Cluster Detectors Research Articles

Geant4 simulations for the [formula omitted]-ray detectors of gSPEC at GSI/FAIR

A design study for the γ-ray detector array of the gSPEC project, which aims at measuring nuclear moments at GSI/FAIR, is presented. Foreseen setups, involving DEGAS and the new gDEGAS triple cluster detectors for γ-ray spectroscopy are simulated using the Geant4 framework. The main characteristics associated to these detector assemblies with the envisaged configurations, namely the photo-peak efficiency and the angular resolution, are discussed. A new correction procedure for a better reconstruction of the time-perturbed angular distribution is proposed.

Dual-Polarization Ambient Backscatter Communications and Signal Detection.

Ambient backscatter communication (AmBC), an emerging mechanism for batteryless communications that can utilize ambient radio-frequency signals to modulate information and thus reduce power consumption, has attracted considerable attention and has been considered as a critical technology in green "Internet of Things" sensor networks due to its ultra-low power consumption. This paper presents the first a complete dual-polarization AmBC (DPAm) system model, which can extend AmBC into polarization diversity and improve the data-transmission rate of backscatter symbols. We proposed two scenarios: direct dual-polarization-based DPAm node structures and polarization-conversion-based DPAm node structures. In addition, we consider a parallel backscatter mode with differential coding and develop corresponding detectors, which also give the analytical detection thresholds. Moreover, we consider a simultaneous backscatter mode with Manchester coding in order to avoid complex-parameter estimation. To address the power imbalance problem of the DPAm system that arises because the polarization deflection angle would cause the power level to change with different polarization patterns, we also develop a power-average detector and a clustering detector. Simulation results show the throughput performance on each DPAm node structure with each detector, demonstrating the feasibility and efficiency of the proposed DPAm nodes and detectors. Compared with single-polarization AmBC (SPAm), the proposed DPAm node can achieve higher throughput in most cases. Finally, the clustering detector is shown to be more robust to short training sequences and complex environments.

Agata detector technology: recent progress and future developments

gamma -ray tracking is based on a new generation of position sensitive high-purity germanium (HPGe) detectors. A novel type of cluster detector was successfully developed and assembled for the high-resolution gamma -ray spectrometer Advanced Gamma Tracking Array AGATA. The core part of the detector consists of three encapsulated, 36-fold segmented HPGe detectors which are operated in a common cryostat. The Ge crystal is hermetically sealed inside an aluminium can. All energy channels provide best energy resolution of core and segment signals for an extended energy range well above 50 MeV. A low cross-talk level was determined for the HPGe detectors and its preamplifier circuitry. Related cross-talk corrections are essential for highest energy resolution and improved position dependent pulse shape information. Recently a new encapsulation technology was put into operation which is based on a renewable metal elastic seal. HPGe detector developments are concerned with technologies for the production of p+ and n+ contacts, the segmentation and passivation of encapsulated HPGe crystals. Semiconductor processing research specifically aimed to develop a stable, thin and easy to segment n+ contact. A novel process, based on pulsed laser melting PLM, was successfully employed to produce very thin n+ and p+ contacts preserving the Ge purity. The contacts were segmented using a photolithographic process and then the intrinsic surface between contacts was passivated to assure the electrical insulation between them. A small detector prototype with three segments was made using these new techniques and then successfully tested.

Angular correlation of the two gamma rays produced in the thermal neutron capture on gadolinium-155 and gadolinium-157

Abstract The ANNRI-Gd collaboration studied in detail the single γ-ray spectrum produced from the thermal neutron capture on 155Gd and 157Gd in our previous publications. Gadolinium targets were exposed to a neutron beam provided by the Japan Spallation Neutron Source (JSNS) in J-PARC, Japan. In the present analysis, one new additional coaxial germanium crystal was used in combination with the 14 germanium crystals in the cluster detectors to study the angular correlation of the two γ rays emitted in the same neutron capture. We present for the first time angular correlation functions for two γ rays produced during the electromagnetic cascade transitions in the (n, γ) reactions on 155Gd and 157Gd. As expected, we observe mild angular correlations for the strong, but rare transitions from the resonance state to the two energy levels of known spin-parities. Contrariwise, we observe negligibly small angular correlations for arbitrary pairs of two γ rays produced in the majority of cascade transitions from the resonance state to the dense continuum states.

