Chapter 30 Notes

1
Chapter 30 Notes

• The Nucleus, Page 691

2
Forms of Radioactivity

• Alpha particle radiation Helium nucleus.
• consists of two protons and two neutrons
• Beta-particle/wave radiation.
• High-energy electrons.

• Gamma-wave radiation.
• Electromagnetic waves

3
Mass and Charge of the Nucleus

• Nuclear charge Z x e (where Z atomic number
  or number of protons and e the elementary
  charge or 1.60 x 10-19 C, the charge of an
  electron)
• Nuclear mass A x u (where A atomic mass
  number number of protons number of neutrons
  and u atomic mass unit 1.66 x 10-27 kg)

4
Size of the Nucleus

• 10-14 m
• Held together by Strong Nuclear Force which
  opposes the repulsion force that exists between
  the protons.
• Binding energy holding the nucleus together E
  mc2 (where E energy, m mass in kg and c the
  speed of light, which is 3.00 x 108 m/s)

5
Detecting Radioactivity

• Cloud Chamber
• Detects alpha and/or beta particles
• The chamber is filled with water, as a charged
  particle travels through the chamber the water
  condenses around the ions, and makes a visible
  path or particles.

6
Isotopes

• Forms of an element that have the same number of
  protons but different numbers of neutrons.
• Nuclide the nucleus of an isotope.
• Examples 2010Ne The top number the atomic
  mass number (20) the bottom number the atomic
  number. 2210Ne (has 2 more neutrons than 2010Ne.

7
Practice Problems 1-4, Page 694

• 142 neutrons 143 neutrons 146 neutrons
• 7 neutrons
• 120 neutrons
• 11H, 21H, 31H

8
Nuclear Reactions page 696

• Alpha Decay radioactive isotope decays to
  produce a stable element plus an alpha particle
  (42He).
• Beta Decay radioactive isotope decays to
  produce a stable element plus a beta particle
  (0-1e) and an antineutrino (00?).
• Example Problems Page 697.

9
Practice Problems - Pages 697 and 698 (5 8)

• 23492U 23090Th 42He
• 23090Th 22688Ra 42He
• 22688Ra 22286Rn 42He
• 21482Pb 21483Bi 0-1e 00?

10
Half-Life Page 698

• The time required for half of the atoms in any
  given quantity of a radioactive isotope to decay.
• Activity the decay rate, or number of decays
  per second, of a radioactive substance. The SI
  unit for decays per second is a Bequerel (Bq).
• Page 699 practice problem 9.

11
Practice Problems Page 699

• For number 9, first find out how many half-lives
  occurred t/t1/2 number of half-lives.
• 24.6 years 1 half-life 2 half-lives
• 12.3 years
• Then, use Figure 30 5, page 699.
• On the graph, at 2 half-lives, ¼ of the nuclei
  are remaining, therefore, ¼ x 1.0 g 0.25 g
  remaining.

12
Page 699 Do Practice Problems 10 and 11

• 8 days 1 half-life 4 half-lives
• 2.0 days
• at 4 half-lives, 1/16 of the nuclei are
  remaining, therefore, 1/16 x 4.0 g 0.25 g
  remaining.

13
Practice Problem 11

• 9 months x 30 days 270 days (273 days)
• 270 days / 138 days 1.96 half-lives (2)
• At 2 half-lives, ¼ of the original sample would
  be left, therefore, the samples activity would
  be ¼ its original activity.
• 0.25 x (2 x 106) decays / second (Bq) 5
  x 105 Bq

14
Page 707 Energy Equivalent of Mass / Binding
Energy

• Basic Equation E mc2
• Matter / antimatter interactions conversion of
  matter to energy in the form of gamma rays.
• Electron Positron Gamma Rays
• 0-1e 01e ?

15
Energy from electron positron interaction

• E mc2 m 9.11 x 10 31kg
• E 2 (9.11 x 10 31kg) x (3.00 x 108 m/s)2
• E 1.64 x 10-13 J
• Conversion of Joules to electron volts (eV)
• 1 eV 1.60 x 10-19J
• Energy in eV 1.64 x 10-13 J 1 eV
• 
  1.60 x 10-19 J

16
Energy in eV

• E 1.02 x 106 eV or 1.02 MeV (M 106)
• Page 708 Do Practice Problem 13 a,b,c.
• 1.50 x 10-10 J
• 9.38 x 108 eV or 938 MeV
• 1.88 x 109 eV or 1.88 GeV (G giga 109)
• Assignment Do Chapter 30 Review Problems 18
  27, 29, 31 Page 714.