H. Glättli

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

Abstract 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 a2 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 ai,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 nd scattering length, which is known experimentally with an accuracy of 2.4×10−4.

Neutron scattering from polarised proton domains

Abstract We report on time-resolved small-angle polarised neutron scattering from domains of polarised protons created by dynamic nuclear polarisation in frozen deuterated glycerol–water solutions containing a small amount of paramagnetic centres. In order to observe the rapid build-up of the polarisation of the protons around the paramagnetic ions and to separate it from the much slower polarisation change of the protons in the solvent, we have developed techniques that include stroboscopic SANS and NMR synchronised to cyclic microwave irradiation.

Magnetic coherence in the paramagnetic state of mixed-valence manganites

Abstract Small-angle neutron scattering measurements have been carried out on a ferromagnetic La0.75Sr0.25MnO3 single crystal. In the paramagnetic state, the observed variation of the neutron intensity above q = 0.1 A -1 indicates the presence of nanometre size scattering objects. This in turn indicates the existence of magnetic coherence above TC, a situation comparable to that encountered in Fe and Ni. A model involving a new expression for the spin correlation function has been developed, which gives very good fit to the data. This is however not consistent with the presence of spin polarons in the paramagnetic state of LaSrMnO ferromagnetic manganites.

An Accurate Measurement of the Spin-Dependent Neutron-Deuteron Scattering Length

We briefly report on the progress of an experiment that has the goal to directly determine the bound spin‐dependent neutron‐deuteron scattering length bi,d by measuring the pseudomagnetic precession of polarized cold neutrons passing through a target with polarized nuclei. A precise measurement of bi,d can be used to increase the accuracy of the only poorly known doublet neutron‐deuteron scattering length b2,d which is a crucial input parameter for novel effective field theories. Results of exploratory measurements of bi,d are shown, which illustrate the capability of the adopted experimental method.

A High-Accuracy Measurement Of The Spin- Dependent Neutron Scattering Length Of The Deuteron

We give a brief report on the status of an experiment that has the goal to improve significantly the accuracy of the doublet neutron‐deuteron scattering length a2. This poorly known value is crucial for a better understanding of few‐nucleon systems, in particular as an input for novel effective field theories of nuclear interactions. The value of a2 can be obtained from a linear combination of the spin‐independent nd scattering length ac,d and the spin‐dependent one, ai,d. The latter one is limiting the total accuracy and shall be determined at PSI in the present project with a relative accuracy of 10−3 using the method of pseudomagnetic precession of polarised neutrons passing through a polarised target.