Study of a Compton camera based on CsI(Tl) scintillator bars for radiological environmental imaging

Compton cameras are used for radiological imaging, which can be useful in environmental applications and especially in determining the position of hidden sources. Current Compton cameras are based on pixelated detectors with complex electronic instrumentation and these devices are usually expensive. In order to overcome these issues, a Compton camera consisting of scintillator bars with two photo-sensors placed at both ends is a promising option. In addition, it is expected that these kind of detectors make the Compton camera lightweight and robust.Characterization of two identical CsI(Tl) scintillator bars with two silicon photomultipliers each was done. The basic characterization parameters of detectors, such as the attenuation coefficient, position resolution and energy resolution, were determined experimentally with a collimated Cesio-137 point source. Different light attenuation coefficients were found for identical scintillators, causing different position resolutions. This fact highlights the importance of carrying out a control analysis for each detector. In addition, the position resolution and energy resolution were found to be independent of the position of ¿-ray interactions within the crystal. Monte Carlo (MC) simulations with PENELOPE/penEasy were carried out to design a Compton camera. In order to achieve this, the MC simulations needed to be validated. This was done by comparing both simulated and experimental data obtained in two different experimental measurement campaigns. In the first campaign, two detectors were irradiated individually with a collimated point source, while the second campaign consisted of irradiating a simple Compton camera made of two CsI(Tl) scintillator bars. The geometry defined in the MC simulations and the codes used to calculate the image for a Compton camera based on CsI(Tl) scintillator bars were validated with these experimental campaigns. The response of each individual detector, the Compton camera efficiency, the angular resolution and images obtained with MC simulations and experimental measurements were compared. Results show good agreement between experimental and simulated data.Once the MC simulations were fully validated, the design of a Compton camera consisting of two layers with four CsI(Tl) scintillator bars each was done. The cross-section size of crystals and distance between layers were optimized based on Compton camera efficiency, angular resolution and image resolution. This analysis was carried out with an energy range of 360-1330 keV. The final optimized Compton camera consists of two layers separated by 10 cm. Each layer has four 2×2×10 cm3 CsI(Tl) scintillator bars. The characterization of the Compton camera was then carried out. The field of view, efficiency, angular resolution and image resolution were calculated. In addition, the ability of the Compton camera to make use of the simple back-projection method to identify radioactive material in the environment has also been evaluated by simulating several point sources. The Compton camera was able to detect several point sources simultaneously, however, as the number of sources increases, the images became blurred. The capacity of the Compton camera is promising, since it can detect several sources in the environment according to MC simulations. Therefore, the construction of a Compton camera based on eight 2×2×10 cm3 CsI(Tl) scintillator bars should prove to be useful for environmental measurements and for installation on unmanned aerial systems, commonly called “drones”.Las Cámaras Compton son utilizadas para realizar imágenes radiológicas, lo cual puede ser de utilidad en aplicaciones medioambientales y en especial en la localización de fuentes. Las cámaras Compton actuales están formadas por un conjunto de pequeños detectores por lo que necesitan de una instrumentación electrónica compleja, haciendo que estos sistemas de detección sean normalmente caros. La utilización de barras de centelleo con dos foto-sensores colocados a ambos lados es una opción prometedora para hacer una cámara Compton económica y sencilla de utilizar. Además, se espera que una cámara Compton formada por este tipo de detectores sea ligera y robusta. Las caracterizaciones de dos barras de centelleo de CsI(Tl) con dos fotomultiplicadores de silicio cada uno fueron llevadas a cabo. Los parámetros básicos de la caracterización son el coeficiente de atenuación, la resolución en posición y la resolución en energía. Estos fueron determinados experimentalmente con una fuente puntual colimada de Cesio-137. Se encontraron diferentes coeficientes de atenuación para centelladores idénticos, haciendo que los detectores presenten una distinta resolución en posición. Este hecho pone de manifiesto la importancia de llevar a cabo un análisis de cada detector. Además, se comprobó que la resolución en energía y en posición son independientes de la posición de la interacción del rayo-gamma en el cristal.Simulaciones de Monte Carlo (MC) con PENELOPE/penEasy fueron llevadas a cabo para diseñar una cámara Compton. Para llevar a cabo esta tarea, las simulaciones MC necesitan primero ser validadas. Esto se realizó comparando datos simulados y experimentales obtenidos en dos campañas de medidas. En la primera campaña, los dos detectores fueron irradiados individualmente con una fuente colimada, mientras que la segunda campaña consistió en irradiar una cámara Compton simple formada por dos barras de centelleo de CsI(Tl). La geometría definida en las simulaciones MC y los códigos utilizados para calcular las imágenes para una cámara Compton formada por barras de centelleo de CsI(Tl) fueron validados con estas medidas experimentales. La respuesta de cada detector individual, la eficiencia de la cámara Compton, la resolución angular y las imágenes obtenidas fueron comparadas. Se encontró que los resultados experimentales están de acuerdo con los resultados de las simulaciones.Una vez que las simulaciones de MC fueron completamente validadas, el diseño de la cámara Compton fue llevado a cabo. La cámara Compton está formada por dos capas de detectores con cuatro centelladores de CsI(Tl) cada una. El tamaño de la sección transversal de los cristales y la distancia entre las capas fueron optimizadas en base a la eficiencia, resolución angular y resolución en imagen. Este análisis fue llevado a cabo en un rango de energías de 360-1330 keV. La cámara Compton optimizada está formada por dos capas de detectores separada 10 cm. Cada capa tiene cuatro barras de centelleo de CsI(Tl) de tamaño 2×2×10 cm3. La caracterización de la cámara Compton fue entonces llevada a cabo. El campo de visión, eficiencia, resolución angular y resolución en imagen fueron calculados. Además, la habilidad de la cámara Compton usando el método "Simple back-projection method" para identificar material radiactivo en el medioambiente ha sido evaluado simulando varias fuentes puntuales. La cámara Compton fue capaz de detectar varias fuentes puntuales simultáneamente, sin embargo, a medida que el número de fuentes aumenta, las imágenes se hacen más ruidosas. La capacidad de la cámara Compton es prometedora, ya que puede detectar varias fuentes en el medioambiente de acuerdo con las simulaciones MC. Por tanto, la construcción de la cámara Compton formada por ocho detectores de CsI(Tl) de tamaño 2×2×10 cm3 debería resultar útil para las medidas ambientales y para la instalación en sistemas aéreosPostprint (published version

