Why some nuclei refuse to break

Science · Quantum & Modern Physics · ages 21-22

Name ______________________ Date ____________

What happens to binding just past a magic count?
- It stays exactly flat forever
- The next nucleon binds far more loosely
- All nucleons escape at once
Which of these is a magic number?
- 28
- 30
- 24
The liquid drop picture alone explains why the magic numbers are special.
Circle one: True False
A model without spin orbit splitting predicts magic numbers up to which value?
- 126
- 82
- 20
A nuclide chart shows a binding spike at 50 with a sharp drop right after. What does the drop mark?
- The start of a new higher shell above a filled one
- Proof that shells do not exist
- A mistake in weighing the nucleus
An odd-A nucleus has one neutron past a closed shell in an orbit with known momentum and parity. What sets its ground state spin and parity?
- The average over all nucleons together
- That last unpaired nucleon alone
- The total mass of the nucleus
Finding the predicted spin and parity in a real odd-A nucleus counts against the shell model.
Circle one: True False
A student predicts spins for a deformed nucleus that rotates as a whole, using only single orbits, and the answers miss badly. What went wrong?
- Magic numbers never exist in any nucleus
- Spin orbit splitting is always zero
- Single orbits are the wrong tool for collective rotation; the drop picture fits better there

Answer key

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

The next nucleon binds far more loosely · A new shell starts higher up, so the next nucleon holds loosely.
28 · 28 sits in the magic list; 24 and 30 do not.
False · The drop gets broad trends but has no levels, so no special counts.
20 · Plain level spacing lands 2, 8, and 20, then stalls.
The start of a new higher shell above a filled one · The step down is the shell gap made visible in binding data.
That last unpaired nucleon alone · The closed shells cancel out, leaving the lone nucleon to call the spin.
False · Matching predictions is exactly how the model earns its keep.
Single orbits are the wrong tool for collective rotation; the drop picture fits better there · Collective motion lies outside the shell picture, where the drop model wins.