1. Nuclear Chemistry

2. 10.1 Radioactivity
Radioactivity: process in which an atomic nucleus emits charged particles and energy

3. Radioisotope: any atom containing an unstable nucleus

4. During nuclear decay, atoms of one element can change into atoms of a different element altogether
Uranium – 238 decays into Thorium – 234 (also a radioisotope)   

5. Common nuclear radiation types
Nuclear Radiation: charged particles and energy that are emitted from the nuclei of radioisotopes
Common nuclear radiation types
alpha particle
beta particle
gamma rays

6. Alpha Decay
Alpha Particle (): a positively charged particle made up of 2 protons and 2 neutrons (the SAME as a HELIUM NUCLEUS)
Common symbol = 

7. Example of alpha decay of uranium – 238

8. Dangers of Nuclear Radiation
Least penetrating type of nuclear radiation, can be stopped by sheet of paper or clothing

9. Beta Particle (): an electron emitted by an unstable nucleus
Beta Decay
Beta Particle (): an electron emitted by an unstable nucleus
Written as: 
Assigned atomic # of -1 mass of 0 (zero)
How can a nucleus (which is positive), emit a negatively charged particle?

10. During beta decay, a neutron
decomposes into a proton and an e-

11. Proton stays trapped in the nucleus, e- released

12. Example of beta decay of thorium –234

13. Product isotope has 1 proton more and 1 neutron fewer than the reactant isotope
Mass number of the isotopes are equal because the emitted beta particle has essentially NO MASS

14. Beta particles pass through paper, but stopped by thin sheet of metal

15. Gamma Decay
Gamma Ray (): a penetrating ray of energy emitted by an unstable nucleus

16. Gamma Decay
NO mass and NO charge
 During Gamma Decay:
Atomic number and mass number of the atom remains the same
Energy of nucleus decreases

17. Gamma decay often accompanied by alpha or beta decay
Example of thorium – 234 emitting both beta particles and gamma rays as it decays:

18. Gamma rays much more penetrating – takes several centimeters of lead or several meters of concrete to stop gamma radiation

20. Effects of Nuclear Radiation
Background Radiation: nuclear radiation that occurs naturally in the environment

21. When nuclear radiation exceeds background levels, it can damage the cells and tissues of your body

23. Effects of Nuclear Radiation
Nuclear radiation can ionize atoms (when cells are exposed to nuclear radiation, the bonds holding together proteins and DNA molecules may break cells may no longer function properly)

24. Effects of Nuclear Radiation
, , and  are all forms of ionizing radiation
The extent of the damage of external nuclear radiation is dependent on the penetrating power of the radiation…

25. Beta particles cause more damage than alpha particles, but less than gamma rays
Gamma rays can penetrate deeply into the human body, potentially exposing all organs to ionization damage

26. Detecting Nuclear Radiation
Although you can’t see, hear, or feel the radioactivity around you, scientific instruments can measure nuclear radiation
Geiger Counters
Film Badges

27. 10.2  Rates of Nuclear Decay

28. Nuclear Decay
By studying the radioactive nuclei of an object we can determine how old the object is.
Because most materials contain at least trace amounts of radioisotopes, scientists can estimate how old they are based on rates of nuclear decay.

30. Half-Life
Half-life: the time required for one half of a sample of a radioisotope to decay
After one half-life, half of the atoms in a radioactive sample have decayed, while the other half remain unchanged
After two half-lives, half of the remaining have decays, leaving one quarter of the original sample unchanged

31. Half-Life Example Iodine Half-life= 8.07 days
After one half-life (8.07 days) half of the original sample remains
After 2 half-lives (16.14 days) one quarter of the original remains
After 3 half-lives (24.21 days) one half of one quarter remains, or 1/8 (one eighth)
…and so on

32. Half-Lives Vary
Half-lives can vary from fractions of a second to billions of years
Unlike chemical reaction rates, which vary with the conditions of a reaction, nuclear decay rates are constant!!!

33. Radioactive Dating
Method used for determining the age of objects using the half-lives of Carbon – 14
Radiocarbon dating: determining the age of an object by comparing its carbon-14 levels with carbon-14 levels in the atmosphere. 

34. Radioactive Dating Carbon-14 has a half-life of 5,730 years.
Carbon-14 is formed in the upper atmosphere when neutrons produced by cosmic rays collide with nitrogen-14 atoms.
The radioactive carbon-14 undergoes beta decay to form nitrogen-14.

37. Using Carbon-14 to Date
Living organisms absorb the carbon (CO2) from the atmosphere, but when they die they stop absorbing it and the levels do not change.
From this point levels start to decrease as the radioactive carbon decays.
The levels in the object are then compared with levels in the atmosphere. 

