Shielding the RadPhi Photon Beam Line

Abstract

During the brief data-taking periods obtained by RadPhi in 1997 a high background rate was observed in the trigger counters that was not associated with events from the target. Subsequently it was shown that these rates are in good agreement with what is expected for the e^± halo around an unshielded bremsstrahlung beam. In this report a series of Monte Carlo simulations are presented which test the effectiveness of a variety of shielding schemes for reducing this background. A solution is found which reduced background from the beam halo to a level consistent with running at the rates for which the experiment was designed. This solution fits into the immediate constraints on time and resources for 1998, and is currently being implemented. Possibilities for further improvements are discussed.