Investigation of instabilities of photomultiplier tubes for multi-element detector systems

This paper presents an investigation into response of instabilities of EJ-309 liquid scintillator detectors. A brief review of common instabilities associated with the photomultiplier tubes (PMTs) is presented. The energy response, energy linearity and warm-up duration of sixteen EJ-309 detectors coupled to PMTs tested is presented. A single-channel mixed-field analyser digitiser system was used for data acquisition. Furthermore, timing information of the common instability behaviours is presented alongside suggestions on how to correct for such instabilities. The results show that a single-energy energy calibration is sufficient to ensure energy linearity; the detectors must be warmed-up by ~45 minutes before stable response is achieved; the re-warm-up duration depends on the duration of the high voltage supplied to the PMT being switched off. The results indicate that the PMTs take approximately 2 hours to reach "cold" state, where a full warm-up duration must be applied. The reported instability effects will be taken into account when developing a sophisticated auto-calibration methodology for a multi-element scintillator detector system

Real-time capabilities of a digital analyzer for mixed-field assay using scintillation detectors

Scintillation detectors offer a single-step detection method for fast neutrons and necessitate real-time acquisition, whereas this is redundant in two-stage thermal detection systems using helium-3 and lithium-6, where the fast neutrons need to be thermalized prior to detection. The relative affordability of scintillation detectors and the associated fast digital acquisition systems have enabled entirely new measurement setups that can consist of sizeable detector arrays. These detectors in most cases rely on photomultiplier tubes, which have significant tolerances and result in variations in detector response functions. The detector tolerances and other environmental instabilities must be accounted for in measurements that depend on matched detector performance. This paper presents recent advances made to a high-speed FPGA-based digitizer. The technology described offers a complete solution for fast-neutron scintillation detectors by integrating multichannel high-speed data acquisition technology with dedicated detector high-voltage supplies. This configuration has significant advantages for large detector arrays that require uniform detector responses. We report on bespoke control software and firmware techniques that exploit real-time functionality to reduce setup and acquisition time, increase repeatability, and reduce statistical uncertainties

Automated Response Matching for Organic Scintillation Detector Arrays

This paper identifies a digitizer technology with unique features that facilitates feedback control for the realization of a software-based technique for automatically calibrating detector responses. Three such auto-calibration techniques have been developed and are described along with an explanation of the main configuration settings and potential pitfalls. Automating this process increases repeatability, simplifies user operation, enables remote and periodic system calibration where consistency across detectors’ responses are critical

Real-time, digital pulse-shape discrimination in non-hazardous fast liquid scintillation detectors: Prospects for safety and security

Pulse-shape discrimination (PSD) in fast, organic scintillation detectors is a long-established technique used to separate neutrons and γ rays in mixed radiation fields. In the analogue domain the method can achieve separation in real time, but all knowledge of the pulses themselves is lost thereby preventing the possibility of any post- or repeated analysis. Also, it is typically reliant on electronic systems that are largely obsolete and which require significant experience to set up. In the digital domain, PSD is often more flexible but significant post-processing has usually been necessary to obtain neutron/γ-ray separation. Moreover, the scintillation media on which the technique relies usually have a low flashpoint and are thus deemed hazardous. This complicates the ease with which they are used in industrial applications. In this paper, results obtained with a new portable digital pulse-shape discrimination instrument are described. This instrument provides real-time, digital neutron/γ separation whilst preserving the synchronization with the time-of-arrival for each event, and realizing throughputs of 3×10 6 events per second. Furthermore, this system has been tested with a scintillation medium that is non-flammable and not hazardous

Real-time source localisation by passive, fast-neutron time-of-flight with organic scintillators for facility-installed applications

Fast neutron time-of-flight (ToF) has been used to characterise the location of a source of a mixed radiation field. Two EJ-309 organic scintillators and a fast, digital, data acquisition system have been used in a variety of positions to identify the location of a 252Cf neutron source inside a steel, water-filled tank. A methodology for extracting the distance between the neutron source and the neutron detector has been developed and verified with MCNP simulations. A reconstruction algorithm using the ToF data has been developed. The location of the neutron source has been estimated on this basis to be within 20 cm of its known location with a spatial resolution of ±7.8 cm. p-values extracted from the null test hypothesis have been estimated to be 0.975 and 0.996 for experimental and simulation data, respectively. By correctly identifying the location of the source, the potential for the system to discern between scattered and unscattered neutrons is demonstrated

Review of U.K.A.E.A. criticality detection and alarm systems 1963/64 Part 1: provision and design principles

LD:9091.9F(AHSB(S)R--92). / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Wireless information transfer with fast neutrons

Fast neutrons propagate significantly in free space with interaction properties that contrast markedly with those of electromagnetic radiation, the latter being fundamental to most wireless communications. Here, we report on the configuration and operation of a nuclear instrumentation set-up designed to transmit digitally encoded information using fast neutrons. We demonstrate the potential of fast neutron radiation as a medium for wireless communications for applications where conventional electromagnetic transmission is either not feasible or is inherently limited

Characterizing Corrosion-Born Defects in Oil Pipelines Using Fast-Neutron Elastic Scattering

Neutrons can provide information related to the materials with which they interact, that is, to some extent complementary to that provided by X-rays for use in non-intrusive applications. The majority of studies to date have focused on the use of thermal neutrons with there being fewer reports concerning the use of fast neutrons despite the latter being able to penetrate deeper into substances. This record describes an investigation into the use of neutron radiation (from sources such as californium-252 and americium-beryllium) to characterize defects in the walls of oil pipelines. Both sources yield a mixed radiation field of fast neutrons and γ rays which can be collimated and directed towards the steel pipeline under study. Fast neutrons are either transmitted or reflected by the pipe wall. Since the incident radiation flux on the pipeline can be determined and the scattered neutron flux can be measured, the potential exists for an assessment of the ratio of transmitted and reflected fast neutrons to be made. If defects within the pipeline are present, the ratio may be observed to change as a result relative to that of the defect-free alternative. The scattered flux will be measured by an array of organic liquid scintillation detectors, coupled with a real-time, pulse-shape discrimination system. Both γ rays and neutrons are thus retained to provide transmission information about the pipeline sector being tested. A Monte Carlo model is used to simulate a generic pipeline section in order to understand its fast-neutron scattering response under different conditions. For instance, with the pipe filled with crude oil or partially filled with a combination of oil and gas, as well as for different types of effects to its inner structure. The results of these simulations will be presented to justify the choice of scatter arrangement, the optimum angle for the detector deployment and as evidence for the assessment of defects filled with air and for pits filled with oxide-based corrosion residues