Research reactors host a wide range of activities that make use of the intense neutron fluxes generated at these facilities. Recent interest in performing measurements with relatively low event rates, e.g. reactor antineutrino detection, at these facilities necessitates a detailed understanding of background radiation fields. Both reactor-correlated and naturally occurring background sources are potentially important, even at levels well below those of importance for typical activities. Here we describe a comprehensive series of background assessments at three high-power research reactors, including γ-ray, neutron, and muon measurements. For each facility we describe the characteristics and identify the sources of the background fields encountered. The general understanding gained of background production mechanisms and their relationship to facility features will prove valuable for the planning of any sensitive measurement conducted therein.
A new high-performance metrology gantry system has been developed within the scope of collaborative efforts of optics groups at the US Department of Energy synchrotron radiation facilities as well as the BESSY-II synchrotron at the Helmholtz Zentrum Berlin (Germany) and the participation of industrial vendors of x-ray optics and metrology instrumentation directed to create a new generation of optical slope measuring systems (OSMS) [1]. The slope measurement accuracy of the OSMS is expected to be < 50 nrad, which is strongly required for the current and future metrology of x-ray optics for the next generation of light sources.The fabricated system was installed and commissioned (December 2012) at the Advanced Photon Source (APS) at Argonne National Laboratory to replace the aging APS Long Trace Profiler (APS LTP-II). Preliminary tests were conducted (in January and May 2012) using the optical system configuration of the Manometer Optical Component Measuring Machine (NOM) developed at Helmholtz Zentrum Berlin (HZB)/BESSY-II. With a flat Si mirror that is 350 mm long and has 200 nrad rms nominal slope error over a useful length of 300 mm, the system provides a repeatability of about 53 nrad. This value corresponds to the design performance of 50 nrad rms accuracy for inspection of ultra-precise flat optics. (c) 2012 Elsevier B.V. All rights reserved.
Recent results of CERN RD39 collaboration on the development of radiation hard Si detectors operated at low to cryogenic temperatures will be presented in this paper. It has been found, in comparisons of results of simulation and charge collection data of pad and strip detectors, the charge-injected-diode (CID) operation mode of Si detectors reduces the free carrier trapping, resulting in a much higher charge collection at the SLHC fluence than that in a standard Si detector. The reduction in free carrier trapping by almost a factor of 3 is due to the fact that the CID mode pre-fills the traps, making them neutral and not active in trapping of particle-induced free carriers (signal). It has been found that, electron traps can be pre-filled by injection of electrons from the n+ contact. The CID mode of detector operation can be achieved by a modestly low temperature of ≤−40 °C and a operation bias of <600 V. Results of one CID detector application as LHC beam-loss-monitor (BLM) will be presented. Non-irradiated Si detectors has been shown, with tests by laser using our cryogenic transient-current-technique (TCT), to work quite well at LHe temperature (4 K), which are very stable with no polarization and good charge collection efficiency.
For the development of radiation-hard Si detectors for the SiD BeamCal program for the future ILC (International Linear Collider), n-type MCZ Si detectors have been irradiated first by fast neutrons to flueneces of 1.5×1014 and 3×1014 neq/cm2, and then by gamma up to 500 Mrad. The motivation of this mixed radiation project is to develop a Si detector that can utilize the gamma/electron radiation that exists in the ICL radiation environment, which also includes neutrons. By using the positive space charge (SC) created by gamma radiation in MCZ Si detectors, one can cancel the negative space charge created by neutrons, thus reducing the overall/net space charge density and therefore the full depletion voltage of the detector.
We report R&D results on two integrated circuit designs: a 5 Gbps 16:1 serializer and a 5 GHz LC phase-locked-loop (PLL). The prototypes were fabricated with a commercial thin-film silicon-on-sapphire 0.25 μm CMOS technology. Both the serializer and the PLL have been evaluated to meet design goals and tested against operation conditions in the environment of a particle physics detector front-end for the proposed HL-LHC upgrade.
