The number of fusion reactions that are critical for astrophysics is scarce. Among these, the 12C + 12C reaction that is essential for the life cycle of massive stars, may occur at different stages of stellar evolution: explosive scenarios like Type Ia supernovae which can be used as cosmological standard candles, quiescent carbon burning in the contracting core of a massive star at temperatures of the order of 1 GK, and densities above a million g/cm3 and possibly in superbursts of x-ray binary systems.
The obstacle to reliable extrapolation of the 12C + 12C cross section into the astrophysically relevant Gamow energy window is the presence of resonances in the cross section around the Coulomb barrier that continue down to the lowest collision energies accessible experimentally. This behaviour is strikingly different from the smooth variation in cross section as a function of energy typical of fusion in other heavy-ion systems.
The presence of resonances in the 12C + 12C reaction has been hotly debated for over 60 years. The conventional wisdom is that they correspond to the formation of short-lived molecular states, and this early suggestion has led on to far wider discussion of clustering in alpha-conjugate systems. However, this model remains controversial: an alternate picture is that the resonant behaviour is simply an artifact of the low level density of the 12C + 12C compound system.
Together with the IPHC Laboratory in Strasbourg, we have developed a dedicated experiment called STELLA for studying carbon burning in the laboratory using intense 12C beams. Initial studies led to a high impact publication and in the coming years, we intend to push down in energy to the region relevant to massive stars. This project will entail detector design and development, data taking and data analysis. There is scope also to model the astrophysical implications of the results. Extended data taking will take place at the IPN Orsay facility near Paris.
Academic entry requirements: at least a class 2:1 MSc or MPhys degree in Physics.
How to apply:
Applicants should apply via the University’s online application system at https://www.york.ac.uk/study/postgraduate-research/apply/. Please read the application guidance first so that you understand the various steps in the application process