Proceedings of the sixth meeting of the task force on shielding aspects of accelerators, targets and irradiation facilities Stanford Linear Accelerator Center (SLAC), Menlo Park, CA, USA, 10-12 April 2002 jointly organised by Organisation of Economic Co-operation and Development, Stanford Linear Accelerator Center (SLAC), Radiation Safety Information Computational Center (RSICC), Shielding Working Group of the Reactor Physics Committee of Japan