Lifetime measurements of excited states in Cr55

Excited states in $^{55}\mathrm{Cr}$ have been populated via the fusion-evaporation reaction $^{48}\mathrm{Ca}(^{11}\mathrm{B},p3n){\phantom{\rule{0.16em}{0ex}}}^{55}\mathrm{Cr}$ at a beam energy of 32 MeV. The Cologne plunger device surrounded by a $\ensuremath{\gamma}$-ray detector array was employed to determine lifetimes with the recoil-distance Doppler-shift method. $\ensuremath{\gamma}$ rays were observed by one Ge EUROBALL cluster detector and five HPGe detectors. $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence data were analyzed with help from the differential decay-curve method, and precise lifetimes for the first excited states were extracted from the $5/{2}^{\ensuremath{-}}\ensuremath{\rightarrow}3/{2}^{\ensuremath{-}}$ and the $9/{2}^{\ensuremath{-}}\ensuremath{\rightarrow}5/{2}^{\ensuremath{-}}$ transitions. Reduced transition strengths $B(\ensuremath{\sigma}\ensuremath{\lambda})$ were determined and compared to shell-model calculations employing four interactions KB3G, FPD6, GXPF1A, and GXPF1Br. The calculations were also performed for the $N=31$ isotonic chain from $^{53}\mathrm{Ti}$ to $^{61}\mathrm{Zn}$. Inspection of the wave functions as well as particle-plus-rotor model calculations allow for a detailed understanding of the excited states and the reduced transition strength in $^{55}\mathrm{Cr}$. The interactions GXPF1A and GXPF1Br reproduce well the experimental findings in $^{55}\mathrm{Cr}$ and in other isotones.

A Two-Stage Clustering Detector for SM-MIMO Communications

In this letter, we propose a novel two-stage clustering detector for spatial modulation multiple-input multiple-output (SM-MIMO) systems. Firstly, the quality of the clustering result (i.e., cluster centroids) of the conventional KMC detector will be checked through the proposed rule in the first stage. Then, with the aid of the good cluster centroids of the bad clustering result and the symmetry property of the good cluster centroids, the bad cluster centroids are obtained from the first stage will be corrected to good cluster centroids in the second stage. Furthermore, a new two-stage clustering detector is proposed correspondingly. Our simulation results show that the proposed two-stage clustering detector outperforms other clustering detectors and is capable of achieving near maximum-likelihood (ML) performance with considerably low complexity.

A clustering detector with graph theory for blind detection of spatial modulation systems

This paper considers the blind detection of spatial modulation systems multiple-input multiple-output systems. In this system, we propose a clustering detection framework with graph theory that conducts signal detection without the training of channel state information. In detail, firstly, by dynamically controlling the size of each cluster, we transform the original optimization problem of the traditional K-means clustering detector into a new optimization problem. In addition, the cluster assignment subproblem of the iterative clustering algorithm for solving the new optimization problem makes it equivalent to a minimum cost flow linear network optimization problem of graph theory, which can be addressed by the breadth-first algorithm. Moreover, a novel clustering detector with the breadth-first algorithm is presented correspondingly. Numerical results show that the proposed detector is efficient in avoiding the undesired local optima and can closely approach the performance of the optimal detector.

Ship Security Relative Integrated Navigation with Injected Fault Measurement Attack and Unknown Statistical Property Noises

In this work, the ship relative integrated navigation approaches are studied for the navigation scenarios with the measurements disturbed by unknown statistical property noises and with the injected fault measurement attacks. On the basis of the limited energy property of system noises, the navigation states are estimated by the local finite horizon H∞ filter to satisfy the performance index function. Then, the local estimates are fused in the relative integrated navigation system with the weight fusion parameters obtained by using the local estimate error measurements. Further, the injected fault measurement attacks are considered in the relative integrated navigation systems. Due to the system noises and the measurement noises having unknown statistical property, the classical Chi-square test can hardly be utilized to detect the injected fault measurements. Therefore, a secure relative integrated navigation method is proposed with a distance-based clustering detector. The finial simulation results illustrate the effectiveness of the proposed relative integrated navigation approach and the proposed secure relative integrated navigation approach.

