A Neutron Spin-Echo Concept for Elastic Scattering Spectroscopy (ESS) for Dynamics of Complex (Bio-) Systems

TL;DR

This paper proposes a neutron spin-echo method for elastic scattering spectroscopy (ESS-NSE) to study dynamics in complex and biological systems, offering a wide temporal range and potential for small sample focusing.

Contribution

It introduces a neutron spin-echo based ESS method, expanding the temporal resolution and applicability for small biological samples compared to existing options.

Findings

ESS-NSE can access relaxation times from nanoseconds to tens of picoseconds.

It provides a parameterless measurement of overall relaxation times.

Potential for focusing neutron beams on small biological samples.

Abstract

Recently, a new neutron spectroscopy for the dynamics in complex (bio-) systems has been proposed [A. Benedetto, and G. J. Kearley, Sci. Rep. 6, 34266, (2016)]. This spectroscopy is ideal where only the overall relaxation time in a parameterless way is required, for example in complex systems, because only the elastic-scattering intensity as a function of the energy resolution is required. This has been termed "Elastic Scattering Spectroscopy" (ESS). It is based on the inflection points in the elastic-scattering intensity at the energy-resolution value corresponding to the overall system relaxation-time. A Constant wavelength (CW) option, more suitable for reactor sources, and the time-of-flight (TOF) option, more suitable for spallation sources, have already been proposed, and here we examine the concept of a third option based on neutron spin-echo (NSE), called ESS-NSE. In principle, this consists of simply measuring depolarisation at the relatively-intense elastic echo-condition, as a function of resolution, with the basic set-up being similar to standard spin-echo. In its basic set-up, ESS spin-echo can access 5 orders of magnitude in time from nanoseconds to tens of picoseconds, reaching slower relaxation processes than the CW and TOF options recently presented. However, spatial focussing is important for the small sample-sizes of biological systems, so we also explore how the fields may be shaped to enable a small neutron beam to be focussed on the sample.