We have used commercially available molecular sieves (zeolites) to adsorb radioactivity onto small (approximately 2.1 mm diameter) beads for use in various applications in nuclear medicine. Soaking the beads in [99mTc]-NaTcO4 solution of approximately 3 GBq ml(-1) for 1-2 min can produce point sources containing 3-6 MBq total. Radioactive uptake was strongly dependent on bead size. We have employed the sources for gamma camera uniformity and as point source markers for interactive identification of anatomical landmarks. Due to their small size (<< system spatial resolution), relatively high uptake and negligible scattering contribution they provide excellent devices with which to measure spatial resolution, detector uniformity and energy resolution. The molecular sieves are inexpensive and readily usable with both single photon and positron emitting radionuclides.
We describe the design and report on the experimental results of a novel thermal and cold neutron imaging detector utilizing neutron sensitive ( 10 B-doped) microchannel plates (MCPs). In this detector, the incoming neutron interaction products produce secondary electrons at the pores adjacent to the absorption point within the MCP glass. This electron signal is then multiplied by a stack of conventional MCPs within those adjacent pores limiting the spread of the signal to less than two pore diameters (currently 6-10 μm pores on 8-12 μm centers). The event position then can be encoded by a number of readout techniques already developed for photon/charged particle counting applications. This paper presents the results of experimental evaluation of neutron sensing MCP detector with Medipix2 readout allowing operation at high counting rate mode (>100 MHz level) at a spatial resolution limited by the 55 μm pixel size of the Medipix2 readout. Other attractive features of MCP neutron detectors are their high detection efficiency (approaching 50% levels) for thermal and cold neutrons and the absence of readout noise.
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