A compact beam stop for a rare kaon decay experiment

We describe the development and testing of a novel beam stop for use in a r are kaon decay experiment at the Brookhaven Alternating Gradient Synchrotro n. The beam stop is located inside a dipole spectrometer magnet in close pr oximity to straw drift chambers and intercepts a high-intensity neutral had ron beam. The design process, involving both Monte Carlo simulations and be am tests of alternative beam-stop shielding arrangements, had the goal of m inimizing the leakage of particles from the beam stop and the resulting kit rates in detectors, while preserving maximum acceptance for events of inte rest. The beam tests consisted of measurements of rates in drift chambers, scintillation counter hodoscopes, a gas threshold Cherenkov counter, and a lead glass array. Measurements were also made with a set of specialized det ectors which were sensitive to low-energy neutrons, photons, and charged pa rticles. Comparisons are made between these measurements and a detailed Mon te Carlo simulation. (C) 1999 Elsevier Science B.V. All rights reserved.