SPL Set ID: 50415c27-1928-4307-b1dc-648f47edf65d

Sodium Iodide I 123 (Na 123 I) for diagnostic use is supplied in capsules for oral administration. The capsules are available in strengths of 3.7 and 7.4 megabecquerels (MBq) (100 and 200 μCi) I 123 at time of calibration. Each capsule contains 0.3 µg - 3 µg Sodium Thiosulfate as a stabilizer. The radionuclidic composition at calibration is not less than 97.0 percent I 123, not more than 2.9 percent I 125 and not more than 0.1 percent all others (I 121 or Te 121.) The radionuclidic composition at expiration time is not less than 87.2 percent I 123, not more than 12.4 percent I 125 and not more than 0.4 percent all others. The ratio of the concentration of I 123 and I 125 changes with time. Graph 1 shows the maximum concentration of each as a function of time. Graph 1 Radionuclidic Concentration of I 123 and I 125 Physical Characteristics Sodium Iodide I 123 decays by electron capture with a physical half-life of 13.2 hours. The photon that is useful for detection and imaging studies is listed in Table 1 . Table 1 Principal Radiation Emission Data 1 1 Kocher, David C., Radioactive Decay Data Tables, DOE/TIC-11026, 122, (1981) Radiation Mean %/Disintegration Mean Energy (keV) Gamma-2 83.4 159 External Radiation The specific gamma ray constant for I 123 is 1.6 R/hr-mCi at 1 cm. The first half value thickness of lead (Pb) for I 123 is 0.005 cm. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from the interposition of various thicknesses of Pb is shown in Table 2 . For example, the use of 1.63 cm of lead will decrease the external radiation exposure by a factor of about 1,000. Table 2 Radiation Attenuation by Lead Shielding 2 2 Shleien, Bernard, The Health Physics and Radiological Health Handbook, Table 6.1.2, 169, (1992) Shield Thickness (Pb), cm Coefficient of Attenuation 0.036 0.5 0.120 10 -1 0.240 10 -2 0.358 10 -3 0.477 10 -4 Note that these estimates of attenuation do not take into consideration the presence of contaminants. To correct for physical decay of I 123, the fractions that remain at selected intervals after the time of calibration are shown in Table 3 . Table 3 Sodium Iodide I 123 Decay Chart: Half-Life 13.2 Hours *Time of Calibration Hours Fraction Remaining Hours Fraction Remaining 0* 1.000 18 .389 3 .854 21 .332 6 .730 24 .284 9 .623 27 .242 12 .535 30 .207 15 .455 Graph 1