Silicon Photomultipliers (SiPMs) have many advantages when used in radiation detectors. Low bias voltage, compactness and immunity to electromagnetic interference are among their prominent benefits. However, due to their small size, usually an array of SiPM components is required in order to cover the coupling surface area of a scintillator. Since the SiPM is a semiconductor, biased in a reversed voltage, gain variation and strong temperature dependence are introduced. As a result, SiPM-based detectors, particularly an array of SiPMs, undergo spectral signal to noise ratio reduction. This work studies the effect of the SiPM breakdown voltage variation on the obtained energy spectrum and proposes an electronic approach to overcome this technological drawback. This developed technology provides an adequate temperature-dependent, commonly distributed high bias voltage and an individual offset-voltage fine tuning that enables adjustment of all the SiPM components to their optimum operating points. Powerwise it is beneficial to operate SiPM at lower voltages, where undesirable gain variation is more dominant. The proposed solution enables working at lower bias voltages, which provides lower power consumption and better radiation hardness, while yielding an enhanced spectrum resolution. The proposed electronic approach enhances the obtained spectra, reducing the noise threshold by 16 % when working at 1 V overvoltage. Hence provides an enhanced signal to noise ratio over the traditional biasing methods.

Pulse shape discrimination is a name of a group of techniques used to detect and distinguish between different types of radiation interactions. Analog pulse shape discrimination methods can be more suitable than digital methods, for high-speed scintillators both from rate and power consumption perspectives. Common analog discrimination methods are based on pulse-height and pulse-energy discrimination techniques. Other techniques rely on the time difference in the pulse width such as the ZeroCrossing methods. Neither of the above combine both amplitude and time methods. We present a novel analog pulse shape discrimination topology that combines both height and time domain. The topology is based on discrimination according to the pulse duration in time combined with compensation function of the pulse height. Amplitude of the pulse is used as a restraining factor. Subsequently, our topology correctly identifies fast pulses that are prolonged in time due to their high amplitude. The topology yields superior discrimination capabilities, under degraded light collection conditions, with an uncertainty gap smaller than 1 ns in pulse width. The ability to control both the time and the amplitude parameters individually, provides tailored adjustment for various detectors and pulse shape discrimination applications.

This article presents a model setup of neutron sensors consisting of a Li-glass scintillator coupled with a silicon photomultiplier (SiPM) array. The newest developments based on SiPMs array enable high-gain and the low-light detection capabilities of the traditional photomultiplier tube (PMT) while offering the benefits of a solid-state sensor: low-voltage operation, insensitivity to magnetic fields, reduced dimensions, and mechanical robustness. Measurements conducted with the presented setup were complemented with the Monte Carlo N-Particle Transport Code (MCNP) numerical simulations for larger systems. The results indicate the feasibility of utilizing the presented technology for highly sensitive handheld neutron radiation detectors in compliance with the requirements of IEC 62534 standards.

A method to improve radioactive waste drum activity estimation in Segmented Gamma Scanning (SGS) systems was developed for homogenous content. We describe a method to quantify the activity of spatially distributed gamma-emitting isotopes (‘hot spots’) in homogenous content waste drums without the use of a collimator. Instead of averaging all the detector's readings we treat it as many different spatial samples as if we have multiple detectors surrounding the waste drum ("virtual detectors"). From these readings, we form a general linear model. Next, we derive the Maximum Likelihood Estimator (MLE) for the multiple sources position and activity. We solve this hyper-dimensional search problem using an Alternating Projections (AP) technique which transforms the problem into a simpler one-dimensional maximization problem. We tested this method using a mathematical simulation with a various number of sources, at random activities and positions for several energy bands. The preliminary results are consistent and show large improvement of the accuracy with comparison to industrial SGS systems and the same accuracy as new methods which exploits the spatial samples. Furthermore, since this method eliminates the need for heavy led collimator, none of the sources is blocked for the whole measurement period, which provides increased count rates and decreases the total measurement time.

