Simulation of the Response of the Solid State Neutron Detector for the European Spallation Source

The characteristics of the Solid-state Neutron Detector, under development for neutron-scattering measurements at the European Spallation Source, have been simulated with a Geant4-based computer code. The code models the interations of thermal neutrons and ionising radiation in the 6Li-doped scintillating glass of the detector, the production of scintillation light and the transport of optical, scintillation photons through the the scintillator, en route to the photo-cathode of the attached multi-anode photomultiplier. Factors which affect the optical-photon transport, such as surface finish, pixelation of the glass sheet, provision of a front reflector and optical coupling media are compared. Predictions of the detector response are compared with measurements made with neutron and gamma-ray sources, a collimated alpha source and finely collimated beams of 2.5 MeV protons and deuterons.Comment: Preprint 22 pages, 12 figures, published in NIM

Response of a Li-glass/multi-anode photomultiplier detector to collimated thermal-neutron beams

The response of a position-sensitive Li-glass scintillator detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using collimated beams of thermal neutrons. The detector was moved perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and vertical steps. Scintillation was detected in an 8 X 8 pixel multi-anode photomultiplier tube on an event-by-event basis. In general, several pixels registered large signals at each neutron-beam location. The number of pixels registering signal above a set threshold was investigated, with the maximization of the single-hit efficiency over the largest possible area of the detector as the primary goal. At a threshold of ~50% of the mean of the full-deposition peak, ~80% of the events were registered in a single pixel, resulting in an effective position resolution of ~5 mm in X and Y. Lower thresholds generally resulted in events demonstrating higher pixel multiplicities, but these events could also be localized with ~5 mm position resolution.Comment: 23 pages, 8 figure

Light-yield response of liquid scintillators using 2–6 MeV tagged neutrons

Knowledge of the neutron light-yield response is crucial to the understanding of scintillator-based neutron detectors. In this work, neutrons from 2–6MeV have been used to study the scintillation light-yield response of the liquid scintillators NE 213A, EJ 305, EJ 331 and EJ 321P using event-by-event waveform digitization. Energy calibration was performed using a GEANT4 model to locate the edge positions of the Compton distributions produced by gamma-ray sources. The simulated light yield for neutrons from a PuBe source was compared to measured recoil proton distributions, where neutron energy was selected by time-of-flight. This resulted in an energy-dependent Birks parameterization to characterize the non-linear response to the lower energy neutrons. The NE 213A and EJ 305 results agree very well with existing data and are reproduced nicely by the simulation. New results for EJ 331 and EJ 321P, where the simulation also reproduces the data well, are presented

Time- and energy-resolved effects in the boron-10 based Multi-Grid and helium-3 based thermal neutron detectors

The boron-10 based Multi-Grid detector is being developed as an alternative to helium-3 based neutron detectors. At the European Spallation Source, the detector will be used for time-of-flight neutron spectroscopy at cold to thermal neutron energies. The objective of this work is to investigate fine time- and energy-resolved effects of the Multi-Grid detector, down to a few $\mu$eV, while comparing it to the performance of a typical helium-3 tube. Furthermore, it is to characterize differences between the detector technologies in terms of internal scattering, as well as the time reconstruction of ~ $\mu$s short neutron pulses. The data were taken at the Helmholtz Zentrum Berlin, where the Multi-Grid detector and a helium-3 tube were installed at the ESS test beamline, V20. Using a Fermi-chopper, the neutron beam of the reactor was chopped into a few tens of $\mu$s wide pulses before reaching the detector, located a few tens of cm downstream. The data of the measurements show an agreement between the derived and calculated neutron detection efficiency curve. The data also provide fine details on the effect of internal scattering, and how it can be reduced. For the first time, the chopper resolution was comparable to the timing resolution of the Multi-Grid detector. This allowed a detailed study of time- and energy resolved effects, as well as a comparison with a typical helium-3 tube.Comment: 37 pages, 21 figure

Response of a Li-glass/multi-anode photomultiplier detector to α-particles from ²⁴¹Am

