A B S T R A C T The cyclotron-produced radionuclide, 13N, was used to label ammonia and to study its metabolism in a group of 5 normal subjects and 17 patients with liver disease, including 5 with portacaval shunts and 11 with encephalopathy. Arterial ammonia levels were 52-264 ,AM. The rate of ammonia clearance from the vascular compartment (metabolism) was a linear function of its arterial concentration: Amol/min = 4.71 [NH3Ia + 3.76, r = +0.85, P < 0.005. Quantitative body scans showed that 7.4+±0.3% of the isotope was metabolized by the brain. The brain ammonia utilization rate, calculated from brain and blood activities, was a function of the arterial ammonia concentration: ,umol/ min per whole brain = 0.375 [NH3]a -3.6, r = +0.93, P < 0.005. Assuming that cerebral blood flow and brain weights were normal, 47 + 3% of the ammonia was extracted from arterial blood during a single pass through the normal brains. Ammonia uptake was greatest in gray matter. The ammonia utilization reaction(s) appears to take place in a compartment, perhaps in astrocytes, that includes <20% of all brain ammonia. In the 11 nonencephalopathic subjects the [NH3Ia was 100±8 ,uM and the brain ammonia utilization rate was 32±3 ,umol/min per whole brain; in the 11 encephalopathic subjects these were respectively elevated to 149±18 AM (P < 0.01), and 53 ± 7 ,umol/min per whole brain (P <0.01). In normal subjects, -50% of the arterial ammonia was metabolized by skeletal muscle. In patients with portal-systemic shunting, muscle may become the most important organ for ammonia detoxification.

New Experiments With Spheres-Gas (NEWS-G) is a direct dark matter detection experiment using SphericalProportional Counters (SPCs) with light noble gases to search for low-mass Weakly Interacting Massive Particles (WIMPs). We report the results from the first physics run taken at the Laboratoire Souterrain de Modane (LSM) with SEDINE, a 60 cm diameter prototype SPC operated with a mixture of Ne + CH 4 (0.7 %) at 3.1 bars for a total exposure of 9.7 kg · days. New constraints are set on the spin-independent WIMP-nucleon scattering cross-section in the sub-GeV/c 2 mass region. We exclude cross-sections above 4.4 × 10 −37 cm 2 at 90 % confidence level (C.L.) for a 0.5 GeV/c 2 WIMP. The competitive results obtained with SEDINE are promising for the next phase of the NEWS-G experiment: a 140 cm diameter SPC to be installed at SNOLAB by summer 2018.

Spherical Proportional Counters (SPCs) are a novel gaseous detector technology employed by the NEWS-G low-mass dark matter search experiment for their high sensitivity to single electrons from ionization. In this paper, we report on the first characterization of the single electron response of SPCs with unprecedented precision, using a UV-laser calibration system. The experimental approach and analysis methodology are presented along with various direct applications for the upcoming next phase of the experiment at SNOLAB. These include the continuous monitoring of the detector response and electron drift properties during dark matter search runs, as well as the experimental measurement of the trigger threshold efficiency. We measure a mean ionization energy of W = 27.6 ± 0.2 eV in Ne + CH4 (2%) for 2.8 keV X-rays, and demonstrate the feasibility of performing similar precision measurements at sub-keV energies for future gas mixtures to be used for dark matter searches at SNOLAB.

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A method was developed for producing several hundred mCi of 13NH 3 with subsequent enzymatic synthesis of large amounts ot' 13N-labeled glutamine and glutamic acid. Dynamic measurements and quantitative whole body scans demonstrated greater glutamine uptake in the liver region of mongrel dogs than uptake of glutamic acid or NH 3, although all concentrated in the liver to a significant degree. Myocardial uptake of glutamine and glutamic acid was low, while NH 3 was incorporated into the heart, brain, bladder, and kidneys at a greater rate than the amino acids.

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