Unsupervised Clustering for Nonlinear Equalization in Indoor Millimeter-Wave Communications

Millimeter-wave (mmWave) systems have been considered as a promising candidate for 5G networks because of their potential advances in significant bandwidth enhancement. However, due to the extremely high operating frequency of mmWave systems, they generally suffer from severe frequency-selective propagation and nonlinear distortion in the power amplifier, which introduces unfavorable impact on the signal detection process. We discover that for indoor mmWave communications, the constellation of signals becomes much more “clean and tidy” at the receiver side compared with the current wireless systems (e.g., LTE and WiFi), thanks to the channel sparsity characteristic of mmWave communications. Motivated by this observation, we propose in this paper several detection algorithms. Specifically, K-means clustering (KMC) algorithm is first introduced into clustering signal detection due to its advantage in the circle or spherical cluster shape. Then, an improved KMC detector is proposed to avoid the deficiencies of KMC for the error floor and high complexity. Moreover, a density and distance-based clustering detector, a non-iterative algorithm, is proposed and it does not need to preset the number of clusters. The above-proposed algorithms do not require any prior information about the power amplifier and the channel state information at the receiver end, which presents noticeable practical achievements on cost, complexity, and hardware constraints. The simulation results verify the effectiveness of the proposed schemes.

Layered and Real-Valued Negative Selection Algorithm for Fault Detection

In this paper, the challenging task of the development of a generic fault detection (FD) method is addressed. While the past FD research has primarily focused on modeling and signal-processing methods that are problem specific and require complete knowledge of the system model and fault types, this paper presents a novel layered and real-valued negative-selection algorithm (LRNSA)-based FD method independent of prior knowledge of fault types and patterns. Specifically, in the training phase, the nonself-space is divided into different layers for effective generation and distribution of detectors using normal (self) data. The major accomplishments of the proposed method are improved nonself-space coverage of the uncovered gaps (holes), followed by the formation of cluster detector with large radius. To test the capabilities of the developed method, the generated specialized detector distribution is studied using bearing fault modeling in a three-phase induction motor. The proposed method is subsequently investigated and validated by applying it to an actual induction motor for different types of bearing faults. Finally, the comparative results on the benchmark dataset demonstrate the superiority of the proposed method compared to the state-of-the-art machine learning algorithms in terms of higher FD accuracy and quick detection with reduced online detection time.

Shell Evolution towards ^{78}Ni: Low-Lying States in ^{77}Cu.

The level structure of the neutron-rich ^{77}Cu nucleus is investigated through β-delayed γ-ray spectroscopy at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center. Ions of ^{77}Ni are produced by in-flight fission, separated and identified in the BigRIPS fragment separator, and implanted in the WAS3ABi silicon detector array, surrounded by Ge cluster detectors of the EURICA array. A large number of excited states in ^{77}Cu are identified for the first time by correlating γ rays with the β decay of ^{77}Ni, and a level scheme is constructed by utilizing their coincidence relationships. The good agreement between large-scale MonteCarlo shell model calculations and experimental results allows for the evaluation of the single-particle structure near ^{78}Ni and suggests a single-particle nature for both the 5/2_{1}^{-} and 3/2_{1}^{-} states in ^{77}Cu, leading to doubly magic ^{78}Ni.

Study for s-process using neutron beam provided from ANNRI of J-PARC

Most isotopes heavier than iron are synthesized by the slow neutron capture reaction process (s-process) in stars. Isomers in stable isotopes have sometimes an important role as a branching point in nucleosynthesis flow in the s-process. An isomer with a half-life of 14.1 y in 113 Cd is a branching point from which a nucleosynthesis flow reaches to a rare isotope 115 Sn. The astrophysical origin of 115 Sn has remained still an open question. The s-process abundance of 115 Sn depends on the ratio of the 112 Cd(n, γ ) 113 Cd m reaction cross section to the 112 Cd(n, γ ) 113 Cd gs reaction cross section. However, the isomer production ratio following the neutron capture reaction has not been measured in the energy region higher than the thermal energy. An intense neutron beam experimental system, ANNRI, in J-PARC has a high purity germanium (HPGe) detector system consisting of two cluster detectors. We have measured γ -rays decaying to the ground state and the isomer using the HPGe detectors in conjunction with a time-offlight method at ANNRI.

Coding-Aided K-Means Clustering Blind Transceiver for Space Shift Keying MIMO Systems

In this paper, we propose coding-aided K-means clustering (CKMC) blind transceiver for space shift keying (SSK) multiple-input multiple-output (MIMO) systems, where the training of channel state information (CSI) is not required for detection. For the scenario where transmitter is with limited processing capability and limited power such as Internet Of Things (IOT) and wireless sensor network (WSN), SSK is preferable to typical MIMO due to its simplicity and improved energy efficiency. The proposed CKMC blind communication trades off receiver complexity for training overhead, which provides better spectral efficiency compared to training-based transceiver. In CKMC, the blind communication problem is converted to the problems of clustering and permutation; for the clustering problem, we propose K-means clustering (KMC) detector to reduce detection complexity; for the permutation problem, we propose to perform depermutation with the aid of channel decoding. The analysis of CKMC blind transceiver is conducted, and the verification of performance of CKMC is presented in the simulations section. The results show that the performance of CKMC blind communication can closely approach the performance of optimal receiver with perfect CSI under certain scenarios.