Study of a Compton camera based on CsI(Tl) scintillator bars for radiological environmental imaging

Compton cameras are used for radiological imaging, which can be useful in environmental applications and especially in determining the position of hidden sources. Current Compton cameras are based on pixelated detectors with complex electronic instrumentation and these devices are usually expensive. In order to overcome these issues, a Compton camera consisting of scintillator bars with two photo-sensors placed at both ends is a promising option. In addition, it is expected that these kind of detectors make the Compton camera lightweight and robust.Characterization of two identical CsI(Tl) scintillator bars with two silicon photomultipliers each was done. The basic characterization parameters of detectors, such as the attenuation coefficient, position resolution and energy resolution, were determined experimentally with a collimated Cesio-137 point source. Different light attenuation coefficients were found for identical scintillators, causing different position resolutions. This fact highlights the importance of carrying out a control analysis for each detector. In addition, the position resolution and energy resolution were found to be independent of the position of ¿-ray interactions within the crystal. Monte Carlo (MC) simulations with PENELOPE/penEasy were carried out to design a Compton camera. In order to achieve this, the MC simulations needed to be validated. This was done by comparing both simulated and experimental data obtained in two different experimental measurement campaigns. In the first campaign, two detectors were irradiated individually with a collimated point source, while the second campaign consisted of irradiating a simple Compton camera made of two CsI(Tl) scintillator bars. The geometry defined in the MC simulations and the codes used to calculate the image for a Compton camera based on CsI(Tl) scintillator bars were validated with these experimental campaigns. The response of each individual detector, the Compton camera efficiency, the angular resolution and images obtained with MC simulations and experimental measurements were compared. Results show good agreement between experimental and simulated data.Once the MC simulations were fully validated, the design of a Compton camera consisting of two layers with four CsI(Tl) scintillator bars each was done. The cross-section size of crystals and distance between layers were optimized based on Compton camera efficiency, angular resolution and image resolution. This analysis was carried out with an energy range of 360-1330 keV. The final optimized Compton camera consists of two layers separated by 10 cm. Each layer has four 2×2×10 cm3 CsI(Tl) scintillator bars. The characterization of the Compton camera was then carried out. The field of view, efficiency, angular resolution and image resolution were calculated. In addition, the ability of the Compton camera to make use of the simple back-projection method to identify radioactive material in the environment has also been evaluated by simulating several point sources. The Compton camera was able to detect several point sources simultaneously, however, as the number of sources increases, the images became blurred. The capacity of the Compton camera is promising, since it can detect several sources in the environment according to MC simulations. Therefore, the construction of a Compton camera based on eight 2×2×10 cm3 CsI(Tl) scintillator bars should prove to be useful for environmental measurements and for installation on unmanned aerial systems, commonly called “drones”.Las Cámaras Compton son utilizadas para realizar imágenes radiológicas, lo cual puede ser de utilidad en aplicaciones medioambientales y en especial en la localización de fuentes. Las cámaras Compton actuales están formadas por un conjunto de pequeños detectores por lo que necesitan de una instrumentación electrónica compleja, haciendo que estos sistemas de detección sean normalmente caros. La utilización de barras de centelleo con dos foto-sensores colocados a ambos lados es una opción prometedora para hacer una cámara Compton económica y sencilla de utilizar. Además, se espera que una cámara Compton formada por este tipo de detectores sea ligera y robusta. Las caracterizaciones de dos barras de centelleo de CsI(Tl) con dos fotomultiplicadores de silicio cada uno fueron llevadas a cabo. Los parámetros básicos de la caracterización son el coeficiente de atenuación, la resolución en posición y la resolución en energía. Estos fueron determinados experimentalmente con una fuente puntual colimada de Cesio-137. Se encontraron diferentes coeficientes de atenuación para centelladores idénticos, haciendo que los detectores