# Nuclear Physics Flashcards

What is the nuclear scale and the proton charge radius?

~ 10^-15 m = fm

Proton charge radius = 0.877 fm

Define an atomic mass unit, amu

A scale on which 12 amu = mass of NEUTRAL C-12 in its ground state configuration.

How find the atomic mass (weight) of an element with natural isotopes?

Weight each isotopic mass by its natural abundance and add together.

What does A equal?

A = Atomic mass = Z+N

If an element has an m in the top right corner what does it mean?

It is a metastable isomer, i.e. a state that is not stable but has a significant lifetime.

Define the terms isotope, isotone and isobar and what they look like on a Segrè chart.

- Isotope: same protons (Z), different neutrons (N). Horizontal line in Segrè chart.
- Isotone: same neutrons (N), different protons (Z). Vertical line in Segrè chart.
- Isobar: same atomic mass (A). Diagonal line line in Segrè chart.

Describe the Segrè chart.

A plot of proton number (Z) vs neutron number (N), roughly straight line for medium N, then tilts to right for large N (more neutrons than protons). Top line is proton drip line, bottom is neutron drip line.

Nuclei above central line undergo β(+) decay and below central line β(-) decay, heavy nuclei undergo α-decay.

What are drip-lines?

Where the addition of a proton/neutron produces a nuclear which decays back by proton/neutron emission (Fermi-level lies above the nuclear potential).

Why are some vertical and horizontal bands in the Segrè chart associated with longer lifetimes?

They highlight nuclei with magic numbers of neutrons or protons.

How can some nuclei exist beyond the drip-lines?

If there is a barrier (e.g. Coulomb barrier) then nucleus can have significant lifetime even if beyond drip-line.

What does it mean if parity of a nuclear state is positive, or negative?

If parity is positive the spatial part of the nuclear wave-function is even.

If parity is negative the spatial part of the nuclear wave-function is odd.

What notation is uses to label the spin and parity of a nuclear state?

J^π

- J= Total angular momentum of nucleus = Vector sum of angular momenta (j) of nucleons
- π = parity = (-1)^l, where l is the orbital angular momentum of the last unpaired nucleon

What are the possible values of orbital angular momentum for a nucleon?

l = 0 : s l = 1 : p l = 2 : d l = 3 : f

What is the spin-parity (J^π) of even-even nuclei, and why?

0^+, because all nucleons are paired (hence spins cancel and parity is positive)

How do you find the spin-parity of even-odd nuclei?

Find spin and parity of unpaired nucleons.

How do you find the degeneracy of an orbital?

2j + 1

What are m(l) and m(s)? How many values do they have?

The quantum numbers for orbital and intrinsic angular momentum.

• m(l) has 2l+1 values (-l, -l+1,…,l-1, l).

• m(s) is either +-1/2 for protons and neutrons.

What is the mean field?

A potential corresponding to the average interaction encountered by nucleons.

How do you find the parity of a nuclear state?

(-1)^l , if multiple unpaired nucleons then product of all these.

How do you find the total angular momentum (J) of a nuclear state?

Vector sum of total angular momenta (j) of all nucleons.

What is the mass and lifetime of a neutron?

- 6 MeV

881. 5 seconds

How are atomic mass and BE related?

Atomic mass = (mass of protons, neutrons, electrons) - BE

In terms of atomic mass and binding energy, which nuclei are most stable?

Those with higher binding energy and lower mass.

Why is atomic mass (and not nuclear mass) used in BE calculations?

Some processes involve electron participation.