SCIENCE · INVESTIGATE AND EXPLAIN

Compare fission and fusion without confusing balance with feasibility

Compare selected fusion and fission reaction ledgers and distinguish conservation, energy release and rate.

Learning outcome: Compare selected fusion and fission reaction ledgers and distinguish conservation, energy release and rate.

Starting recap

Fusion combines lighter nuclei; fission divides a heavier nucleus. Both require complete initial and final particle accounting.

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Try

Compare 2/1H+3/1H→4/2He+? with 235/92U+neutron→141/56Ba+92/36Kr+?.

Open the experiment

Predict

Does calling a process fission or fusion determine the number of omitted neutrons?

Your prediction and reason

Experiment

Select fusion and fission cases and test all four omitted-product candidates. Explain separate A and Z residuals for one failed candidate each.

Balance nuclear mass number and charge

Worked teaching model · synthetic values · Conservation of nucleon number and electric charge is necessary, not sufficient for a possible reaction. Beta− includes an electron and antineutrino; no reaction rates, branching probabilities, reaction construction or radiation handling.

Reaction: 0=alpha,1=beta−,2=gamma,3=fusion,4=fission: 0 case Candidate omitted product: 0 choice

Reset keeps your prediction, captures and practice history.

Quantity	Calculated value	Unit
Initial mass number	238.0000	integer accounting
Final mass number	238.0000	integer accounting
Initial charge number	92.0000	integer accounting
Final charge number	92.0000	integer accounting

Both accounting checks pass.

238/92 U → 234/90 Th + ? Candidate: alpha (A4,Z2). Initial-minus-final residuals: A=0, Z=0. Charge and nucleon counts alone do not prove energy feasibility or branching probability.

The candidate selector uses these four entries for the selected reaction:

alpha (A4,Z2)
neutron (A1,Z0)
proton (A1,Z1)
gamma (A0,Z0)

Model boundary: Conservation of nucleon number and electric charge is necessary, not sufficient for a possible reaction. Beta− includes an electron and antineutrino; no reaction rates, branching probabilities, reaction construction or radiation handling.

All investigations are virtual. Do not obtain radioactive sources, expose eyes to bright beams, or build high-voltage apparatus. Notebook captures preserve selected recipes, not physical measurements.

Both accounting checks pass.

238/92 U → 234/90 Th + ? Candidate: alpha (A4,Z2). Initial-minus-final residuals: A=0, Z=0. Charge and nucleon counts alone do not prove energy feasibility or branching probability.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Compare equations at the same level of detail

The selected fusion equation combines deuterium and tritium: total A is 2+3=5 and total charge number is 1+1=2. Helium-4 accounts for A 4 and Z 2, leaving A 1 and Z 0 for an emitted neutron. A gamma photon would preserve charge but fail the nucleon ledger. This is a statement about the specified channel, not every fusion reaction.

The fission example begins with uranium-235 and a neutron, so initial totals are A 236 and Z 92. The selected barium-141 and krypton-92 products total A 233 and Z 92. Three neutrons complete both ledgers. Real fission has a distribution of fragment channels; this example does not assign a universal fragment pair or universal neutron yield.

Explain why either can release energy

Energy release depends on total final rest mass relative to total initial rest mass. Some light-nucleus fusion reactions and some heavy-nucleus fission reactions lead to more tightly bound products and positive Q. The names fusion and fission alone do not supply a numerical Q or establish that every such reaction releases energy.

Use the separate mass-energy investigation only when a complete mass difference is supplied. A balanced A/Z equation cannot replace that information. It also does not calculate the distribution of kinetic energy among products; momentum conservation and particle masses are needed for that question.

Separate an allowed ledger from an accessible process

Nuclei with positive charge repel electrically. Fusion probabilities depend on quantum processes and the conditions of the reacting population; conservation alone does not say that cold nuclei will combine at an appreciable rate. Fission likewise depends on the nucleus, incident particle conditions and possible channels. Neither classroom ledger is a recipe for inducing a reaction.

Transfer: challenge two claims

“Balanced means rapid” is unsupported because no cross section or rate model is provided. “All energy becomes electricity” is also unsupported because Q describes released energy before any device losses or conversion constraints. A defensible conclusion is narrower: the selected missing particles satisfy nucleon and charge conservation for the given channel.

Cumulative modern-evidence explanation

Write a short comparison using three earlier lessons: photon line energies come from selected energy gaps; nuclear Q comes from complete rest-energy differences; half-life describes a probability law for an ensemble. All three concern energy or change, but none can be substituted for the others. State one measurement or source datum needed to go beyond each teaching model. These are exclusively virtual activities, not instructions for nuclear experiments.

Source and authorship

Reference for the physical relationship. Source checked 30 October 2026. The explanations, numerical cases, questions and diagrams here are original; reference material is not copied. Exact h,c,e follow NIST SI definitions.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

Compare what the balanced equation establishes with the additional evidence needed for Q, rate and practical control.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Account for rest mass and released energy Next: Physics and physical systems and next units

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