Interlaboratory comparison of techniques for measuring lung burdens of low-energy photon-emitters

An interlaboratory exercise was conducted to assess techniques of detection and calibration in the direct measurement of lung contamination with plutonium and other nuclides emitting only low-energy X-rays. Three volunteers, of small intermediate and large physique, inhaled an aerosol incorporating 103Pd, a 20-keV X-ray emitter, and visited 13 other laboratories in the U.K., Europe and North America. Participants in the exercise were asked to estimate each subject's lung content, using their procedures for assessing burdens of plutonium, and their estimates were compared with values derived independently from measurements of 51Cr, also incorporated in the inhaled particles, by gamma-ray spectrometry. Laboratories' calibration procedures were in most cases based on elaborate thorax phantoms, and these generally led to underestimates of the subjects' contents, in some cases by a factor of three or more; only one such laboratory produced estimates in satisfactory agreement with the independently known values. The phoswich detectors, employed by most participants, appeared to be more sensitive than gas counters. If a standard configuration were required, offering the highest sensitivity in most situations, the choice would be a pair of 12-cm diameter phoswich detectors viewing the left and right anterior surfaces of the upper thorax. No improvement in sensitivity would result from increasing the size, although larger units may offer other advantages. (author)