Gizmos Student Exploration: Nuclear Decay Answer Key NEW TOP PREDICTION

Student Exploration: Nuclear Decay

Vocabulary: alpha particle, atomic number, beta particle, daughter product, gamma ray,

isotope, mass number, nuclear decay, positron, radioactive, subatomic particle

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+ 1 u

Neutron Nucleus 0 1 u

Electron Orbitals 1– 0 u

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? 4

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? 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? Protons and neutrons

2. Click Play and observe. Besides the alpha particle, what else is emitted from the nucleus

during alpha decay? Gamma rays

Gamma rays are energetic electromagnetic waves; they are often emitted in nuclear decay.

Activity A:

Alpha decay

Get the Gizmo ready:

• Click Reset ( ).

• Check that Alpha decay and 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: The number of protons will decrease by 2

B. The mass number of the atom: The mass number will decrease by 4

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. In the next set of boxes, 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:

234 Th + 4 H

 90 2

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.

(Activity A continued on next page)