In this article, a new method to quantify the activity of spatially distributed gamma-emitting isotopes (hotspots) in homogenous content waste drums without the use of a collimator is presented. The method utilizes a spatial digital filter derived using maximum likelihood (ML) to determine multiple sources’ positions and then calculate their activities. To solve the multidimensional maximization problem, we use an alternating projection (AP) technique, which transforms the problem into a considerably simpler 1-D maximization problem. A dynamic grid search was developed to further decrease the computational load. The mathematical simulations demonstrate the improved accuracy when compared to that of industrial segmented gamma scanning (SGS) systems and the same accuracy as that of newer methods. Furthermore, the new method offers the benefit of replacing the heavy mechanical collimator with a “virtual collimator” formed by digital filters and an advanced algorithm to create a “digital virtual scan” of drum volume to locate hotspots.

A new cold neutron detector has been developed at the NIST Center for Neutron Research (NCNR) for the CANDoR (Chromatic Analysis Neutron Diffractometer or Reflectometer) project. Geometric and performance constraints dictate that this detector be exceptionally thin (similar to 2 mm). For this reason, the design of the detector consists of a (LiF)-Li-6:ZnS(Ag) scintillator with embedded wavelength shifting (WLS) fibers. We used the GEANT4 package to simulate neutron capture and light transport in the detector to optimize the composition and arrangement of materials to satisfy the competing requirements of high neutron capture probability and light production and transport. In the process, we have developed a method for predicting light collection and total neutron detection efficiency for different detector configurations. The simulation was performed by adjusting crucial parameters such as the scintillator stoichiometry, light yield, component grain size, WLS fiber geometry, and reflectors at the outside edges of the scintillator volume. Three different detector configurations were fabricated and their test results were correlated with the simulations. Through this correlation we have managed to find a common photon threshold for the different detector configurations which was then used to simulate and predict the efficiencies for many other detector configurations. New detectors that have been fabricated based on simulation results yielding the desired sensitivity of 90% for 3.27 meV (5 angstrom) cold neutrons. The simulation has proven to be a useful tool by dramatically reducing the development period and the required number of detector prototypes. It can be used to test new designs with different thicknesses and different target neutron energies.

Low-level radioactive surface-contamination measurements require lightweight, large-area, and high-efficiency detectors. In the previous work, we utilized wavelength shifting (WLS) fibers, coupled to a beta-sensitive plastic scintillator (PS) layer on one side, and to an alpha-sensitive ZnS(Ag) layer on both sides, for detecting both alpha and beta particles. In this work, the main goal was to improve the light collection (maximizing the number of photons reaching the PMT) by optimizing the WLS fibers structure, for getting better signal-to-noise ratio and to minimize the low-energy threshold of the detector. In most cases, improving the light collection mostly influenced the detector resolution. In our case, improving the light collection will improve the detection efficiency by ability to detect more events at low-energy spectrum, which is limited by the noise level. Aiming to improve the scintillation light-collection efficiency, we investigated and compared four different detector configurations. Two of them described in the previous work presents utilization of WLS fibers, with different diameters ( 1 mmφ, 1.5 mmφ), coupled on the PS. Two other configurations present utilization of WLS fibers ( 1.5 mmφ) installed into a flat groove on the PS layer, while in one configuration we utilized straight WLS fibers and in the other we utilized bent WLS fibers. It was found that the utilization of WLS fibers in bent configuration gives the highest light-collection efficiency. Additionally, there is improved light collection achieved by using WLS fibers with wider diameter ( 1.5 mmφ), which maximizes the capture fraction. Additionally, since ZnS(Ag) and PS have different decay times (200 ns and 2.4 ns, respectively), we were able to separate alpha from beta events. An algorithm script was developed to calculate the full width at half maximum (FWHM) of each pulse and a histogram was generated of the FWHM values for the pulse shape discrimination (PSD). Efficient PSD was achieved for alpha energies above 100 keV with figure of merit (FOM) of 1.92. GEANT4 simulation was carried out and compared with experimental results. The results of both were matched, showed that the light-collection efficiency from the bent WLS fibers configuration was the best. The simulation results and the experiments, including full description of the detector structure, ionization stage, and the WLS light collection, are presented.

