The Application of VMM3A Readout for Multi-Grid Neutron Detectors

TL;DR

This work evaluates the suitability of VMM3A-based readout for the T-REX Multi-Grid neutron detector by direct comparison with CREMAT electronics using a TRP-1 prototype measured at EMMA. A combined Garfield++ and Geant4 simulation framework predicts the pulse-height distributions and MG/BM efficiency as a function of neutron capture position, and these predictions are tested against beam-scanned data. The results show that VMM3A can support high-rate operation with only modest efficiency losses due to the shorter shaping time, while CREMAT offers better pulse-height uniformity near voxel corners but suffers from pileup and lower bandwidth in large systems; simulations reproduce the main trends and quantify systematic uncertainties. These findings support deploying VMM3A readout for the ESS T-REX MG detector, with potential improvements in shaping time if hardware constraints allow. The work demonstrates a robust methodology for validating readout electronics in voxelised neutron detectors.

Abstract

The T-REX neutron spectrometer at the European Spallation Source will use Multi-Grid Technology, which is a voxelised proportional counter relying on\mathrm{^{10}B_{4}C} coatings to detect the scattered neutrons. Measurements of the position dependence of pulse-height and relative detection efficiency of a Multi-Grid prototype of the T-REX spectrometer are presented for two different schemes of signal-processing electronics based on the VMM3A ASIC and CREMAT technology. These measurements, intended to test the suitability of VMM3A for readout of the T-REX Multi-Grid, are compared with Monte Carlo simulations based on the Garfield++ and Geant4 tool kits.

Figures (9)

• Figure 1: Left: a single grid from the T-REX prototype TRP-1. Middle: a single voxel of the grid showing equipotential contours calculated by Garfield++. Right: a photograph of TRP-1 at ESS with the outer gas enclosure vessel removed, showing the stack of 12 grids.
• Figure 2: Schematic diagram of the readout electronics. Either VMM hybrids or CREMAT pre-amps were connected to the TRP-1 wires and grids via adapter cards.
• Figure 3: Schematic of the measurement at EMMA, showing the positioning of the TRP-1 multi-grid prototype with respect to the neutron beam line.
• Figure 4: Sample of 100 anode-wire waveforms from VMMA and CREMAT electronics, taken at voxel $x$ coordinates 0.0 and 8.00 mm
• Figure 5: PH spectra obtained for the position scan with VMM3A readout. Pulse-height alignment is described in the text. Count Ratio is the quotient of TRP-1 and BM counting rates. 12 measured spectra (black shading) are displayed for positions x=0.0 (top left plot) to x=11.0 mm (bottom right) in 1 mm steps. Equivalent Garfield++ simulations are red shaded.