Gregory S. Mitchell

Radiotracers labeled with high-energy positron emitters, such as those commonly used for positron emission tomography studies, emit visible light immediately following decay in a medium. This phenomenon, not previously described for these imaging tracers, is consistent with Cerenkov radiation and has several potential applications, especially for in vivo molecular imaging studies. Herein we detail a new molecular imaging tool, Cerenkov Luminescence Imaging, the experiments conducted that support our interpretation of the source of the signal, and proof-of-concept in vivo studies that set the foundation for future application of this new method.

We report on a precision measurement of the neutron spin structure function ${g}_{1}^{n}$ using deep inelastic scattering of polarized electrons by polarized ${}^{3}\mathrm{He}$. For the kinematic range $0.014<x<0.7$ and $1<{Q}^{2}<17(\mathrm{GeV}/c{)}^{2}$, we obtain $\ensuremath{\int}{0.014}^{0.7}{g}_{1}^{n}(x)dx\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.036\ifmmode\pm\else\textpm\fi{}0.004(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.005(\mathrm{syst})$ at an average ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5(\mathrm{GeV}/c{)}^{2}$. We find relatively large negative values for ${g}_{1}^{n}$ at low $x$. The results call into question the usual Regge theory method for extrapolating to $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ to find the full neutron integral $\ensuremath{\int}{1}^{}{g}_{1}^{n}(x)\mathrm{dx}$, needed for testing the quark-parton model and QCD sum rules.

We have measured the spin structure functions g2p and g2d and the virtual photon asymmetries A2p and A2d over the kinematic range 0.02⩽x⩽0.8 and 0.7⩽Q2⩽20GeV2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and 6LiD targets. Our measured g2 approximately follows the twist-2 Wandzura–Wilczek calculation. The twist-3 reduced matrix elements d2p and d2n are less than two standard deviations from zero. The data are inconsistent with the Burkhardt–Cottingham sum rule if there is no pathological behavior as x→0. The Efremov–Leader–Teryaev integral is consistent with zero within our measured kinematic range. The absolute value of A2 is significantly smaller than the A2<R(1+A1)/2 limit.