Radioactivity detector flow cell design

We determined the efficiency for Carbon-14 at about 20% in our rebuilt cell. We have done no work with Tritium. We found that the detector s radioactivity response does not reach a maximum with increasing high voltage but steadily increases. At a count efficiency of 20%, the background is 100 cpm. Simplified details of the LSM-1 flow cell design are given in Figure 11 by permission of Nuclear Enterprises, Inc. The cell consists of ... 

The decision to use either NMR or LC-NMR for the analysis of mixtures in the pharmaceutical industry depends on factors related to their chromatographic separation and the ability of NMR to elucidate the structure of organic compounds whether hyphenated or not. The major technical considerations of LC-NMR, discussed below, are NMR sensitivity, NMR and chromatographi-cally compatible solvents, solvent suppression, NMR flow-probe design, and LC-NMR sensitivity or compatibility of the volume of the chromatographic peak with the volume of the NMR flow cell for better detection. Figure 20-1 shows the schematic setup of the LC-NMR connected to other devices, such as radioactivity detector and MS (see Section 20.4). 

Unfortunately the counting efficiency of the system was relatively poor, 0.2% for tritium and 17% for carbon. However, the advantage of this method is that due to the cell being packed with beads, it would have little flow resistance and limited peak dispersion and thus if used in conjunction with suitable low dispersion connecting tubes, it could be used with relatively high efficiency columns. As a consequence, many modem commercial radioactivity detectors are designed on the same principle, but with more efficient scintillators and more efficiently designed sensors. 

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