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Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons...

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Radioactivity Nucleus – center of the atom containing protons and neutrons – How are the protons and neutrons held together? Strong Force - an attractive force that holds protons and neutrons together – The protons and neutrons must be close together for this force to keep them together – As the nucleus increases in size, the strong force diminishes and the electrical force (force between charges) becomes more powerful
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Page 1: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

Radioactivity

• Nucleus – center of the atom containing protons and neutrons– How are the protons and neutrons held together?

• Strong Force - an attractive force that holds protons and neutrons together

– The protons and neutrons must be close together for this force to keep them together

– As the nucleus increases in size, the strong force diminishes and the electrical force (force between charges) becomes more powerful

Page 2: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Radioactivity – process of nuclear (nucleus) decay

– Stability of Nuclei1. Larger nuclei are less stable – all nuclei that

contain more than 83 protons are radioactive

2. The ratio of neutrons to protons also determines if an element is radioactive• Nuclei with too many or too few neutrons compared to

protons are usually unstable, and thus, radioactive

Page 3: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Nucleus numbers representation– A nucleus can be represented by the following

isotope notation

– In this carbon-12 isotope, there are 6 protons and 6 neutrons, which makes it stable and not radioactive

– What would carbon-14 look like?– Would carbon-14 be radioactive? Why?

C126

element symbolmass number

atomic number

C146

radioactive, because it has too many neutrons compared to its protons

Page 4: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Nuclear Radiation – when an unstable nucleus decays, particles and energy are emitted (given off)

– 3 types of Nuclear Radiation1. Alpha Particles

2. Beta Particles

3. Gamma Rays

Page 5: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

Radioactivity Uses• Treating cancer• Internal inspection• Radioactive dating of artifacts• Tracing• Smoke detectors• Sterilization• Food irradiation• Thickness monitoring• Nuclear energy

Page 6: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Alpha Particles – made of 2 protons and 2 neutrons– Also known as a helium-4 nucleus with a

charge of 2+ (no electrons)• As the alpha particle leaves the atom, it passes

through other matter and takes electrons, leaving behind ions

• This process causes it to lose much of its energy

– The largest of the radiation types – has an atomic mass unit of 4

– Least penetrating of radiations - can be stopped with a sheet of paper or clothing

– Symbol He42

Page 7: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Transmutation – process of changing one element to another through nuclear decay

- Alpha particle nuclear reaction

– During the transmutation, the total mass and charges of the nuclei at the end are the same as the nucleus at the beginning

Po210

84 Pb206

82

+

He42

+84 +82 +2

Page 8: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Beta Particles – a neutron decays into a proton and emits an electron in the process– the beta particle has a negative charge– Smallest of the radiation particles – has an

atomic mass unit of 0.0005– Much faster and more penetrating than alpha

particles– Can be stopped by a sheet of aluminum foil or

wood– Symbol e0

-1

Page 9: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

– Beta particle nuclear reaction

– During the transmutation, the total mass and charges of the nucleus and the electron emitted at the end are the same as the beginning

-

I131

53 Xe131

54

+

e0-1

+53 +54 -1

Page 10: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Gamma Rays – electromagnetic wave– usually emitted from a nucleus when an alpha

decay or beta decay occurs– gamma rays have no mass or charge and

travel at the speed of light– Deepest penetrating of radiation, but is not as

damaging to living tissue as alpha and beta– Requires dense, thick materials such as

concrete blocks or lead to stop

Page 11: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

Alpha particles have a greatercharge and mass than betaparticles and gamma rays do.Alpha particles travel about7 cm through air and arestopped by paper or clothing.

Beta particles have a 1 or 1 charge and almost no mass. They are more penetrating than alpha particles. Beta particles travel about 1 m through air but are stopped by 3 mm of aluminum.

Gamma rays have no charge or mass and are the most penetrating. They are blocked by very dense, thick materials,such as a few centimeters of lead or a few meters of concrete.

Page 12: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Radioactive Half-life – the amount of time it takes for half of the nuclei in a sample of an isotope to decay– Example, the half-life of (hydrogen-3) is

12.3 years.• The H-3 will beta decay to He-3• If a sample has 20 atoms of hydrogen, after

12.3 years, 10 atoms will have decayed to He-3, and the other 10 will still be H-3

• After 12.3 more years, another 5 will have decayed to He-3, and 5 will still be H-3

H31

Page 13: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.
Page 14: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.
Page 15: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Radioactive Dating – using known half-lives to date certain rocks, fossils, and other materials– Carbon dating – radioactive isotope carbon-

14 is found in plants and animals.• Has a half-life of 5,730 years• Used to get the approximate age of plants

and animals up to 50,000 years– Uranium Dating – used to date some rocks

that contain small amounts of uranium

Page 16: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.
Page 17: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

n

n

n

Nuclear Reactions• Nuclear Fission – The process of splitting

a nucleus into several smaller nuclei– Only large nuclei, such as uranium and

plutonium, undergo fission– A neutron collides with a large nucleus and

splits in two• Some of the mass actually converts to a

tremendous amount of energy

n

Ba142

56

+ energy

U235

92

Kr90

36

Page 18: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Chain Reaction - When a nuclear fission reaction occurs, the neutrons emitted can strike other nuclei in the sample, and cause them to split.

Page 19: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

• Nuclear Fusion – two nuclei of smaller mass are combined to form one larger nucleus– Produces even more energy than fission– Temperature must be extremely hot (millions

of degrees Celsius) for nuclei to be moving so fast that they get close enough for fusion to occur

+ energy

H-1

H-2

He-3

Page 20: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

Nuclear Power – Fission

• How a Fission Nuclear Power Plant Works– Energy comes from a controlled fission

nuclear reaction– Uses Uranium -235– As the nuclei split, tremendous heat is

released– Heat is used to produce steam that turns a

turbine which rotates an electric generator

n +1

0 U235

92 Sn + Mo + n132 101

50 42

1

03

Page 21: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

Nuclear Power – Fission

• Advantages– does not release

pollutants like fossil fuels

– provides about a million times more energy per pound than fossil fuels

• Disadvantages– radioactive material

could be released into environment in an accident

– disposal of waste material is expensive and difficult

– uranium is non-renewable

Page 22: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

Nuclear Power – Fusion

• How Fusion Nuclear Power Works– Fusion of 2 small nuclei

• Hydrogen nuclei fuse to form Helium

– Must occur at extremely high temperatures– Releases huge amounts of energy, even more

than fission reactions

H +1

1 e0

-1 He4

24 2

Page 23: Radioactivity Nucleus – center of the atom containing protons and neutrons –How are the protons and neutrons held together? Strong Force - an attractive.

Nuclear Power – Fusion

• Advantages– uses hydrogen as a

fuel which is very abundant on earth

– the product is helium, a non-radioactive and non-polluting element

– most concentrated energy source known

• Disadvantages– occurs only at temps

of millions of degrees Celsius

– use more energy to produce the reaction than energy given off

– containment of the reaction will be extremely difficult


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