Chapter 6 nuclear changes

1
Chapter 6 nuclear changes

• What do you think of when you think about
  nuclear energy or radioactivity?

2
Explosions?
3
Solar flare
4
Radiation all around you
5
Four types of nuclear radiation

• Alpha, beta. Gamma, neutron
• Copy Table 9-1 page 285 below

6
Alpha particles

• Symbol
• Total of four (2 protons and 2 nuetrons
• Two are protons
• Charge 2
• If xenon emitted an alpha particle it would be
  ????
• Does not travel far through materials. Causes
  ionization

7
Symbols used in nuclear reactions
8
Beta

• Beta Formed when a neutron becomes a proton and
  a beta electron. Beta particles are fast moving
  electrons. Does not penetrate far into materials
  and ionizes.

9
Beta radiation

• Symbol
• Charge -1
• No change in the total number of neutrons and
  protons, no significant change in mass
• Gains a proton
• If xenon emitted a beta particle it would be
  ?????

10
Nuclear Decay
11
Gamma rays

• Gamma rays are the highest energy electromagnetic
  waves. Can penetrate matter and pose a higher
  health risk. Gamma rays are throughout the
  Universe. Very few gamma rays make it through the
  earths atmosphere.
• Symbol
• No charge

12
Neutron radioactivity

• Neutron radioactivity a fast moving neutron, can
  penetrate, does not ionize
• Occurs in neutron rich nucleus
• Symbol
• No charge

13
More nuclear decay
14
Nuclear equations

• Nuclear decay Can be written showing atomic mass
  and atomic number. Remember atomic mass number is
  the number of neutrons and protons.
• Mass numbers and atomic numbers balance.
• Top numbers are the number of protons and
  neutrons
• Bottom numbers are the of protons

15
Balanced nuclear equations

• Page 189

16
Practice

• Write the example of an alpha particle decay from
  Plutonium to Uranium.
• Copy the two nuclear equations
• Page 189

17
Beta decay

• Uranium has beta decay

18
More practice

• Beta decay example of carbon 14 to Nitrogen with
  a neutron to a proton and a beta particle
  radiation.
• Do practice problems on page 191

19
Radioactive decay

• Half-life the time required for half a sample
  of radioactive nuclei to decay.
• Half-life may be a nanoseconds or billions of
  years.
• Carbon 14 has a half-life of 5,730 years. Living
  organisms have some C-14 that remains constant
  until they die.
• Copy chart 6-2 page 192

20
Exponential decay

• Graph on page 290
• Does the matter left ever reach 0?

21
6-2Nuclear fission and fusion

• Nuclei are held together by a special force.
  This holds positive charged protons together. It
  only acts on small distances. Three protons
  width.
• Elements with more than 83 neutrons are unstable

22
Fission

• Fission the process by which a nucleus splits
  into two or more smaller fragments, releasing
  neutrons and energy. Notice page 197 the
  breakdown of uranium 235 bombarded with a
  neutron. Large amounts of energy.

23
The fission equation
24
Nuclear power Is it the future?
25
Inside the core
26

• Mass- energy equation Emc squared
• Neutrons released by fission can start a chain
  reaction. These reactions can be controlled

27
Speed of light in a vacuum Space and air can be
considered close to a vacuum
28
Your mass converted into energy
29
Fusion in the sun

• Fusion the process in which light nuclei combine
  at extremely high temperatures, forming heavier
  nuclei and releasing energy.
• Stars produce energy using hydrogen and deuterium
  hydrogen to produce lots of energy and helium.
• Difficult to reproduce why?

30
Two Laws of Black Body Radiation
0
1. The hotter an object is, the more energy it
emits
Energy Flux
F sT4
where
F Energy Flux Energy given off in the form
of radiation, per unit time and per unit surface
area J/s/m2
s Stefan-Boltzmann constant
31
Energy Production
0
Energy generation in the sun (and all other
stars)
Binding energy due to strong force on short
range, strongest of the 4 known forces
electromagnetic, weak, strong, gravitational
Nuclear Fusion
fusing together 2 or more lighter nuclei to
produce heavier ones.
Nuclear fusion can produce energy up to the
production of iron
For elements heavier than iron, energy is gained
by nuclear fission.
32
Energy Generation in the Sun The Proton-Proton
Chain
0
Basic reaction 4 1H ? 4He energy
Need large proton speed (? high temperature) to
overcome Coulomb barrier (electrostatic repulsion
between protons).
4 protons have 0.04810-27 kg ( 0.7 ) more mass
than 4He.
T 107 0K 10 million 0K

• Energy gain Dmc2
• 0.4310-11 J
• per reaction.

Sun needs 1038 reactions, transforming 5 million
tons of mass into energy every second, to resist
its own gravity.
33
The Solar Constant
0
The energy we receive from the sun is essential
for all life on Earth.
The amount of energy we receive from the sun can
be expressed as the Solar Constant
Energy Flux
F 1360 J/m2/s
F Energy Flux Energy received in the form
of radiation, per unit time and per unit surface
area J/s/m2
34
Luminosity Classes
0
Ia Bright Supergiants
Ia
Ib
Ib Supergiants
II
II Bright Giants
III
III Giants
IV Subgiants
IV
V
V Main-Sequence Stars
35
Black Holes in Supernova Remnants
0
Some supernova remnants with no pulsar / neutron
star in the center may contain black holes.
36
Black Hole X-Ray Binaries
0
Accretion disks around black holes
Strong X-ray sources
Rapidly, erratically variable (with flickering on
time scales of less than a second)
Sometimes Quasi-periodic oscillations (QPOs)
Sometimes Radio-emitting jets
37
Gamma-Ray Bursts (GRBs)
0
Short ( a few s), bright bursts of gamma-rays
GRB a few hours after the GRB
Same field, 13 years earlier
Later discovered with X-ray and optical
afterglows lasting several hours a few days
Many have now been associated with host galaxies
at large (cosmological) distances.
38
6-3 Nuclear radiation

• Background radiation every day you are exposed
  to nuclear radiation from the sun, universe,
  soil, water and plants.
• Nuclear radiation can ionize tissues in the body
  changing them. High concentrations can be harmful
  and possibly cause birth defects.

39
Daily radiation sources
40
Useful radiation

• Radiation is used in medicine to treat cancer, as
  tracers in agriculture, and medicine and in
  science.
• Nuclear power using fission produces electric
  power.

41
Fusion in the sun is believed to occur in steps.
Four protons produce one atom, two positrons, and
two neutrinos. The first two steps shown below
must occur twice before the third step takes
place
42
(No Transcript)
43
Pros and cons

• Benefits of nuclear power No green house
  gasses, more radiation comes from mining coal
  than any nuclear reactors, no pollution. It has
  proven to be very dependable. No Dependence on
  foreign oil.
• Problems with nuclear power the plants are
  expensive, storage of the radioactive waste is
  expensive but plausable.

44
Power

• Nuclear fusion not yet possible. Waste would be
  helium. Problems are the high level of heat, and
  pressure. Duplicating the sun.
• Other choices of power solar, geothermal, green
  architecture, wind, hydroelectric.
• Why do we care?