Instrumentation and Methods A) lon Chamber Measurements All environmental exposure cate measurements were obtained using a Reuter Stokes anvironmencal radiation monitor model RSS-111. The tnscrumene ts designed to neasure environmental radiation as low as 100 uwRad/year. The RSS<11l consists of a spherical high pressure ion chamber filled to 25 atmospheres of azgon. Incident radiation produces {on pairs within the active volume of che chamber which result in a current flow. The current flow is measured by an electrometer and is directly related to the free air exposure trace (1). The active volume of the stainless steel fonization chamber is known to +01%. The current produced inthe chamber is a function of incident radiarion from am external field, cosmic ray-response and contamination found in the stainless steel. The equation relating instrumenc response to energy of the incident radiation is: Rj = K} Tj + Ra + Ke Te where R4 =™ current produced in the chamber by che incident gamma field x} =* proportionality constant scating the variability of instrument response to the energy af che incident gamma field Ij = intenstty of the gamma field in -R/hr Ry = current sroduced by activity in che stainless steel Ke ™ proportionalicy constane for cosmic rays Ic ™ intensity of cosmic rays