Search

Lu2(1–x)Y2xSiO5 (LYSO) crystals readout by a silicon photomultiplier (SiPM) will be used in the barrel timing layer of a precision timing detector for the Compact Muon Solenoid (CMS) experiment at the High-Luminosity Large Hadron Collider (HL-LHC). This detector is expected to be exposed up to 5-Mrad γ-ray dose, 2.5 × 1013 charged hadrons/cm2, and 3 × 1014 neq/cm2 at the HL-LHC for 10 years of operation. We present results of the photocurrent in LYSO+SiPM packages induced by Co-60 γ-rays and Cf-252 neutrons of the expected dose rate and neutron flux, respectively. The γ-ray-induced readout noise is about 30 keV, which is negligible when compared to the 4.2-MeV signal from the minimum ionization particle signals. The neutron-induced readout noise is about 7 keV, which is more than a factor of 4 smaller than that from the γ-rays. [ABSTRACT FROM AUTHOR]

Many radionuclide identification algorithms use statistical inference to collect a variety of features from gamma-ray spectra to deduce the presence of particular radionuclides. More modern algorithms require large amounts of data to learn and use latent features from spectra for classification. Both approaches are computationally expensive, which is reflected in their power consumption, and require large amounts of user intervention to prepare. In this article, we introduce a low-power, neuromorphic algorithm for the real-time identification of radionuclides which simultaneously considers the entire shape of a gamma-ray spectrum. Utilizing the output of a traditional gamma-ray detector, our spiking, locally competitive algorithm uses sparse coding optimization to compare global patterns in a gamma-ray spectrum with a dictionary of radionuclide templates. This approach allows us to model informative global features resulting from both photoelectric absorption and Compton scattering. For the purpose of radiation threat reduction, the dictionary consists of data from the Nuclear Wallet Cards, a list of radionuclides and their properties compiled by the National Nuclear Data Center. To test our algorithm, we use a variety of gamma-ray spectra created using radionuclides measured under laboratory conditions with varying durations, distances, activity levels, and backgrounds, resulting in a wide range of signal-to-noise ratios. We have created test sets for three different gamma-ray detector types, with 57Co, 137Cs, 152Eu, 60Co, 239Pu, and 235U sources, to quantify the effect of resolution, efficiency, and background on the accuracy of the algorithm. We demonstrate a true positive accuracy of 91% with a high-resolution detector and 89% with a low-resolution detector on the corresponding test sets. Experimenting with the same radionuclides included in the test sets in a variety of special nuclear material (SNM) masking configurations, we show that our algorithm is capable of correctly identifying both SNM and mask even when the activity level of the mask is several times higher than that of the SNM. We also determine that our algorithm achieves over a 99% reduction in power consumption over other radionuclide identification software applications, which is critical for long-term, independent monitoring and is the goal of this research. [ABSTRACT FROM AUTHOR]

ALTAIR is an application-specific integrated circuit (ASIC) developed for the readout of CdTe/CdZnTe detectors for X-γ-ray spectroscopic imaging. ALTAIR is composed of 16 channels with analog and mixed-signal sections specifically designed for high energy resolution and high-rate applications with the constraints of a low power consumption and operation at room temperature. The ASIC has three selectable ranges for input charge signals covering photon energies up to 90, 160, or 300 keV, which allow to optimize the signal-to-noise ratio under different experimental conditions. Eight peaking times of the pulse shaper are selectable from 200 up to 2.3 μs. ALTAIR includes a 180 bits register and an integrated serial peripheral interface (SPI) interface to configure the signal-processing parameters globally or independently for each channel. The power consumption is 950 μW/channel or 1.35 mW/channel for single-ended or differential output versions, respectively. A minimum equivalent noise charge (ENC) of 37 electrons rms [386 eV full-width at half-maximum (FWHM) in CdTe] has been measured at 500 ns peaking time and 90-keV energy range. With a CdTe pixel detector connected to ALTAIR and operated at +24 °C, a pulser FWHM of 1.7 keV (160 el. rms) and 1.9-keV FWHM on 59.54 keV line of 241 Am have been achieved at a peaking time of 500 ns. [ABSTRACT FROM AUTHOR]

