HS-PS1-8: Modeling Fission, Fusion and Radioactive Decay
In plain English: HS-PS1-8 is the NGSS high school performance expectation that asks students to develop models, such as drawings and nuclear equations, that show how the protons and neutrons in a nucleus change during fission, fusion and alpha, beta and gamma decay, and how much energy these processes release compared with chemical changes. It is usually taught in Chemistry, Physics or Physical Science.
Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.
Clarification Statement: Emphasis is on simple qualitative models, such as pictures or diagrams, and on the scale of energy released in nuclear processes relative to other kinds of transformations.
Assessment Boundary: Assessment does not include quantitative calculation of energy released. Assessment is limited to alpha, beta, and gamma radioactive decays.
Next Generation Science Standards · Disciplinary Core Idea: Matter and Its Interactions · Official standard
Students build and use models of the nucleus to show what changes in fission, fusion and radioactive decay. They track the number of protons (the atomic number Z, which sets the element) and the total number of protons and neutrons (the mass number A) in pictures, bead or chip models and nuclear equations such as 23892U → 23490Th + 42He. They also place the energy released by nuclear and chemical changes on a powers-of-ten scale, to see that one nuclear event releases roughly ten thousand to a hundred million times the energy of one chemical reaction between two molecules. No radioactive sources are used anywhere in this lesson: every activity uses paper models, dominoes and invented or published data.
The NGSS Clarification Statement says: "Emphasis is on simple qualitative models, such as pictures or diagrams, and on the scale of energy released in nuclear processes relative to other kinds of transformations." The Assessment Boundary says: "Assessment does not include quantitative calculation of energy released. Assessment is limited to alpha, beta, and gamma radioactive decays." So students never calculate the energy released: every energy value on this page is a standard approximate value that students read, place on a scale and compare. Radioactive decay on this page means alpha, beta (a neutron changes into a proton and an electron is emitted) and gamma decay only. Students do the practice of developing and using models: they build nuclei from chips, draw before-and-after pictures, write and check nuclear equations, and critique models made by others.
Learning Objectives
By the end of this lesson, students will be able to:
Use the atomic number and mass number to describe the protons and neutrons in a nucleus, and explain that the number of protons sets the element
Develop models (drawings, chip models and nuclear equations) of alpha, beta and gamma decay that show how the nucleus changes
Develop models of fission and fusion that show how nuclei split or join while the total number of protons and neutrons stays the same
Use a powers-of-ten scale to compare the energy released per event in nuclear processes with the energy released in chemical reactions
Critique a model of a nuclear process by checking what it conserves and what it leaves out
Prior Knowledge Required
Students should already be comfortable with:
Atoms made of protons, neutrons and electrons, and models of the atomic composition of substances MS-PS1-1
Reading atomic numbers and element symbols from the periodic table HS-PS1-1
Writing and comparing numbers as powers of ten 8.EE.A.3
The idea that energy is conserved and can change form
Write two statements on the board: "When charcoal burns, carbon atoms end up in carbon dioxide." and "In a nuclear reactor, uranium atoms end up as barium and krypton." Then ask:
Warm-Up Prompt
"In a chemical reaction, carbon stays carbon. In the reactor, uranium becomes different elements. Draw a quick sketch of an atom and circle the part that must change for one element to become another. What does that tell you about where nuclear changes happen?"
Collect sketches. Students who circle the electrons are thinking of chemical change; ask which particle number defines the element. Lead to the idea that nuclear processes change the nucleus itself.
Direct Instruction15-20 minutes
Modeling the nucleus. Write a nucleus as 23892U: the top number is the mass number A (protons plus neutrons), the bottom number is the atomic number Z (protons), and the number of neutrons is A - Z = 146. In every nuclear process on this page, the total A and the total Z (the charge) are the same before and after, so a model is correct only if both totals match. An alpha particle is a helium-4 nucleus, 42He, and a beta particle is an electron, 0-1e, made when a neutron in the nucleus changes into a proton. A gamma ray, γ, is a high-energy photon with no mass number and no charge. Diagram 1 shows how each decay moves a nucleus on a chart of protons against neutrons.
