Half-Life and Radioactivity
(7.2 and 7.3)
By Kira Nishi-Beckingham
What is Half-Life?
A half-life is the amount of time it takes for half the
nuclei in a sample to decay.
A half-life is constant for any radioactive isotope (
isotope - an atom of the same element with a
different number of neutrons)
Number of Half Lives Percentage Decayed Percentage Left
0 0% 100%
1 50% 50%
2 75% 25%
3 87.5% 12.5%
4 93.75% 6.25%
A decay curve is a curved line on a graph that shows
the rate of decay of a radioisotope (an isotope that is
It will look the same no matter what radioisotope you
graph, the only difference will be the length of the
Common Isotope Pairs and Dating
There are many pairs of isotopes that can be used for
The parent isotope is the one undergoing radioactive
decay and the daughter isotope is the result or
product of the radioactive decay.
Historians and scientists use radioactive isotopes to date
The most commonly known is Carbon-14
Every living thing contains Carbon-14, but when they die
it starts to decay into Nitrogen-14. To be able to tell when
the plant or animal died, you just have to compare the
amount of Carbon-14 to the amount of Nitrogen-14
Lets say a sample contained 20g of Carbon-14 and 20g of
Nitrogen-14. This means that one half-life has occurred
If there is more of the parent isotope then less than one
half-life has occurred and if there is more of the daughter
isotope then more than one half-life has occurred.
Answer the following questions correctly or Radioactive
Man will take over the world!
1. Define the following
2. What is the daughter isotope of Carbon-14?
3. a) If there is more of the parent isotope this means..
b) If there is more of the daughter isotope?
c) If there is the same amount of the parent and daughter
Nuclear fission is the splitting of a heavy atom into
two smaller ones, subatomic particles, and energy
Nuclear fission is accompanied by a huge release of
energy. We use this energy to generate power in
While nuclear reactors reduce the amount of burning
fossil fuels, they produce dangerous waste that needs
to be stored for hundreds of thousands of years, the
physical deterioration is a large problem, and the
concern that the nuclear material could be used to
make dangerous weapons
Chemical Reaction Vs. Nuclear Reaction
Chemical reactions involve electrons and change the
way atoms are arranged
Nuclear reactions change the atom’s nucleus
In nuclear reactions, a small change creates a large
amount of energy.
Natural nuclear reactions are Alpha, Beta, and
Non-Natural nuclear reactions are called induced
nuclear reactions. These occur when scientists
bombard a nucleus with an alpha particle, beta
particle, or gamma rays
Rules and Symbols
The rules for writing nuclear equations are:
1. The sum of the mass numbers on each side of the
equation stays the same
2. The sum of the charges on each side of the equation
stays the same
This table shows the
symbols for each
When Uranium-235 is bombarded with a neutron, it
absorbs it making it Uranium-236 which is highly
unstable causing it to split immediately.
When it splits, it also releases energy and more
This is important because if there is more atoms of
Uranium-235 around, these neutrons hit the atoms
causing them to split and release more neutrons
which hit more atoms and so on
This is called a chain reaction
Nuclear fusion is when two smaller, light weight
atoms fuse together to create one large one.
This happens at the core of our sun and other stars
where there is enough heat and pressure to force the
This creates a large amount of energy that eventually
brings light and heat to us
Scientists have been searching for ways to use
nuclear fusion to create energy however it is
extremely difficult to reach the temperature and
amount of pressure needed as well as finding a way
to contain the heat and pressure
Answer the following questions correctly or
Radioactive Man will take over the world!
1. Define the following
2. What are the rules for writing a Nuclear Equation?
3. What is the name of an isotope that can create a
4. Where does nuclear fusion occur naturally?
Answers to Quiz #1
1. Half-Life – the amount of time it takes for half of a
sample of radioactive nuclei to decay
Isotope – an atom of the same element with a different
number of neutrons
Decay Curve – a curved line on a graph that shows the
decay rate of a radioisotope
Parent Isotope – The isotope that is undergoing the
Daughter Isotope – The isotope that is the stable product of
the radioactive decay
2. Nitrogen- 14
3. a) Less than one half-life has occurred
b) More than one half-life has occurred
c) Exactly one half-life has occurred
Answers to Quiz #2
1. Nuclear Fission – One heavy and large atom splits into two
smaller ones releasing a large amount of energy
Nuclear Fusion – Two small, light weight atoms fuse together to
create one large one releasing a large amount of energy
Nuclear Reaction – When the nucleus of an atom is changed
Chain Reaction – One thing that causes another thing that causes
another thing and so on
2. The sum of the mass numbers on each side of the equation
stays the same
The sum of the charges on each side of the equation stays the
4. The sun
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