SPL Set ID: 46b8d7ba-432d-d610-84f2-550bf9d0bae3

11.1 Chemical Characteristics Sodium Iodide I 131 Capsules Diagnostic is a radiodioactive diagnostic agent containing sodium iodide I 131 and supplied for oral administration in a gelatin capsule. Each capsule contains no-carrier-added sodium iodide I 131, disodium edetate dihydrate USP as a stabilizer, sodium thiosulfate pentahydrate USP as a reducing agent, and dibasic sodium phosphate anhydrous USP. Sodium Iodide I 131 is designated chemically as Na131I and has a molecular weight of 153.99. 11.2 Physical Characteristics Iodine I 131 decays by beta emission and associated gamma emission with a physical half-life of 8.04 days. The principal radiation emissions are listed in Table 4. Table 4 Principal Radiation Emission Data from Decay of Sodium Iodide I 131 Radiation Mean % per Disintegration Mean Energy (keV) Beta-1 2.13% 69.4 Beta-3 7.20% 96.6 Beta-4 89.4% 191.6 Gamma-7 6.14% 284.3 Gamma-14 81.2% 364.5 Gamma-18 7.12% 637.0 11.3 External Radiation The specific gamma-ray constant for iodine I 131 is 4.26 x 10 -13 C•m 2 •kg -1 •MBq -1 •s -1 (2.2 R•cm 2 /mCi•hr). The first half-value thickness of lead (Pb) for iodine I 131 is 0.27 cm. A range of values for the relative attenuation of the radiation emitted by iodine I 131 that results from interposition of various thicknesses of Pb is shown in Table 5. For example, the use of 2.59 cm of Pb will decrease the external radiation exposure by a factor of about 100. Table 5 Radiation Attenuation of Iodine I 131 by Lead Shielding Shield Thickness (Pb) cm Coefficient of Attenuation 0.27 0.5 0.56 0.25 0.99 10 -1 2.59 10 -2 4.53 10 -3 To correct for physical decay of iodine I 131, the fractions that remain at selected intervals after the time of calibration are shown in Table 6. Table 6 Physical Decay Chart: Iodine I 131, Half-Life 8.04 days Days Fraction Remaining Days Fraction Remaining Days Fraction Remaining 0 Calibration Time 1.000 11 0.388 22 0.151 1 0.918 12 0.356 23 0.138 2 0.842 13 0.327 24 0.127 3 0.773 14 0.300 25 0.116 4 0.709 15 0.275 26 0.107 5 0.651 16 0.253 27 0.098 6 0.597 17 0.232 28 0.090 7 0.548 18 0.213 29 0.083 8 0.503 19 0.195 30 0.076 9 0.461 20 0.179 10 0.423 21 0.164