Commissioning of Neutron Scattering Instrumentation - Open Session

Monday 7 Jul 2025, 15:30 → 18:00 Europe/Stockholm

Location: Auditorium 10

 

We were asked to allow for a better room change and start 30 min later, so all times will change accordingly.

 

This symposium focuses on the techniques, tools and approaches to pass a neutron scattering instrument from construction to the usage state. With the ESS shortly having several instruments in commissioning, the SNS just having put instruments through this process and planning its second target station here we aim to collect the knowledge associated with that process.

During operation the characterisation of the scattered neutrons in an neutron instrument depends on a number of parameters which first have to be reliably established at startup, among those the relation between timestamping and wavelength profile, absolute incoming intensity, spatial setup of the detector and background.

Here we will adress each of those issues in a section of the mini symposium:

• Measurements of Incident Beam
• Round Robin and Standard Samples
• Background and Detectors
• Comparison between Simulation and Experiment

 

In this symposium we target to collect expertise and nurture discussion about 

• the current methods and approach
• issues and challenges with those
• and hopefully a way forward

 

Interested participants are therefore cordially invited to join the mini symposium and join the discussion about methods, challenges and approaches during commissioning of a neutron scattering instrument for scientific use.

No registration is necessary for this event.

Measurements of Incident Beam¶

1 Methods used for neutron beam characterization at ISIS¶

Speaker: Robert Bewley (STFC UKRI)

2 ESS Test Beamline: Measuring the first neutrons of the new facility and characterizing the ramp-up¶

Unlike traditional short-pulsed spallation sources, the ESS accelerator will deliver long proton pulses—2.86 milliseconds—at maximum energy of 2 GeV and a frequency of 14 Hz. High-brightness neutron beams will be achieved through the use of a compact (3 cm tall) low-dimensional moderator, referred to as the butterfly moderator, and comprising both water at room temperature and liquid para-hydrogen at around 20 K. This allows for the slowing down of spallation neutrons to thermal and cold energies.
The ESS Test Beamline (TBL) has been developed internally to support commissioning of the facility. The experimental cave of the TBL is attached directly to the common shielding ‘bunker’ wall. Most of beamline components are located inside this bunker area, including collimators, a filter stage, a double-disk chopper and the instrument shutter. Positioned perpendicular to incident proton beam, the TBL provides a direct
line of sight to the full moderator surface (approximately 28 cm x 3 cm). Employing a camera obscura principle, the design allows detections of not only moderated neutrons, but also epithermal and fast neutrons as well as gamma rays. During the first three months of operation, the beam power will gradually increase from a modest 20 W (BoT) up to 200 kW. The primary focus of the TBL during this phase is to validate the
success of slow neutron production as well as to give feedback to both accelerator and target(+moderator) operators. Given the initially low neutron flux, particular care in planning is essential to ensure meaningful data can be obtained from the very first BoT events.
As the TBL is designed to receive neutron beams at different beam powers (20 W – 5 MW), the pinhole changer is designed to facilitate different aperture cross sections. An adjustable collimator features 3 different collimator channels, i.e. 3-mm, 10-mm, and 30mm25mm, coupled with optional pinholes (sized 1-10 mm). No neutron guide is used, allowing an unperturbed beam characteristics and direct flight path from
the moderator to the detector. The collimator can be moved in the vertical direction to accommodate trajectories of long wavelength neutrons. A double-disk chopper can be used to select bandwidth of neutrons up to 16 Å at 14 Hz without frame overlap. Neutron filters can be moved to the beam to tailor the neutron spectrum for different purposes.
The TBL hosts a suite of detectors to facilitate comprehensive measurements. During first BoT day, two arrays of He-3 tubes (1 bar and 10 bars) are planned to capture this first low intensity neutron beam. As the facility ramps up from first producing short pulses (5 µs) to the designed long pulse (2.86 ms), other TBL detectors will be positioned to characterize the neutron emission from the moderator surface also with
spatial resolution. The latter will be achieved by using a neutron gas-electron multiplier (nGEM) detector, Multiblade (MB) detector as well as scintillator-camera based detectors with adjustable active areas, among them the neutron event camera system, so-called, LumaCam.