The response of a position-sensitive Li-glass scintillator detector to -particles from a collimated ²⁴¹Am source scanned across the face of the detector has been measured. Scintillation light was read out by an 8 x 8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector

Compton Scattering from the Deuteron Above Pion-Production Threshold

The electromagnetic polarizabilities of the nucleon are fundamental nucleon-structure observables that characterize its response to external electromagnetic fields. The neutron polarizabilities can be accessed from Compton-scattering data on light nuclear targets. Recent measurements of the differential cross section for Compton scattering on the deuteron below the pion-production threshold have decreased the uncertainties in the neutron polarizabilities, yet the proton polarizabilities remain known substantially more accurately. As the sensitivity of the cross section to the polarizabilities increases with incident photon energy, measurements above the pion threshold may offer a way for an improved determination of the neutron polarizabilities. In this Rapid Communiciation, the first measurement of the cross section for coherent Compton scattering on the deuteron above the pion-production threshold is presented

Recent Developments SoNDe High-Flux Detector Project

New high-flux and high-brilliance neutron sources demand a higher count-rate capability in neutron detectors. In order to achieve that goal, the Solid-State Neutron Detector (SoNDe) project is developing a scintillation-based neutron detector. It will be capable of fully exploiting the available flux at small-angle neutron scattering (SANS) instruments at high brilliance sources, such as SKADI at the European Spallation Source (ESS). The read-out of the scintillator is based on a pixelized multi-anode PMT (MaPMT), where each pixel is treated separately. In addition to enabling higher achievable count-rates, one of the design goals was to develop a modular and scalable solution that can also be used in other instruments or even contexts, such as for laboratory setups. This has been achieved by combining the complete read-out electronics along with the MaPMT into modules that can be controlled and read-out individually via a network without additional any infrastructure. An overview of the present state of development and current test results is presented, highlighting the results of previously published project reports

The light-yield response of a NE-213 liquid-scintillator detector measured using 2–6 MeV tagged neutrons

The response of a NE-213 liquid-scintillator detector has been measured using tagged neutrons from 2 to 6 MeV originating from an Am/Be neutron source. The neutron energies were determined using the time-of-flight technique. Pulse-shape discrimination was employed to discern between gamma-rays and neutrons. The behavior of both the fast (35 ns) and the combined fast and slow (475 ns) components of the neutron scintillation-light pulses were studied. Three different prescriptions were used to relate the neutron maximum energy-transfer edges to the corresponding recoil-proton scintillation-light yields, and the results were compared to simulations. The overall normalizations of parametrizations which predict the fast or total light yield of the scintillation pulses were also tested. Our results agree with both existing data and existing parametrizations. We observe a clear sensitivity to the portion and length of the neutron scintillation-light pulse considered

GEANT4-based calibration of an organic liquid scintillator

A light-yield calibration of an NE 213A organic liquid scintillator detector has been performed using both monoenergetic and polyenergetic gamma-ray sources. Scintillation light was detected in a photomultiplier tube, and the corresponding pulses were subjected to waveform digitization on an event-by-event basis. The resulting Compton edges have been analyzed using a GEANT4 simulation of the detector which models both the interactions of the ionizing radiation as well as the transport of scintillation photons. The simulation is calibrated and also compared to well-established prescriptions used to determine the Compton edges, resulting ultimately in light-yield calibration functions. In the process, the simulation-based method produced information on the gain and intrinsic pulse-height resolution of the detector. It also facilitated a previously inaccessible understanding of the systematic uncertainties associated with the calibration of the scintillation-light yield. The simulation-based method was also compared to well-established numerical prescriptions for locating the Compton edges. Ultimately, the simulation predicted as much as 17% lower light-yield calibrations than the prescriptions. These calibrations indicate that approximately 35% of the scintillation light associated with a given gamma-ray reaches the photocathode. It is remarkable how well two 50 year old prescriptions for calibrating scintillation-light yield in organic scintillators have stood the test of time