Measurement of the delayed neutron fraction and correction of small angle scattering data from a pulsed spallation source
Abstract The fraction of delayed neutrons in a moderated beam from the enriched uranium, pulsed spallation source at the intense pulsed neutron source at Argonne National Laboratory has been measured and found to be 0.0283 for 450-MeV protons. Delayed neutrons produce a sample-dependent background in time-of-flight instruments. Because of the distribution of neutron wavelengths in the prompt pulse, the significance of the delayed neutron contribution to the observed scattering profile is strongly dependent on the wavelength and therefore on the magnitude of the momentum transfer. This effect is demonstrated, and a general correction procedure in current use for small angle neutron scattering data is described.
Pulsed spallation neutron sources for slow neutron scattering
Abstract The role of pulsed spallation neutron sources for slow neutron spectroscopy is sketched. Various methods of neutron production, and some aspects of the spallation neutron production process are outlined. Accelerators for pulsed spallation neutron sources are discussed. Materials and coolants for neutron-producing targets and moderators are surveyed. The performance of moderators and the effects of varying size, composition, and temperature are summarized. Expressions for estimating moderator performance are given. The effect of moderator-reflectors, which enhance the slow neutron beam current at low energies, are examined. The ZING-P prototype pulsed neutron source and the proposed Intense Pulsed Neutron Source are described. Pulsed spallation sources are a new generation of sources for slow neutron spectroscopy which offer an order of magnitude improvements over currently available thermal neutron flux and several orders of magnitude greater epithermal flux.
Pharmacokinetics of amikacin and chloramphenicol in the aqueous humor of rabbits
Composite data describing ocular pharmacokinetics are unreliable because of intersubject variation. To address this problem, an animal model was developed in which multiple aqueous samples from single subjects were obtained. Following direct anterior chamber or intravenous administration of amikacin or chloramphenicol, pharmacokinetic analysis of drug concentrations in the serum and anterior chamber was performed by using a nonlinear least-squares regression program. The number of anterior chamber paracenteses performed did not alter the beta elimination rates or percent penetration into the anterior chamber. The aqueous humor and peripheral-compartment terminal slopes were identical. These data indicate that complete ocular concentration-time curves can be obtained without altering antibiotic pharmacokinetics. Following direct injection into the anterior chamber, the elimination rates for both antibiotics followed a one-compartment model, whereas those following intravenous administration best fit an open, first-order, two-compartment model. Following intravenous administration, the anterior chamber elimination rate constants for both drugs were equal to that of the serum and significantly longer than that following direct injection. The elimination rates of both drugs following direct injection were similar. Systemic administration resulted in drug levels in aqueous humor that persisted longer than those following direct injection. Chloramphenicol, a lipophilic compound, gave higher mean concentrations in aqueous humor than did amikacin. Our model provides a new approach which rigorously examines ocular pharmacokinetics and provides data which suggest that for selected compounds the parenteral route of administration is preferable.