1. The Atomic Nucleus

2. Review…the nucleus
The nucleus is composed of particles called nucleons..__ & __
Neutrons and protons have the same mass, with ___ being slightly greater.
Neutrons have nearly 2000 times the mass of
_____.
protons and neutrons
neutrons
electrons

3. Review…the atom
The mass of an atom is almost equal to the mass of the _____ alone
Nucleons are bound together by an attractive nuclear force called the ____ force
The positively charged protons in the nucleus hold the negatively charged electrons in their ____
nucleus
strong
orbits

4. Review…the atom
The number of ___ in the nucleus determines the chemical properties of the atom
The # of protons determines the # of ____ that orbit the atom
The # of ___ has no direct effect on the # of electrons
protons

5. Review…the atom
The principal role of the neutrons in the nucleus is to act as a sort of ____ to hold the nucleus together
The electrical force acts as a ____ force between protons
The atom needs a certain balance of neutrons and protons for ___
cement
repulsive
stability

6. The symbol was created in 1946 UC- Berkeley to represent “activity coming out of a atom”

7. What is Radioactivity?
Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.
There are numerous types of radioactive decay. The general idea in all of them:
An unstable nucleus releases energy to become more stable

8. Radioactive Decay

9. Radioactive Decay
A neutron is very unstable. A lonely neutron will spontaneously decay into a proton + an electron.
Fun Fact: If you have a lot of neutrons, within 11 minutes ½ of them will have decayed
Particles that decay are said to be radioactive
A lone neutron is radioactive

10. All the elements heavier than Bismuth (At # 83)

11. Their atoms emit 3 things…alpha, beta particles and gamma rays

18. Which is more penetrating?

19. Radioactive Isotope
Iodine-131, a beta emitter, is taken as sodium iodide in drinking water. Almost all of it will find its way to the thyroid

20. Isotopes
They are atoms of the same element that have different numbers of neutrons.

28. Radioactive Half-life

29. Radioactive Half-Life
The half-life of an element is the time it takes for half of the material you started with to decay Remember, it doesn’t matter how much you start with. After 1 half-life, half of it will have decayed.
Each element decays into a new element
C14 decays into N14 while U238 decays into Pb206 (lead), etc
The half-life of each element is constant. It’s like a clock keeping perfect time

30. Half-life

31. Half-life

32. Half-life

33. Half-life

34. “How much of this element remains after 4 half-lives?
Just remember that at the end
of one half-life, 50% of the
element will remain. Find 50%
on the vertical axis, Follow the
blue line over to the red curve
and drop straight down to find
the answer:

35. Carbon Dating
The radioactivity of once living things decreases at a predictable rate

36. Uranium Dating
The dating of older, non-living things (like rocks) is accomplished by radioactive minerals, such as Uranium. Uranium decays very slowly.
Rocks on Earth have been dated to 3.7 bil yrs old
Rocks on Moon dated to 4.2 bil yrs old
The Earth has been dated to 4.6 bil yrs old

37. Review…whew!

38. Radiation Penetrating Power

39. Three Common Types of Radioactive Emissions - Penetrability
Alpha particles may be completely stopped by a sheet of paper, beta particles by aluminum shielding. Gamma rays, however, can only be reduced by much more substantial obstacles, such as a very thick piece of lead.

40. Radiation Penetrating Power

41. Radiation and You (and me)!

42. Is there radon in your home?

43. Sources of Radioactivity
Primordial - from before the creation of the Earth
Cosmogenic - formed as a result of cosmic ray interactions
Human produced - enhanced or formed due to human actions (minor amounts compared to natural)

44. Radiation Exposure to Americans

45. Review
Name three of the science pioneers in the study of Radioactivity?
Why does a nucleus decay?
Order these emissions from least to greatest penetrability: Gamma, Alpha, Beta.
What is the greatest source of exposure to radioactivity in our everyday lives?

46. Nuclear Fusion - Energy released when two light nuclei combine or fuse
However, a large amount of energy is required to start a fusion reaction:
Need this energy to overcome ________ forces of protons.
Extremely high temperatures can provide start-up energy.
repulsion
More energy in fusing hydrogen that fission of uranium

47. - Energy released when one large, unstable atom breaks apart into two smaller atoms.
Nuclear Fission
Can produce a chain reaction where free neutrons will initiate more atoms to split and it continues. This can produce way too much energy and heat.
More energy in fusing hydrogen that fission of uranium