Well counter

Solvent Extraction. The procedures used are described elsewhere (9, 10). Although preliminary experiments showed that equilibrium was established within two hours, all samples were mixed for 24 hours. Duplicate 1-ml. aliquots of the organic phase were counted either in a well counter (for gamma emission) or as dry samples in a 2tt proportional counter (for beta emission). 

Gamma (y) Sodium iodide doped with thallium iodide are used pSlal(Tl)] thallium, which is present at 0.1-0.4% of sodium emits 420 nm scintillations. This phosphor is very efficient in absorbing y-radiation because of high atomic number of iodine and high density of sodium iodide. Sodium iodide is hermetically sealed. It is normally used in well counters. A typical well counter used in laboratory and that used in cameras in nuclear medicine are show in Figs. 3 and 4. 

Fig. 3 A typical well counter used for measurement of gamma rays.

The crystal itself is usually a circular cyHiider machined from a single crystal of sodium iodide that was carefully grown to ensure optical clarity for efficient light collection. A small amount of thallium is added to the mother liquor to improve performance. The high atomic number of iodine and the density of sodium iodide (3.7g/cm ) favor the absorption of y-radiation. For this reason, a well counter is often referred to as a y-counter. For a typical well detector, the counting efficiency for expressed as the percentage of decays that produces counts, approximates 70%. 

SepPak RP-C18 cartridge was measured in a well counter under similar geometric conditions. 

Analyses based on FPLC were performed using a Superose 12 or Superdex peptide HR 10/30 column (Pharmacia). Samples were injected into the unit and eluted using a 50mM PBS at a flow rate of 35 mL/h. Fractions of 1 mL were collected and counted in a 1272 Clinigamma gamma well counter. 

Here, a similar procedure was used for analysis. A sample of approximately 1,000 counts/s is applied to silica gel fiberglass sheets and developed in acetone. Parallel to the labeled product, sodium " Tc-pertechnetate is also analyzed. After development, the dried strips are cut into 1-cm pieces and measured in an NK-350 type scintillation well counter coupled with an automatic sample sorter. Tc-HSA remained at the start Rf=0.0), Tc-pertechnetate moved with the solvent front (liy=0.9-1.0). 

MeV Proton Bombardment. Sources produced by 15-MeV protons were shown by a two-component fit half-life analysis of the multiscaled well counter data to contain about 1% (by activity) and no detectable or... 

Measurement of Total Counts. We usually determined total in samples by placing the sample in Nal(Tl) well counters with data fed to the same computing system as for the above analyses for background and half-life correction (15). Calibration is by a standard 2Na source dissolved in water and placed in a test tube. The well counters had the most reproducible counting geometry of any of our detection systems and thus were used to obtain total amount of source added to any experiment. present in the samples was corrected by using the two-component decay curve analysis. 

The first of Hal s major contributions to biochemistry and nuclear medicine had been tbe invention of the well counter for measurement of radioactivity in liquid samples in 1951 (Rev. Sci. Instr. 22, No. 12, 912-914,1951). Well counters soon became the most widely used instrument in radiation chemistry. 

An isotope dose calibrator is shaped as a cylinder and is often built in beneath the working area in the safety cabinet. It measures the radioactivity of a prepared dose in a vial or syringe. Each individual radionuclide can be measured accurately. Other equipment to measure radioactivity are scintillation counters (e.g. the Nal well counter) and semiconductor-based instruments (e.g. the Germanium detector). 

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