Gizmos Student Exploration: Nuclear Decay Answer Key

Gizmos Student Exploration: Nuclear Decay Answer Key

Name:_ Date: ________________________

Lab 8 - 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? Consists of two protons and two neutrons bound

together into a particle identical to helium nucleus.

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

during alpha decay? Gamma rays are also emitted.

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: It goes down by exactly two, as a result of the loss

of two protons.

B. The mass number of the atom: it decreases by 4 due to the loss of 4 nucleons in the

alpha particle_

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:

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.)

234 TH

+

4 He

90 2

238U

92

New mass

number

New atomic

number

Thorium-234

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.

3. Practice: Click Reset, turn off Show equation, and select Polonium. Write an equation for

the alpha decay of polonium, and then use the Gizmo to check your answer.

What isotope remains after the alpha decay of polonium-212? Lead-208

4. Practice: Click Reset, turn off Show equation, and select Radium. Write an equation for

the alpha decay of radium, and then use the Gizmo to check your answer.

What dangerous gas is produced by the decay of radium-226? Ranon

208 Pb

+

4 He

82 2

222 Rn

+

4 He

86 2

212Po

84

New mass

number

New atomic

number

226Ra

88

New mass

number

New atomic

number

5. Practice: Americium-241 is a radioactive isotope used in smoke detectors. Write an equation

for the alpha decay of Americium-241 below.

6. Analyze: In each equation, how is the mass number on the left side of the arrow related to

the sum of mass numbers on the right side of the arrow? Is this true for atomic numbers?

The mass number of the left side is equal to the sum of the mass on the right side of the

arrow. This is also true for atomic number.

_________________________________________________________________________

7. Summarize: In general, how can you determine the mass number of the daughter product

after alpha decay has taken place? How can you determine the atomic number?

In alpha decay, the mass number of the daughter product is four less than the original mass

number. The atomic number of the daughter product is two less than the original atomic

number.

_________________________________________________________________________

8. Think and discuss: Helium is the second most abundant element in the universe, but it is

rare in Earth’s atmosphere. Most of the helium used to fill balloons and blimps must be

extracted from Earth’s crust. How do you think this helium formed?

It is created by the natural radioactive decay of heavy radioactive elements.

Helium and Earth’s crust was probably produced by alpha decay of radioactive elements

within the crust.

237 Np

+

4 He

93 2

241Am

95

New mass

number

New atomic

number

Activity B:

Beta decay

Get the Gizmo ready:

 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?

1. Observe: Click Play and watch the animation.

A. What happens to the decaying neutron during beta decay? During Beta decay, a

neutron turns into a proton and an electron.

B. What is emitted from the nucleus during beta decay? _An electron and a gamma ray.

C. What is the mass number and charge of the emitted particle?

Mass number: 0 Charge: -1

2. 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?

Beta decay decreases the atomic number by one and leaves the mass number unchanged.

3. 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.)

14 N

+

0 e

7 -1

14C

6

New mass

number

New atomic

number

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? Nitrogen-14

4. 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.

131 Xe

+

0 e

54 -1

24 Mg

+

0 e

12 -1

131I

53

New mass

number

New atomic

number

24Na

11

New mass

number

New atomic

number

Activity C:

Protons into

neutrons

Get the Gizmo ready:

 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?

1. Observe: Click Play and watch the animation.

A. What happens to the decaying proton during positron emission? During positron

emission, a proton turns into a neutron and a positron.

B. What is the mass number and charge of the emitted positron?

Mass number: 0 Charge: +1

2. 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?

Positron emission decreases the atomic number by one and leaves the mass number

unchanged.

3. 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.)

11 B

+

0 e

5 1

11C

6

New mass

number

New atomic

number

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? Boron-11

4. Practice: Turn off Show equation. Fill in the equations for the positron emission of xenon118 and manganese-50 in the spaces below. Use the Gizmo to check your

answers.

5. Observe: Click Reset. Select Electron capture, and make sure Tungsten is selected.

Click Play and watch the animation.

A. What happened to the proton after absorbing an electron? The proton turned into a

neutron as gamma rays were emitted.

B. What is the mass number and charge of the absorbed electron?

Mass number: 0 Charge: -1

6. Predict: During electron capture, an electron is absorbed into the nucleus, causing a

proton to transform into a neutron. How will electron capture affect the atomic number and

mass number of the atom?

Electron capture will decrease the atomic number by one and leave mass unchanged.

118 I

+

0 e

53 1

50 Cr

+

0 e

24 1

118Xe

54

New mass

number

New atomic

number

50Mn

25

New mass

number

New atomic

number

7. Calculate: Note that in this equation the particle is absorbed, rather than emitted. Fill in

the first set of boxes with the mass number and atomic number of the absorbed electron. Fill

in the last set of boxes with the mass number and atomic number of the daughter product.

Turn on Show equation and click Play to check. Modify your equation if necessary.

What isotope is produced when tungsten-179 absorbs an electron? Tantalum-179

8. Practice: Turn off Show equation. Fill in the electron capture equations for gold-195 and

neodymium-141 in the spaces below. Use the Gizmo to check your answers.

9. Think and discuss: What do electron capture and positron emission have in common?

_________________________________________________________________________

Electron capture and positron emission both involve a proton transforming into a neutron.

Both processes reduce the atomic number by one and have no effect on the mass number.

0 e

+

179 Ta

-1 73

0 e

+

195 Pt

-1 78

0 e

+

141 Pr

-1 59

179W

74

New mass

number

New atomic

number

195Au

79

New mass

number

New atomic

number

141Nd

60

New mass

number

New atomic

number

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