A porous hexagonal boron nitride powder compact for the production and release of radioactive 11C

A porous pre-sintered hexagonal boron nitride powder compact was recently developed as target for the production of intense $^{11}$C beams for Positron Emission Tomography-aided hadron therapy. In a previous study, this target has been characterized regarding its operational limitations. In this work, microstructural characterization with respect to the target's grain size, porosity and pore structure, and a dedicated fractional release study from activated targets, i.e. how much $^{11}$C is extracted by a short heat treatment, is presented. Corresponding results include an average grain size of approximately 1.7(1) μm, total and open porosity of 40(5) and 21(7)%, respectively, which is mostly composed of pores with sizes ranging from 120 to 470 nm. From the measured release fraction the order of magnitude of carbon's diffusion coefficient$ D(1500 °C) = 10^{-15} - 10^{-14}$ cm$^2$ s$^{-1}$ in porous boron nitride, and a $^{11}$C extraction efficiency of about 10% at 1500 °C target temperature were estimated.