Direct current and pulse counting measurements on in-vivo mercuric iodide medical probes

Miniature mercuric iodide nuclear detectors which are cased in either a large 6 mm or smaller 1.7 mm outer diameter probes for potential use as gamma medical probe detectors have been fabricated and tested. The larger probes have been used mainly to monitor the dc output produced by high fluxes of 40 keV X-rays or of a 10 mCi 226Ra source which was 15 mm long and which was placed at distances of 1-10 cm from the HgI2 probe. The smaller probe, encased in a 16 gauge syringe needle was used mainly in the counting mode and resolved the 28 and 35 keV photopeak of 125I. The nuclear response of the tiny planar detector encased in the needle probe is anisotropic in the ratios of about 1.4:1.0 and 1.2:1.0 for monitoring 60 and 122 keV gamma rays perpendicular or parallel to the detector contact area respectively. (Auth.)