Detectors

Coordinator: Nigel Rhodes (STFC)
Partners: STFC, ILL, ESS, PSI, TUM, Juelich, CEA, TU Delft, LIP

The need for high rate, high resolution detectors are common across all neutron sources: whether reactor or spallation sources. This RTD seeks to develop neutron detectors with high rate capability and high spatial resolution, for reflectometry applications at the ESS constituting a critical, highly demanding need. It will also evaluate whether potentially disruptive future technologies, developed for other applications, are applicable in neutron detectors. One of these technologies, will also be explored for detectors for muon spectroscopy.

For higher resolution detectors, in the range 1-3mm, estimates of detector requirements for ESS instruments show that there is a clear requirement gap between desired detector performance and the best that is currently available. In particular, the instantaneous, local rate requirements for ESS reflectometry will be enormous, up to 2 orders of magnitude beyond present sources. This requirement gap is most clearly expressed in terms of detectors which have, simultaneously:

• Spatial resolution of 1-3mm, with a perspective of improvement into the sub-mm regime.
• Time resolution better than 100μs.
• Local instantaneous rate capability of several kHz/mm².

Task 1. Involving industry and the wider European neutron and muon detector communities

Task Leader: STFC
Partners: all

This task seeks to involve industry and the wider European neutron and muon detector communities in the detector development of this RTD. This will be achieved in three ways:

1. Manufacturers of critical detector components will be invited to selected RTD meetings to facilitate an exchange of information on detector and component development.
2. Would-be detector manufacturers will be invited to selected RTDs, to expose them to the detector developments carried out in this RTD and stimulate the transfer of detector requirements and technology to industry.
3. Personnel from relevant detector development groups outside of this RTD will be invited to participate in RTD meetings. They will provide advice on the detector work of the RTD and disseminate their own work in detector development. Groups from CNR Perugia, MTA EK, CNR Milano, CSIC, HZG, ESS Bilbao and ENEA have already expressed an interest in participating in this activity.

These three activities will be highly beneficial in determining the direction of detector development as the RTD progresses.

Task 2. Development of scintillation detectors with high rate capability for reflectometry

This task is devoted to the development of scintillation detectors with high rate capability and is broken down into two sub-tasks according to the way in which the scintillator is read out.

Task 2.1. ZnS scintillation detector with WLS fibre readout

Task Leader: STFC
Partners: FZJ, PSI, TUD, ILL

Scintillator detector systems with WLS fibre readout are already in use at the SNS and J-PARC and have been developed within FP7 NMI3-II for large area detectors. However, the afterglow associated with this scintillator limits its rate capability to ~ 20kHz per photomultiplier tube (PMT) channel. For high rate applications this is a severe problem. In the case of a reflectometer detector, most of the detector data is limited to one to three bright lines across the face of the detector. If this high intensity data on the detector can be distributed across all its PMTs rather than only a few, the count rate capability of the detector can be effectively increased for reflectometry applications. This task seeks to develop a detector in which adjacent vertical and horizontal pixels in the detector are deliberately coded to different PMTs.

Task 2.2. Scintillation detector with direct PMT readout

Task Leader: FZJ
Partners: STFC, PSI, TUD, ILL

To provide a detector in which each pixel has a count rate of a few kHz/mm², a scintillation detector will be developed in which each detector pixel is readout by a PMT. This will involve a large number of PMT channels and a large number of signal processing channels. The light collection in such a detector will be excellent and the electronics will be relatively simple. The challenge is to keep the cost of the PMTs and signal processing electronics to an affordable level. This will necessitate the use of highly pixelated multi anode PMTs and low cost signal processing electronics. The flat panel PMTs produced by Hamamatsu are seen as good candidates for the PMT and Hamamatsu are continuing to develop these products with increased performance at lower costs. Application specific integrated circuits (ASICs) will be used to minimise the cost of the signal processing electronics.

Task 3. A ³He based microstrip gas chamber with a novel 2D readout

Coordinator: ILL
Partners: STFC

The aim of this task is to develop a two-dimensional position sensitive Microstrip gas chamber (MSGC) based on a novel resistive cathode layout. A final detector size of 200 mm x 200 mm, extendable in one direction, is anticipated, with 1 mm x 2 mm position resolution and local data rates > 10 kHz. Such a detector will meet many of the needs of reflectometry applications at the ESS as well as those of other facilities. The detector will use ³He as the neutron converter, but the volume envisaged is very low, in the range of 10 litres. The rational for using this converter is justified in terms of the expected performance gain, versus the low volume of ³He required.

Task 4. Emergent Detector Technologies for neutron scattering and muon spectroscopy

Coordinator: ESS
Partners: all

There are a number of technologies with the potential to significantly impact the future direction of detector development for neutron scattering. This RTD has identified three such technologies for evaluation. One of these detector technologies is also highly applicable to the complementary technique of muon spectroscopy. Knowledge, expertise and resources can be effectively utilised by exploring the potential of this technology for both neutron scattering and muon spectroscopy applications, within the same task.

4.1 Resistive plate chambers (RPCs)

Coordinator: LIP
Partners: TUM

Radiation detection with RPCs is a well-established technique which is widely used for large area detectors (>100 m² in High Energy Physics (HEP) and astro-particle physics). However, these devices have been largely neglected for the detection of thermal neutrons. Neutron sensitivity can be achieved by coating the resistive electrodes of a multigap RPC with thin layers of enriched ¹⁰B₄C. They offer the potential of a low cost, large area detector without the need for ³He.

4.2. Silicon photomultipliers for neutron scattering

Coordinator: PSI
Partners: all

SiPMs have many advantages over their vacuum counterparts, including insensitivity to high magnetic fields. However, their high intrinsic noise is a significant limitation for neutron scattering applications. Recently PSI have started to develop signal processing routines to extract the neutron events from the noisy data signals in a one-dimensional position sensitive ZnS scintillation detector read out with WLS fibre and SiPMs. PSI will develop the potential of SiPMs by seeking to apply this technique to two-dimensional position sensitive detectors.

4.3. Silicon photomultipliers for muon spectroscopy

Coordinator: PSI
Partners: STFC

Novel detector technologies for muon spectroscopy based on SiPMs were developed during FP7 and proved crucial for constructing the fast timing array required for the PSI high field instrument. The capability of commercial SiPMs has, however, advanced rapidly in recent years. This sub task will evaluate the latest SiPM technology for scintillation-based detector arrays for muon spectroscopy with particular regard for fast timing applications. The potential of SiPMs will be compared with other emerging technologies such as the Micro Channel Plates (MCPs).

4.4. Micromegas detectors

Coordinator: CEA
Observers: STFC, ILL

The micromegas development in this task is based on the bulk micromegas design which has been developed by IFRU for high energy physics applications and has proved to be robust, low cost and suitable for large area detectors. The devices can be made neutron sensitive by coating the micromegas grids with enriched B₄C. The challenge is to find an efficient way to extract the charge from multiple grids. This will be pursued by CEA, via a combination of Monte Carlo simulation and experimental development, building on the work started in FP7 which demonstrated the potential of this detector for small numbers of grids.