A "tentative" estimate of the doses involved was made in 1948, based on dozens of assumptions, some of which are now known to be incorrect. In the absence of personal dosimetry badges, the study authors relied on measurements of sodium activation in the victims' blood and urine samples as their primary source of data. This activation would have been caused by neutron radiation, but they converted all doses to equivalent doses of gamma or X-ray radiation. They concluded that Daghlian and Slotin had probably received doses equivalent to 290 and 880 rem, respectively, of gamma rays. Minimum and maximum estimates varied from about 50% to 200% of these values. The authors also calculated doses equivalent to a mix of soft 80 keV X-rays and gamma rays, which they believed gave a more realistic picture of the exposure than the gamma equivalent. In this model, the equivalent X-ray doses were much higher, but would be concentrated in the tissues facing the source, whereas the gamma component penetrated the whole body. Slotin's equivalent dose was estimated to be 1930 R (roentgen) of X-ray with 114 R of gamma, while Daghlian's equivalent dose was estimated to be 480 R of X-ray with 110 R of gamma. Five hundred roentgen equivalent man (rem) is usually a fatal exposure for humans.