Alpha decay
Uranium-238 emits an alpha particle: 23892U → 23490Th + 42He.
Result: A: 238 = 234 + 4. Z: 92 = 90 + 2. The nucleus loses 2 protons and 2 neutrons, so uranium becomes thorium, two places earlier in the periodic table. The energy released leaves mostly as the kinetic energy of the fast alpha particle.
Beta decay
Carbon-14 in a dead tree emits a beta particle: 146C → 147N + 0-1e.
Result: A: 14 = 14 + 0. Z: 6 = 7 + (-1). One neutron becomes a proton, so the nucleus goes from 6 protons and 8 neutrons to 7 protons and 7 neutrons: carbon becomes nitrogen with the same mass number. The electron (and a nearly massless antineutrino) carries the energy away.
Gamma decay
After cesium-137 decays, its product is often left as an excited barium-137 nucleus, which then emits a gamma ray: 137m56Ba → 13756Ba + γ.
Result: A: 137 = 137. Z: 56 = 56. The protons and neutrons do not change, so the element stays barium. The nucleus moves from a higher-energy arrangement to a lower one, and the difference leaves as a gamma photon.
Fission
A slow neutron strikes uranium-235, which splits: 10n + 23592U → 14156Ba + 9236Kr + 3 10n.
Result: A: 1 + 235 = 236 = 141 + 92 + 3. Z: 0 + 92 = 92 = 56 + 36 + 0. One heavy nucleus becomes two medium nuclei and three free neutrons, so the number of nuclei changes while the totals do not.
Fusion
In a fusion experiment, deuterium and tritium nuclei join: 21H + 31H → 42He + 10n.
Result: A: 2 + 3 = 5 = 4 + 1. Z: 1 + 1 = 2 = 2 + 0. Two light nuclei join into a heavier one and release a fast neutron, which carries away most of the released energy as kinetic energy.
The scale of the energy. Use Diagram 2. Burning one methane molecule releases about 9 eV, while one nuclear event releases from about 0.16 MeV (160,000 eV) to about 200 MeV. The nuclear values sit about four to seven powers of ten higher. The reason is in the model: chemical changes rearrange electrons and bonds between atoms, while nuclear changes rearrange protons and neutrons held together by the strong nuclear force, which is far stronger over the tiny distances inside a nucleus. Students read these values; they do not calculate them. To close the explanation, ask: "Every nucleus that fuses is positively charged. What must be true about how two nuclei move for them to get close enough to join?"
Guided Practice15 minutes
Pairs use Diagram 1 to follow the first three steps of the uranium-238 decay series. For each step they write the nuclear equation, check the A and Z totals, and record the counts in the table. Then they sketch a before-and-after picture of each step with circles for protons and neutrons, using a single labeled circle for "the rest of the nucleus".
Guided practice: first steps of the uranium-238 decay series
Nucleus
Protons Z
Neutrons N
Mass number A
Next step
U-238
92
146
238
alpha decay
Th-234
90
144
234
beta decay
Pa-234
91
143
234
beta decay
U-234
92
142
234
(continues)
Write the equation for each step and check that A and Z match on both sides.
Compare U-238 and U-234: why are they the same element even after three decays?
After one alpha and two beta decays, how many protons and how many neutrons has the nucleus lost in total?
Explain in one sentence why the chart has no arrow for gamma decay.
Independent Practice10-15 minutes
Each student builds a model of a later part of the same series: radon-222, a gas found in some basements, decays by alpha emission, and its product decays by alpha emission again. Students write both equations, draw a before-and-after picture for each, and explain what the nucleus loses. Answers: 22286Rn → 21884Po + 42He and 21884Po → 21482Pb + 42He. In total the nucleus loses 4 protons and 4 neutrons, going from 86 protons and 136 neutrons to 82 protons and 132 neutrons.
