Atoms, nuclei, and radiation
Understand the tiny structures that store most visible matter's mass and release nuclear energy.
Introduce atomic identity, isotopes, binding energy, decay, detectors, dose, fission, and fusion with responsible safety boundaries.
Before you begin
- • Course 1: Measurement
- • Course 2: Matter and energy
By the end, you can
- • Relate proton and neutron counts to elements and isotopes.
- • Explain mass defect and binding energy qualitatively.
- • Distinguish activity, exposure, and biological dose.
- • Compare decay, fission, fusion, and lattice-assisted reaction claims.
Interactive model
Explore before calculating
Live laboratory
Isotope decay and mass-energy ledger
Follow a modeled isotope population through elapsed half-lives, then connect a declared mass defect to transformation energy and detector efficiency without confusing counts, emitted energy, or absorbed dose.
Remaining: 1.250e+11
Transformations: 8.750e+11
Activity now: 8.664e+7 Bq
Energy each: 9.315e-1 MeV
Modeled emitted energy: 1.306e-1 J
Expected detected counts: 8.750e+10
Each elapsed half-life halves the population that remains, not the original population again. The current activity falls with the remaining nuclei, while the integrated transformation count grows.
This single-branch model assigns one mass defect and one efficiency to every transformation. Real inference needs decay branches, daughter chains, geometry, backgrounds, dead time, emitted spectra, calibration, and uncertainty. Emitted energy is not absorbed dose; dose additionally requires deposited energy, exposed mass, radiation type, and biological weighting.
Level 1 · Foundations teaching kit
Record the investigation. Teach the reasoning.
A learner-facing lab record and a course-specific instructor guide turn the live model into a repeatable classroom investigation.
Learner record
Isotope decay and detection record
How do elapsed half-lives change remaining nuclei, present activity, total transformations, and expected detector counts?
Download learner recordInstructor guide
Teach for evidence, not button pushing
Learners distinguish exponential population decay, present activity, integrated transformations, detector counts, emitted energy, and dose.
Download instructor guideLesson 1 of 3
Elements and isotopes
How can atoms of one element have different masses?
The proton count defines the element. Isotopes share the same proton count but contain different numbers of neutrons.
Some isotope combinations are stable; others transform through radioactive decay toward lower-energy configurations.
Worked example
Carbon-12 and carbon-14 both have six protons. How do they differ?
- 1. Carbon-12 has 12 total nucleons, so 6 neutrons.
- 2. Carbon-14 has 14 total nucleons, so 8 neutrons.
- 3. Their chemistry is similar but nuclear stability differs.
They are isotopes of carbon; carbon-14 is radioactive.
Try it
Isotope card model
Materials: Coins or paper tokens in two colors.
- 1. Choose one color for protons and one for neutrons.
- 2. Build several isotopes of one element.
- 3. Keep proton count fixed.
- 4. Compare total nucleon counts.
Notice: Element identity stays fixed while nuclear mass and stability can change.
Check your understanding: What changes when one isotope of an element becomes another isotope of the same element?
Answer: The neutron count.
The proton count must remain the same for the element identity to remain unchanged.
Lesson 2 of 3
Binding energy and nuclear reactions
Why can rearranging nuclei release far more energy per atom than chemistry?
A bound nucleus has less total mass-energy than its separated protons and neutrons. The difference is binding energy, related by E = mc².
Fission splits heavy nuclei; fusion joins light nuclei. Both can move products toward more tightly bound configurations.
Worked example
A reaction's products have 0.001 atomic mass unit less mass than its inputs. Where did the mass go?
- 1. Mass is one form of energy.
- 2. The lower product mass corresponds to released energy.
- 3. Measure all kinetic energy and radiation to close the account.
The mass difference appears as other energy forms; conservation applies to total mass-energy.
Try it
Binding-energy landscape
Materials: Paper and a printed or sketched binding-energy-per-nucleon curve.
- 1. Locate light nuclei.
- 2. Locate iron-region nuclei.
- 3. Locate very heavy nuclei.
- 4. Draw arrows showing why fusion and fission can both release energy.
Notice: Both processes move toward more tightly bound nuclei near the curve's peak.
Check your understanding: Does E = mc² mean matter can disappear without an energy product?
Answer: No.
It means mass contributes to total energy; reaction accounting must include every output form.
Lesson 3 of 3
Radiation, detectors, and dose
How do we measure radiation without confusing counts, energy, and biological effect?
Activity counts nuclear transformations per second. A detector count depends on geometry and efficiency. Absorbed dose measures deposited energy per mass, while biological weighting depends on radiation type and tissue.
Radiation work requires trained supervision, controlled sources, time-distance-shielding practice, and legal safety procedures. This course uses simulations and public data, not sources.
Worked example
A detector records 120 counts in one minute while background is 90 counts per minute.
- 1. Measured total: 120 counts/min.
- 2. Expected background: 90 counts/min.
- 3. Simple net estimate: 30 counts/min.
- 4. Compare repeated statistical variation before claiming a source.
The background-subtracted estimate is 30 counts/min, but uncertainty and detector efficiency still matter.
Try it
Background-count simulation
Materials: Two dice and a tally sheet.
- 1. Roll both dice 30 times as a background run.
- 2. Count a chosen outcome as a detection.
- 3. Repeat for several runs.
- 4. Compare variation even though the rules never change.
Notice: Random count data fluctuate naturally, so one elevated run may not establish a new source.
Check your understanding: Why is detector count rate not automatically the same as biological dose?
Answer: Counts do not by themselves state deposited energy, radiation type, geometry, or tissue response.
Dose requires additional physical and biological information.
Continue into the evidence
Source-linked next reading
Chapter 12: Lattice Confinement Fusion
A measured nuclear-reaction program with its energy limits stated separately.
Lecture 12: LCF and the integrated picture
Places nuclear observations on the season evidence ladder.
Method and confidence tiers
How the site labels measured effects and unresolved extrapolations.