Theoretical design of a solid scintillation detector for tritium surface contamination measurement based on CaF2(Eu) sheet and self-coincidence technology of MCP-PMT.

Measurement of tritium surface contamination is important for tritium related facilities, especially for fusion devices. A novel detector has been designed for tritium surface contamination measurements based on CaF2(Eu) sheet and Microchannel plate photomultiplier tube (MCP-PMT). Self-coincidence technology has been introduced to obtain lower detection limit by diminishing the background noise caused by γ-rays and hot electrons. Performance of the detector was optimized by specifying the key parameters including the distance of the scintillator and sample, the thickness of light guide, the number of annular electrodes et al., using Monte Carlo method. Results indicate that detection efficiency of 49.4 % and the response deviations at different positions less than 0.5 % could be achieved. The detection limit of tritium under the simulation conditions is 0.09 Bq/cm2 and 0.03 Bq/cm2 when the counting time is 10 s and 60 s, respectively.

Low-Dose High-Resolution TOF-PET Using Ionization-activated Multi-State Low-Z Detector Media.

We propose PET scanners using low atomic number media that undergo a persistent local change of state along the paths of the Compton recoil electrons. Measurement of the individual scattering locations and angles, deposited energies, and recoil electron directions allows using the kinematical constraints of the 2-body Compton scattering process to perform a statistical time-ordering of the scatterings, with a high probability of precisely identifying where the gamma first interacted in the detector. In these cases the Line-of-Response is measured with high resolution, determined by the underlying physics processes and not the detector segmentation. There are multiple such media that act through different mechanisms. As an example in which the change of state is quantum-mechanical through a change in molecular configuration, rather than thermodynamic, as in a bubble chamber, we present simulations of a two-state photoswitchable organic dye, a 'Switchillator', that is activated to a fluorescent-capable state by the ionization of the recoil electrons. The activated state is persistent, and can be optically excited multiple times to image individual activated molecules. Energy resolution is provided by counting the activated molecules. Location along the LOR is implemented by large-area time-of-flight MCP-PMT photodetectors with single photon time resolution in the tens of ps and sub-mm spatial resolution. Simulations indicate a large reduction of dose.