Closure5 minutes
Exit ticket: "Sodium-24, used as a tracer in industry, decays by beta emission. Write the equation, and name what changed inside the nucleus." (2411Na → 2412Mg + 0-1e: a neutron became a proton, so Z rose from 11 to 12 and A stayed 24.) Return to the warm-up: nuclear processes change the nucleus, so one element can become another.
Differentiation Strategies
For Struggling Students
Give a three-column template, "before", "what leaves or joins", "after", with boxes for A and Z, so students fill in one number at a time
Start with the small nuclei in Activity 1 (beryllium-8, boron-12, nitrogen-16), where every proton and neutron can be a chip, before moving to uranium
Post a reference card: alpha = 2 protons and 2 neutrons leave; beta = a neutron becomes a proton and an electron leaves; gamma = only energy leaves
For Advanced Students
Ask students to extend Diagram 1 through the next alpha decays of the uranium-238 series and explain why the series moves down and to the left on the chart
Have students compare the per-event energies in Diagram 2 with energy per kilogram of fuel, and explain why the two comparisons give different ratios (the masses of the particles differ)
Ask students to design a better physical model of a chain reaction than dominoes and explain which features of fission it shows more faithfully
Assessment Guidance
What to Look For
Check that every model conserves both the mass number and the charge, and that students change the element symbol whenever the number of protons changes. Listen for students who describe beta decay as the nucleus losing a proton, or who say gamma decay turns one element into another. In energy comparisons, look for reasoning in powers of ten ("four or more powers of ten larger") and for an explanation that names the nucleus, not the electrons, as the source of nuclear energy.
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Classroom Activities
3 Activities
1
Chip Models of Alpha, Beta and Gamma Decay
20 minPairs
Pairs build small real nuclei from paper chips on a paper plate (one color for protons, one for neutrons) and act out each decay by moving chips. They record the nucleus before and after and write the equation. No radioactive sources are used anywhere in this lesson: every activity uses paper models, dominoes and invented or published data.
Procedure
Card 1, alpha decay: build beryllium-8 (4 protons, 4 neutrons). Move 2 protons and 2 neutrons off the plate as an alpha particle. What is left? (84Be → 42He + 42He: the rest is also an alpha particle.)
Card 2, beta decay: build boron-12 (5 protons, 7 neutrons). Swap one neutron chip for a proton chip and push an electron chip off the plate. (125B → 126C + 0-1e.)
Card 3, beta then gamma: build nitrogen-16 (7 protons, 9 neutrons). Do a beta decay, then place a star card on the plate to show the new nucleus is excited. Remove the star card as a gamma ray. (167N → 16*8O + 0-1e, then 16*8O → 168O + γ.)
Card 4, a heavy nucleus: use the printed uranium-238 card (92 protons, 146 neutrons) instead of chips, and change the numbers on the card for an alpha decay.
Recording Table
For each card, record the protons, neutrons and mass number before and after, the particle that left, and the element before and after. Check that the total mass number and the total charge are the same before and after.
Discussion Questions
In which decays did the element change, and how could you tell from the chips alone?
In Card 3, the gamma step changed no chips. What did it change, and how does your model show it?
What does the chip model leave out? Think about the energy released and the forces that hold the chips together.
Modification for Distance Learning
Students use two colors of coins, buttons or cut paper at home, photograph each before-and-after model, and post the photos with their equations to the class board.
2
Domino Chain Reaction Model of Fission
25 minGroups of 3-4
Groups model a fission chain reaction with dominoes. Each domino stands for one uranium-235 nucleus, and each fall stands for a fission that releases neutrons, as in 10n + 23592U → 14055Cs + 9337Rb + 3 10n. Groups compare a branching layout with a single line and discuss what the model gets right and wrong.
Procedure
Layout A (controlled): stand 31 dominoes in a single line, so each fall knocks over exactly one more. Time the whole line from the first push.