The RedGOLD cluster detection algorithm and its cluster candidate catalogue for the CFHT-LS W1

We present RedGOLD (Red-sequence Galaxy Overdensity cLuster Detector), a new optical/NIR galaxy cluster detection algorithm, and apply it to the CFHT-LS W1 field. RedGOLD searches for red-sequence galaxy overdensities while minimizing contamination from dusty star-forming galaxies. It imposes an Navarro–Frenk–White profile and calculates cluster detection significance and richness. We optimize these latter two parameters using both simulations and X-ray-detected cluster catalogues, and obtain a catalogue ∼80 per cent pure up to z ∼ 1, and ∼100 per cent (∼70 per cent) complete at z ≤ 0.6 (z ≲ 1) for galaxy clusters with M ≳ 10^(14) M_⊙ at the CFHT-LS Wide depth. In the CFHT-LS W1, we detect 11 cluster candidates per deg^2 out to z ∼ 1.1. When we optimize both completeness and purity, RedGOLD obtains a cluster catalogue with higher completeness and purity than other public catalogues, obtained using CFHT-LS W1 observations, for M ≳ 10^(14) M_⊙. We use X-ray-detected cluster samples to extend the study of the X-ray temperature–optical richness relation to a lower mass threshold, and find a mass scatter at fixed richness of σ_(lnM|λ) = 0.39 ± 0.07 and σ_(lnM|λ) = 0.30 ± 0.13 for the Gozaliasl et al. and Mehrtens et al. samples. When considering similar mass ranges as previous work, we recover a smaller scatter in mass at fixed richness. We recover 93 per cent of the redMaPPer detections, and find that its richness estimates is on average ∼40–50 per cent larger than ours at z > 0.3. RedGOLD recovers X-ray cluster spectroscopic redshifts at better than 5 per cent up to z ∼ 1, and the centres within a few tens of arcseconds.

Conceptual design of a high resolution Ge array with tracking and imaging capabilities for the DESPEC (FAIR) experiment

We present results of Monte Carlo simulations for the conceptual design of the high-resolution DESPEC Germanium Array Spectrometer (DEGAS) proposed for the Facility for Ion and Antiproton Research (FAIR) under construction at Darmstadt, Germany. The project is carried out in three phases, although only results for the two first phases will be addressed in this work. The first phase will consist of a re-arrangement of the EUROBALL cluster detectors previously used in the RISING campaign at GSI. The second phase is based on coupling AGATA-type triple-cluster detectors with EUROBALL cluster detectors in a compact geometry around the active ion implantation target of DESPEC.

A novel approach for modelling the cluster detector and the SPI spectrometer

A probabilistic approach has been presented in six recent papers (R Kshetri, J. Instrum. 2012 7 P04008; ibid., P07006; ibid., P07008; ibid., P08015; ibid., P12007; Appl. Radiat. Isotopes 2013 75 30) for modelling a general composite detector. In this paper, a simplistic view has been presented on the application of our formalism to composite detectors consisting of hexagonal closely packed encapsulated HPGe detector modules. We have presented modified calculations for the peak-to-total (PT) and peak-to-background (PB) ratios of the cluster and spectrometer for integral satellite (SPI) for the first time considering up to four-fold events. Instead of using an empirical method or simulation, we present a novel approach for calculating the peak-to-total ratio of the SPI spectrometer for high γ energies. Our work can provide guidance for designing new composite detectors and for performing experimental studies with the SPI spectrometer for high-energy γ-rays.

Analysis of Laser and Detector Placement in Incoherent MIMO Multimode Fiber Systems

