K.H. Andersen

3He neutron spin filter at ILL

Abstract The strongly spin-dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize neutrons over the full-spectrum of cold, thermal and epithermal neutrons. At ILL a neutron spin filter (NSF) development started which uses the direct optical pumping of metastable 3He atoms in a 3He plasma at 1 mbar. At present 0.5 bar 1 of gaseous 3He can be polarized within 1 h. Subsequent polarization-preserving compression by a two-stage compressor system enables one to prepare NSF cells of about 300 cm3 volume in the required pressure range of several bars. A remote type of operation based on relaxation times of up to 100 h has been demonstrated in a first survey of experiments. Two representative examples are discussed which demonstrate the high potentiality for many polarized neutron-scattering applications.

Structure of poly(ethylene oxide) (PEO and PEO·LiSO3CF3) studied with spin polarised neutrons

Abstract Over the last two decades, poly(ethylene oxide) (PEO), one of the model solid polymer electrolytes, has been investigated by various techniques. Neutron scattering using spin polarised neutrons with spin polarisation analysis provides a unique opportunity to study both the structure and dynamics in the same experiment. This is feasible due to the experimental separation of the coherent and incoherent scattering, and it gives increased confidence in the models proposed. Using this technique, we studied PEO complexed with lithium triflate, LiSO 3 CF 3 , at different concentrations, below and above T g . PEO below its glass transition has a strong tendency to crystallise, and even above T g , displays considerable short-range order. In turn, this affects the analysis of the dynamics of the matrix (hence conductivity). The results obtained are compared with those obtained by others.

Recent news on ILL polarised 3He developments

Abstract The Institut Laue Langevin operates a polarised 3He gas production facility based upon the “Mainz” system using metastable exchange optical pumping at low pressure. The current state of the development of polarised 3He neutron spin filters at the ILL is discussed. Target cells with long wall relaxation times have been produced and two methods for producing homogeneous guide fields on the neutron beam-line have been pursued. A first test of a 3He spin filter in the stray field of a superconducting magnet is discussed.

Two-dimensional excitations of superfluid confined in 72% porosity xerogel

Abstract We present neutron inelastic-scattering measurements of the low-energy excitation spectrum of superfluid 4 He confined in porous xerogel glass. In addition to the bulk-like excitation, we also observe a broad peak centred at energies of less than that of the bulk-like peak. The dependence on filling fraction of both peaks has been investigated and we find that the second broad peak exhibits behaviour that is consistent with that of an excitation confined to the high-density liquid layers near the pore walls, i.e. with that of a two-dimensional excitation.

Short-range order in blends of polycarbonates with polystyrenes

Abstract The local structure of a series of blends of bisphenol-A polycarbonate (BPA-PC) and tetramethyl BPA-PC (TMPC) with various styrene-based polymers (poly(para-chlorostyrene), polystyrene, poly(meta-chlorostyrene) and poly(ortho-chlorostyrene)) has been investigated. Measurements on the D7 diffractometer at ILL were carried out at room temperature. We show that while the amorphous halo of TMPC is only slightly perturbed by blending, major differences are observed in all BPA-PC blends. We conclude that inter-chain correlations in BPA-PC blends are considerably altered compared to the pure component.

High-resolution neutron measurements of the roton line shape under pressure

Abstract High-resolution inelastic neutron scattering measurements of the dynamic structure factor S(q, ω) of superfluid 4He at the roton minimum are presented. The temperature dependence of the roton energy and line width at 24 bar between 0.8 and 1.1 K are reported.