Modern mosaic cameras have grown both in size and in number of sensors. The required volume of sensor testing and characterization has grown accordingly. For camera projects as large as the LSST, test automation becomes a necessity. A CCD testing and characterization laboratory was built and is in operation for the LSST project. Characterization of LSST study contract sensors has been performed. The characterization process and its automation are discussed, and results are presented. Our system automatically acquires images, populates a database with metadata information, and runs express analysis. This approach is illustrated on 55Fe data analysis. 55Fe data are used to measure gain, charge transfer efficiency and charge diffusion. Examples of express analysis results are presented and discussed.
Tight requirements on the Large Synoptic Survey Telescope point spread function (PSF) demand sensor contribution to PSF be both small and well characterized. The sensor PSF is determined by the lateral charge diffusion on the drift path from the photon conversion point to the gates. The maximum drift path occurs for photons converted at the window, for blue optical photons in particular. Charges generated at the window surface undergo "worst case" charge spreading and the blue optical PSF is used to characterize the sensor's PSF.Different techniques for charge diffusion characterization have been developed, each with its own systematics and measurement difficulties. A new way to measure charge diffusion using an X-ray source is presented. We demonstrate the effectiveness and limitations of our technique and discuss relation of charge diffusion value obtained with X-ray measurements to sensor PSF.
We present results for detection of X-rays by large area avalanche photodiodes (APDs) in strong magnetic fields and at cryogenic temperatures. Whereas at room temperature we observe essentially no effects on the response, at cryogenic temperature we observe significant distortion when the magnetic field is in the plane of the APD surface (and thus perpendicular to the electric field in the APD). At all temperatures, effects are minor when the magnetic field is normal to the APD surface (and thus parallel to the electric field in the APD). We performed measurements of the response of an APD to illumination by X-rays in fields between 0 and 4.6T, for temperatures between 77 and 250K. Measurements were performed using 241Am and 55Fe sources, and 1.5keV X-rays produced by aluminum fluorescence. The data indicate that the effects are associated with those X-rays that are absorbed in the drift region of the APD.
In Computed Tomography applications a major opportunity has been identified in the exploitation of the spectral information inherently available due to the polychromatic emission of the X-ray tube. Current CT technology based on indirect-conversion and integrating-mode detection can be used to some extent to distinguish the two predominant physical causes of energy-dependent attenuation (photo-electric effect and Compton effect) by using dual-energy techniques, e.g. kVp switching, dual-source or detector stacking. Further improvements can be achieved by transitioning to direct-conversion technologies and counting-mode detection, which inherently exhibits a better signal-to-noise ratio. Further including energy discrimination, enables new applications, which are not feasible with dual-energy techniques, e.g. the possibility to discriminate K-edge features (contrast agents, e.g. Gadolinium) from the other contributions to the x-ray attenuation of a human body. The capability of providing energy-resolved information with more than two different measurements is referred to as Spectral CT. To study the feasibility of Spectral CT, an energy-resolving proprietary photon counting ASIC (ChromAIX) has been designed to provide high count-rate capabilities while offering energy discrimination. The ChromAIX ASIC consists of an arrangement of 4 by 16 pixels with an isotropic pitch of 300 μm. Each pixel contains a number of independent energy discriminators with their corresponding 12-bit counters with continuous read-out capability. Observed Poissonian count-rates exceeding 10 Mcps (corresponding to approximately 27 Mcps incident mean Poisson rate) have been experimentally validated through electrical characterization. The measured noise of 2.6 mVRMS (4 keV FWHM) adheres to specifications. The ChromAIX ASIC has been specifically designed to support direct-converting materials CdZnTe and CdTe.
