PASTIS- XYZ polarization analysis using 3He

We present a finite element calculation of the magnetic field (MagNet software) taken with the newly proposed PASTIS Coil, which uses a wide-angle banana shaped 3He Neuton Spin Filter cell (NSF) to cover a large range of scattering angle. The goal of this insert is to enable XYZ polarization analysis to be installed on the future thermal time-of flight spectrometer TOPAS. Introduction: Polarization analysis, PA, of polarized neutrons is a powerful tool for separation of nuclear spin-incoherent background, analysis of complex magnetic structures and the study of magnetic excitations. Several wide angle spectrometers with polarization analysis exist or are under construction in which PA is used. The PA can be performed in a variety of ways depending on the instrument’s parameters, but with performance limited by the analyzer height and integration over the height of the detectors. Installation of a new longer, heightposition sensitive detector bank gives a unique opportunity to prototype and test a polarized 3 He XYZ analysis system which could utilize the full height and position resolution of these new detectors. We present an initial design study with finite element magnetic field (FEM) calculations of possible XYZ field configurations suitable for polarized 3He and adapted to the DNS instrument geometry. Two clear options exist, a magnetized mu-metal geometry, similar to ref [1], or a resistive coil set similar to ref [2], however in our proposed designs, certain key differences exist which build on the experiences from prior devices. Helium-3 relaxation time: The Helium-3 polarization in NSF cell decays to thermal equilibrium with characteristic time constant T1. The longitudinal relaxation rate 1 Γ = T1 -1 consists on three main mechanisms for relaxations of spins and characterized by: wall dd T T T T G 1 1 1 1 1 1 1 1 1 : + + = = Γ (1) dd T1 is the dipole-dipole relaxation time due to interaction between colliding 3 He atoms. The magnetic dipole coupling of atoms during a binary collision results in the loss of nuclear polarisation. This rate is well known and described by: