Studies of Beam Loss Patterns and Dose Distributions around the
                    TPS LINAC During Beam Commissioning

                               Ang-Yu Chen
            National Synchrotron Radiation Research Center, Taiwan

Abstract:
The Taiwan Photon Source (TPS) in National Synchrotron Radiation Center (NSRRC)
will soon become one of the most advanced light source facilities in the world.
The TPS accelerator system consists of a 3.0GeV storage ring with a
circumference of 518.4m, a concentric booster synchrotron with a circumference
of 496.8m, and a pre-injector 150MeV electron LINAC. Due to some delay of the
TPS civil construction, NSRRC has built a simple bunker made of 1.0m thick
concrete for the assembly and acceptance test of the outsourcing LINAC. During
the test of the LINAC, a lot of radiation safety related works or studies have
been carried out including beam loss patterns and dose distributions. Radiation
surveillance indicated that beam loss pattern had changed drastically over time
during the first few weeks of the test, which caused some difficulties and
troubles for health physics program. Gamma-ray and neutron dose rates around the
bunker were repeatedly measured during that period of time. To facilitate
shielding analysis and beam loss diagnosis, a series of FLUKA simulations was
performed with respect to some assumed simple beam loss scenarios. FLUKA is a
three-dimensional general-purpose particle transport and interaction Monte Carlo
code capable of simulating hadronic and electromagnetic cascades in considerable
detail. A full-scale geometry model including the main components of the
accelerator, the bunker structure and local shielding arrangement has been built
to make the simulation as realistic as possible. The resultant dose
distributions could regarded as useful response functions to various beam loss
scenarios. During beam commissioning, this study demonstrates that a reasonable
beam loss pattern and detailed dose distribution could be obtained through a
synthetic analysis of calculated results and measurements.