALPHA PARTICLE (α)
BETA PARTICLE (β)
GAMMA RAYS (γ)

8. ALPHA PARTICLE 2 protons & 2 neutrons nucleus of a helium atom
weakest type of radiation
can be stopped by a piece of paper
12 inches max. distance travel

9. What happens to the numbers of particles in the nucleus after alpha decay?

10. BETA PARTICLE an electron emitted from around the nucleus
A neutron splits into a proton & electron
The electron is expelled out of the nucleus
The proton stays and increases the number of protons by one.
The atomic number of the element increases by one
The element changes into the next higher element on the periodic table.
100x stronger than an alpha particle

11. What happens to the numbers of particles in the nucleus after beta decay?

12. Gamma Rays An electromagnetic wave A packet of energy
The energy readjustment in the nucleus
Most powerful form of radiation
The sun is a great source of gamma radiation

13. Gamma Radiation, Cont
Gamma rays are very harmful to cells. They can damage the DNA of your cells and mutate them, which can cause cancer
High amounts of gamma ray exposure can cause death
Low amounts are normal and you are exposed to them all the time
Cannot be easily blocked. Inches of concrete lined with lead can stop a gamma ray

14. Gamma Ray Photography From Space

15. REMEMBER! Gamma rays are light!

16. Antoine Henri Becquerel
In 1896, radioactivity was first discovered.
Used uranium salts = placed them near a photographic film plate.
exposed the film (below)
Awarded Nobel Prize in 1903 in Physics

17. Pierre & Marie Curie (1898)
Discover the radioactive properties of radium & polonium
Together awarded the Nobel Prize in 1903 (physics) along with Henri Becquerel
Marie is award a second Nobel Prize in 1911 (chemistry)
Pierre is killed in an accident in 1906, Marie continues working with radioactive substances. She eventually dies of cancer

18. Transmutation
= changes from one element to another element during α and β decay.
Alpha Decay = mass number decreases by 4 and the atomic number decreases by 2
Beta Decay = mass number does not change and the atomic number increases by 1

19. Alpha Decay Uranium-238 has 92 protons
After alpha decay (2 protons & 2 neutrons leave the nucleus)
Becomes Thorium-234 and has 90 protons

20. Beta Decay Carbon-14 has 6 protons & 8 neutrons
After beta decay (a neutron is split into a proton and electron & the electron is expelled from the nucleus)
Becomes Nitrogen-14 and has 7 protons and 7 neutrons

21. Half Life
= the time it takes for one half of the mass of a radioactive substance to decay.
Ex: carbon-14 = 5730 years
100 gram sample
In 5730 yrs = 50 grams C-14 & 50 grams N-14
In11,460 yrs = 25 grams C-14 & 75 grams N-14
In 17,190 yrs = 12.5 grams C-14 & 87.5 grams N-14

22. Radioactive Dating
Half life is used by scientists to find out how old a fossil or a rock is
Carbon 14 is often used to date fossils
What type of isotope used depends on the material being dated
Uranium is often used to date rocks because many rocks contain uranium already

23. Detecting Radioactivity
Cloud chambers track alpha and beta particles
Chamber is filled with a cloud of vapor
Alpha particles leave short thick trails
Beta particles leave long thin trails

24. Bubble Chamber
Holds a super heated liquid that doesn’t boil due to high pressure
When a radioactive particle passes through the liquid, trails of bubbles form

25. Geiger Counter Pops or clicks in the presence of radiation
Uses electricity and current to cause a flow of electrons
The current is amplified to produce a clicking sound

26. Background Radiation You are exposed to radiation every day
Sources of background radiation vary and amounts are usually not harmful

27. Nuclear Reactions
Nuclear Fission
Nuclear Fusion

28. Nuclear Fission the splitting of the nucleus into two smaller nuclei
Neutrons are used to split the nucleus
Additional neutrons are released to continue on to hit/split other nuclei

29. Chain Reactions
Critical Mass (required) = concentration of radioactive atoms in a sample.
Controlled Chain Reaction = many of the neutrons that are produced are absorbed in “control rods” prevent excess energy to be released.
Ex. Nuclear Power Plants
Uncontrolled Chain Reaction = all the neutrons are allowed to continue to hit/split other nuclei causing massive amounts of energy to be released all at once.
Ex. Atomic Bomb (used on Japan in 1945)

30. Controlled Chain Reaction

31. Generating Electricity
Nuclear power is only one way to generate electricity
It is often cheaper and easier than other forms of energy (ie using wind or coal or water)
However, there are safety concerns that you must take into consideration

32. Nuclear Reactors Used to generate electricity
Used to power ships, submarines
Risk of meltdown, must be kept cool to prevent uncontrolled chain reactions

33. Nuclear Reactor

34. Three Mile Island Accident
March 28, 1979– Harrisburg PA– Three Mile Island Nuclear Power Plant: A partial meltdown occurred in one reactor due to a stuck valve. Negligible amounts of radiation were released into the environment

35. Chernobyl - April 26,1986 Power Plant in the Ukraine
Explosion and fire that was caused by a power surge
31 people died of acute radiation sickness
You still can’t live in that area today
Crops were affected, many cases of cancer recorded, especially in children

36. Chernobyl
Pripyat, Ukraine

37. Fukushima - March 11, 2011
Ongoing nuclear accident in Japan at the Fukushima power plant
Caused partial or full meltdown to reactor, thanks to earthquake and Tsunami
Power failure to coolant main cause
Effects of the disaster are ongoing and unknown at this time

38. Uncontrolled Chain Reaction

39. Nuclear Fusion
= the joining of two smaller nuclei into a single larger nucleus
Powers the sun, very hard to duplicate on Earth because of the high pressure and temperature needed
Extremely more powerful release of energy than fission
Also known as a thermonuclear reaction
ex: H-bomb and the sun/stars

40. Fusion Explosions