Layout B (branching): build rows of 1, 2, 4, 8 and 16 dominoes (31 in all), placed so each domino knocks over two in the next row. Time it the same way.
Before you push, check the uranium-235 equation above: the mass numbers and the atomic numbers must match on both sides.
Safety: work on the floor or a low table and keep the area clear so no one trips over the dominoes.
Sample Data (invented)
Layout A: all 31 dominoes fell in 3.1 s. Layout B: all 31 dominoes fell in 0.6 s. In Layout B the last row had 16 dominoes falling at almost the same moment.
Discussion Questions
Both layouts used 31 dominoes, but Layout B finished about five times faster. What does that tell you about a chain reaction in which every fission causes more than one new fission?
Layout A is like a reactor in which control rods absorb extra neutrons. Which part of the domino setup plays the role of the control rods?
The equation shows three neutrons per fission, but each domino knocks over two. Name two other ways the model differs from real fission.
Challenge Variation
Groups design a layout in which each domino knocks over three in the next row, predict how many dominoes the fourth row needs, and explain why real chain reactions stop growing when neutrons escape or are absorbed.
3
Energy Scale Card Sort
20 minGroups of 3-4
Groups place energy cards on a powers-of-ten number line made from 1 m of string, marked every 10 cm from 1 eV (100) to 109 eV. Every card gives a standard approximate value for the energy released in one event. Students do not calculate energies: they place, compare and explain.
Energy Cards
One photon of green light absorbed by a leaf: about 2 eV
Burning one methane molecule: about 9 eV
One carbon-14 beta decay: about 0.16 MeV (160,000 eV)
One uranium-238 alpha decay: about 4.3 MeV
One deuterium-tritium fusion: about 17.6 MeV
One uranium-235 fission: about 200 MeV
Procedure
Mark the string at 0, 10, 20, ... 90 cm and label the marks 1, 10, 100, ... 109 eV.
Place each card with a clothespin or tape. Write each value as a number times a power of ten first: 9 eV is between the 1 and 10 marks, close to 10.
Draw a line on the string between the last chemical or light card and the first nuclear card.
Discussion Questions
How many 10 cm steps separate burning one methane molecule from one uranium-235 fission? Say what that means in words.
All the nuclear cards are far to the right of the chemical cards. Use a model of the atom to explain why.
Which nuclear card is closest to the chemical cards, and is it still more than ten thousand times larger?
Modification for Distance Learning
Students place the cards on a shared slide with a ready-made powers-of-ten axis and record a short voice or text explanation of the gap between chemical and nuclear cards.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: How Alpha and Beta Decay Move a Nucleus (Uranium-238 Series)
Part of the chart of nuclides, with protons Z up and neutrons N across, drawn to scale. Alpha decay moves a nucleus two down and two to the left; beta decay moves it one up and one to the left. Gamma decay leaves the nucleus in the same square, because only energy leaves. After one alpha and two beta decays, uranium-238 becomes uranium-234: the same element, with 4 fewer neutrons.
Diagram 2: Energy Released per Event, Chemical and Nuclear
Standard approximate values on a powers-of-ten scale: each grid step is ten times the one before. One nuclear event releases from about 105 to about 108 eV, while burning one methane molecule releases about 10 eV. These values are given for comparison; students do not calculate them.
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Homework Assignment
~30 min
HS-PS1-8 Homework: Modeling Changes in the Nucleus
Directions: For every process, write the nuclear equation, check that the mass numbers and the atomic numbers (charges) match on both sides, and draw a simple before-and-after picture. Energy values are given; you compare them and do not calculate them. Use a periodic table for atomic numbers.
Part 1: Radioactive Decay (Problems 1-3)
Polonium-210 (21084Po) decays by alpha emission. (a) Write the equation and identify the product. (b) How many protons and neutrons does the nucleus have before and after? (c) Draw a before-and-after model that shows what left the nucleus.
