En anglais

Tiny cores, enormous densities

Science · Quantum & Modern Physics · ages 19-21

Name ______________________ Date ____________

What is the range of the strong force?
- Across the whole atom
- A few femtometers, then it fades
- Infinite, like gravity
What does A count in a nucleus?
- Protons plus neutrons
- Protons only
- Electrons in shells
Where does binding energy per nucleon peak?
- Near the lightest gases
- At the heaviest elements
- Near iron
Mirror nuclei swap proton and neutron counts yet bind nearly alike. What does that show?
- Protons repel neutrons strongly
- The strong force is nearly charge blind
- Neutrons carry positive charge
A nucleus has nucleon number 8. Type its radius in fm.
Answer: ______________
Why do heavy nuclei carry extra neutrons?
- Extra neutrons dilute the proton repulsion with short range glue
- Neutrons cancel electron charge
- Protons decay without neutrons
Lead and helium nuclei differ hugely in size, yet their densities match. Why?
- Lead has no neutrons
- Helium nuclei are hollow
- Volume scales with nucleon number, so density stays flat
Fusing two light nuclei into a heavier one near iron releases energy.
Circle one: True False

Answer key

For grown-ups. Fold this page away before handing over the rest.

A few femtometers, then it fades · The strong grip spans a few femtometers before repulsion takes over.
Protons plus neutrons · A is the mass number: every nucleon, proton or neutron.
Near iron · The curve climbs to iron and falls past it.
The strong force is nearly charge blind · Swapped counts binding alike means the grip ignores charge.
2.4 · The cube root of 8 is 2, and 1.2 times 2 is 2.4 fm.
Extra neutrons dilute the proton repulsion with short range glue · Extra neutrons add attraction without adding repulsion.
Volume scales with nucleon number, so density stays flat · Volume grows with A, keeping the packing density nearly constant.
True · Binding per nucleon climbs toward iron, and the gain leaves as released energy.