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A 6LiF:ZnS(Ag)-based cold neutron detector with wavelength shifting (WLS) fibers and Silicon photomultiplier (SiPM) photodetector was developed at the NIST Center for Neutron Research. For neutron scattering applications at the NCNR, detector false positives severely diminish the quality of very faint neutron scatter patterns. Thermal noise generated by the SiPM significantly increases the likelihood of false positives by the detector/discriminator. This article describes and evaluates a digital real-time algorithm implemented on a field programmable gate array (FPGA) which quickly differentiates SiPM thermal noise and noise pulse pile-up from neutron signals. The algorithm reduces deadtime spent on examining noise pulses as well as reduces the number of false positives.

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.

We used Gaussian separation and receiver operating characteristic (ROC) curves to optimize the neutron sensitivity and gamma rejection of an ultra-thin (6)LiF:ZnS(Ag)-scintillator-based neutron detector paired with a silicon photomultiplier (SiPM). We recorded the waveforms while operating the detector in a monochromatic cold neutron beam and in the presence of isotopic (137)Cs and (60)Co gamma sources. We used a two-window charge comparison (CC) pulse-shape discrimination (PSD) technique to distinguish the neutron capture events from other types of signals. By feeding the recorded waveforms through variants of this algorithm, it was possible to optimize the duration of the integration windows [(0–100 ns) for the prompt window and (100–2300 ns)] for the delayed window. We then computed the detector’s ROC curve from waveform recordings and compared that with the experimental performance. We also used this procedure to compare a series of detector configurations to select the optimal bias voltage for the SiPM photosensor.

Obtaining directional information is required in many applications such as nuclear homeland security, contamination mapping after a nuclear incident and radiological events, or during the decontamination work. However, many directional radiation detectors are based on directional shielding, made of lead or tungsten collimators, introducing two main drawbacks. The first is the size and weight, making those detectors too heavy and irrelevant for utilization in handheld devices, drone mapping, or space applications. The second drawback is the limited field of view, which requires multiple detectors to cover the whole required field of view or machinery to rotate the narrow field of view detector. We propose a novel 4π directional detector based on a segmented hollow cubic detector, which uses the Compton effect interactions with no heavy collimators. The symmetrical cubical design provides both higher efficiency and 4π detection ability. Instead of traditional two types of detectors (scatterer and absorber) structure, we use the same type of detector, based on GAGG(Ce) scintillator coupled to silicon photomultiplier. Additional advantage of the proposed detector obtained by locating the photon sensors inside the detector, behind the scintillators, which improves the radiation hardness required for space applications. Furthermore, such arrangement flattens the temperature variation across the detector, providing better gain stability. The main advantage of the proposed detector is the ability of 4pi radiation detection for high energy gamma-rays without the use of heavy collimators.

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.

We describe the design, fabrication, and performance of an energy analyzing detector package for cold neutron spectrometers at the NIST Center for Neutron Research (NCNR). The detector package consists of arrays of highly oriented pyrolytic graphite crystals set at takeoff angles corresponding to different neutron energies. Neutrons incident down the array will be selected out by the appropriate crystal and directed onto an associated neutron detector. The arrays are capable of binning neutrons into one of 54 bins over an energy range of 2.29 meV to 5.11 meV. We describe theory of operation, the development of a highly efficient ultrathin neutron sensor, and the development of the arrays themselves. We present preliminary results for this detector array along with a mature design of the scintillator neutron detector. We also present enhancements we are pursuing prior to deployment of this technology.

We describe the design and performance of an ultrathin ( × 30 mm high × 1.4 mm deep. Twenty-four 0.5 mm diameter wavelength shifting fibers conduct the scintillation light out of the plane of the detector and are concentrated onto a 3 mm × 3 mm silicon photomultiplier. The detector is demonstrated to possess a neutron detection efficiency of 93% for 3.27 meV neutrons with a gamma ray rejection ratio on the order of 10−7.

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 ( ∼ 2 mm). For this reason, the design of the detector consists of a 6 LiF: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 A) 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.

We report the optimization of 6LiF:ZnS(Ag) scintillator mixtures for an ultrathin ( $\approx 30$ %). Our optimization took the form of exploring the weight ratios of neutron converter, phosphor, and binder to promote high neutron capture probability and light transport within the medium. We characterized a series of 6LiF:ZnS(Ag):binder mixtures for neutron absorption, light yield, and light transmission properties. In the process, we determined the optimal configuration for our requirements of millimeter thickness and cold neutron energy. Optimized prototypes exhibit excellent absorption and demonstrate neutron sensitivities of above 85% for 3.27-meV neutrons and gamma ray rejection ratios approaching 10−7.

