Key Terms
Radioactivity
Nuclear Radiation
Alpha Particles
Beta Particles
Gamma Rays
Half-life
Nuclear Radiation
Many elements change through radioactivity.
Radioactivity is a process by which an unstable
nucleus emits one or more particles or energy in the form
of electromagnetic radiation.
Why do elements that are unstable go through nuclear
decay?
To become stable. By becoming stable the element
may be an isotope of the original element or an entirely
new element.
Nuclear radiation is the particles that are released during
radioactive decay.
There are four different types of nuclear radiation
1. Alpha Particles
2. Beta Particles
3. Gamma Rays
4. Neutron Emission
1.
Alpha Particles consist of protons and neutrons
- positively charged atom that is released in the
disintegration of radioactive elements and that consists of
two protons and two neutrons.
- can be stopped by a sheet of paper
- massive in size
2.
Beta Particles are electrons produced from neutron
decay
- charged electron emitted during certain types of
radioactive decay, such as beta decay
- easily pass through paper, but are stopped by 3mm of
aluminum or 10mm of wood
- less massive than alpha particles
3.
Gamma Rays are very high energy
- high-energy photon emitted by nucleus during fission
and radioactive decay
- can penetrate up to 60cm of aluminum or 7cm of lead.
Since they are not easily stopped they
pose a greater
danger to health than either alpha or beta particles.
4.
Neutron radioactivity may occur in an unstable
nucleus
- neutron emission consists or matter that is emitted from
an unstable nucleus
- are stopped by lead 15cm thick
Nuclear Decay
Anytime an unstable nucleus emits alpha or beta
particles, the number of protons or neutrons changes.
A nucleus gives up two protons and two neutrons during alpha
decay.
A nucleus gains a proton and loses a neutron during beta decay.
In all cases of beta decay, the mass number before and after the
decay does not change.
Radioactive Decay Rate
Although it is impossible to predict the moment when any particular
nucleus will decay, it is possible to predict the time it takes for half the
nuclei in a given sample to decay. This is a substances half-life.
Half-life is the time required for half of a sample of a
radioactive substance to disintegrate by radioactive decay or by natural
processes.
Start
1st half-life
2nd half-life
3rd half-life
4th half-life
=½
=¼
= 1/8
= 1/16
Half-life is a measure of how quickly a substance decays.
Carbon-14 is used to date materials
Key Terms
Fission
Nuclear Chain Reaction
Critical Mass
Fusion
The stability of a nucleus depends on the nuclear forces
that hold the nucleus together.
Where do these forces act?
Between the protons and neutrons
If like charges repel one another how do protons remain in
the nucleus?
Nuclei are held together by a special force. These special
forces are stronger than the repelling force. However, this
force only occurs over short distances.
Neutrons also contribute to nuclear stability
Too many protons or neutrons can cause a nucleus to
become unstable and decay
While neutrons help hold the nucleus together, if there
are too many or too few the nucleus is unstable and
undergoes decay.
Nuclei with more than 83 protons are always unstable, no
matter how many neutrons there are.
These nuclei always decay releasing large amounts of energy
and nuclear radiation.
Nuclear Fission
Fission is the process by which a nucleus splits into two or more
fragments and releases neutrons and energy
What is released during nuclear fission?
Energy.
The energy that is released makes up for the mass that is lost
during the process.
Neutrons released by fission can start a chain reaction
Nuclear chain reaction is a continues series of nuclear fission
reaction
The ability to create a chain reaction partly depends on the
number of neutrons released.
Chain reaction can be controlled
Critical mass is the minimum mass of a substance that can
undergo a fission reaction and can also sustain a chain reaction.
How do power plants control chain reactions?
By the use of control rods. Control rods are used to regulate
splitting and slowing the chain reaction.
Nuclear Fusion
Fusion is the process by which light nuclei combine at extremely
high temperatures forming heavier nuclei and releasing energy.
Why are high temperatures needed for fusion to occur?
Energy is required to bring the nuclei together
until the repelling forces are overcome by the attractive
nuclear forces between two protons.
Key Terms
Background Radiation
Rem
Radioactive Tracer
Where Is Radiation?
Nuclear radiation is all around us. Most of it comes from
natural sources, such as the sun, heat, soil, rocks, and plants.
This type of radiation is known as background radiation
Background radiation is nuclear radiation that arises
naturally from cosmic rays and from radioactive isotopes in the
soil and air.
Radiation is measured in units of rems.
Rem is the quantity of ionizing radiation that does as
much damage to human tissue as 1 roentgen of highvoltage X-ray
Exposure varies from one location to another ( Table 3 pg
300)
Some activities add to the amount of nuclear radiation
exposure (Table 4 pg 300)
Beneficial Uses of Nuclear Radiation
Nuclear radiation is used in a controlled way to take
advantage of its effects on other materials.
Smoke detectors help save lives by using small radioactive
sources.
Nuclear radiation is used to detect diseases
1. Ultrasound scanning
2. CT scanning
3. PET
4. Magnetic resonance imaging (MRI)
What is a radioactive tracer?
A radioactive material that is added to a substance so
that its distribution can be detected later. They are short-lived
isotopes that tend to concentrate in affected cells and are used
to locate tumors.
Nuclear radiation therapy is used to treat cancer
Radiotherapy is treatment that uses controlled doses of
nuclear radiation for treating diseases such as cancer.
Possible Risks of Nuclear Radiation
Nuclear radiation can ionize atoms by changing the number of
electrons in living material.
The risk depends upon the amounts of radiation. Studies have
shown that exposure to high levels of nuclear radiation can
cause cancer.
High concentration of radon gas can be hazardous
What is Radon?
It is a colorless and inert gas that is produced by the
radioactive decay of uranium-238. Radon emits alpha and
beta particles as well as gamma rays
Nuclear Power
Nuclear fission has both advantages and disadvantages
Advantages
1. Does not produce gaseous
pollution
2. More energy in uranium reserves that coal or
oil
Disadvantages
1. Produce radioactive waste
2. Storage of waste
Nuclear fusion reactors are being tested
Scientist estimate that 1 pound of hydrogen in a fusion reactor
could release as much energy as 16 million pounds of burning
coal. Nuclear fusion also release very little waste or pollution.
Nuclear fusion also has advantages and disadvantages
Advantages
1. Fuel is abundant
Disadvantages
1. Produce fast neutrons
2. Expensive