The effect of gamma-ray and neutron radiations on the variable retention time (VRT) phenomenon occurring in dynamic random access memory (DRAM) is studied. It is shown that both ionizing radiation and nonionizing radiation induce VRT behaviors in DRAM cells. It demonstrates that both Si/SiO2 interface states and silicon bulk defects can be a source of VRT. It is also highlighted that radiation-induced VRT in DRAMs is very similar to the radiation-induced dark current random telegraph signal in image sensors. Both phenomena probably share the same origin, but high-magnitude electric fields seem to play an important role in VRT only. Defect structural fluctuations (without change of charge state) seem to be the root cause of the observed VRT whereas processes involving trapping and emission of charge carriers are unlikely to be a source of VRT. VRT also appears to be the most probable cause of intermittent stuck bits in irradiated DRAMs. [ABSTRACT FROM AUTHOR]

In this paper, the design of a low-power low-noise readout circuit for cadmium zinc telluride (CdZnTe or CZT) detectors is presented. Such sensors are used in a variety of applications, including medical imaging, security, and astrophysics. The readout circuit includes a charge-sensitive amplifier (CSA), a reset network to accommodate the leakage current of the detector, and a first-order pulse shaper with a pole-zero cancellation circuit. The CSA has two gain settings for 0–5- and 5–45-fC injected charge, and the pulse shaper is designed to provide four different shaping times. The discharge time constant of the CSA can also be adjusted to accommodate various event rates. Furthermore, a comprehensive noise analysis of the readout system is presented. To facilitate the noise analysis, the equivalent noise charge (ENC) equations are derived analytically. The optimization of the noise performance of the front-end circuit is also discussed. The application-specific integrated circuit is fabricated in a 0.13- \mu \textm CMOS process. For a detector capacitance of 250 fF, the measured ENC varies from 66 to 101 \bar e -rms depending on the peaking time. The measured power consumption of the readout circuit is just under 1 mW from a 1.2 V supply. [ABSTRACT FROM PUBLISHER]

Gamma-ray radiation effect on the non-resonant third-order optical nonlinearity of the germano-silicate optical fiber has been investigated by the continuous-wave self-phase modulation method. The nonlinear refractive index, n_2, of the gamma-ray irradiated optical fiber was found to increase linearly with the increase of the gamma-ray induced absorption. The increased n_2 has been mainly ascribed to the NBOs and Ge-realted radiation-induced defects having hyperpolarizabilities. [ABSTRACT FROM PUBLISHER]

The effects of Cobalt 60 gamma-ray irradiation on pinned photodiode (PPD) CMOS image sensors (CIS) are investigated by comparing the total ionizing dose (TID) response of several transfer gate (TG) and PPD designs manufactured using a 180 nm CIS process. The TID induced variations of charge transfer efficiency (CTE), pinning voltage, equilibrium full well capacity (EFWC), full well capacity (FWC) and dark current measured on the different pixel designs lead to the conclusion that only three degradation sources are responsible for all the observed radiation effects: the pre-metal dielectric (PMD) positive trapped charge, the TG sidewall spacer positive trapped charge and, with less influence, the TG channel shallow trench isolation (STI) trapped charge. The different FWC evolutions with TID presented here are in very good agreement with a recently proposed analytical model. This work also demonstrates that the peripheral STI is not responsible for the observed degradations and thus that the enclosed layout TG design does not improve the radiation hardness of PPD CIS. The results of this study also lead to the conclusion that the TG OFF voltage bias during irradiation has no influence on the radiation effects. Alternative design and process solutions to improve the radiation hardness of PPD CIS are discussed. [ABSTRACT FROM PUBLISHER]

