Chapter 10 Notes
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Describe the process of nuclear decay
Classify nuclear radiation as alpha particles, beta particles, or gamma rays
Balance nuclear equations
Identify sources of nuclear radiation
Describe how nuclear radiation affects matter.
Describe methods of detecting nuclear radiation
Excerpt from the Physical Science textbook Chapter 10 p292
In 1896, French physicist Antoine Henri Becquerel (1852–1908) was experimenting with
uranium salts. He hypothesized that the salts, which glow after being exposed to light,
produced X-rays while they glowed. To test his hypothesis, Becquerel performed an
experiment. First, he wrapped a photographic plate in paper. Then, he placed some
uranium salts on the plate and set it outside in the sunlight, which caused the salts to
glow. When Becquerel developed the plate, he got a foggy image. At the time, Becquerel
thought that X-rays from the salts had penetrated the paper and fogged the plate.
Like any good scientist, Becquerel wanted to repeat his experiment, but a spell of bad
weather forced him to wait. In the meantime, he left a wrapped photographic plate and
uranium salts in a desk drawer. After several days, Becquerel decided to develop the plate
without exposing the uranium to sunlight. To his surprise, he got the foggy image shown
in Figure 1A. Later, Becquerel determined that the uranium salts had emitted rays that
had never been observed before.
Introduction
We will apply the scientific method to introduce nuclear radiation. It will be based on the
above scenario.
Observation: When exposed to light Uranium salts glowed and produced X-rays.
Hypothesis: If I expose uranium salts to sunlight they will glow and produce X-rays.
Testing the hypothesis:
1. Becquerel placed Uranium salts on a photographic plate and set it outside in the sun.
2. Due to bad weather he left a plate of Uranium salt on a photographic plated and placed
it in a drawer.
Conclusion: Both plates created X-rays even though one of them was exposed to
sunlight. This disproved the initial hypothesis.
Theory: The salts are producing rays whether or not they are exposed to sunlight.
The significance of this experiment was that we were able to identify X-rays, which we
had never seen before, & the discovery of radioactivity.
Nuclear Decay
* Radioactivity- it is the process in which an unstable nucleus emits charged particles a
and energy.
* Any atom that contains an unstable nucleus is called a radioactive isotope or
radioisotope for short.
Obj #1 Examine what is meant by unstable ie valence e When an element is unstable we’re saying that it’s radioactive or it will go out
and try to get to the stable state.
 How does C-12; and C-14 differ (# of neutrons) look at carbon’s mass there is
another
 Carbon-14 is found in fossils like dinosaur bones.
 Oxygen is another common isotope.
 During nuclear decay, atoms of one element can change into atoms of a different
element altogether.
Questions:
1.
2.
What are the two common types of isotopes: Carbon and Oxygen
What element was used in Becquerel’s experiment: Uranium-238
Types of Nuclear Radiation
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In the introduction we talked about X-rays or lights being emitted in our
experiment.
We detect radioactive substances by measuring the nuclear radiation it gives off.
We define nuclear radiation as charged particles & energy (light) that is emitted
from the nuclei of radioisotopes.
Common types of nuclear radiation are
; be
and
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Decay refers to a break down of the nucleus.
Alpha Decay
When the nucleus breaks down it releases alpha particles. Alpha particles are defined as
fast moving positively charged particles composed of 2 protons and 2 neutrons having the
same mass as Helium. Expanded definition
 The symbol for an alpha particle is
 The subscript (bottom #) is the atomic #
 The superscript (the top#) and is the mass number
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Nuclear radiation can be expressed as equations like the one below:
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We still kept the law of conservation of mass. Both sides are equal
Students will have to explain the above equation for the exam. The isotope
converted to Thorium because of the atomic number.
A radioisotope of Uranium-238 reacts to form an isotope of Thorium-234 and
alpha particles with the same atomic # of Helium.
Characteristics of alpha particles
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Alpha particles are the least penetrating type of nuclear radiation.
Usually travels no more than a few centimeters in air and are usually stopped by a
sheet of a paper or clothing.
This makes sense since because they only weigh 4 grams
Beta Decay
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When Thorium-234 (an isotope of Uranium) decays it releases negatively charged
particl
e- from an unstable nucleus
Characteristics of Beta particles
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Beta particles are made of a single electron and -1 represents the atomic number
Therefore the mass number is negative because no protons/neutrons
Because they can move faster they can penetrate more
-particles.
The following equation describes the beta decay of thorium-234. (Classroom illustration)
Gamma Decay ( )
 Releases Gamma rays from the unstable nucleus
 Doesn’t have a mass or a charge
 These are energy rays like X-rays and visible lights.
 They travel at the speed of light.
