Direct analysis half-life

Moreover the energies of these ( -partides (electrons) are known to be 1.39 MeV and that of the gamma-rays 1.38 MeV so that the measnned values of these magnitudes are characteristic of substances containing sodium. (Measurement of the y-radiadon is the usual procedure.) At least 70 of the elements can be activated in this way, by the capture of thermal neutrons, i.e.. by neutron activation analysis. An activation analysis follows a procedure similar to that shown ill Fig. 2. In almost all analyses, the sample materials are not treated before the bombardment, but are placed directly into the bombardment capsule or container. The length of the bombardment interval is usually determined by the half-life of the radionuclide used for the element of interest and the flux of nuclear particles. 

The determination of the concentration of a drug in plasma is an accepted surrogate marker for drug exposure. The use of LC-MS-based approaches for the quantitative analysis of a drug or its metabolite in a physiological sample such as plasma or serum is perhaps the hallmark of PK studies in drug discovery. The PK profiles derived from LC-MS data provide bioavailability and half-life information for drug candidates. These PK profiles are used to directly compare lead compounds and select specific compounds for further study. 

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