Dmitry Yakovlev gives an interesting and entertaining overview of pyconuclear reactions. These density sensitive nuclear fusion processes are manifestations of the QED vacuum, which involves Kindergarten physics and the problem is therefore explained by a young Russian girl. The reaction rate of pyconuclear reactions is independent of temperature, but increases exponentially with increasing density. These processes are thought to allow for the formation of large nuclei in the neutron star crust.
(The image shows George Gamow at young age).
This was a beautifully presented topic. Dr. Yakovlev discussed how pycnonuclear reactions can be suppressed by magnetic fields and the composition of the neutron star crust. It was discussed that enhancement of these reactions is very unlikely... maybe a low frequency mode of oscillation, of the ions forming the solid crust, could present increase in the reaction rate.
ReplyDeleteI found interesting from Dr. Yakovlev talk, the small regime of temperatures and densities where carbon burning can take place and I wonder if this regime matches our estimates for superburst carbon burning.
This comment is actually from Randall Cooper
ReplyDeleteRegarding the suppression of pycnonuclear reactions in the presence of a strong magnetic field: Would a lattice even form in the first place in such a field? Naively, I'd expect the magnetic field to prevent the ions from settling into their lattice sites. Any thoughts?
This is an interesting question. The presence of an external magnetic field increases the zero-point oscillation frequency of the nuclei to a value omegaB=e*Z*B/(2*Mn*c), where Mn is the nucleus mass, e and Z are the proton and atomic charge, B is the magnetic field and c is the speed of light. Hence the approximation of nuclei sited at the center of lattice cells of radius R breaks down when such a frequency equals the zero magnetic field zero-point value omega=e*Z(4*pi*rho/Mn^2), where rho is the density of the system. So omegaB equals omega when rho*c^2=B^2/(16*pi) so when the magnetic energy doubles the mass-energy density of the system ! this clearly does not occur even in a neutron star and therefore the approximation of nuclei sited in their lattice sites is safe.
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