Iodine-131 (13153I), used in medicine to treat thyroid disease, decays by beta emission. (a) Write the equation and identify the product. (b) Explain, using protons and neutrons, why the mass number stays the same while the element changes. (c) Draw a before-and-after model that shows which particle changes identity and which particle leaves.
Technetium-99m is an excited nucleus used in medical imaging: 99m43Tc → 9943Tc + γ. (a) Show that A and Z are conserved. (b) Explain why the element does not change. (c) Rank alpha, beta and gamma decay by how much they change the number of protons, and explain why gamma decay is still called radioactive decay.
Part 2: Fission and Fusion (Problems 4-5)
A uranium-235 nucleus absorbs a neutron and splits: 10n + 23592U → 14054Xe + 9438Sr + ?. (a) Find the missing particles and check both totals. (b) Draw a model of this fission. (c) Suppose every fission released 3 neutrons and each one caused a new fission. How many fissions would happen in the fifth generation if the first generation is one fission? (d) Explain what a reactor does so that, on average, only one neutron from each fission causes another fission.
Two deuterium nuclei can fuse: 21H + 21H → 32He + 10n. (a) Check that A and Z are conserved. (b) Draw a before-and-after model. (c) Compare this reaction with the deuterium-tritium fusion in the lesson: what is the same about the products, and what is different? (d) The energy released per reaction is about 3.3 MeV. Where on the scale in Diagram 2 would it go, and is it closer to the chemical or to the nuclear values?
Part 3: The Scale of Nuclear Energy (Problem 6)
The table gives standard approximate values of the energy released per kilogram of fuel: burning gasoline, about 4.6 × 107 J/kg; fission of uranium-235, about 8 × 1013 J/kg; deuterium-tritium fusion, about 3 × 1014 J/kg. (a) About how many powers of ten separate gasoline and uranium-235 fission? (b) Which releases more energy per kilogram, fission or fusion, and by roughly what factor? (c) Draw a model of an atom that shows which part changes in burning and which part changes in fission, and use it to explain the gap in (a).
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Nuclear Equations
Every equation has the correct product, and both A and Z totals are checked
Equations mostly correct, with one wrong product or one unchecked total
Models
Before-and-after drawings show exactly which protons, neutrons, electrons or energy leave or join
Drawings present but one change is missing or wrong
Energy Scale
Compares values in powers of ten and explains the gap with the nucleus and the strong force
Comparison made but not explained, or explained without numbers
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Use a periodic table for atomic numbers. Energy values are given for comparison, and no question asks you to calculate the energy released. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
A student builds a model of the particle emitted in alpha decay with 2 proton chips, 2 neutron chips and 2 electron chips. What is the best critique of the model?
Answer: C
An alpha particle is a helium-4 nucleus, 42He: 2 protons and 2 neutrons, with a charge of +2 and no electrons. Choice A confuses the nucleus with a whole atom. Choice B has the right mass number (4) but a charge of +4, and choice D has the right charge (+2) but a mass number of only 2, so neither would conserve both A and Z in a decay equation.
Question 2 of 20 · Multiple Choice
Thorium-230 (23090Th) decays by alpha emission. Which nucleus forms?
Answer: A
Alpha decay removes 2 protons and 2 neutrons: A = 230 - 4 = 226 and Z = 90 - 2 = 88, which is radium, so the product is radium-226. Choice C lowers the mass number but keeps Z at 90, so it ignores the 2 protons that leave. Choice D adds an alpha particle instead of removing one.
Question 3 of 20 · Multiple Choice
Cobalt-60 (6027Co), used to sterilize medical supplies, decays by beta emission. Which nucleus forms?
Answer: A
In beta decay a neutron becomes a proton, so Z rises from 27 to 28 (nickel) and A stays 60: nickel-60. Choice C lowers Z, as if a proton had left. Choice B treats beta decay as losing a neutron. Choice D adds a particle to the nucleus.
