University Physics III · Nuclear and Particle Physics · 11.05
The decay law, activity, and decay chains
Separation of variables on dN/dt = −λ N, N = N0 exp(−λ t), half-life as ln 2 over λ, activity A = λ N, the parent-daughter chain equation dN2/dt = λ1 N1 - λ2 N2, and the memoryless per-nucleus probability the exponential rests on.
Course-map guide · not a complete lesson or simulationScope & orientation
What this subsection covers
Separation of variables on dN/dt = −λ N, N = N0 exp(−λ t), half-life as ln 2 over λ, activity A = λ N, the parent-daughter chain equation dN2/dt = λ1 N1 - λ2 N2, and the memoryless per-nucleus probability the exponential rests on.A strong response uses binding-energy-per-nucleon curves and states where the model stops being reliable.
Reasoning checklist
Evidence, assumptions and limits
Assumptions to state
State the system, observable, approximation, and conditions held fixed before using a model.
Evidence to collect
What decay constant and half-life do counting-rate data support once background is subtracted and the counting statistics are propagated?
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What decay constant and half-life do counting-rate data support once background is subtracted and the counting statistics are propagated? Useful evidence includes timed gross and background count totals, a weighted log-linear fit with uncertainties propagated from both counts rather than from the net count alone, residuals, and a stated interval on the half-life.
Limits to state
This GioPhysics course map is an adaptable learning sequence, not academic credit, accreditation, or a universal university syllabus.
Read the complete note
This GioPhysics course map is an adaptable learning sequence, not academic credit, accreditation, or a universal university syllabus. Third-semester content is the least standardised of the introductory sequence: departments place oscillations, waves, optics, and thermal physics differently, and the modern-physics units here are a bounded survey rather than a complete course in relativity, quantum mechanics, atomic, nuclear, or particle physics. Follow your institution's published scope, notation, laboratory programme, and assessment rules. A result should be checked against units, signs, limiting cases, and the conditions under which its model was derived.
Diagram & examples
Work the claim before choosing an equation
Interactive concept map
Follow the model from claim to evidence.
Separation of variables on dN/dt = −λ N, N = N0 exp(−λ t), half-life as ln 2 over λ, activity A = λ N, the parent-daughter chain equation dN2/dt = λ1 N1 - λ2 N2, and the memoryless per-nucleus probability the exponential rests on.
Model, evidence, and boundary
When should a model used for The decay law, activity, and decay chains be revised?
modelModel, evidence, and boundary turns the stated idea into a representation that can make a prediction.
Example questions
Try the reasoning before revealing the structure.
When should a model used for The decay law, activity, and decay chains be revised?
Quick check
Test the reasoning, not recall
When should a model used for The decay law, activity, and decay chains be revised?
Choose an answer to test the model.