A study of beam loss pattern and dose distribution around the TPS LINAC during beam commissioning

Abstract

Beam loss estimation is very important for accelerator shielding design and accurate dose evaluation. The 150-MeV LINAC system of the Taiwan Photon Source (TPS) was assembled and installed in a temporary bunker for acceptance test. Gamma-ray and neutron dose rates around the area were repeatedly measured during beam commissioning. Monitoring results indicated that the beam loss pattern could change drastically over time, especially during the first few weeks of the test, which has caused radiation safety concerns in the area. To facilitate shielding analysis and beam loss diagnosis, FLUKA was used to estimate dose distributions around the area resulting from a series of ideal point beam losses. A full-scale geometry model including main components of the accelerator, structure of the bunker, and additional local shielding has been established to make the simulations as realistic as possible. The resultant dose distributions could be regarded as useful response functions in evaluating combined beam loss scenarios. Taking the beam test on September 23, 2011 as an example, this study has demonstrated that a reasonable beam loss pattern and a detailed dose distribution could be obtained through a synthetic analysis of the calculated response functions and on-site dose rate measurements.