1. Nuclear Reactions

2. Chapter 18 Sec 1

3. Nucleus
Composed of protons and neutrons which comprise most of the atom’s mass

4. What holds these particles together in the nucleus?
The strong force causes protons and neutrons to be attracted to each other in the nucleus.
Strong force is powerful when neutrons and protons are packed closely together
Protons and neutrons in a large nucleus are held less tightly by the strong force than protons and neutrons in a small nucleus

5. Radioactivity
Nuclear decay which happens when the strong force is not large enough to hold the nucleus together
The nucleus will give off matter and energy

6. FYI All nuclei that contain more than 83 protons are radioactive
All nuclei that contain more than 92 protons do not exist naturally on Earth
These can only be produced in laboratories and are called synthetic elements (man-made)
These synthetic elements are unstable, and decay soon after they are created

7. Isotopes role in radioactivity
Isotope – atoms of the same element with varying numbers of neutrons
A nucleus that contains too many or too few neutrons compared to protons is radioactive.

8. The Discovery of Radioactivity
1896 – Henri Becquerel
uranium
1898 – Marie and Pierre Curie
polonium and radium

9. Chapter 18
Section 2

10. Nuclear Radiation
Particles and energy are released from a decaying nucleus

11. Three types of nuclear radiation
Alpha – release particles
Consists of two protons and two neutrons
Beta – release particles
A beta particle is an electron and is emitted when a neutron decays into a proton
Gamma – electromagnetic wave
Gamma rays are electromagnetic waves of very high frequency that usually are emitted when alpha decay or beta decay occurs
Penetration strength increases from
alpha to
beta
gamma

13. Transmutation
Process of one element’s changing to another element through nuclear decay

14. Half-life
The length of time it takes half of the atoms of a sample of the radioactive isotope to decay
Can vary from fractions of a second to “billions of years”

15. Radioactive Dating
Uses half-life of isotopes to determine ages of materials.
Carbon dating is used to date once-living materials
Uses Carbon-14 Isotope
Uranium dating is used to figure ages of rocks

16. Example of radioactive dating
Half life of Iodine-131 is 8 days
How much of a 5-g sample will be left after 32 days?

17. Example of radioactive dating
Half life of Iodine-131 is 8 days
How much of a 5-g sample will be left after 32 days?
Answer: 0.3 grams of Iodine-131 will be left after 32 days

18. Chapter 18 Section 3

19. Detecting Radioactivity
Radiation detectors are instruments used to identify ions formed when radiation passes through matter.
Some instruments that can be used
Cloud chamber
Bubble chamber
Electroscopes

20. Measuring Radiation
Important to monitor the amount of radiation a person is being exposed to because large doses of radiation can be harmful to living tissue.
Ex. Geiger counter – measures radioactivity by producing an electric current when radiation is persent

21. Chapter 18 Sec 4

22. Nuclear Reactions

23. Nuclear Fission
Process of splitting a nucleus into two nuclei with smaller masses; a large amount of energy is released

24. Chain reactions
A chain reaction in nuclear fission is when there is an ongoing series of fission reactions
If this reaction goes uncontrolled an enormous amount of energy is released.
For a chain reaction to occur, a critical mass of material that can undergo fission must be present, this critical mass is the amount of material required so that each fission reaction produces approximately one more fission reaction.

25. Chain reaction

26. Nuclear Fusion
Nuclear fusion occurs when two nuclei with low masses are combined to form one nucleus of larger mass.
Nuclear fusion can happen only when nuclei are moving fast enough to get close to each other
Temperatures in stars (millions of degrees Celsius) are high enough for fusion to occur

28. Nuclear fusion