Introduction

What is data reduction?

The overall purpose of Data Reduction is to remove instrument-specific artifacts. Another definition is “the transformation of a dataset collected from an instrument into a dataset in physical units” [1]. A way to think about raw data and reduced data is that “raw data is instrument-specific (requires knowledge of detector geometry, motor positions, etc.)” while “reduced data is proportional to the neutron scattering cross-section from the sample expressed in terms of physically meaningful variables (e.g., momentum transfer, energy)” [5]. For spectroscopy, although the format and organization of spectroscopy data are generally dependent on the instrument, “the goal of reduction is to produce a quantity (the double differential scattering cross section) which is (almost) independent of the instrument [6]. Other considerations that are made are the “sample itself and on the strength of the interactions between the neutrons and the sample’s constituent elements” [6].

Definitions of Data Reduction are also defined by each instrument category at ORNL below:

Direct Geometry (CNCS, HYSPEC, SEQUOIA, ARCS)

Data Reduction Definition: “For direct geometry spectrometers and BASIS, data reduction transforms collected data from time-of-flight events into S(Q,ω)… The four direct geometry spectrometers use Mantid to perform mostly automatic reduction to S(detector,ω) – the transformation to S(Q,ω) is performed manually in either MSlice, Horace, or Mantid. ” [7]

Triple-Axis (CTAX, PTAX, TAX, & VERITAS)

Data Reduction Definition: “For the triple-axis spectrometers, the data collected is already in the appropriate S(Q,ω) form assuming counts were collected to a fixed incident beam monitor and only small, simple corrections are required (like accounting for higher order contamination in the beam monitor).” [7]

Chemical Spectroscopy (VISION, BASIS)

Data Reduction Definition: “For VISION, the double-focusing analyzers integrate the intensity over a range of scattering angle (or Q), thus the product of reduction is S(ω)… The automatic reduction at BASIS uses Mantid to directly obtain S(Q,ω) with default Q and energy binning. At VISION, two S(ω) spectra corresponding to the backscattering banks (120-150 degree) and forward scattering banks (30-60 degree) are automatically produced with Mantid.” [7]

Spin Echo (NSE)

Data Reduction Definition: “DrSPINE (Data Reduction for SPIN Echo experiments) enables the reduction of neutron spin echo data produced at both reactor and pulsed neutron sources.” [7]