A survey of the Aerial Measuring System (AMS) of the U.S. Department of Energy (DOE), National Nuclear Security Administration (NNSA) and Israel Atomic Energy Commission (IAEC) was done. The goal of the study was to investigate the response of the aerial radiation detection system to varied radioactive surface contamination levels, isotopic composition experienced, the data processing technique and the impact of the detector size. THE IAEC AMS System AirRAM 2000, was designed by the IAEC Nuclear Research Center Negev (NRCN) and built commercially by ROTEM Industries and incorporates two 2''diameter ×2'' long NaI crystals. The AirRAM 2000 mounted on a DOE Bell-412 helicopter for a series of aerial measurements at local test ranges. THE study included carry out operational flight activities collecting radiation data from natural background, dispersed radioactivity, and point sources. All planned flight activities followed by scientific discussions on the collected data were completed.

There is a need to develop new personal radiation detector (PRD) technologies that can be mass produced. On August 2013, DARPA released a request for information (RFI) seeking innovative radiation detection technologies. In addition, on December 2013, a Broad Agency Announcement (BAA) for the SIGMA program was released. The RFI requirements focused on a sensor that should possess three main properties: low cost, high compactness and radioisotope identification capabilities. The identification performances should facilitate the detection of a hidden threat, ranging from special nuclear materials (SNM) to commonly used radiological sources. Subsequently, the BAA presented the specific requirements at an instrument level and provided a comparison between the current market status (state-of-the-art) and the SIGMA program objectives.This work presents an optional alternative for both the detection technology (sensor with communication output and without user interface) for DARPA's initial RFI and for the PRD required by the SIGMA program. A broad discussion is dedicated to the method proposed to fulfill the program objectives and to the selected alternative that is based on the PDS-GO design and technology. The PDS-GO is the first commercially available PRD that is based on a scintillation crystal optically coupled with a silicon photomultiplier (SiPM), a solid-state light sensor. This work presents the current performance of the instrument and possible future upgrades based on recent technological improvements in the SiPM design.The approach of utilizing the SiPM with a commonly available CsI(Tl) crystal is the key for achieving the program objectives. This approach provides the appropriate performance, low cost, mass production and small dimensions; however, it requires a creative approach to overcome the obstacles of the solid-state detector dark current (noise) and gain stabilization over a wide temperature range.Based on the presented results, we presume that the proposed approach of SiPM, with pixel size of 35 mu m, coupled to a scintillation material (for gamma and neutron detection) ensures the availability and low cost of the key components. Furthermore, automated manufacturing process enables mass production, thereby fulfilling the SIGMA program requirements, both as a sensor (assimilated with mobile device) and as a full detection device. (C) 2015 Elsevier B.V. All rights reserved.

Low level radioactive surface contamination measurements require lightweight, large area and high efficiency detector. In most existing scintillation detectors there is a tradeoff between effective area and scintillation light collection. By using wavelength shifting (WLS) fibers the scintillation light may be collected efficiently also in a large area detector. In this study, WLS fibers were coupled to a beta sensitive plastic scintillator layer and to a alpha sensitive silver-activated zinc sulfide ZnS(Ag) layer for detecting both alpha and beta particles. The WLS fibers collect the scintillation light from the whole detector and transfer it to a single PMT. This first prototype unique configuration enables monitoring radioactive contaminated surfaces by both sides of the detector and provides high gamma rejection.In this paper, the detector structure, as well as the detector's measured linear response, will be described. The measured detection efficiency of (PU)-P-238 alpha particles (5.5 MeV) is similar to 63%. The measured detection efficiency for beta particles is similar to 89% for Sr-90-Y-90 (average energy of 195.8 key, 934.8 key), similar to 50% for (CI)-C-36 (average energy of 251.3 key), and 35% for Cs-137 (average energy of 156.8 keV). (C) 2014 Elsevier B.V. All rights reserved.

The silicon photomultiplier (SiPM) is a novel photo-sensor technology. This paper presents the design optimization process for implementing this technology in a scintillator-based radiation detector. The device provides the advantages of low current consumption, small dimensions, and high gain. These properties make SiPM of great interest for applications involving portable instrumentation. However, a novel approach to establish a set of parameters and their limits is required to optimize the performance of this new technology in radiation detection applications. The trade-offs and the influences of factors such as the photon detection efficiency (PDE), dynamic range (DR), various scintillation crystal characteristics, and light-reflecting materials are discussed. This study investigates the incorporation of CsI(Tl) scintillation crystals with SiPMs based on measurements and results for different photo-coupling configurations, and the obtained achievements are described. A method for evaluating the photon collection efficiency of scintillator-SiPM-based detectors is proposed.