Speaker: Robin Woracek (European Spallation Source ERIC)

Round Robin and Standard Samples¶

3 Reproducibility and Reliability - the role of reference samples¶

The aim of a neutron measurement on a sample is usually to obtain information about some material
object that can be used to understand structure or properties. The end-information about a sample
needs to be reliable. Differences in measured data can arise from instrumental effects such as finite
resolution, and the range of wavelengths exploited, the momentum and energy transfer that are
accessible. As a scientific tool, it is important to understand these differences. Commissioning of a
new instrument will require an evaluation of these effects rather than just a verification that raw
data are similar. In this respect, samples that test different aspects are important: these will verify
calibration of intensity and momentum transfer but also need to test resolution, stability, and
background from the sample and the instrument. The talk will illustrate this largely with examples drawn from small-angle scattering.

Speaker: Adrian Rennie (Uppsala University)

Background and Detectors¶

4 Instrument backgrounds – Why does it matter? : Most brightest – not most blinded.¶

In the development of neutron scattering instruments, the primary focus is often on maximizing signal intensity, while managing instrument background tends to receive comparatively less attention. This imbalance is not necessarily due to a lack of awareness of the importance of background reduction but rather reflects the historical reality that mitigating instrument noise has been more of an art than a science. While substantial tribal knowledge exists in this area, there is no standardized methodology or formula for optimizing instrument backgrounds.
In this presentation, we will share several illustrative examples from the Lujan Center at the Los Alamos Neutron Science Center (LANSCE), Los Alamos National Laboratory. These examples will highlight both signal-to-noise challenges and strategies. Additionally, results from beamline source term verification experiments will be presented to further explore the complexities of background characterization and control.

Speaker: Günter Muhrer (European Spallation Source ERIC)

5 Recent progress and applications of high resolution MCP neutron counting detectors with Timepix readouts¶

Detectors using neutron-sensitive Microchannel Plates (MCPs) with Timepix readouts have found niche applications in pulsed neutron sources, where the arrival position of each neutron and its energy are reconstructed with high accuracy. These detectors can localize each neutron with approximately 10 µm spatial resolution and very high timing precision—around 500 ns for thermal neutrons and 10 ns for epithermal neutrons. The detection efficiency of these devices for thermal and cold neutrons is approximately 50%.
In these detectors, neutrons are directly converted into a charge of approximately 10⁵ electrons, all confined within a ~10 µm pore, with no afterpulsing or readout noise. The Timepix readout ASIC is positioned directly beneath the MCP in vacuum, enabling pixelated detection of numerous simultaneous events, thereby significantly increasing the count rate capability to GHz levels.
This talk will review the current state of this detection technology, which is primarily used for energy-resolved neutron imaging at this time, and will present experimental results across various applications, including residual strain mapping, texture analysis, in-situ crystal growth optimization, annealing, and time-resolved imaging of dynamic processes. Additionally, we will discuss upcoming advancements enabled by the latest generation of Timepix4 readouts, highlighting how MCP/Timepix detectors offer a compelling solution for applications requiring neutron counting with high spatial and temporal resolution.

Speaker: Anton Tremsin (University of California at Berkeley)

Comparison between Simulation and Measurement¶

6 From McStas instrument design to commissioning tool: Preparing for operating the ESS instruments¶

The McStas instrument simulation tool has been widely used for designing and optimising the ESS instrument suite. This contribution will outline how the ESS DMSC makes use of McStas for preparation of the data pipeline and transitioning from “as designed” to “as built” models. We will further outline lesser-known features in McStas and related projects to aid beamline staff in the commissioning process.

Speaker: Peter Willendrup (DTU Physics)

7 The software package VITESS for virtual neutron experiments: concept, features and an application in preparing data analysis of the new spectrometer TOPAS at MLZ¶

VITESS is a software package to simulate all kinds of instruments at continuous and pulsed neutron sources. It enables virtual experiments, i.e. the propagation of the neutron beam to the sample position, scattering of neutrons at the sample, and determination of their spatial (and temporal) distribution at the detector.
The output of this simulation can be used to feed data evaluation software and thus enables development and preliminary tests without the use of actual neutrons. This approach has been used for the data reduction and evaluation software of the spectrometer TOPAS, which is currently being assembled at the MLZ in Garching. It will be operated directly after the re-start of the research reactor FRM II.
The new VITESS version 3.7 includes new features to enable tests of the data evaluation software: upgraded modules for handling inelastic scattering events and their evaluation, as well as a new module for writing simulation output in the NeXus format, a standard data file format for scattering measurements.
We will present the concept and basic properties of VITESS, highlight the new features introduced in version 3.7 and demonstrate how these features were utilized for virtual experiments, digital twins, and data handling at TOPAS.

Speaker: Klaus Lieutenant