38. Example: if an object has half the amount of carbon-14 in it as in the atmosphere, then we know the object is about 5, 730 years old (which is one half-life for carbon-14)  

40. Carbon-14 Dating
Carbon-14 or radiocarbon dating can be used to date any carbon-containing object less than 50,000 years old.  
After this point, there is too little carbon-14 left to be measurable  
Objects older than this use radioisotopes with longer half-lives  
The older the object the lower the levels of radioisotopes present  

42. 10.3 Artificial Transmutation

43. Transmutation
Transmutation: the conversion of atoms of one element to atoms of another.  
It involves a nuclear change, not a chemical change.  
Transmutations can either occur naturally (nuclear decay) or artificially.  
Scientists can perform artificial transmutations by bombarding atomic nuclei with high-energy particles such as protons, neutrons, or alpha particles.  

44. Transuranium Elements
Transuranium Elements: Elements with atomic numbers greater than ­92 (uranium)  
All transuranium elements are radioactive and generally not found in nature  
Scientists can create a transuranium element by the artificial transmutation of a lighter element  
Useful transuranium elements  
Americium-241: used in smoke detectors  
Plutonium-238: energy source for space probes

46. Particle Accelerators
Sometimes transmutations will not occur unless the bombarding particles are moving at extremely high speeds.  
To achieve these high speeds scientists use particle accelerators.  

47. Particle Accelerator
These accelerators move charged particles at speeds very close to the speed of light
The particles are then guided toward a target, where they collide with atomic nuclei and transmutations are allowed to occur
These collisions have also lead to the discovery of more subatomic particles
Quarks: protons and neutrons are made up of these even smaller particles

48. Large Hadron Collider (LHC)

49. 10.4  Fission & Fusion

50. Question What holds the nucleus together?
It’s full of positive particles, so why don’t they push each other away?
What keeps the protons and neutrons together?
Clearly, there must be an attractive force that binds the particles

51. Answer
Strong Nuclear Force: the attractive force that binds protons and neutrons together in the nucleus
Over very short distances, the strong nuclear force is much greater than the electric forces among protons

52. Forces in the Atom

53. Electric Force
Question: What determines the strength of the electric force?
Answer: The number of protons

54. Electric Force
The greater the number of protons, the greater is the electric force that repels the protons
Larger nuclei have a stronger repulsive force than a smaller nuclei
As a result, the nucleus will become unstable (or radioactive) when the strong nuclear forces can’t overcome the repulsive electric forces among protons.

55. Nucleus Size & Radioactivity
Because of the size issue, there is a point beyond which all elements are radioactive.
Once they become large enough, the repulsive forces overcome. This occurs with all nuclei with 83 or more protons.
Therefore, all elements with an atomic number greater than 83 are radioactive!

56. Fission
FISSION: the splitting of an atomic nucleus into two smaller parts
In nuclear fission, tremendous amounts of energy can be produced from very small amounts of mass

57. Converting Mass into Energy
During a fission reaction, some of the mass of the reactants is lost!
The Law of Conservation of Mass says this is illegal, highly illegal!
This “lost” mass is converted into energy!

58. Converting Mass into Energy
Since we bent the law a little…we use a revised version of the law: Law of Conservation of Mass and Energy
It basically says: The total amount of mass and energy remains constant!!!

60. E = mc2
30 years before the discovery of fission, Albert Einstein introduced the mass-energy equation.  
E=mc2describes the relationship between mass and energy:
E = energy
m = mass
c = the speed of light (3.0 x 108m/s) 
It shows that the conversion of a small amount of mass releases an ENORMOUS amount of energy. 

61. Lots of Energy!!!
Example: the explosion of the first atomic bomb contained 5kg of plutonium, but created an explosion equivalent to18, 600 tons of TNT!!!  
So, since we bent the law a little, just a little, we use a revised version of the law:
This law is referred to as the Law of Conservation of mass and energy.
It basically says:
THE TOTAL AMOUNT OF MASS AND ENERGY REMAINS CONSTANT!

62. Chain Reaction
Nuclear fission reactions act like rumors being spread throughout school:
One person tells a few friends, they tell a few friends, and on and on…
During a fission reaction each reactant nucleus splits into 2 smaller nuclei and releases 2-3 neutrons.
If one of these neutrons is absorbed by another nucleus, fission can result again, releasing more neutrons.

63. Triggering a Chain Reaction
CHAIN REACTION: neutrons released during the splitting of an initial nucleus trigger a series of nuclear fissions.
Uncontrolled chain reactions occur when each released neutron is free to cause other fissions

64. Chain Reaction

65. Chain Reaction
Nuclear weapons are designed to produce uncontrolled chain reactions
In order for a chain reaction to keep going, the nucleus that splits needs to produce one neutron that causes the fission of another nucleus
The material reacting uncontrolled needs to have a critical mass.
CRITICAL MASS: the smallest possible mass of a fissionable material that can sustain a chain reaction.

66. Fusion
Another type of nuclear reaction can release huge amounts of energy is fusion:
FUSION: a process in which the nuclei of two atoms combine to form a larger nucleus.
Just like fission, a small fraction of the mass is converted into energy

67. Example of Fusion
The sun and stars are powered by the fusion of hydrogen into helium
Fusion requires extremely high temperatures where matter exists as plasma.
This is a problem for scientists wanting to use fusion for an energy source
They cannot get high enough temperatures and have trouble containing plasma here on Earth

68. Fusion in the Core