Acoustoelectric current in graphene nanoribbon due to Landau damping.

We perform self-consistent analysis of the Boltzmann transport equation for momentum and energy in the hypersound regime i.e., [Formula: see text] ([Formula: see text] is the acoustic wavenumber and l is the mean free path). We investigate the Landau damping of acoustic phonons ([Formula: see text]) in graphene nanoribbons, which leads to acoustoelectric current generation. Under a non-quantized field with drift velocity, we observed an acoustic phonon energy quantization that depends on the energy gap, the width, and the sub-index of the material. An effect similar to Cerenkov emission was observed, where the electron absorbed the confined acoustic phonon energy, causing the generation of acoustoelectric current in the graphene nanoribbon. A qualitative analysis of the dependence of the absorption coefficient and the acoustoelectric current on the phonon frequency is in agreement with experimental reports. We observed a shift in the peaks when the energy gap and the drift velocity were varied. Most importantly, a transparency window appears when the absorption coefficient is zero, making graphene nanoribbons a potential candidate for use as an acoustic wave filter with applications in tunable gate-controlled quantum information devices and phonon spectrometers.

OPTIMISATION OF SCATTER RADIATION TO STAFF DURING CT-FLUOROSCOPY: MONTE CARLO STUDIES.

Studies have shown that there is high radiation exposure to medical staff during computed tomography fluoroscopy (CTF)-guided procedures. This study aims to investigate staff dose reduction techniques considering the CTF gantry positioning in the room and room dimensions in addition to the conventional use of thyroid collars, aprons and eye goggles. A Toshiba Aquilion One 640 slice CT scanner and CTF room were modelled using SimpleGeo. Standing and supine adult mesh phantoms were used to represent the staff and patient. The models were spatially put together on one platform using VOXEL2MCNP. Based on this, MCNPX input files were generated for the studies. CTF gantry and staff positions, and CTF room size were varied for different scenarios. Effective, eye lens and thyroid dose to staff were estimated for each scenario. Additional means of possible dose reduction with respect to positioning of the CTF device and room layout are discussed.