A 6 LiF:ZnS(Ag) based cold neutron detector with wavelength shifting (WLS) fibers and SiPM photodetector was developed at the NIST Center for Neutron Research for the CANDoR instrument (Chromatic Analysis Neutron Diffractometer or Reflectometer). The scintillation response of ZnS(Ag) to 6Li fission products is a long and irregular delayed fluorescence lasting more than 50 μ s. To wait as long as 60 μ s for complete fluorescence decay would impose an unreasonably long deadtime to the system and would severely limit the count rate of this detector. A real-time algorithm was implemented to compensate for the long fluorescence decay, reducing but not eliminating sensitivity for a 60 μ s period. This greatly reduces the deadtime to approximately 3 μ s compared to imposing a 60 μ s hold-off time, while also achieving a double-count fraction (counting the same event multiple times) below 1E−4. Timestamping capabilities of the detector system were used to compile arrival time statistics. Comparisons of the measured arrival time statistics with Poisson arrival statistics illustrates features in the fluorescence compensation algorithm and enables the calculation of deadtime and double-count fraction.

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~\hbox{mm}\phi $ , $1.5~\hbox{mm}\phi $ ), coupled on the PS. Two other configurations present utilization of WLS fibers ( $1.5~\hbox{mm}\phi $ ) 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~\hbox{mm}\phi $ ), 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 6LiF:ZnS(Ag) based cold neutron detector with wavelength shifting (WLS) fibers and SiPM photodetector was developed at the NIST Center for Neutron Research for the CANDoR instrument (Chromatic Analysis Neutron Diffractometer or Reflectometer). A series of detectors were irradiated with neutron doses ranging between 1E+11 n/cm2 to 6E+12 n/cm2. It was found that the neutron absorbing 6Li isotope was not measurably depleted, but the photonic yield of the detector deteriorated with increasing neutron dose. Photonic yields were compared before and after neutron exposure by comparing pulse energy spectrum photopeaks before and after exposure. A typical detector used in the CANDoR instrument is expected to withstand a cumulative cold neutron dose of at least 1E+12 n/cm2 before degrading to an unfit state. The component parts of the detector could not be separated, so the degradation of the bulk scintillator and WLS fibers could not be gauged separately.

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.

A new radio-HPLC detection system for measuring radioactivity in plasma samples during Positron Emission Tomography [PET] studies was developed. It is based on detecting both the positron and one of the annihilation photons. The system focused on improving the measurement of radioactivity concentrations on an unmetabolized positron emitting a radiopharmaceutical [PER] in the presence of its radioactive metabolites, all containing the same positron emitter. This paper presents a new detection configuration that improves the minimal detectible activity (MDA), simplify the measuring systems and reduces the error caused by the metabolites. The detector is based on a plastic scintillator and a BGO scintillation crystal, that produces different light output spectra for signal and noise events. By summing the positron and the annihilated photon light outputs, different spectra are obtained for the metabolite and for the parent compound tracer and for tracer marked by different positron emitting isotopes. This new detection system can improve quantitative analysis of plasma samples. The spectrum change provides up to a three-fold improvement in sensitivity compared to the currently used detection systems that measure only the annihilation coincidence events. Results showed that for 11C the MDA was improved by approximately 520%. Furthermore, it provides the additional advantage of reliability by providing a method for separating the signal and noise readings from the gross detector readout. Accurate reconstruction algorithm of the signal was achieved over a wide measuring range even when the signal was only 5% of the gross measurement.