Dose dependence of radiation-induced optical attenuation (RIA) at 1310 nm of the Co/Fe co-doped alumino-silicate optical fiber was investigated under gamma-ray irradiation at dose rates from 6.7 to 78.3 Gy/min. From the measured RIA, radiation dose sensitivity (ΔRIA/ΔDose) and rate of RIA change with irradiation time (ΔRIA/ΔTime) at the different dose rates were estimated. RIAs at various wavelengths (800 to 1600 nm) of the optical fiber were also measured and the RIA characteristics at 800 and 1310 nm under discrete gamma-ray irradiation were investigated. The measured RIA of the Co/Fe co-doped fiber showed very high dose sensitivity regardless of the dose rates and the ΔRIA/ΔTime was found to show linear response with respect to the dose rate. The significantly large RIA was attributed to Co, Fe, and Al-related defects in the fiber core which were formed by the irradiation, and it became larger at shorter wavelength. The high radiation dose sensitivity, linear response of the ΔRIA/ΔTime with respect to dose rate, and the high reproducibility of the dose dependence of RIA under the discrete irradiation clearly indicate that the Co/Fe co-doped fiber is able to provide highly accurate information of not only total accumulated dose but also dose rate of the radiation with irradiation time. [ABSTRACT FROM PUBLISHER]

Optical fibers can be a medium to produce Cerenkov light due to their dielectric components, and radiation-induced light signals can be obtained using optical fibers without any scintillating material. In this study, we measured and characterized gamma-ray induced Cerenkov light in silica optical fibers, a plastic optical fiber, and a plastic wavelength shifting fiber in order to select the adequate optical fiber for producing Cerenkov light. Also, we measured the intensity of Cerenkov light as functions of irradiated length, irradiation angle, and thickness of various scatterers using the chosen optical fiber. [ABSTRACT FROM PUBLISHER]

This work analyzes the optimal combination between HPGe detectors and sample geometries that result in the lowest Minimum Detectable Activities (MDA) for a given type of shielding. The minimum MDA for a set of nuclides is the criteria to optimize the HPGe detector and the sample geometry. The analysis is made on a large set of detectors of different sizes, p-n junction configuration and aspect ratio available from Canberra Industries Inc., whose response has been characterized with the In-Situ Object Counting System (ISOCS) software. Background spectra in two standard shielding configurations have been acquired and a spectra library has been assembled. This offers the extended capability to establishing the optimal detector for a given application, before purchasing the detector. For each detector, the absolute efficiency is calculated for various sample geometries using ISOCS and an interface that uses the standard Genie2000 spectroscopy software engine. We present two comparisons, one of a coaxial detector and a Broad Energy Ge detector (BEGe) a.k.a planar point contact detector of the same relative efficiency, and comparison of two coaxial detectors of different relative efficiency. The preliminary conclusion is that a larger detector with more efficiency is not always the best choice for the given measurement geometry. Instead, the optimal matching of the detector size with measurement geometry provides the best experimental and economical solution. [ABSTRACT FROM PUBLISHER]

The scanning of cargo for radiological and nuclear material is vital in detecting the illicit trafficking of such materials. The deployment of technologies such as Radiation Portal Monitors (RPMs) has enabled screening for the presence of gamma and neutron emitting radionuclides. [ABSTRACT FROM PUBLISHER]

A front-end ASIC with spectroscopic capability was developed to construct a prototype CdTe pixel detector for future use in focusing hard X-ray telescopes. The ASIC is designed for a hybrid configuration, where each CdTe sensor pixel is vertically connected to a corresponding pixel cell fabricated in the readout ASIC. The readout chip consists of a 12\,\times\,12 matrix of identical 270 \times 270\ \mum^2 pixel cells, and was implemented with TSMC 0.35 \mum CMOS technology. The low noise performance achieved an equivalent noise charge distribution of 50 \pm 10 e^-. A CdTe pixel detector was mounted on the ASIC using an In/Au-stud bump-bonding technique. The detector was operated in self-trigger mode, and showed good spectral performance with energy resolution of 870 eV (FWHM) at 59.5 keV. [ABSTRACT FROM AUTHOR]

We report on the recent development of a 32-channel low-noise analog front-end ASIC “KW03” for hard X-ray and gamma-ray detectors. The ASIC aims for the readout of strip or pixel (pad) detectors utilizing silicon and cadmium telluride (CdTe) as detector materials. Each readout channel includes a charge-sensitive amplifier, bandpass filters and a sample-and-hold circuit. It also includes a leakage current compensation and pole-zero cancellation circuits to meet the various detector requirements. The equivalent noise level of a typical channel reaches 89 e^- @ 0 pF (rms) and shows an input-capacitance characteristic of 7.5 e^-/pF between 0 pF and 10 pF with a power consumption of 3 mW per channel. We mounted the ASIC on a low-temperature co-fired ceramic (LTCC) package and evaluated the spectral performance by combining with a CdTe diode detector. As a result, the gamma-ray spectrum of radioactive source ^241Am was obtained with a good energy resolution of 2.23 keV (FWHM) for gamma rays of 59.5 keV at -\20~^\circC. [ABSTRACT FROM PUBLISHER]