presenten una distinta resolución en posición. Este hecho pone de manifiesto la importancia de llevar a cabo un análisis de cada detector. Además, se comprobó que la resolución en energía y en posición son independientes de la posición de la interacción del rayo-gamma en el cristal.Simulaciones de Monte Carlo (MC) con PENELOPE/penEasy fueron llevadas a cabo para diseñar una cámara Compton. Para llevar a cabo esta tarea, las simulaciones MC necesitan primero ser validadas. Esto se realizó comparando datos simulados y experimentales obtenidos en dos campañas de medidas. En la primera campaña, los dos detectores fueron irradiados individualmente con una fuente colimada, mientras que la segunda campaña consistió en irradiar una cámara Compton simple formada por dos barras de centelleo de CsI(Tl). La geometría definida en las simulaciones MC y los códigos utilizados para calcular las imágenes para una cámara Compton formada por barras de centelleo de CsI(Tl) fueron validados con estas medidas experimentales. La respuesta de cada detector individual, la eficiencia de la cámara Compton, la resolución angular y las imágenes obtenidas fueron comparadas. Se encontró que los resultados experimentales están de acuerdo con los resultados de las simulaciones.Una vez que las simulaciones de MC fueron completamente validadas, el diseño de la cámara Compton fue llevado a cabo. La cámara Compton está formada por dos capas de detectores con cuatro centelladores de CsI(Tl) cada una. El tamaño de la sección transversal de los cristales y la distancia entre las capas fueron optimizadas en base a la eficiencia, resolución angular y resolución en imagen. Este análisis fue llevado a cabo en un rango de energías de 360-1330 keV. La cámara Compton optimizada está formada por dos capas de detectores separada 10 cm. Cada capa tiene cuatro barras de centelleo de CsI(Tl) de tamaño 2×2×10 cm3. La caracterización de la cámara Compton fue entonces llevada a cabo. El campo de visión, eficiencia, resolución angular y resolución en imagen fueron calculados. Además, la habilidad de la cámara Compton usando el método "Simple back-projection method" para identificar material radiactivo en el medioambiente ha sido evaluado simulando varias fuentes puntuales. La cámara Compton fue capaz de detectar varias fuentes puntuales simultáneamente, sin embargo, a medida que el número de fuentes aumenta, las imágenes se hacen más ruidosas. La capacidad de la cámara Compton es prometedora, ya que puede detectar varias fuentes en el medioambiente de acuerdo con las simulaciones MC. Por tanto, la construcción de la cámara Compton formada por ocho detectores de CsI(Tl) de tamaño 2×2×10 cm3 debería resultar útil para las medidas ambientales y para la instalación en sistemas aéreo

The design and testing of a novel compact real-time hybrid Compton and neutron scattering instrument.

The requirement for multiple-purpose imaging system occurs regularly within the field of radioactive materials safeguard and security applications. Current instrumentation utilised within the field of dual gamma-ray and neutron imaging systems suffer with limited portability, long scan times, and cover limited energy ranges. Conversely, the imaging system designed, built and tested in this work is not only capable of locating both gamma rays and neutrons, but is also capable of operating in near real time, covers a large energy range and is portable to a desktop degree. The imaging concept applied simultaneously combines Compton and neutron scattering techniques within a threelayer design comprising of a unique combination of scintillators backed with pixelated arrays of photodetectors in the form of 8 x 8 Silicon Photomultipliers (SiPMs). The system features the organic scintillator EJ-204, neutron sensitive lithium glass and thallium doped caesium iodide utilised along with associated SiPMs and front-end electronics, all enclosed within a volume of 120 mm x 120 mm x 200 mm. Further backend electronics is situated within a separate unit where each of the data channels are simultaneously interrogated in order to determine the location of the incident gamma rays and neutrons. The validity of the instrument has been computationally verified using MCNP6 and Geant4 Monte Carlo simulation codes and experimentally tested using Cs-137 gamma sources of ~300 kBq and a Cf-252 neutron source featuring an emission rate of 106 neutrons per second. The developed instrument offers a real-time response with a scan time of 60 seconds and a further data analysis time of 60 seconds. The intrinsic efficiency of the instrument has been experimentally measured to be in the order of 10-4 for both gamma rays at 0.667 MeV and fast neutrons at average energy of 2.1 MeV, and 0.78 for thermal neutron

