The Collider-Accelerator complex just completed a 2-month maintenance period. The major effort was the installation of the J10 beam stop in the AGS ring. This is an ALARA device designed to capture all injection, acceleration, and extraction losses. It is a narrow aperture that will also collect the particles that comprise the beam "halo". This should, in principle, reduce exposures related to maintenance activities in the ring by collecting all losses at one location and effectively shielding them.
Presently, the g-2 experiment is preparing for a 2 month run. This running period had been in some doubt due to the discovery of elevated levels of tritium in groundwater 250 feet from the beam dump. A routine quarterly groundwater sample in July showed 5000 pCi per liter. A follow up sample three months later in October showed approximately 40,000 pCi per liter. The laboratory took decisive actions and immediately installed an array of geoprobe wells about 125 feet closer to the dump. Higher concentrations of tritium were found in several of these groundwater samples. We looked closely at the design of the g-2 beam transport system and realized that there was a loss point upstream of the target and dump which was shielded on one side by several feet of soil. Soil samples were obtained and analyzed for radioactivity. Sodium-22 concentrations were determined to be about 200 pCi per gram. The area immediately above this loss point was not capped, so that rainwater was free to percolate down through this activated soil. Thin sidewall shielding around the soil hastened the percolation process by lowering resistance to the downward flow of rainwater. The sidewall shielding, then, acted like a "wick" for the rainwater.
Corrective actions, besides the installation of additional monitoring wells, included the extension of the beam dump gunnite cap upstream so that it covered the activated soil. Additional loss monitors were installed at the beam loss point to provide for better transport optics. Additionally, reviews of all beam transport system designs were performed to identify potentially similar situations where excessive localized soil activation may be occurring. The department will also revise ALARA procedures to focus attention on designs of new beam line systems to ensure possibilities of soil activation are minimized, and to prevent rainwater intrusion into activated soils.