Conventional large-core multimode fibers (MMFs) are preferred for use in short to medium haul optical fiber links, owing to their tolerance to misalignment and low deployment costs; however, data rates through MMFs are limited by modal dispersion. Digital signal processing with multiple-input multiple-output (MIMO) techniques has offered promising solutions to overcome the dispersion limitations of MMFs, but the impact of the geometry of laser and detector arrays on the achievable data rate is not established. To this end, we use a field-propagation-based model to gauge the impact the geometry of lasers and detectors can have on the achievable ergodic and outage rates of incoherent MIMO-MMF links. Laser and detector array geometries were investigated using a grid-based method to optimize the positions of lasers and detectors for a 1 km MIMO-MMF link. Simulations reveal that systems with appropriately designed laser/detector geometries could improve the achievable rate over the fiber by more than 200% over random laser/detector arrays. The grid-based search technique, however, is limited due to high computational requirements for fine grids. As an alternative, we developed a suboptimal “greedy” selection approach to design detector geometries, which produces detector geometries that attain more than 90% of the rate obtained with an exhaustive search, while requiring less than 0.2% of the computation. The low computation requirements and high performance of the greedy selection approach also motivate the use of dynamically reconfigurable detector arrays to achieve high data rates with reduced signal processing complexity. Methods are also presented for clustering detector elements to obtain more consolidated segmented detectors with better fill factors, while still offering significant data rate benefits. The achievable ergodic rate using these systems is verified to be close to the link’s ergodic capacity.

Identification and rejection of scattered neutrons in AGATA

γ Rays and neutrons, emitted following spontaneous fission of 252Cf, were measured in an AGATA experiment performed at INFN Laboratori Nazionali di Legnaro in Italy. The setup consisted of four AGATA triple cluster detectors (12 36-fold segmented high-purity germanium crystals), placed at a distance of 50cm from the source, and 16 HELENA BaF2 detectors. The aim of the experiment was to study the interaction of neutrons in the segmented high-purity germanium detectors of AGATA and to investigate the possibility to discriminate neutrons and γ rays with the γ-ray tracking technique. The BaF2 detectors were used for a time-of-flight measurement, which gave an independent discrimination of neutrons and γ rays and which was used to optimise the γ-ray tracking-based neutron rejection methods. It was found that standard γ-ray tracking, without any additional neutron rejection features, eliminates effectively most of the interaction points due to recoiling Ge nuclei after elastic scattering of neutrons. Standard tracking rejects also a significant amount of the events due to inelastic scattering of neutrons in the germanium crystals. Further enhancements of the neutron rejection was obtained by setting conditions on the following quantities, which were evaluated for each event by the tracking algorithm: energy of the first and second interaction point, difference in the calculated incoming direction of the γ ray, and figure-of-merit value. The experimental results of tracking with neutron rejection agree rather well with Geant4 simulations.

Boron-Coated Straw Detectors for Backpack Monitors

The limited inventory and minute natural abundance of 3He gas on Earth necessitate the adoption of new technologies for the detection of neutrons, especially in homeland security applications, where large volume deployments are required. We investigate the neutron detection efficiency of a backpack radiation detector based on an unmoderated array of boron-coated straws (BCS). A neutron module was configured that would be light and small enough to fit inside a regular-sized backpack. The module consisted of 36 tubes, arranged in two rows, for a total number of BCS detectors equal to 36 × 7=252. The overall dimensions of the neutron module were 3.18 cm × 26.7 cm × 38.1 cm, and its weight was 1.62 kg (3.57 lbs). The module was fitted immediately inside the back side of the backpack. The detectors are thus very close to the torso of the operator, which, together with a plastic scintillator for gamma detection, act as moderators for high-energy neutrons. In order to maintain a low weight, no other moderating material was installed inside the backpack. The weight of the pack containing both neutron and gamma detector panels, along with foam packing, electronics, and battery, was 5.36 kg (11.8 lbs). The compact dimensions of the design afforded use of a computer style backpack of minimal dimension providing significant additional operational advantages. The testing results indicate that, through use of high-density straw cluster detectors, the proposed design meets both neutron and gamma response government requirements for backpack monitors.

Improved energy resolution of highly segmented HPGe detectors by noise reduction

Built-in redundancies in highly segmented high-purity Ge detectors are exploited to increase the energy resolution of these semiconductor devices for detection of electromagnetic radiation in the X-ray and γ-ray regime. The information of the two electronically decoupled independent measurements, the cathode and the anode electrodes, provides an improved signal-to-noise ratio through a combination of the individually measured signals performed on an event-by-event basis. The average energy resolution values of the AGATA triple cluster detector for an energy deposition of 60keV was measured to be 1.1 keV (FWHM) for the 36 segments and 1.2 keV for the core. The averaged signals of the core and the segments show an improved resolution value of 0.87 keV which is close to the expected theoretical limit. At higher γ-ray energy the averaging technique allows for an enhanced energy resolution with a FWHM of 2.15keV at 1.3MeV. By means of the position sensitive operation of AGATA a new value for the Fano factor was determined and the noise contributions to the FWHM of a γ-ray peak separated.