An Analysis of the Processes By Which Be-7 is Spread Throughout the Experimental End Stations of a Continuous Electron Beam Accelerator Facility. JAMES MURLA (St. Vincent College Latrobe, PA 15650) ROBERT MAY (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

In the Continuous Electron Beam Accelerator Facility of Jefferson Lab, there is a certain amount of radiation caused by the unintended interaction of the electron beam with surrounding surfaces, especially the walls of the downstream beam line after the beam passes through the physics target in the experimental end station. Be-7 is one of the radioisotopes formed by the interaction of this radiation with molecules of oxygen and nitrogen in the air is Be-7. Apparently, Be-7 atoms either become attached to dust, are transported as an aerosol, or are spread throughout the end station by some combination of both where they tend to collect on air filters, fan surfaces, and electrostatically charged surfaces. Although its radiotoxicity is very low, when Be-7 collects, it can exceed surface contamination limits in localized areas, called hot spots, requiring decontamination. A detailed mathematical model has been developed to describe ion production, attachment, and interaction with Be-7, based on the conceptual model presented by Bob May (2003) [2], which has been simplified by incorporating some well-researched assumptions. This model considers the influence of electrostatics, kinetics, and aerosol particle growth. Although Be-7 has a valence of +2, it remains electrically neutral and, being a relatively light ion with a high root mean square (RMS) velocity, electrostatics seems to play a small role in comparison to that of kinetics. Because of this, it appears that the most prevalent means by which Be-7 attaches to aerosols is by impaction on surfaces. A possible solution to the problem of Be-7 contamination is considered; a method of hydrating the air local to the Be-7 source to catalyze the production and growth of condensation nuclei, which serve as a mechanism for the collection of Be-7 atoms. These condensation nuclei may be collected and easily discarded.