Question 4 of 20 · Multiple Choice
A phosphorus-32 nucleus has 15 protons and 17 neutrons. After one beta decay, what does the nucleus contain?
Answer: D
In beta decay one neutron changes into a proton and an electron leaves, so the nucleus has 16 protons and 16 neutrons (sulfur-32), and the mass number stays 32. Choice A turns a proton into a neutron, the reverse change. Choice B removes a neutron without making a proton. Choice C removes a proton, as if a proton had left.
Question 5 of 20 · Multiple Choice
An excited krypton-83 nucleus (83m36Kr) emits a gamma ray. Which nucleus remains?
Answer: C
A gamma ray has no mass number and no charge, so A stays 83 and Z stays 36: the nucleus is still krypton-83, now in a lower-energy state. Choice B subtracts 4 from the mass number, as in alpha decay. Choice D raises Z by 1, as in beta decay, and choice A lowers it.
Question 6 of 20 · Multiple Choice
In the Sun, one step of energy release is 32He + 32He → 42He + 2 11H. Which process is this, and is it modeled correctly?
Answer: B
Two light nuclei join into a heavier helium-4 nucleus, so it is fusion. A: 3 + 3 = 6 = 4 + 2(1). Z: 2 + 2 = 4 = 2 + 2(1). Choice A is wrong because no heavy nucleus splits. Choice D is wrong because alpha decay starts from one unstable nucleus, not from two colliding nuclei.
Question 7 of 20 · Multiple Choice
A uranium-235 nucleus absorbs a neutron and splits: 10n + 23592U → 13752Te + ? + 2 10n. What is the missing nucleus?
Answer: A
Mass number: 1 + 235 = 236, and 236 - 137 - 2 = 97. Atomic number: 92 - 52 = 40, which is zirconium, so the missing nucleus is zirconium-97. Choice B forgets the two neutrons on the right. Choice C uses the wrong atomic number (38 is strontium).
Question 8 of 20 · Multiple Choice
Why can the fission of uranium-235 become a chain reaction?
Answer: D
A chain reaction needs each event to trigger more events. The free neutrons released in each fission can be absorbed by other uranium-235 nuclei and split them. Choice A confuses heat with the neutron trigger. Choice B is true of many fragments, but radioactivity of the fragments does not cause new fissions.
Question 9 of 20 · Multiple Choice
A student claims: "One uranium-235 fission releases about as much energy as burning a few methane molecules." Use the energy scale in Diagram 2 to evaluate the claim.
Answer: B
On the scale, burning one methane molecule is about 10 eV and one fission is about 108 eV, so the gap is about seven powers of ten. Choice A ignores the size of the gap. Choice D is wrong: the point of a common energy scale is to compare different kinds of change.
Question 10 of 20 · Multiple Choice
Some space probes carry a sealed block of plutonium-238, which decays by alpha emission, as a power source. The block stays hot for decades without burning anything. Which model explains where the thermal energy comes from?
Answer: D
The energy comes from the nucleus: each alpha decay releases energy mostly as the kinetic energy of the alpha particle, which slows down inside the block and warms it. Choice A describes a chemical change, but nothing burns and the block is sealed. Choice B cannot explain heat that lasts for decades in the dark of space. Choice C does not describe plutonium-238, which decays by alpha emission: no electrons are captured by its nuclei.
Question 11 of 20 · Multiple Choice
Why does fusion need extremely high temperatures, such as the millions of degrees in the core of a star?
Answer: C
Both nuclei are positive, so they repel. Only at very high temperatures do they move fast enough to get close enough for the short-range strong force to pull them together. Choice A describes the opposite of fusion. Choices B and D describe changes that heating does not cause.
Question 12 of 20 · Multiple Choice
A student models beta decay of a nucleus by drawing one proton leaving it. What is wrong with this model?
