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Nuclear Decay SE - WORKSHEET
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Name: ______________________________________ Date: ________________________
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
- 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 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? _____
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.
- Click Play ( ), and then click Pause ( ) when the alpha particle is clearly visible. What is
an alpha particle made of? _____________________________________________
- Click Play and observe. Besides the alpha particle, what else is emitted from the nucleus
during alpha decay? ________________________________________________________
Gamma rays are energetic electromagnetic waves; they are often emitted in nuclear decay.
4
2
2 protons and 2 neutrons
a gamma ray
Activity A:
Alpha decay
Click Reset ( ). Check that Alpha decay and Uranium are selected.
Question: How does alpha decay change the nucleus of a radioactive atom?
- 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: _________________________________________
B. The mass number of the atom: __________________________________________
- 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? ______________
B. In the bottom left box, write the atomic number of the daughter product and press
“Enter.” What is this number? ______________
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:
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.)
- Check: Turn on Show equation , and click Play. The equation will appear at the end of the
animation. Was your prediction correct? _____________ If not, modify your equation above.
(Activity A continued on next page)
decrease by 2
decrease by 4
234
90
234
90 Th
4
2 He
Th - 234
Yes
Activity B:
Beta decay
Click Reset , and turn off Show equation. Select Beta decay from the Type of decay menu. Check that Carbon is selected.
Question: How does beta decay change the nucleus of a radioactive atom?
- Observe: Click Play and watch the animation.
A. What happens to the decaying neutron during beta decay? ____________________
B. What is emitted from the nucleus during beta decay? _________________________
C. What is the mass number and charge of the emitted particle?
Mass number: _______ Charge: _______
- Predict: During beta decay, a neutron is transformed into a proton and an electron (the beta particle ), which is emitted. Gamma rays are often emitted during beta decay as well.
How will beta decay affect the atomic number and mass number of the atom?
- Calculate: Turn on Write equation. Fill in the first set of boxes with the mass number and atomic number of the daughter product and the next set of boxes with the mass number and atomic number of the beta particle. (Note: The atomic number of an electron is -1.)
Check your answer by turning on Show equation and clicking Play. Modify your equation if
necessary. What isotope is produced by the beta decay of carbon-14? _________________
- Practice: Turn off Show equation. Fill in the equations for the beta decay of iodine-131 and sodium-24 in the spaces below. Use the Gizmo to check your answers.
The neutron becomes
a proton
Electron and gamma ray
0 -
The atomic number will increase by one, and the mass number will remain the same
14
7 N
0
-1 e^-
N - 14
0
0
-
-
e^-
e^-
131
24
12
54 Xe
Mg
Activity C: Protons into neutrons
Click Reset , and turn off Show equation. Select Positron emission. Check that Carbon is selected.
Introduction: A positron is a type of antimatter that is equivalent to an electron. If a positron and an electron meet, they will annihilate one another in a burst of gamma rays.
Question: How do positron emission and electron capture change an atom?
- Observe: Click Play and watch the animation.
A. What happens to the decaying proton during positron emission? ________________
B. What is the mass number and charge of the emitted positron? __________________
Mass number: _______ Charge: _______
- Predict: During positron emission, a proton is transformed into a neutron and a positron, which is emitted. The positron will fly through space until it encounters an electron. How will positron emission affect the atomic number and mass number of the atom?
- Calculate: Turn on Write equation. Fill in the first set of boxes with the mass number and atomic number of the daughter product and the next set of boxes with the mass number and atomic number of the positron. (Note: The atomic number of a positron is 1.)
Check your answer by turning on Show equation and clicking Play. Modify your equation if
necessary. What isotope is produced when carbon-11 emits a positron? _______________
- Practice: Turn off Show equation. Fill in the equations for the positron emission of xenon- 118 and manganese-50 in the spaces below. Use the Gizmo to check your answers.
(Activity C continued on next page)
It gives off a
positron and gamma ray in order to convert to a neutron
0 1
The mass number will remain constant, while the atomic number will decrease by 1
11
5 B
0
1 e^+
B - 11
0
1 e^+
0
1
e^+
118
50
24
53
I
Cr