Design and Optimisation of a Three Layers Thermal Neutron, Fast Neutron and Gamma-Ray Imaging System

The design and configuration of a multi-layered imaging system with the ability to detect thermal neutrons, fast neutrons and gamma rays has been developed and its efficacy demonstrated. The work presented here numerically determines the systems efficiency and spatial resolution, using 252Cf and 137Cs as a case study. The novelty of this detection system lies in the use of small form factor detectors in a three-layer design, which utilises neutron elastic scattering and Compton scattering simultaneously. The current configuration consists of 10 mm thick natural lithium glass (GS10) scintillator integrated with a 20 mm thick plastic scintillator (EJ-204) in the first layer, a 15 mm thick lithium glass (GS10) scintillator in the second and a 30 mm thick CsI(Tl) scintillator forming the final layer. Each of these layers is backed with an 8 x 8 silicon photomultiplier diode (SiPM) array. The overall size of the imaging system is 27 mm x 27 mm x 135 mm. MCNPv6.1 and Geant4-10.04 were alternatively used to optimise the overall configuration and to investigate detection modalities. Results show promising performance with high precision source localisation and characterization abilities. Measurements were virtually obtained of two gamma-ray sources within steel enclosures at angles of 15o, 30o and 50o separation in order to test spatial resolution ability of the system. With the current active size of the system and the 8x8 SiPM configuration, the results estimate the spatial resolution to be close to 30o. The ability of the system to characterise and identify sources based on the type and energy of the radiation emitted, has been investigated and results show that for all radiation types the system can identify the source energy within the energy range of typical reported sources in literature

First demonstration of a Compton gamma imager based on silicon photomultipliers

We are developing a rugged and person-transportable Compton gamma imager for use in security investigations of radioactive materials, and for radiological incident remediation. The imager is composed of layers of scintillator with light collection for the forward layers provided by silicon photomultipliers and for the rear layer by photomultiplier tubes. As a first step, we have developed a 1/5th-scale demonstration unit of the final imager. We present the imaging performance of this demonstration unit for Cs-137 at angles of up to 30 degrees off-axis. Results are also presented for Sn-113 and Na-22. This represents the first demonstration of the use of silicon photomultipliers as an embedded component for light collection in a Compton gamma imager.Comment: 19 pages, 6 figure

Monte Carlo investigations of megavoltage coneâ beam CT using thick, segmented scintillating detectors for soft tissue visualization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134940/1/mp8957.pd

Observation of Coherent Elastic Neutrino-Nucleus Scattering

The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross-section is the largest by far of all low-energy neutrino couplings. This mode of interaction provides new opportunities to study neutrino properties, and leads to a miniaturization of detector size, with potential technological applications. We observe this process at a 6.7-sigma confidence level, using a low-background, 14.6-kg CsI[Na] scintillator exposed to the neutrino emissions from the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. Characteristic signatures in energy and time, predicted by the Standard Model for this process, are observed in high signal-to-background conditions. Improved constraints on non-standard neutrino interactions with quarks are derived from this initial dataset

A fast and portable imager for neutron and gamma emitting radionuclides

Here a novel, real-time, highly-compact imaging system capable of detecting and localising gamma rays, thermal and fast neutrons is reported. The imaging system presented in this research comprises of a front-end containing three detection layers with a unique combination of scintillators optimised for multi-particle detection, and backed with silicon photomultiplier diode arrays to enable source localisation and to maximise efficiency. The system exploits Compton and neutron scattering techniques simultaneously to constitute a dual-mode radiation camera. Application-specific software algorithms are implemented here to process the numerous signals from the system and to reconstruct the location of radioactive sources using a back-projection technique. The three front-end detection layers fit within a volume of 120 mm 120 mm 200 mm, offering a uniquely compact imaging solution. A prototype of the instrument and the associated electronics have been designed using Monte Carlo simulations, and tested with Cs-137 (given its singular gamma-ray component) and Cf-252 (for its mixed neutron and gamma-ray emission). Experimental results indicate that the system can detect and localise both gamma-ray and neutron sources successfully, with intrinsic efficiencies in the order of 10−4. All results have been achieved within a scan time of 60 s and with a further data processing time of less than 60 s, for gamma sources of 300 kBq and neutron sources of 10neutrons per second (total) in close proximity (< 300 mm). Whilst high-speed, mixed-field, particle-imaging systems have numerous applications within both nuclear and non-nuclear fields; this particular system has been optimised for use within the areas of nuclear materials assay and proliferation prevention