Answer: D
The model shows the number of protons going down, but in beta decay it goes up by 1 because a neutron becomes a proton. The particle that leaves is an electron. Choice A repeats the error. Choice B describes part of alpha decay, and choice C describes gamma decay.
Question 13 of 20 · Multiple Choice
A student models a fission as 10n + 23592U → 14456Ba + 8936Kr + 3 10n. Which evaluation of the model is correct?
Answer: C
Mass number: 1 + 235 = 236 and 144 + 89 + 3 = 236. Atomic number: 0 + 92 = 92 and 56 + 36 + 0 = 92. Both totals match, so the model is correct. Choice B is wrong because fission always changes the number of nuclei. Choice D is wrong because only the totals of A and Z must match: free neutrons are counted in A, and neutrons can end up in different nuclei.
Question 14 of 20 · Multiple Choice
Thorium-232 (23290Th) undergoes one alpha decay followed by one beta decay. Which nucleus is left?
Answer: B
Alpha: A = 232 - 4 = 228 and Z = 90 - 2 = 88 (radium-228). Beta: Z rises to 89 and A stays 228, so the result is actinium-228. Choice A stops after the alpha decay. Choice C adds a second beta decay. Choice D keeps the mass number of 232, ignoring the alpha particle.
Question 15 of 20 · Short Answer
Americium-241 (24195Am) decays by alpha emission. Write the equation, identify the product, and describe a before-and-after model of the nucleus. (The americium in smoke detectors is sealed: never open a smoke detector.)
24195Am → 23793Np + 42He. A: 241 = 237 + 4. Z: 95 = 93 + 2. The product is neptunium-237. Model: a nucleus of 95 protons and 146 neutrons loses a cluster of 2 protons and 2 neutrons, leaving 93 protons and 144 neutrons, with an arrow for the kinetic energy carried away by the alpha particle.
Question 16 of 20 · Short Answer
Potassium-40 (4019K), found in small amounts in all potassium, including the potassium in bananas, decays by beta emission. Write the equation and explain what changes in the nucleus.
4019K → 4020Ca + 0-1e. A: 40 = 40 + 0. Z: 19 = 20 + (-1). A neutron changes into a proton, so the nucleus goes from 19 protons and 21 neutrons to 20 protons and 20 neutrons: potassium becomes calcium, and the electron carries energy away.
Question 17 of 20 · Short Answer
In the Sun, a proton and a deuterium nucleus join and release a gamma ray: 11H + 21H → 32He + γ. Name the process, check A and Z, and describe a model that shows where the energy goes.
This is fusion: two light nuclei join into a heavier one. A: 1 + 2 = 3. Z: 1 + 1 = 2. A model shows one proton and one proton-neutron pair joining into a nucleus of 2 protons and 1 neutron, with a wavy arrow for the gamma photon that carries the released energy away.
Question 18 of 20 · Short Answer
A teacher demonstrates fission with a box of set mousetraps, each holding two ping-pong balls. One ball thrown in sets off a trap, which launches its two balls into other traps. Describe what each part of the model represents and name two ways the model differs from real fission.
Each set trap represents a uranium-235 nucleus, each ball represents a neutron, and a trap snapping represents a fission that releases neutrons. The rapid spread shows a chain reaction. Differences: (1) a real fission releases two or three neutrons and splits the nucleus into two new, smaller nuclei, while a trap stays a trap; (2) a real fission releases tens of millions of times more energy per event than a chemical change, while the trap only releases the energy stored in its spring; (3) in a reactor some neutrons are absorbed or escape, which the box shows only if balls fly out.
Question 19 of 20 · Short Answer
A student says: "A nuclear power plant is just like a coal plant with a different fuel that burns." Use a model of the atom and the energy scale to critique this claim.
Both plants use the released energy to boil water, but the processes differ. Burning coal is a chemical change: electrons rearrange as carbon bonds with oxygen, and the nuclei do not change. Fission is a nuclear change: uranium nuclei split into new elements. Because nuclear changes rearrange protons and neutrons held by the strong nuclear force, one fission releases about 108 eV, compared with a few eV for one chemical reaction between molecules, so nothing in a reactor "burns".
