Calculation of Photoneutron Contamination of Varian Linac in ICRU Soft-Tissue Phantom Using MCNPX Code.

Purpose: The aim of this research was to calculate the fluence, dose equivalent (DE), and kerma of thermal, epithermal and fast photoneutrons separately, within ICRU soft-tissue-equivalent phantom in the radiotherapy treatment room, using MCNPX Monte Carlo code.

Materials And Methods: For this purpose, 18 MV Varian Linac 2100 C/D machine was simulated and desired quantities were calculated on the central axis and transverse directions at different depths.

Results: Maximum fluence, DE and kerma of total photoneutrons on central axis of the phantom were 43.

Polarization-induced stiffness asymmetry of optical tweezers.

A tightly focused, linearly polarized laser beam, so-called optical tweezers, is proven to be a useful micromanipulation tool. It is known that there is a stiffness asymmetry in the direction perpendicular to the optical axis inherited from the polarization state of the laser. In this Letter, we report our experimental results of stiffness asymmetry for different bead sizes measured at the optimal trapping condition.