News
Recent proposal rounds have seen significant number of beamtime proposals rejected by the panel for similar reasons. The Excitations group and Facility Access Panel wish to help users to submit good proposals so would point out the following reoccurring issues of missing information in proposals that is detrimental to their scores, together with straightforward remedies:
- Lack of evidence that a large single crystals exists or that a sufficient number of co-aligned crystals can be aligned for the experiment. This can be resolved by including a picture (with scale bars)
- Lack or unclear presentation of relevant structural and physical property characterisation of the materials to be studied. This can be resolved by presenting diffraction and physical properties characterisation of your samples in the proposal.
- Lack of details regarding what will be measured during the experiment which makes it challenging or in some cases impossible for the viability and merit of the proposal to be assessed during review. This can be resolved by proposers contacting ISIS staff prior to proposal submission.
Overview
MARI has a wide angular coverage and a wide energy range and good resolution making it ideal for the study of phonon densities of states in crystalline and disordered systems, and crystal field excitations in magnetic materials. MARI is the only chopper spectrometer at ISIS not to be equipped with a pixilated detector array using position sensitive detectors. This makes MARI the instrument of choice for studies of polycrystalline and powdered samples, and liquids. MARI also boasts the lowest instrumental background of the ISIS suite of chopper spectrometers, making the machine highly sensitive despite the relatively low incident neutron flux.
The MARI 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 named after Professor Ishikawa's daughter, Mari. The Japanese Symbol for Mari also happens to be the Japanese for truth.
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 Details
MARI has a unique vertical scattering geometry (the detectors form an arc
below the sample position) due to space constraints which
restricts the available sample environment equipment which can be used.
MARI has a dedicated CCR with a hot-stick which can handle temperatures
from 5-500K, whilst a dedicated furnace covers the temperature range
20-1000°C. We are due to receive a new dedicated orange cryostat in 2023
which can be cooled to 1.5K. MARI cannot use any cryomagnet or the
3He or dilution inserts.
As with other direct
geometry time-of-flight spectrometers there is much flexibility to chose
operating conditions to optimise count rate, resolution and dynamic
range. Typically the instrument is run to maximise flux with a
relatively coarse energy resolution of 4% of incident energy. MARI can
cover an incident energy range from 5 to 2000 meV. A typical high flux
RRM mode setting (with the chopper rotating at 200Hz) yields neutron
pulses with incident energy of 100meV (ΔE=5meV), 23meV (ΔE=0.7meV) and 10meV (ΔE=0.25meV), whilst in high resolution mode (chopper at 400Hz), the flux (around 2×104n/cm2/s) is reduced by half, and the resolution improved to
3meV (Ei=100meV), 0.5meV (Ei=23meV) and 0.2meV (Ei=10meV) respectively.
Instrument Links
Contact information for MARI instrument
Location and contact information for the MARI beamline
Building
| R55 - EXPERIMENTAL HALL
|
Telephone
| 01235 446486
|
