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Liquid scintillation samples with Th were prepared a few hours after the separation of the progeny. During the measurements, Th and its daughters are not in radioactive equilibrium. The counting efficiencies of the individual radionuclides of the decay chain differ from each other and the activity of an individual progeny relative to the activity of Th varies with time. Hence, the overall counting efficiency varies with time as well. The counting efficiency ε of Th and its progeny was determined by means of the CIEMAT/NIST efficiency tracing method. The free parameter is derived from the quench-indicating parameter, SQP(E), and from H tracer measurements. This makes it possible to compute the efficiency ε as a function of time. The individual efficiencies of all progeny are to be combined, taking correction factors and activity ratios into account. Thereby, a new, time-dependent correction, namely for the decay during the measurements, is applied. With this method, activity results are obtained that are stable over a long period of time. A least-squares method yields the time of the chemical separation as well as the Th half-life, which was also obtained by means of measurements in an ionization chamber. The weighted mean of the two methods (CIEMAT/NIST efficiency tracing and measurements in ionization chambers) was found to be T = 18.681(9) d.
This article was published in the following journal.
Name: Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine
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The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacologic, physiologic, or radiologic activity.
Inorganic compounds that contain TECHNETIUM as an integral part of the molecule. Technetium 99m (m=metastable) is an isotope of technetium that has a half-life of about 6 hours. Technetium 99, which has a half-life of 210,000 years, is a decay product of technetium 99m.
Normal human serum albumin mildly iodinated with radioactive iodine (131-I) which has a half-life of 8 days, and emits beta and gamma rays. It is used as a diagnostic aid in blood volume determination. (from Merck Index, 11th ed)
The first artificially produced element and a radioactive fission product of URANIUM. Technetium has the atomic symbol Tc, atomic number 43, and atomic weight 98.91. All technetium isotopes are radioactive. Technetium 99m (m=metastable) which is the decay product of Molybdenum 99, has a half-life of about 6 hours and is used diagnostically as a radioactive imaging agent. Technetium 99 which is a decay product of technetium 99m, has a half-life of 210,000 years.
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