| Moderator | Liquid-methane (CH4) at 105 K (poisoned with Gd at 2.5 cm) | ||||
| Incident energy | 7 – 1000 meV | ||||
| Energy resolution | Depends on the choice of Fermi chopper, incident energy and energy transfer
D hw /Ei = 1.5-8 % |
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| Primary flight path | 11.739 m | ||||
| Secondary flight path | 4.020 m | ||||
| Fermi chopper | 10.050 m
50-600 Hz phased to ISIS pulse ± 0.1 μs 4 chopper packages are commonly used on MARI optimised for different incident energy and resolution requirements
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| Detectors | Low-angle bank
4.020 m from sample 256 10 atm 3He tubes in 8 fold array covering 3 – 13º scattering angle |
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| High-angle bank
4.020 m from sample 10 atm 3He tubes covering 12º – 135º scattering angle |
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| Monitors | Monitor 1: 07.000 m from moderator Monitor 2: 10.297 m from moderator Monitor 3: 17.559 m from moderator |
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| Flux at sample | [× 104 n cm-2 s-1] | ||||
| 7 meV | 25 meV | 100 meV | 500 meV | ||
| G-Chopper 4% ΔE/E | 0.5 | 1.4 | 0.9 | n/a | |
| S-Chopper 5% ΔE/E | 0.5 | 1.5 | 0.9 | 1.3 | |
| A-Chopper 2.5% ΔE/E | n/a | n/a | 0.3 | 0.4 | |
| R-Chopper 4% ΔE/E | n/a | 0.8 | 0.5 | 0.7 | |
In this section
MARI
MARI is dedicated to the study of atomic dynamics in powders and disordered materials. The unique arrangement of its detectors, buried underground gives it the lowest background at ISIS. Since most newly discovered materials are only available as powders and often not in huge quantities the excellent signal to noise on MARI is exploited by researchers from around the world in areas such as advanced, energy and quantum materials.
Instrument scientists
To find out more about each team member, click the + symbol.
Overview
The key to MARI’s low instrument background is its unique vertical scattering geometry, with detectors forming an arc below the sample position. Although this design was adopted due space constraints it also allows the detectors to be more heavily shielded. However, this vertical geometry limits the types of sample environment equipment that can be used: MARI has a dedicated CCR with a hot-stick that can handle temperatures from 5 – 500 K; a dedicated Orange cryostat which can be cooled to 1.5 K; and a dedicated furnace that covers the temperature range 20 – 1000°C, but cannot use any cryomagnet or the 3He or dilution inserts. As with other direct geometry time-of-flight spectrometers, there is flexibility to choose operating conditions that optimise count rate, resolution and dynamic range. Typically, the instrument is run to maximise count-rate with a relatively coarse energy resolution of 4% of incident energy, and incident flux of ≈104 n/cm2/s. MARI can cover an incident energy range from 5 – 2000 meV. This online calculator can be used to estimate the resolution and flux of the different configurations of MARI and other chopper spectrometers.
The MARI (Multi-Angle Rotor Instrument) spectrometer was funded by the Japanese Ministry of Education, Science and Culture (Monbusho) as part of the UK-Japan Collaboration on neutron scattering. This collaboration, initiated in 1986, was the creation of the late Professor Yoshikazu Ishikawa. The spectrometer is also named after Professor Ishikawa’s daughter, Mari. The characters for Mari (真理) means “truth” (in the scientific sense). MARI has contributed seminal work in fields such as quantum-fluids, the dynamics of disordered materials and low-dimensional magnetism. It is also used for studies of biological and polymeric materials, catalysts, thermo-electric materials, geological samples, high-temperature superconductors and liquid dynamics. In 2018, MARI was upgraded with new m=3 supermirror guides giving an approximate 5-fold increase in flux. The disk chopper was also replaced to allow it to use repetition-rate-multiplication (RRM) like on MERLIN and LET. Details of the upgrade may be found in this paper.
Technical Information
Instrument parameters, energy resolutions and fluxes
Sample environment
The vertical detector geometry on MARI has implications for the optimal sample geometry and the design of sample environment equipment. As such much of the sample environment used on MARI is unique to the instrument. The following list describes the sample environment equipment suitable for use on MARI:
5 K – 500 K Top Loading Closed Cycle Refrigerator (CCR)
The CCR is a top loading system that allows samples to be changed without the necessity of bringing the main sample tank to air. The design is such that the absolute amount of aluminium in the beam is minimised and the IVC and 1st stage shield are domed to match the MARI detector geometry and minimise shadows and spurions. The sample space is filled with a low pressure He exchange gas to improve sample cooling. The standard sample stick has an integrated heater for use above room temperature up to a maximum of ≈500K (≈250°C)
1.5 K – 300 K Orange cryostat
We also have a dedicated low temperature helium flow “Orange” cryostat if temperatures below liquid helium is required. The thicker IVC of this cryostat means that the background will be larger than for the CCR.
The MARI Furnace Tmax = 1000°C
This is a special low mass furnace where the thin niobium heating element acts as the outer wall of the sample can. The geometry is horizontal and cylindrical and the background very low. By varying the number of niobium heating elements temperatures in the range between 100°C and 1000°C are achievable.
In addition, MARI can also use the standard ISIS gas panels to load various gases into sample cells (up to 10 bar) at temperatures below 300K in our CCR. We have also previously used a gas pressure cell up to 5 kBar (500 MPa) in a dedicated bottom loading CCR but this requires consultation with the instrument and sample environment teams. MARI cannot use any of the cryomagnets or low temperature inserts available for other instruments.
For more information, please contact the MARI instrument scientists.
Software
- Mantid – RAW file access, data reduction and scripting with Python, including crystal field fitting.
- Mantid MSlice – Viewing processed data in |Q| and energy.
- Matlab – Viewing data with MSlice, and other legacy software
Recent publications
Instrument reference
All publications and datasets based on experiments using Mari should cite that the data is collected by DOI: 10.5286/isis.instrument.8362. Experiment DOIs follow the format 10.5286/ISIS.E.RBXXXXXXX, where XXXXXXX is the 7-digit experiment (RB) number and these can be viewed via the Data Gateway.