Definitions

Question 1

Penetrability

Answer 1

Probability for projectile
to reach the target
nucleus for interaction. It’s affected by the angular momentum barrier (l=0 s-wave, l=1 p-wave etc.) and the coulomb barrier.

Question 2

s-process

Answer 2

Nucleus undergoes neutron capture to form an isotope of one higher mass number.
If the new isotope is stable then a series of increases in mass can occur, but if it is unstable then beta-decay will occur, producing something with z+1.
The process is slow because there is sufficient time for this radioactive decay to occur before another neutron is captured.
A series of these reactions produces stable isotopes by moving along the valley of beta-decay stable isobars in the table of nuclides.
Abundance peaks at magic neutron numbers arise because the full shells don’t want another neutron so the process flow is broken.

Question 3

Thermonuclear runaway in Type-I X-ray bursts

Answer 3

Mass transferred from donor star accumulates on the surface of the neutron star until it ignites and fusion begins via the CNO-cycle. Continued accretion creates a degenerate shell of matter causing an increase in temperature and the triple-alpha cycle becomes favoured, resulting in a helium flash. The additional energy from the flash allows the CNO burning to breakout into thermonuclear runaway. Early phase is powered by the alpha-p process, which quickly changes to the rp-process.

Main observational features are: fast rise time, short duration, and sometimes a double peak in luminosity.

Question 4

Yeild

Answer 4

Total number of reactions / Total number of incident particles

Question 5

Degeneracy

Answer 5

• When average distance < de Broglie wavelength matter becomes degenerate
• Pauli exclusion principle: no two fermions in same quantum state
• Electrons fill quantum states up to certain energy
• degenerate gas strongly resists further compression (degeneracy pressure against
  forcing particles into higher energy states)
• unlike ideal gas, pressure is NOT proportional to temperature (only density)
• increase of temperature DOES NOT affect pressure
• at high enough temperature the degeneracy can be lifted à gas becomes ideal
• maximum mass that can be supported by electron degeneracy given by
  Chandrasekhar limit: ~ 1.44 M¤

Question 6

Binding energy

Answer 6

Energy needed to break nucleus into Z protons and N neutrons.

Question 7

Separation energy S

Answer 7

Energy required to remove nucleon from nucleus of mass A+1 = Energy gained when adding nucleon to
nucleus of mass A

Question 8

Resonance strength

Answer 8

Integrated cross-section over resonant region.

Question 9

r-process

Answer 9

Rapid neutron capture. Nucleus reacts before capturing decay.

Question 10

p-process

Answer 10

In the γ process, a seed distribution (from s- and r- nucleosynthesis) is
eroded by photodisintegration reactions at high temperatures