 The atomic number and the mass number remains unchanged.
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 Are stopped by several centimeters of lead or several meters of concrete.
For example, thorium-234 emits both beta particles and gamma rays as it decays. See the
equation below:
The above radioisotope decays into Protactinium + beta particles + gamma rays
Practice Balancing Nuclear Equations on p295
1.Write a balanced nuclear equation for the alpha decay of
Thorium-232.
2. Write a balanced nuclear equation for the beta decay of carbon-14.
3.Determine the product of alpha decay for americium-241.
4.Determine the product of beta decay for strontium-90.
Effects of Nuclear Radiation
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Exposure to nuclear radiation occurs everyday
Background radiation is defined as nuclear radiation that occurs naturally in the
environment ie Air, rocks, plants & animals
Background radiation occurs in low enough doses that it is safe.
If background radiation exceeds safe levels it can damage cells and tissues
Nuclear radiation ionizes atoms
When the cells are exposed to higher doses of radiation it can break the bonds
holding proteins and DNA molecules may break. This also changes how the cells
can function.
Alpha particles aren’t serious health hazards unless you inhale or ingest them (in
foods)
Radon releases alpha particles and it is dangerous.
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Radon starts in the ground and work its way upwards in the air. If you have a
basement you have a higher chance of inhaling Radon gas if the basement lacks
proper ventilation.
Prolonged exposure can cause lung cancer.
Detecting nuclear radiation
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Can detect with Geiger counters and film badges.
Section 10.2 Rates of Nuclear Decay p298
 A nuclear decay rate describes how fast nuclear changes take place in a
radioactive substance. Every radioisotope decays at a specific rate that can be
expressed as a half-life. A half-life is the time required for one half of a sample of
a radioisotope to decay.
 A half-life of Uranium-238 is the time it took for half of it to decay. At 1 half- life
50% decayed. 2 half-lives 75% decayed. 3 half lives 87%. etc
 Nuclear decay rates are constant and don’t have conditions to speed them up.
 Calculating how many half- lives have elapsed over time. (p300)
 Half lives elapsed= total time of decay/half-life
Radioactive dating (p300)
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Radioactive dating simply explains the age of the radioisotope.
How long it takes for decay
How much is still remaining
If an object is over 50,000 years old we can’t do radiocarbon dating because the
levels are two low at that point.
Nuclear reactions in the Lab
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Transmutation is the conversion of atoms of one element to an atom of another
element. This is what alchemist where trying to do when they were attempting to
create Gold.
It involves a nuclear change and not a chemical change.
Ernest Rutherford performed the 1st artificial transmutation
Achieved by bombarding atomic nuclei with high energy particles ie p+ and eWhat else is Rutherford known for?
What was the main premise of Rutherford’s transmutation experiment? That
nitrogen converted to an isotope of Oxygen.
Elements with atomic numbers greater than 92(Uranium) are known as TransUranium elements.
All trans-uranium elements are radioactive and are generally not found in nature.
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We can build a trans-uranium element by the artificial transmutation of a higher
element.
Examples: Amercium-241 is used in smoke detectors. It emits alpha particles. The
emission of alpha particles ionizes the air inside a smoke detector to allow an ecurrent to flow. When smoke enters the detector it disrupts the e- current and the
alarm goes off.
A particle accelerator is a device that speeds up electrically charged particles to
high speeds and then contains them.
Interesting Facts: The largest known particle accelerator known to is 16-miles
long. There are 2 types: Linear (straight line) or circular (circle)
Section 10.4 Nuclear Fission & Nuclear Fusion
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Used in Transmutation
Nuclear energy is the energy released by nuclear reactions
Nuclear Fission it is very similar to cell fission (cell splicing)
Sometimes in transmutation the nuclei splits into 2 smaller parts through a process
called nuclear fission.
A relation of how mass and energy are related was introduced by Albert Einstein.
The formula was E=mc2
E represents (Energy); M represents (mass) and c represents (speed of light)= 3.0
x 108
To determine the total amount of energy you would consider how much energy
was lost + remaining divided by two.
Nuclear Fusion
The process in which the nuclei of 2 atoms combine to form a larger nucleus
 Nuclear radiation release glowing lights
 Fusion of the He & H+ causes the sun to shine and the stars to glow.
 Fusion requires high temperatures.
 Because the temperatures are so high the atoms are stripped of their e The atoms now exist in gaseous forms known as plasma (think of it as cell
plasma)
 Scientists are currently working on Fusion reactors to produce electricity.
 Two things that are hindering this discovery are the lack of high temperatures and
plasma.
Nuclear Power Plants:
 Mainly they provide energy sources for us with less pollution
 We will be watching a video that relates to this topic also.