| Date | November 2019 | Marks available | 3 | Reference code | 19N.3.HL.TZ0.17 |
| Level | Higher level | Paper | Paper 3 | Time zone | 0 - no time zone |
| Command term | Discuss | Question number | 17 | Adapted from | N/A |
Question
Proxima Centauri is a main sequence star with a mass of 0.12 solar masses.
Estimate .
Describe why iron is the heaviest element that can be produced by nuclear fusion processes inside stars.
Discuss one process by which elements heavier than iron are formed in stars.
Markscheme
realization that lifetime ✔
✔
the binding energy per nucleon is a maximum for iron ✔
formation of heavier elements than iron by fusion is not energetically possible ✔
NOTE: For MP2 some reference to energy is needed
ALTERNATIVE 1 — s-process
s-process involves «slow» neutron capture ✔
in s-process beta decay occurs before another neutron is captured ✔
s-process occurs in giant stars «AGB stars» ✔
s-process terminates at bismuth/lead/polonium ✔
ALTERNATIVE 2 — r-process
r-process involves «rapid» neutron capture ✔
in r-process further neutrons are captured before the beta decay occurs ✔
r-process occurs in type II supernovae ✔
r-process can lead to elements heavier than bismuth/lead/polonium ✔
NOTE: If the type of the process (r or s/rapid or slow) is not mentioned, award [2 max].