Recently a PIN photodiode is more widely used than a conventional PMT, because it requires less bias to operate it and it is very compact. A PIN photodiode was designed and fabricated for a matching with a CsI(Tl) scintillator in consideration of low leakage current and high biasing voltage. Leakage current and spectral response were measured with the fabricated PIN photodiode as preliminary tests. A CsI(Tl)/PIN photodiode radiation detector was also fabricated and about 10.4% FWHM was achieved at 662 keV gamma-ray. In this study, characteristics of a fabricated PIN photodiode and a CsI(Tl)/PIN photodiode radiation detector were presented. Several important aspects to consider in the fabrication of a Si PIN photodiode radiation detector are also addressed. [ABSTRACT FROM AUTHOR]

The effect of radiation-introduced defects on the behaviour of HfO2 -based metal-insulator-metal (MIM) capacitors as a function of gamma-ray radiation dose from 10 to 1000 krad are reported. Half the capacitors studied showed no degradation after exposure to 1000 krad from a 60Co source, whilst the remaining half showed no change to parameters, such as barrier height and dielectric constant. For the good devices, the I-V characteristics are controlled by Poole-Frenkel model, at a corresponding interface trap energy of 0.39 ~ 0.46 eV before radiation and 0.37 ~ 0.44 eV after 1000 krad. The failed devices show an substantial increase in the trap density from the as fabricated level of 1019 cm-3 to in excess of 1020 cm-3, in contrast to the good devices which show almost no change. We relate this change in defect density to the failure of devices by means of a percolation model, with a trap separation of around 2 nm. [ABSTRACT FROM AUTHOR]

GEANT4 is a versatile Monte Carlo code for simulating the interactions of radiation with matter. GEANT4 has proven to be an effective toolkit for the simulation of a wide variety of detectors. We are interested in the application of GEANT4 to a new type of sensor technology being developed for X-ray and gamma-ray measurements. Microcalorimeter detectors based on transition-edge sensors coupled to bulk absorbers are an emerging technology for hard .X-ray and soft gamma-ray measurements with unprecedented energy resolution. In this work, we assess the ability of the GEANT4 electromagnetic physics package to reproduce measured microcalorimeter data. We also use the simulations to explore the design space of absorber materials and cryostat design. [ABSTRACT FROM AUTHOR]

Various Cs-137 source distributions were imaged with the UCL (University College London) Germanium Compton camera. A reduced camera setup was used consisting of 16 pixels of 4 x 4 x 4 mm³ size each in the front detector and 4 pixels of 4 x 4 x 10 mm³ size each in the back detector. The preamplifier signal was digitised by GRT4 VME readout cards. The deposited energy was extracted online using the moving window deconvolution technique implemented in the FPGAs of the GRT4 cards. A pulse height determination algorithm leading to worse energy resolution was applied offline for comparative studies. For the image reconstruction ITEM (Imaginary Time Expectation Maximization) was used, an iterative algorithm based on quantum mechanics energy minimization. ITEM is very flexible and can easily be applied to every possible Compton camera geometry. An improved backprojection taking into account the changing camera sensitivity in the image space has been used and its limitations investigated. ITEM is shown to work very fast. An image with 10000 pixels can be reconstructed from 40000 events in about 20 s using one 3 GHz Pentium CPU. Data was taken with point, line and circular sources in a plane 2 cm from the front detector. Through analysis of point and line spread functions the angular resolution of the camera was estimated to be around 10 deg. [ABSTRACT FROM AUTHOR]

