Table l. Description of Radioisotope-Labeled Sand Fed to Dairy Cows Isotope Weight per Particle** Label (mg) (g) 20 14la. 9.7 x 107° 19 173 80 855, 6.2 x 10° 15 116 200 Aun 9.7 x 10° 16 85 450 466. 1.5x 10! 40 96 Nominal Size* (ym) size is used in discussing *The nominal the results. Dose per Cow (uCi) The size descriptions are: 20 um -— 95% of mass between 15 and 20 um, and no particles greater than 25 um; separated by liquid sedimentation. 80 um - pass 88 ym and retained on 74 um sieves. 200 um pass 246 um and retained on 175 um sieves. 450 um - pass 495 um and retained on 417 um sieves. **Weight of nominal spherical size particle with specific gravity of 2.3. Table 2. Characteristics of Isotopes Used to Label Sand Particles Isotope Gamma Half-Life Energy (Days) (MeV) Branching Ratio 141c. 32.5 0.145 48% 825, 64.0 0.514 100% oA Mn 312.5 0.835 100% 465, 83.9 0.889 1.120 1002 100% 153