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NaI(Tl) scintillators can detect thermal neutrons with surprising efficiency, even in the presence of ambient gamma radiation. This is due to a peculiarity of the 128I level scheme. Deexcitation cascades following neutron captures in 127I, a main constituent of NaI with quite large neutron capture cross section, unexpectedly often involve the 167.4 keV state of 128I with 175 ns half-life, which feeds another isomeric level at 137.9 keV having a half-life of 845 ns. The 29.5 keV transition between both levels, as well as the subsequent deexcitation sequence to ground state comprising 137.9 keV sum energy, are almost certainly absorbed in the crystal. Signals including three scintillation pulses within few microseconds, the first one caused by a prompt part of the cascade, the second and third one disclosing 30 and 138 keV energy depositions and characteristic delays, are clearly related to such neutron captures. Double-pulse sequences comprising only the primary pulse and a delayed 138 keV signal are also distinctive but more prone to load-dependent background by random pulse pileups. This article demonstrates neutron detection with a Ø2” $\times2$ ” NaI(Tl) scintillation detector by finding and analyzing such double- and triple-pulse sequences in digitized detector signals. It quantifies effect and background rates as a function of the detector load ranging up to 30 kcps. Complementary measurements with a 6Li codoped Ø2” $\times2$ ” NaI(Tl) (NaIL) scintillator allow relating the neutron detection yield by delayed-coincidence counting to the 6Li capture rate in the same crystal and thus to evaluate prospects and limits of this technique. [ABSTRACT FROM AUTHOR]

Precise measurement under high counting rates has been a major challenge for γ -ray spectroscopy, where signals generally pile up with each other and their characteristic values are deeply coupled. An off-line pile-up pulse recovery algorithm based on template matching is developed for LaBr 3 scintillation detectors and has been applied to data from China Spallation Neutron Source (CSNS) Back-n white neutron beamline. As an improvement to the traditional Template Matching methods, the predetermined template shape is associated with pulse amplitudes, which is found crucial to achieve the best fitting results. Moreover, a universal strategy of setting the initial values of fitting allows to resolve signals that are separated in time by less than the characteristic rise time. Processing of simulated pulses demonstrates that the lower limit of interval to distinguish successive events is 10 ns, which is a significant improvement to the previous works. The algorithm performs well under a counting rate of 6 × 1 0 7 s−1, and is still effective up to 1 0 8 s−1. Analysis of experimental data indicates that this algorithm recovers over 98% count yield under a counting rates of no more than 4 × 1 0 6 s−1 in this work, providing a more reliable approach to deduce neutron-induced reaction cross sections. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Basic concepts and the development of a high counting rate digital spectrometry system based on efficient ADCs and latest available FPGA are presented with the aim of using such a system, coupled to fast scintillators, in plasma experiments. The prototype system is a 1 channel 12-bit 1 GSPS digitizer with 2~\mathrm V\mathrm {pp} input voltage. Preliminary results tested with different radioactive sources are shown for low (0.03 Mcps) and high (2.2 Mcps) counting rates. A comparison of energy spectra and energy resolution with what obtained by a commercial device is also shown. [ABSTRACT FROM PUBLISHER]

The shape of the nuclear signal from scintillators contains information about the detection material from which it originated and its current temperature. A digital filter for this type of signals is presented that automatically extracts both of these pieces of information from the shape of the signals and controls the temperature dependency of the resolution by continuous adaption to this shape. Hereby, nuclear signals are a-priori modelled by an all-pole filter. The concept combines a deconvolution approach based on this model with a least-mean-squares iteration. Beneath the iteration, there is a continuous assessment of the signal shape where the mean-squared distance between the assumed shape and measured shape acts as control parameter for the resolution. From the information stored inside the dynamic filter parameters, the material characteristics are retrieved to identify the detector material. An implementation into a multi-channel-analyser is shown and the technique is verified under real-world environmental conditions. [ABSTRACT FROM AUTHOR]

Gamma ray spectrometry measurements at high detector counting rates (on the order of 107 s−1 and higher) are relevant for high-temperature plasma diagnostics for existing tokamaks and during the development of gamma ray diagnostic systems for the ITER tokamak under construction. At high loads, to obtain spectra without distortion and with a small amount of dead time, it is necessary to use advanced scintillation detector signal processing methods, which can resolve superimposed pulses. Two algorithms that can be used for digital signal processing of scintillation gamma ray detectors with many piled-up pulses are considered in this article, the fitting and deconvolution methods. These algorithms are compared with both one another and two less sophisticated pulse-height analysis algorithms (maximum height and total sum under the peak) in applications that process model and measured signals. Baseline detection algorithms are also considered, which are necessary when processing signals from detectors. The algorithms are applied to LaBr 3 (Ce) detector signal processing. For the modeled signals, the best results in terms of the number of resolved events and energy resolution at counting rates up to 2 × 107 s−1 of the LaBr 3 (Ce) detector are demonstrated by the fitting method. In the real gamma ray measurements at a loading of 5.1 106 s−1, the deconvolution method demonstrated the best energy resolution. [ABSTRACT FROM AUTHOR]

A digital data acquisition system together with MATLAB software for data analysis were utilised to measure the pulse specification of the scintillation detector assembly. Besides, the sensitivity of a photomultiplier tube (PMT) window to gamma-rays was studied to discriminate the signals produced as a result of gamma-ray interactions inside the glass window from those originating from the scintillator cell. The result showed that an algorithm based on the time features was capable to evaluate the contributions of these two different signals. [ABSTRACT FROM AUTHOR]