A computed tomography (CT) system using high-energy monochromatic photons is one of the best choices for non-destructive tests, to detect flaws or defects in manufactured items for the purpose of improving quality control, and quality assurance. We have developed such a CT system based on laser-Compton X-rays, which were generated with an electron accelerator and a laser beam. Using 10 MeV laser-Compton X-rays, an experimental study for non-destructive tests of concrete specimens with computed tomography were performed. We. successfully obtained CT images. [ABSTRACT FROM AUTHOR]

98 SPEAR sensors from eV Products have been evaluated for their use in a portable Compton camera. The sensors have a 5 mm × 5 mm × 5 mm CdZnTe crystal and are provided together with a preamplifier. The energy resolution was studied in detail for all sensors and was found to be 6% on average at 59.5 keV and 3% on average at 662 keV. The standard deviations of the corresponding energy resolution distributions are remarkably small (0.6% at 59.5 keV, 0.7% at 662 keV) and reflect the uniformity of the sensor characteristics. For a possible outside use the temperature dependence of the sensor performances was investigated for temperatures between 15 and 45 deg Celsius. A linear shift in calibration with temperature was observed. The energy resolution at low energies (81 keV) was found to deteriorate exponentially with temperature, while it stayed constant at higher energies (356 keV). A Compton camera built of these sensors was simulated. To obtain realistic energy spectra a suitable detector response function was implemented. To investigate the angular resolution of the camera a 137Cs point source was simulated. Reconstructed images of the point source were compared for perfect and realistic energy and position resolutions. The angular resolution of the camera was found to be better than 10 deg. [ABSTRACT FROM AUTHOR]

The spectral response of several crystals grown by the Traveling Heater Method (THM) were investigated. An energy resolution of 0.98% for a Pseudo Frisch-Grid of 4 times 4 times 9 mm3 and 2.1% FWHM for a coplanar-grid of size 11 times 11 times 5 mm3 were measured using 137Cs-662 keV. In addition a 4% FWHM at 122 keV has also been measured on 20 times 20 X 5 mm3 monolithic pixellated devices. The material shows great potential toward producing large-volume detectors with spectral performance that meets the requirement for high-resolution gamma-ray spectroscopy. [ABSTRACT FROM PUBLISHER]

An ICI (Insulator-Conductor-Insulator) gamma-ray detector designed for measurement of fast rising, high intensity pulsed gamma-ray fluxes has been developed. Like vacuum Compton diode (VCD) and dielectric Compton diode (DCD) devices, the ICI detector operates by utilization of the Compton effect. It has a very fast time response (rise time is less than 1 ns), a large linearity and a wide dynamic range. It is designed to measure intense and rapidly changing gamma-ray fluxes in highly mixed neutron-gamma radiation fields. Its sensitivity to 1.25 MeV gamma rays is about 1.8 × 10-20 Coulombs · cm²/γ, for the 50 mm collimation diameter, which is relatively high compared with VCD and DCD devices. The simulated gamma-ray sensitivity agrees well with the experimental value. The gamma-to-neutron sensitivity ratio is about three orders of magnitudes for neutron energies below 14.1 MeV and 1.25 MeV gamma rays. Compared to existing VCD and DCD devices, the ICI detector requires no vacuum and power supply in operation, and also minimally attenuates a collimated gamma-ray beam due to its overall thickness of 3 mm in beam path. [ABSTRACT FROM AUTHOR]

An approach is proposed, and its potentialities are studied, for single-sided gamma-ray in-depth sensing and tomography of dense opaque media. The approach is based on lidar (Llgth Detection And Ranging) principle or, in the present case, graydar (Gamma RAY Detection And Ranging) principle, that is, time-to-range resolved detection of the backscattering-due radiative returns from the probed object irradiated by pulsed gamma-photon pencil beams. The basic analysis and data processing delta-pulse single-scattering graydar equation is formulated by analogy with the lidar equation and is shown to be applicable, under some determinate conditions, to the problems of gamma-ray in-depth profiling of dense media. It is shown analytically and by computer simulations that the approach developed in the work would enable one, at large-enough but reasonable sensing photon fluxes and measurement time intervals, to determine with good controllable accuracy and resolution the location, the material content, and the mass density of different homogeneous ingredients inside the probed object as well as the mass (or electron) density distribution within one-material objects. This approach can be widely applied, e.g., for nondestructive material examination in industry and aviation, detection of landmines and explosives, investigating the constitution of archeological artifacts, etc. [ABSTRACT FROM AUTHOR]

