irections: Follow the instructions to go through the simulation. Respond to the questions and
prompts in the orange boxes.
Vocabulary: alpha particle, atomic number, beta particle, daughter product, gamma ray, isotope, mass
number, nuclear decay, positron, radioactive, subatomic particle
Prior ...
Student Exploration: Nuclear Decay
Directions: Follow the instructions to go through the simulation. Respond to the questions and
prompts in the orange boxes.
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
The chart below gives the locations, charges, and approximate masses of three subatomic particles. The
approximate mass of each particle is given in universal mass units (u).
Particle Location Charge Approximate mass
Proton Nucleus 1+ 1u
Neutron Nucleus 0 1u
Electron Orbitals 1– 0u
1. The mass number of an atom is equal to the sum of protons and neutrons in the nucleus.
A helium atom has 2 protons and 2 neutrons. What is the mass number of this atom?
The mass number is 4 u.
2. The atomic number of an element is equal to the number of protons in each atom of the element. All
helium atoms have 2 protons. What is the atomic number of helium?
The atomic number of helium is 2.
Gizmo Warm-up
While most atoms are stable, some are radioactive, which means that
they have a tendency to undergo spontaneous nuclear decay. The
decay of radioactive atoms generally results in the emission of particles
and/or energy.
Several types of nuclear decay can be explored with the Nuclear Decay
Gizmo. On the Gizmo, check that Alpha decay and Uranium are
selected.
1. Click Play ( ), and then click Pause ( ) when the alpha particle is clearly visible. What is an alpha
particle made of? 2 protons and 2 neutrons
2. Click Play and observe. Besides the alpha particle, what else is emitted from the nucleus during alpha
, Get the Gizmo ready:
Activity A:
● Click Reset ( ).
Alpha decay ● Check that Alpha decay a
nd Uranium are
selected.
Question: How does alpha decay change the nucleus of a radioactive atom?
1. Predict: As you observed in the warm-up activity, an alpha particle consists of two protons and two
neutrons. How will the emission of an alpha particle affect the following?
A. The atomic number of the atom: Will decrease
B. The mass number of the atom: Will decrease
2. Calculate: Turn on Write equation. What you see is an equation that shows the original uranium atom on
the left. The boxes on the right represent the daughter product—the atom produced by radioactive
decay—and the emitted alpha particle.
A. In the top left box, write the mass number of the daughter product and press “Enter” on your
keyboard. What is this number? 234
B. In the bottom left box, write the atomic number of the daughter product and press “Enter.” What is
this number? 90
C. ✏ Click on the picture below , select ✏ edit. Enter the mass number and atomic number of the
alpha particle, which has the same composition as the nucleus of a helium (He) atom. After filling in
the boxes in the Gizmo, write the completed equation below:
D. According to your equation, what isotope remains after the alpha decay of
uranium-238? (Note: You can look up element symbols on the periodic table.)
Thorium-234
3. Check: Turn on Show equation, and click Play. The equation will appear at the end of the animation. Was
your prediction correct? Yes If not, modify your equation above.
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