ISS-TAO is a mission selected for a concept study by NASA, and proposed by GSFC for launch to the International Space Station (ISS) in order to observe transient high-energy astrophysical sources. It is composed of an X-ray Wide-Field Imager (WFI), and a multi-directional Gamma-ray Transient Monitor (GTM). WFI will be built by NASA/GSFC while the secondary GTM, described in this article is contributed by the Israel Space Agency (ISA) and developed at the Technion, Israel Institute of Technology, in collaboration with Israel space industries. ISS-TAO's main science goal is to detect electromagnetic (EM) counterparts to gravitational waves (GW) detected by GW observatories, such as the Laser Interferometer GW Observatory (LIGO). Observations of simultaneous GW and EM counterparts will address fundamental questions on the nature of coalescing neutron stars and black holes as astrophysical GW sources. An EM detection will also increase LIGO’s sensitivity to detecting these events above the GW background. Promising candidates for LIGO GW sources and EM counterparts are coalescing neutron star binaries, which are now known to also emit a short Gamma-Ray Burst (sGRB). The GTM will measure these GRBs and other transient gamma-ray events, and will trigger the WFI, with or without a GW trigger. The concept of the GTM detector consists of a compact configuration of 4 segments, which will allow a fair angular resolution of a few hundred square degrees, which will facilitate a prompt follow up. Each of the GTM segments consists of a crystal scintillator, a photo-multiplier tube (PMT), followed by analog and digital electronics designed to reconstruct the energy of each incoming photon, and to yield the light-curve and spectrum of any gamma-ray transient. A central CPU then calculates the ratio of the signal of each one of the segments, and deduced the transient position relative to the GTM.

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 238 Pu alpha particles (5.5 MeV) is ~63%. The measured detection efficiency for beta particles is ~89% for 90 Sr– 90 Y (average energy of 195.8 keV, 934.8 keV), ~50% for 36 Cl (average energy of 251.3 keV), and 35% for 137 Cs (average energy of 156.8 keV).

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 μm, 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.

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.

The alarming personal radiation detector (PRD) is a device intended for Homeland Security (HLS) applications. This portable device is designed to be worn or carried by security personnel to detect photon-emitting radioactive materials for the purpose of crime prevention. PRD is required to meet the scope of specifications defined by various HLS standards for radiation detection. It is mandatory that the device be sensitive and simultaneously small, pocket-sized, of robust mechanical design and carriable on the user's body. To serve these specialized purposes and requirements, we developed the SENTIRAD, a new radiation detector designed to meet the performance criteria established for counterterrorist applications. SENTIRAD is the first commercially available PRD based on a CsI(Tl) scintillation crystal that is optically coupled with a silicon photomultiplier (SiPM) serving as a light sensor. The rapidly developing technology of SiPM, a multipixel semiconductor photodiode that operates in Geiger mode, has been thoroughly investigated in previous studies. This paper presents the design considerations, constraints and radiological performance relating to the SENTIRAD radiation sensor.

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.

A novel spectroscopic personal radiation device (SPRD) with sub-milliwatt power consumption is proposed. The SPRD is based on a compact, low-power, high-gain silicon photomultiplier (SiPM) coupled to a high-light-yield CsI(Tl) scintillator. The SiPM is operated in a special mode, in which its output is voltage rather than charge. In this mode, the SiPM output becomes higher and rises more slowly than in the charge amplification mode. Such a mode allows us to use a lower-frequency frontend amplifier with a lower gain and lower power consumption. Moreover, the very beginning of the slower, large-amplitude pulses is easier to detect with a comparator. At each detection event, the rest of the SPRD circuitry is activated only for the time needed for the pulse-processing. Because at background the radiation count rate is very low, some tens per second, and the duration of the signal-processing is very short, about 10 ms, the power-demanding SPRD circuitry is not activated most of the time, and its average power consumption is very low. Proper matching of the scintillator and the SiPM helps us to achieve the required gain from the radiation sensor with a relatively low-power, low-gain front-end amplifier. Optimizing the input impedance of the front-end amplifier helps us to obtain the required SiPM output amplitude and shape. Because it takes some time for the signal processing circuit to be activated, an additional passive delay and shaping circuit is used. An experimental model of this device is built, and tested. It is superior to other devices due to its very low power consumption, its portability, and its non-sensitivity to microphonics. The power consumption of the SPRD is about 0.3 mW by the radiation sensor and about 0.3 mW by the electronics (for a total of 0.6 mW as compared to above 20 mW consumed by conventional spectroscopic radiation devices). The power consumption has been measured at count rates up to a few hundreds per second, which are much higher than expected in practice.

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.

Radiation Portal Monitors (RPMs) are radiation detection devices which provide passive, non-intrusive means for fast screening of transportation of vehicles, baggage and passengers for the presence of nuclear and radiological materials.