This work presents a comprehensive study of the Silicon Photomultiplier (SiPM) properties as a novel alternative for radiation detector light sensor. The SiPM low current consumption, its diminutive dimensions and the high gain make this technology of great interest for applications in portable radiation detection instrumentation based on scintillation material.The development progress in investigation of the performance of the device incorporation with CsI(Tl) scintillation crystal during the R&D timeline is presented. The research shows the improvement in two major parameters: the noise level and the resolution.The finding emphasizes that the utilization of the SiPM as the light converting device in radiation sensors is potentially applicable for radiation detection and isotope identification.

Several of the commonly used industrial isotopes that are of concern for use as a radiological dispersal device (RDD) can easily be shielded with metal. Therefore, an approach that combines the detection of radiation and shielding provides an advanced solution. This paper introduces the embedment of a radiation detection unit within a metal detector. The radiation sensor, based on the silicon photomultiplier (SiPM) coupled to a scintillation crystal, was successfully incorporated into a common metal detection unit. The advantages of the silicon photomultiplier over traditional light sensors and their results are presented. The sensitivity obtained complies with Homeland Security international standards for personal radiation detectors. Background threshold adjustment and various application notes are discussed.

In this paper a method for improving the signal to noise ratio (SNR) is described. This method is based on matched filter algorithm. The prospective application for the described method would be in Radiation Portal Monitors (RPM), where the signal is observed to have a fixed pattern. The comparison of the proposed method to the traditional integration is presented. The improvement in the SNR is shown to be a factor of 10.

A radiation detector providing enhanced identification capabilities aimed for use in the homeland security market is presented. This need arises from operational difficulties derived from the high probability for innocent alarm and masking scenarios. In order to approach these operational requirements, a new Spectroscopic Personal Radiation Detector (SPRD) was developed based on the advanced LaBr(Ce) scintillation crystal. The detector's high resolution together with an internal sophisticated algorithm enables decreasing the false alarm rate generated by innocent material as well as missed alarms caused by masking scenarios. The role of this device as part of the comprehensive methodology to combat the Homeland Security nuclear/radiological threat is discussed. The device designed constrains and configuration, as well as its functionality and performance, are presented and discussed.

Fast deployment, real time Environmental Radiation Monitoring System (ERMS), developed to meet pre and post radiological event necessities. The full system enables online environmental and radiation data transfer to multiple clients from a variety of sensor's types, e.g. radiation gamma field, wind direction and speed, assembled on a fast deployment monitoring station. The complete system enables temporal and spatial analysis for radiation safety and post event risk analysis.

This work describes the measurements and obtained results for various photo-coupling configurations of a CsI(Tl) scintillation crystal with SiPM and the impact of alternating operating conditions on the unstable features. An investigation of the dominant parameters, such as noise level, resolution, and dynamic range, is discussed and concluded.

The homeland security nuclear/radiological threat, accentuates the need for a Spectroscopy Personal Radiation Detector (SPRD). The CsI(Tl) capacity to discriminate the energy-lines of a gamma-radiation source along side with robust nature, makes these detectors suitable for isotope identification under harsh environmental conditions. However the CsI(Tl) detectors are also known for the temperature dependence of their response presenting itself in varying pulse time constant and crystal light yield. When observing a detection system as a whole this dependence appears as spectrum gain shift. For a radioisotope identification device it is paramount to correctly evaluate and compensate for any variation in spectrum parameters that may result in a faulty identification result. This work presents a theoretical analysis along side its practical application aiming at handling temperature transients. Step by step method for constructing a comprehensive scintillation detector temperature gain compensation schema will be presented and an application example will be demonstrated. Experimental lab work combined with digital signal processing techniques, including system identification and digital filtering methods are being used throughout this work and implemented for the solution of the real life problem of scintillation detector temperature gain compensation.