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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 lifetime on main sequence of Proxima Centaurilifetime on main sequence of Sun.

[2]
a.

Describe why iron is the heaviest element that can be produced by nuclear fusion processes inside stars.

[2]
b.

Discuss one process by which elements heavier than iron are formed in stars.

[3]
c.

Markscheme

realization that lifetime Tmassluminosity

TT=MM-2.5=0.12-2.5=200 

a.

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

b.

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].

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Option D: Astrophysics » Option D: Astrophysics (Additional higher level option topics) » D.4 – Stellar processes (HL only)
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Option D: Astrophysics » Option D: Astrophysics (Additional higher level option topics)
Option D: Astrophysics

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