Instrument & Specifications

Overview

HODACA (HOrizontally Defocusing Analyzer Concurrent data Acquisition spectrometer) is a multiplex-type inelastic neutron spectrometer installed at the C1-1 cold-neutron beam port of JRR-3.

HODACA combines the high signal-to-noise characteristics of a triple-axis spectrometer with simultaneous measurements over a wide range of scattering angles. The secondary spectrometer consists of 24 analyzer–detector channels arranged at 2° intervals. A total of 132 pyrolytic graphite (PG) analyzer crystals are used.

The spectrometer is optimized for low-energy excitations in condensed-matter systems, including magnetic excitations and phonons.

Instrument concept

HODACA is based on the inverse Rowland inelastic spectrometer (IRIS) concept.

The analyzer channels are arranged along a Rowland circle. Scattered neutrons from the sample are reflected by the analyzer crystals at a fixed final energy and are detected simultaneously by an array of detectors.

This multiplex configuration allows HODACA to measure many Q points at the same energy transfer simultaneously, while retaining the advantages of crystal-analyzer spectroscopy. Radial collimators are installed around the analyzer system to suppress cross-talk and background between neighboring channels.

Specifications

Beam port
C1-1, JRR-3

Spectrometer type
Multiplex triple-axis / inelastic neutron spectrometer

Number of analyzer–detector channels
24

Analyzer crystals
132 pyrolytic graphite (PG) crystals

Angular spacing between channels
2°

Final neutron energy, Ef
3.635 meV (fixed)

Incident neutron energy, Ei
2.1–11 meV

Typical energy-transfer range
Approximately −1 to 7 meV

Energy resolution
Approximately 0.1–0.2 meV

Beam size at the sample
25 mm (H) × 40 mm (V)

Scattering-angle and Q range
The accessible range depends on the incident energy and instrument geometry. See the HODACA Q-range document below for details.

Incident neutron flux

The incident neutron flux depends on the selected incident energy.

Expected intensity

The observed intensity depends strongly on the sample volume, magnetic or structural scattering cross section, sample environment, Q position, and measurement conditions.

The values below, obtained from previous HODACA measurements, may be used only as a rough guide when planning an experiment.

mass (g) moment size (μB) Intensity(counts/min)

1 ~ 2 1 0 ~ 10

1.2 2 0 ~ 50

Reference

H. Kikuchi, S. Asai, T. J. Sato, T. Nakajima, L. Harriger, I. Zaliznyak, and T. Masuda,
“A New Inelastic Neutron Spectrometer HODACA,”
Journal of the Physical Society of Japan 93, 091004 (2024).

[Instrument paper] [Preprint]

For a detailed description of the HODACA concept, design, specifications, and commissioning measurements, see the instrument paper above.

Further details on the development and design of HODACA are available in Part I, “Next-Generation Triple-Axis Spectrometer HODACA,” of Dr. Hodaka Kikuchi’s doctoral thesis.

[Doctoral thesis]