Modern Physics and Radioactivity
Track nuclear changes, calculate repeated half-lives, interpret radiation evidence, and distinguish fission, fusion, and radioactive decay.
Modern Physics and Radioactivity
Not yet verified on this browser.
Conserve mass number and atomic number when a nucleus changes
Isotopes have the same number of protons but different numbers of neutrons. Radioactive nuclei change spontaneously, releasing particles or electromagnetic energy.
Alpha radiation ionizes strongly but penetrates poorly. Beta penetrates farther. Gamma is highly penetrating and usually needs dense shielding.
Half-life means repeated halving
After n half-lives, the remaining fraction is (1/2)^n. It does not mean every individual nucleus decays on a schedule.
Nuclear and chemical changes are different
Chemical reactions rearrange electrons. Nuclear reactions change the nucleus and can convert a small mass defect into substantial energy.
Use the change in the two nuclear numbers
Mass −4 and atomic number −2: alpha decay.
Mass unchanged and atomic number +1: beta-minus decay.
Both unchanged but energy released: gamma emission.
For half-life, write the actual chain: 160 → 80 → 40 → 20. This prevents subtracting equal amounts instead of halving repeatedly.
Why it works
The two conserved numbers identify an emission more reliably than memorizing isolated decay examples.
Five forms you should recognize
Problem: A 160 mg sample undergoes three half-lives.
160 → 80 → 40 → 20 mgParent: mass 226, atomic number 88.
Daughter: mass 222, atomic number 86.
The changes −4 and −2 identify alpha emission.
Carbon-14: atomic number 6.
After beta-minus decay, mass remains 14 while atomic number becomes 7.
Fission: A heavy nucleus splits and may release chain-reaction neutrons.
Fusion: Light nuclei combine; this powers the Sun.
A bound nucleus has slightly less mass than its separated nucleons.
binding energy = Δmc²Check before you commit
- Subtracting the same amount every half-life
- Assuming all nuclei decay exactly at one half-life
- Changing mass number during beta-minus decay
- Changing atomic number during pure gamma emission
- Confusing fission with fusion
- Using penetration and ionization as though they increase together
Do you need the lesson-or just practice?
One original question in each form recommends your next step. It does not yet verify mastery.
Work at the level you need.
Foundations
Build the core procedure with immediate explanations.
Core Practice
Use mixed forms with less scaffolding.
UPCAT-Style Transfer
Apply the competency in unfamiliar representations.
Ready to verify this competency?
A score of 5/5 verifies mastery. An unsuccessful attempt loads a different five-form bank.
Modern Physics and Radioactivity FAQ
Does a sample become completely nonradioactive after one half-life?
No. Half remains on average; later half-lives continue halving the remainder.
Why is alpha dangerous if paper stops it?
External alpha is easily blocked, but an alpha-emitting material taken inside the body can deposit intense ionization over a short range.
Why does fusion release energy?
The fused nucleus has lower total mass than its separated starting nuclei; the mass defect appears as released energy.
Continue your science review.
Your progress stays on this browser.
Mastery results save to your Teacher Abi study profile.
Return to Student Hub View UPCAT Coverage
No comments:
Post a Comment