title: Absorption-edge transmission technique using Ce- 139 for measurement of stable iodine concentration.
abstract: We have investigated a technique for measuring stable iodine concentrations by absorption-edge transmission measurements using a Ce 139 radiation source. The lanthanum daughter emits characteristic x-rays whose energies just bracket the absorption edge of iodine at 33.2 keV. Relative transmission of these x-rays is sensitive to iodine concentration in the sample, but is relatively insensitive to other elements. By applying energy-selective beam filtration, it is possible to determine the relative transmission of these closely spaced x-ray energies with NaI(Tl) detectors. Optimizations of sample thickness, detector thickness, and Ce-139 source activity are discussed. Using sample volumes of about 10 ml, one can determine iodine concentration to an uncertainty (standard deviation) of +/- 5 microgram/ml with a 5-mCi source in a measurement time of 400 sec. Potential clinical applications of the in vitro technique are discussed, along with comparative aspects of the Ce-139 technique and other absorption and fluorescence techniques for measuring stable iodine.
mesh_terms: D000818:Animals; D002588:Cesium Radioisotopes; D004285:Dogs; D007455:Iodine / Q000032:analysis* / Q000097:blood; D007811:Lanthanum; D008956:Models, Chemical; D011868:Radioisotopes; D012974:Sodium Iodide; D013052:Spectrometry, X-Ray Emission / Q000379:methods*
chemical_list: D002588:Cesium Radioisotopes; D011868:Radioisotopes; D007811:Lanthanum; D007455:Iodine; D012974:Sodium Iodide