Speaker
Description
Carbon burning is the third stage of stellar evolution
determining
the final destiny of massive stars and of low-mass stars in
close binary systems.
Only stars with a mass larger than a critical value
$M_{up}^* \sim 10 M_\odot$, can ignite C in non-degenerate conditions
and proceed to the next advanced burning stages up to the
formation of a gravitationally unstable iron core.
Various final destinies are possible, among which a direct
collapse into a black hole or the formation of a neutron star
followed by the violent ejection of the
external layers (type II SN).
Less massive stars $M < M_{up} \sim 7 M_\odot$, never attain the conditions
for C ignition and will evolve into CO White Dwarfs.
The values of $M_{up}^*$ and $M_{up}$ are linked to the
$^{12}C + ^{12}C$ reaction rate:
the little knowledge we have of
it at astrophysical energies
is the greater contribution to the uncertainty
of these masses.
Stellar C burning proceeds mainly through the
$^{12}C(^{12}C, \alpha) ^{20}Ne$
and
$^{12}C(^{12}C, p) ^{23}Na$
channels.
The cross-sections can be measured either detecting
the emitted charged particles or the $\gamma$-rays
produced by the decay of the excited states of
$^{20}Ne$ and $^{23}Na$.
$^{12}C + ^{12}C$ fusion reactions were investigated in a wide
energy range, down to $2.2$ MeV, still above the astrophysical energies.
A direct measurement is necessary for both stellar evolution models
and the correct analysis of indirect data.
The aim of my PhD project is the direct determination of the cross section of the
$^{12}C + ^{12}C$ reaction at astrophysical energies through $\gamma$ spectroscopy
at LNGS.
Here a devoted setup is being developed to reach an extremely low background condition.
The project will also make use of the new MV accelerator available at the Bellotti Ion
Beam Facility at LNGS, in the context of the LUNA MV research project.
This accelerator is
capable of producing a high intensity carbon beam
($\sim 0.15$ mA) with great energy resolution and stability:
as of our knowledge this is the highest C beam intensity
available in the world.
The detection setup will be made of several NaI scintillators and
an HpGe. NaI detectors will be placed
in a compact arrangement around the HpGe, covering a $2\pi$ angle:
such a configuration guarantees a high detection efficiency, while
preserving the excellent HpGe resolution ($1.2$ keV at $1.33\, \mathrm{MeV}$).
The NaI configuration will also function as an active veto for
beam-induced background.
In this contribution I will present details of recent results in setup development.
