Abstract
This paper describes the construction and calibration of the NIST large area x-ray counting system. (238)Pu sources 8 in (20.32 cm) by 5 in (12.70 cm) thick, emitting L x rays in the range of 12-20 keV are calibrated for total emission rate and also for rate through a centrally located 3 in (7.63 cm) diameter aperture. Alpha particle emission rates are obtained using the known x-ray to alpha particle abundances. The sources will be used to calibrate alpha-particle surface monitors.