For measuring X-rays and gamma-rays with better energy resolution and higher efficiency than conventional semiconductor detectors such as Si and Ge detectors, we are studying InSb radiation detectors. Previously, we fabricated p-InSb Schottky type, pn-junction type detectors, and undoped InSb Schottky type detectors with an electrode of 3 mm in diameter, and measured alpha particles of 241Am. For measuring gamma-rays, we fabricated undoped InSb Schottky type detectors with smaller electrode areas. Gamma-ray signals were clearly separated from the background, and differences between energy spectra of 241 Am and 133Ba gamma-rays were observed [ABSTRACT FROM PUBLISHER]

The radiation-induced optical absorption in ionic crystals is remarkably removed by a room-temperature ultrasonic treatment of the crystals. It is shown that the effect can be explained by defect migration processes occurring in ultrasonic fields. The experimental results display features consistent with a recent theory of the quantum diffusion. This new method of a cold annealing of radiation defects in solids can be termed as ultrasonic defect manipulation [ABSTRACT FROM PUBLISHER]

We are developing low noise analog ASICs for hard X-ray and gamma-ray astronomy. They are based on a sub-micron CMOS process. Our design includes a finely-adjustable high-resistance circuit, which, for example, enables us to realize a pole-zero- cancellation in the analog chain. A two-dimensional ASIC with a fast read-out scheme and a one-dimensional ASIC with an improved analog design are developed and verified. With the latter ASIC connected with a CdTe detector, we have obtained a radioactive source spectrum with an energy resolution of 4.6 keV(FWHM) at 59.5 keV. [ABSTRACT FROM AUTHOR]

Pebble bed reactors are characterized by multipass fuel systems in which spherical fuel pebbles are circulated through the core until they reach a proposed burnup limit (80 000-100 000 MWD/MTU). For such reactors, the fuel is assayed on-line to ensure that the burnup limit is not breached. We considered assaying the fuel using an HPGe detector to perform passive gamma-ray spectrometry of fission products. Since neither fresh nor irradiated fuel is readily available, computer simulations were utilized to identify the radionuclides that can be used as burnup. indicators, and to visualize the gamma-ray spectra at various levels of burnup. Specifically, we used the ORIGEN-MONTEBURNS-MCNP code system. This allowed the establishment of the burnup dependent one-group gas reactor cross-sections for the radionuclides of interest. Subsequently, ORIGEN was used to simulate in-core pebble depletion to establish the irradiated pebble isotopics. Finally, the codes MCNP and SYNTH were used to simulate the response of the HPGe gamma-ray spectrometer. The results show that absolute and relative indicators can be used on-line to determine unambiguously the enrichment and burnup on a pebble-by-pebble basis. The activity of Cs-137 or the activity ratio of Co-60/Cs-134 can be combined with the activity ratio of Np-239/I-132 to yield the enrichment and burnup information. To use the relative indicators, a relative efficiency calibration of the gamma-ray spectrometer can be performed using the La-140 gamma lines that are emitted by the irradiated pebble. I-132, Cs-134, Cs-137, La-140, and Np-239 are produced upon the irradiation of the fuel. Co-60 is produced by doping the fuel with a small amount (∼ 100 ppm) of Co-59. Using this approach, the uncertainty in burnup determination due to factors such as power history variation, detector efficiency calibration, and counting statistics is expected to remain in the range of ±5% to ±10%. [ABSTRACT FROM AUTHOR]

Recent results from the Schottky CdTe diode detectors employing a guard-ring (GR) electrode are reported. A cathode electrode, made of platinum, was separated into an active electrode(s) and a surrounding GR. Typical leakage current of a device with active area of 2 × 2 mm² and 0.5 mm thickness surrounded by a GR, is 7 and 20 pA at a bias of 100 and 500 V, respectively, operated at 20 ° Spectral resolution of this device is 0.93 and 1.2 keV (FWHM) at 59.5 and 122 keY, respectively, operated at 20 °C with a bias of 800 V. Detailed study of the characteristics of these devices working as a gamma-ray detector is presented. [ABSTRACT FROM AUTHOR]