5. Theoretical Physics (CSN4)

Rainbows with positrons and carbon nanotubes

by N. Nešković (Laboratory of Physics, Vinča Institute of Nuclear Sciences)

Aula Seminari (LNF)

Aula Seminari


Via Enrico Fermi, 40 00044 Frascati (Roma)
The lecture is devoted to a quantum mechanical consideration of the transmission of positrons of a kinetic energy of 1 MeV through very short (11, 9) single-wall chiral carbon nanotubes. The nanotube lengths are between 50 and 320 nm. The transmission process is determined by the rainbow effects. The interaction potential of a positron and the nanotube is deduced from the Molière's interaction potential of the positron and a nanotube atom using the continuum approximation. The time-dependent Schrödinger equation is solved numerically, and the spatial and angular distributions of transmitted positrons are calculated. The initial positron beam is assumed to be an ensemble of non-interacting Gaussian wave packets. The spatial and angular distributions are generated using a computer simulation method. The examination is focused on the spatial and angular primary rainbows. It begins with an analysis of the corresponding classical rainbows, and continues with a detailed investigation of the amplitudes and phases of the wave functions of transmitted positrons. These analyses enable one to identify the principal and supernumerary primary rainbows appearing in the spatial and angular distributions. They also result in a detailed explanation of the way of their generation, which includes the effects of wrinkling of each wave packet during its deflection from the nanotube wall, and of its concentration just before a virtual barrier lying close to the corresponding classical rainbow. The wrinkling of the wave packets occurs due to their internal focusing. In addition, the wave packets wrinkle in a mutually coordinated way.