Question 20 of 20 · Short Answer
Invented data: a model of a decay series gives the nuclei in order: lead-214 (Z 82, A 214), bismuth-214 (Z 83, A 214), polonium-214 (Z 84, A 214), lead-210 (Z 82, A 210). Identify each decay and explain how the numbers show it.
Pb-214 to Bi-214: Z rises by 1 and A stays the same, so beta decay. Bi-214 to Po-214: again Z + 1 with the same A, so beta decay. Po-214 to Pb-210: Z falls by 2 and A falls by 4, so alpha decay. Gamma rays may also be released, but they would not change these numbers.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-PS1-8 mean?
HS-PS1-8 asks students to develop models, such as pictures, diagrams and nuclear equations, that show how the nucleus changes in fission, fusion and radioactive decay, and how the energy released compares with other changes. The code means High School, Physical Science, core idea 1 (Matter and Its Interactions), performance expectation 8.
Is HS-PS1-8 taught in chemistry or physics?
Both are common. It often sits in a Chemistry unit on the atom and nuclear chemistry, and it also appears in Physics and in Physical Science courses. The math is light: adding mass numbers and atomic numbers and comparing powers of ten.
What is the assessment boundary for HS-PS1-8?
The official Assessment Boundary says that assessment does not include quantitative calculation of energy released and is limited to alpha, beta and gamma radioactive decays. Students compare given energy values but do not compute them from masses. This page uses beta decay in which a neutron becomes a proton and an electron is emitted; positron emission and electron capture are not modeled here.
Do students need E = mc² for HS-PS1-8?
No. Using E = mc² to calculate the energy from a mass difference is beyond this standard. Students may hear that the products of a nuclear reaction have slightly less mass than the reactants, but the lesson keeps energy qualitative and on a scale.
Is it safe to teach radioactivity in a high school classroom?
Yes, when the lesson uses models and data only, as this page does. Use paper chips, dominoes, drawings and invented or published data sets. Do not bring radioactive sources, ore samples or old consumer items that contain radioactive materials into class, and never open a smoke detector. If a school owns sealed sources and a radiation safety plan, follow that plan and the manufacturer’s instructions.
How do you balance a nuclear equation?
Add the mass numbers (top numbers) on each side and make them equal, then do the same with the atomic numbers (bottom numbers). The atomic number of any unknown nucleus tells you its element from the periodic table. A neutron counts as mass number 1 and charge 0, an electron as 0 and -1, and a gamma ray as 0 and 0.
What is the difference between fission and fusion?
In fission a heavy nucleus splits into two medium nuclei and a few neutrons. In fusion two light nuclei join into a heavier one. Both release energy and both conserve the total number of protons plus neutrons. Students can tell them apart in an equation by looking at whether one large nucleus breaks up or two small nuclei combine.
What models work well for HS-PS1-8?
Before-and-after drawings, colored chip or bead nuclei for small nuclides, printed number cards for heavy nuclei, a chart of protons against neutrons, domino or mousetrap chain reactions, and a powers-of-ten energy line. Ask students to say what each model shows and what it leaves out, since critiquing a model is part of the practice.
What mistakes do students make with nuclear decay?
Many students think beta decay removes a proton, forget to change the element symbol when the atomic number changes, or believe gamma decay changes the element. A quick check of both totals, A and Z, catches most of these errors.
What comes after HS-PS1-8?
HS-ESS1-1 uses fusion to model how the Sun releases energy over its life span, and Earth science standards such as HS-ESS1-5 use radioactive decay to explain the ages of rocks. In Physics, energy conservation standards such as HS-PS3-1 extend the energy ideas.
07
Related Standards
5 standards
These standards connect to HS-PS1-8: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-PS1-1Prerequisite
Develop models of the atomic composition of simple molecules and extended structures
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