Progress in the description of stellar evolution is driven by the collaborative effort
of nuclear physics, astrophysics and astronomy. Using those developments, the
theory of the origin of elements in the Universe is challenged. This thesis addresses
the problem behind the abundance of 44Ti and the origin of 26Al.
The mismatch between the predicted abundance of 44Ti as produced by the
only sites known to be able to create 44Ti, core collapse supernovae (CCSNe),
and the observations, highlight the current uncertainty that exists in the physics
of these stars. Several satellite based γ-ray observations of the isotope 44Ti have
been reported in recent times and confirm the disagreement. As the amount
of this isotope in stellar ejecta is thought to critically depend on the explosion
mechanism, the ability to accurately model the observed abundance would be
a pivotal step towards validating that theory. The most influential reaction to
the amount of 44Ti in supernovae is 44Ti(α, p)47V. Here we report on a direct
study of this reaction conducted at the REX-ISOLDE facility, CERN. The experiment
was performed at a centre of mass energy 4.15±0.23 MeV, which is,
for the first time, well within the Gamow window for core collapse supernovae.
The experiment employed a beam of 44Ti extracted from highly irradiated components
of the SINQ spallation neutron source of the Paul Scherrer Institute.
No yield above background was observed, enabling an upper limit for the rate
of this reaction to be determined. This result is below expectation, suggesting
that the 44Ti(α, p)47V reaction proceeds more slowly than previously thought.
Implications for astrophysical events, and remnant age, are discussed.
In Wolf-Rayet and asymptotic giant branch (AGB) stars, the 26gAl(p,γ)27Si
reaction is expected to govern the destruction of the cosmic γ-ray emitting nucleus 26Al. The rate of this reaction, however, is highly uncertain due to the unknown
properties of several resonances in the temperature regime of hydrogen burning.
We present a high-resolution inverse kinematic study of the 26gAl(d, p)27Al reaction
as a method for constraining the strengths of key astrophysical resonances in
the 26gAl(p,γ)27Si reaction. In particular, the results indicate that the resonance
at Er = 127 keV in 27Si determines the entire 26gAl(p, γ)27Si reaction rate over
almost the complete temperature range of Wolf-Rayet stars and AGB stars. The
measurements of spectroscopic factors for many states in 27Al and a shell model
calculation of nuclear properties of rp-resonant states in 27Si also allow for testing
the structure model
