The spin-dependent nd scattering length - a proposed high-accuracy measurement

The understanding of few-nucleon systems at low energies is essential, e.g. for accurate predictions of element abundances in big-bang and stellar fusion. Novel effective field theories, taking only nucleons, or nucleons and pions as explicit degrees of freedom, provide a systematic approach, permitting an estimate of theoretical uncertainties. Basic constants parameterising the short range physics are derived from only a handful of experimental values. The doublet neutron scattering length a_2 of the deuteron is particularly sensitive to a three-nucleon contact interaction, but experimentally known with only 6% accuracy. It can be deduced from the two experimentally accessible parameters of the nd scattering length. We plan to measure the poorly known "incoherent" nd scattering length a_{i,d} with 10^{-3} accuracy, using a Ramsey apparatus for pseudomagnetic precession with a cold polarised neutron beam at PSI. A polarised target containing both deuterons and protons will permit a measurement relative to the incoherent np scattering length, which is know experimentally with an accuracy of 2.4\times 10^{-4}.Comment: 5 pages LaTeX2e, 1 .eps figure. To be published in Nucl. Inst. Methods A as part of the Proceedings of the 9th International Workshop on Polarized Solid Targets and Techniques in Bad Honnef (Germany), 27th - 29th October 200

Unresectable Malignant Biliary Obstruction: Treatment by Self-Expandable Biliary Endoprostheses

The primary goal in the treatment of malignant obstruction is the relief of jaundice. Although operative biliary bypass is a reliable method of palliation, nonoperative palliation may be desirable in selected patients

Time-resolved nuclear spin-dependent small-angle neutron scattering from polarised proton domains in deuterated solutions

Abstract.: We have investigated the process of dynamic proton polarisation by means of time-resolved polarised small-angle neutron scattering (SANS) on frozen solutions of EHBA-CrV molecules in glycerol-water mixtures as a function of the concentration of EHBA-CrV and for different degrees of deuteration of the solvent. In the EHBA-CrV complex, the spins of the 20 protons which surround the paramagnetic CrV can be oriented using the method of dynamic nuclear polarisation (DNP), thereby offering the possibility to create locally a nuclear spin-dependent contrast for SANS. The time constants which describe the build-up of polarisation around the paramagnetic centre and the subsequent diffusion of polarisation in the solvent were determined by analysing the temporal evolution of the nuclear polarisation, which in turn was obtained by fitting a core-shell model to the time-dependent SANS curves. The results on the spin dynamics obtained using the scattering function of a core-shell could be independently confirmed by evaluating the integrated SANS intensity. A thermodynamic one-centre model is presented which is able to reproduce the observed dependence of the proton polarisation times on the proton concentration of the solven

Spin-lattice relaxation measurements and spin conversion in methane below 1 K

Resonant spin conversion on the ordered sites has been observed in CH 4 through the time dependence of T1 at 0.18 K. The increase in the A-F level splitting at low F-species concentration P F has been confirmed. Resonant E → F conversion has given a direct measurement of the E → F level splitting. T1 at fixed PF has been measured as a function of temperature to 80 mK for 9 x 10-4 < PF < 2 × 10-2.La conyersion de spin résonnante sur les sites ordonnés de CH4 a été observée et contrôlée par l'évolution de T1 avec le temps. L'accroissement de l'écart entre les niveaux A et F, à basse concentration PF d'espèce F, a été vérifié. La conversion résonnante E → F, pour la première fois observée, a fourni une valeur de l'écart E → F. La dépendance de T1 avec la température à PF fixée a été suivie jusqu'à 80 mK, pour PF comprise entre 9 x 10-4 et 2 x 10-2

Spin-lattice relaxation in partially converted CH4 above 0.3 K

The proton spin-lattice relaxation time has been measured in the range of F-species concentrations between 3 % and 37 % and at temperatures from 0.3 K to 4.2 K. A simple relaxation model is proposed which takes into account the spin-isomer environment of a relaxing molecule.Le temps de relaxation spin-réseau des protons dans CH4 a été mesuré dans la gamme de concentration des espèces F de 3 % à 37 % et à des températures allant de 0,3 K à 4,2 K. Un modèle simple de relaxation est proposé qui tient compte du voisinage isomérique d'une molécule relaxante

Spin-dependent scattering and absorption of thermal neutrons on dynamically polarized nuclei

Dynamic nuclear polarization and the spin-temperature concept of nuclear Zeeman reservoirs are systematically used to obtain spin-dependent scattering lengths bN of separate isotopes in the same target A simple generalization shows the way to measure bN for nuclei invisible by nuclear magnetic resonance. It shows also how to obtain precise ratios of bN for different isotopes or of spin-dependent absorption and scattering of the same isotope. Values of bN are given for 13C, 35Cl, 79Br, 81Br as well as upper limits for 31P, 37Cl and 41K.La polarisation dynamique nucléaire ainsi que le concept de température de spin de réservoirs d'énergie Zeeman sont utilisés pour obtenir des longueurs de diffusion dépendant du spin bN d'isotopes différents, présents dans la même cible. Une généralisation simple permet de montrer la possibilité de mesurer bN même pour des noyaux invisibles par résonance magnétique nucléaire. On montre aussi comment on peut obtenir des rapports précis de bN pour différents isotopes ou des rapports de diffusion et d'absorption pour le même isotope. On donne des valeurs numériques de bN pour 13C, 35Cl, 79Br, 81Br ainsi que des limites supérieures pour 31 P, 37Cl et 41K

Spin contrast in SANS of polymers in solution

We present a small angle neutron scattering study of polymers in solution. The contrast between the scattering lengths of the polymer and the solution is created by dynamic polarization of the nuclei in the sample. We used the spectrometer PAON at G5-3 of the LLB-Saclay- reactor Orphée which is a prototype of a SANS spectrometer using dynamic nuclear polarization. The power of this method can be seen from the results obtained on two different samples: a solution of the homopolymer polystyrene in orthoterphenyl, and a mixture of two homopolymers dissolved in toluene. We observed for the polystyrene sample the decrease in contrast at positive polarization and increase in contrast for negative polarization. For the sample of the polymer mixture in solution we obtained the different structure factors by taking the SANS spectra for different polarizations. The interference term, obtained separately in the same sample, confirms the mutual interaction