Triple rule-out coronary CT angiography (TRO-CTA) is a new approach for providing noninvasive visualization of coronary arteries with simultaneous evaluation of pulmonary arteries, thoracic aorta and other intrathoracic structures. The increasing use of TRO-CTA examination with longer scan length is associated with the concerns about radiation dose and their corresponding cancer risk. The purpose of this study is to evaluate organ dose and effective dose for the TRO-CTA examination with 2 scan lengths: TROstd and TROext, using 256-slice CT. TRO-CTA examinations were performed on a 256-slice CT scanner without ECG-based tube current modulation. Absorbed organ doses were measured using an anthropomorphic phantom and thermal-luminance dosimeters (TLDs). Effective dose was determined by taking a sum of the measured absorbed organ doses multiplied with the tissue weighting factor based on ICRP-103, and compared to that calculated using the dose-length product (DLP) method. We obtained high organ doses in the thyroid, esophagus, breast, heart and lung in both TRO-CTA protocols. Effective doses of the TROstd and TROext protocols with the phantom method were 26.37 and 42.49 mSv, while those with the DLP method were 19.68 and 38.96 mSv, respectively. Our quantitative dose information establishes a relationship between radiation dose and scanning length, and can provide a practical guidance to best clinical practice.
For the luminosity upgrade of the LHC, the SLHC, the tracking systems of the LHC experiments need to be replaced. A main concern is the extreme radiation hardness requirement up to 1×1016cm-2 1MeV neutron equivalent. This paper describes an extract of recent results on radiation hardening technologies developed within the RD50 Collaboration (http://www.cern.ch/rd50) [1] for the tracker upgrades. Silicon detectors have been designed and produced on n- and p-type wafers made by Float Zone, epitaxy and Czochralski technology. Their charge collection efficiency after proton, neutron and mixed irradiation has been studied. Novel detector concepts, as 3D detectors, have been designed, produced and studied as well. Radiation induced microscopic disorder has been also investigated and correlated with the performance degradation of irradiated detectors.
The Linear Collider Flavour Identification (LCFI) Collaboration is developing the sensors, readout electronics and mechanical support structures for the vertex detector of the International Linear Collider (ILC). High speed readout is needed to ensure that the occupancy due to the pair production background at the ILC is kept below the 1% level. In order to satisfy this requirement, Column Parallel CCDs (CPCCDs), Column Parallel Readout chips (CPRs) and Column Parallel Driver chips (CPDs) have been developed. The CPCCD has to operate at a clock frequency of 50 MHz, which represents a difficult technical challenge due to the large sensor capacitance. The design and performance of the second generation CPCCD sensors, CPC2, and the new driver chip, CPD1, which meet these challenging requirements, are described.
We are developing n+-in-p, p-bulk and n-readout, microstrip sensors, fabricated by Hamamatsu Photonics, as a non-inverting radiation hard silicon detector for the ATLAS tracker upgrade at the super-LHC (sLHC) proposed facility. The bulk radiation damage after neutron and proton irradiations is characterized with the leakage current, charge collection and full depletion voltage. The detectors should provide acceptable signal, signal-to-noise ratio exceeding 15, after the integrated luminosity of 6000 fb−1, which is twice the sLHC integrated luminosity goal.
Using a narrow band positron beam, the response of a large high-resolution NaI(Tl) crystal to an incident positron beam was measured. It was found that nuclear interactions cause the appearance of additional peaks in the low energy tail of the deposited energy spectrum.
The spatial distribution of hydrogen physically adsorbed in a nanoporous carbon at room temperature (RT) as a function of H-2 gas pressure is investigated for the first time using small-angle neutron scattering (SANS). A hierarchical pore structure consisting of micropores and a fractal mesopore network of the used activated carbon is also studied to correlate the relationship between the spatial distribution of hydrogen and the pore confinement. The cylinder-like cluster of aggregated hydrogen is formed and is confined in the disklike micropore. The evolution of spatial structures of adsorbed hydrogen with hydrogen pressure is elucidated. A direct experimental observation of the spatial distribution and the behavior of hydrogen adsorbed in the porous materials at RT is still scarce to date. The analysis results obtained by SANS provide new information for the future investigations of the RT storage mechanism of hydrogen in the nanoporous materials developed for the purpose of on-board hydrogen storage.