The hydriding kinetics of parallelepiped, 50–200 mg LaNi 4 samples were investigated as a function of temperature and pressure in the ranges 245–293 K and 5–70 atm H 2 respectively. Mathematical analyses of the time-dependent agreement with both shrinking core and low-dimensional nucleation and growth-type models. Visual and metallographic examinations of partially hybrided samples do not provide any additional evidence in support of either of the two hybriding models. The temperature dependence of the hydrogenation rate constants follows an Arrhenius-type behavior for a given driving force, determined by a constant ratio between the applied and equilibrium plateau hydrogen pressures. The pressure dependence of the rate constants indicates an interface-controlled phase transition as the rate-determining step of hybride formation. The activation energy for the hydriding process is estimated as 0.37 eV/H atom. This value is independent of the applied model.

Gamma spectrum analysis tool providing enhanced identification capabilities aimed for the use in homeland security applications is presented. The diversities of the radiation sensors in use and of the measurement terms require constant effort and generic approach in adaptation of the existing spectrum analyzing solutions. In order to approach these operational requirements, the SpecIdentifier - new software application - was developed. SpecIdentifier's main program is divided into two main parts: a generic database and a spectrum processing module. In this novel development several peak search and spectrum processing algorithms are implemented in the processing module. Preliminary tests of isotope identification performance according to the standards for Homeland Security (HLS) applications were performed and are presented in this work. The main software blocks, algorithm modules and functionalities are described and their essentiality is discussed.

This work presents specially designed radiation monitoring system for baggage screening at airports and border crossing points for the presence of radioactive and Special Nuclear Materials (SNM). Border monitoring equipment plays a key role in combating illicit trafficking. The conveyor monitor is designed to meet the detection level determined by the standard for Radiation Portal Monitors (RPM). The obtained sensitivity results of the system and an analytical analysis of the implemented algorithms contributing to the detection performances are presented. The system consists of highly sensitive gamma and neutron detectors, electronic data-processing unit, computer interface and unique algorithms. The system's electronic unit interfaces with the conveyor control system using two signals, an input signal for the conveyor operation status and an output signal for stopping the conveyor in case of alarm. This interface and the implemented algorithm reduce the number of false alarms and improve the detection level by considering the background variation. Further significant improvement in the detection level is achieved by implementing an advanced algorithm based on the detector reading profile versus time. The online computer software provides the user with friendly interface for retrieving the archived data and analyzing the history of alarms.

Spectrometers must have the ability to identify Special Nuclear Materials (SNM) that may be present, even if hidden and masked by naturally occurring radioactive materials) NORM). Prediction of the g spectrum is vital to recognize the different combinations, as the shape is determined by absorption and geometrical factors . A program was developed, which utilizes geometric equations and detector characteristics data to produce the synthetic gamma-ray spectra. The program is a convenient tool to check the compliance of the spectrometers to the requirements concerning the identification of different isotopes combinations.

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.

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.

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.

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.

Homeland Security applications use radiation detectors to identify radionuclides by gamma spectroscopy techniques. In order to check compliance of such systems to performance requirements, a computer code which predicts the gamma-ray spectra for various radiation detectors, as NaI(Tl) and Ge was employed. The spectrum of a chosen radio-nuclide is generated according to its activity, its photo peak energy and yield (taken from data libraries). The detector efficiency, resolution and peak to Compton dependence are used to generate a pulse height spectrum for a specific detector. The developed program works with two main libraries of radioisotopes. One is a general library containing all practically encountered radioisotopes, and second library contains the fission products radioisotopes with half life higher than 1 min. The synthetic pulse height spectra can be used as input to evaluate the analysis ability of different systems and to investigate the efficiency of different shielding configurations.

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 summarizes a continuous study of the Silicon Photomultiplier (SiPM) device photo-coupled to various scintillation crystals for profound investigation in the radiation detection and isotope identification research field. Radiological and electrical measurements which have been carried out led to an obvious illation regarding the optimal scintillation crystal to use with SiPM. CsI(Tl) was selected as the most appropriate and further, more intense, tests were performed, among them temperature stability and the obtained energy resolution.

This work introduces a new approach for designing an Advanced Spectroscopic Portal (ASP). The new design is based on multiple, small (7.62 cm x 7.62 cm) and commercially available NaI(Tl) scintillation detectors. A comparison to another approach, which employs very large detectors, is presented in the aspects of source localization, signal to noise ratio (SNR), and identification and detection performances. The advantages of the introduced approach are discussed. In addition, a mathematical model applied within Rotem’s ASP, Radiation Material Detection System (RMDS), for improving the Minimum Detectable Level (MDL) is described. This algorithm shows explicitly the advantage in usage of multiple detector modules over few larger having the same scintillator type and volume.