We report constraints on spin-independent weakly interacting massive particle (WIMP)-nucleon scattering using a 3.35×10^{4}  kg day exposure of the Large Underground Xenon (LUX) experiment. A dual-phase xenon time projection chamber with 250 kg of active mass is operated at the Sanford Underground Research Facility under Lead, South Dakota (USA). With roughly fourfold improvement in sensitivity for high WIMP masses relative to our previous results, this search yields no evidence of WIMP nuclear recoils. At a WIMP mass of 50  GeV c^{-2}, WIMP-nucleon spin-independent cross sections above 2.2×10^{-46}  cm^{2} are excluded at the 90% confidence level. When combined with the previously reported LUX exposure, this exclusion strengthens to 1.1×10^{-46}  cm^{2} at 50  GeV c^{-2}.

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Results from a Search for Dark Matter in the Complete LUX Exposure

The synthesis, crystal growth, and structural and optoelectronic characterization has been carried out for the perovskite compound CsPbBr3. This compound is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photoconductivity response, with detector resolution comparable to that of commercial, state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temperature does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approximately equal. The μτ product for electrons is comparable to cadmium zinc telluride (CZT) and that for holes is 10 times higher than CZT.

Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection

The T2K experiment is a long-baseline neutrino oscillation experiment Its main goal is to measure the last unknown lepton sector mixing angle {\theta}_{13} by observing {\nu}_e appearance in a {\nu}_{\mu} beam It also aims to make a precision measurement of the known oscillation parameters, {\Delta}m^{2}_{23} and sin^{2} 2{\theta}_{23}, via {\nu}_{\mu} disappearance studies Other goals of the experiment include various neutrino cross section measurements and sterile neutrino searches The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem

The T2K Experiment

The paper gives a survey of the upcoming use of X-ray computed tomography (CT) for dimensional quality control purposes: i.e. for traceable measurement of dimensions of technical (mechanical) components and for tolerance verification of such components. It describes the basic principles of CT metrology, putting emphasis on issues as accuracy, traceability to the unit of length (the meter) and measurement uncertainty. It provides a state of the art (anno 2011) and application examples, showing the aptitude of CT metrology to: (i) check internal dimensions that cannot be measured using traditional coordinate measuring machines and (ii) combine dimensional quality control with material quality control in one single quality inspection run.

Computed tomography for dimensional metrology

Newly developed high-speed, synchrotron-based X-ray computed microtomography enabled us to directly image pore-scale displacement events in porous rock in real time. Common approaches to modeling macroscopic fluid behavior are phenomenological, have many shortcomings, and lack consistent links to elementary pore-scale displacement processes, such as Haines jumps and snap-off. Unlike the common singular pore jump paradigm based on observations of restricted artificial capillaries, we found that Haines jumps typically cascade through 10–20 geometrically defined pores per event, accounting for 64% of the energy dissipation. Real-time imaging provided a more detailed fundamental understanding of the elementary processes in porous media, such as hysteresis, snap-off, and nonwetting phase entrapment, and it opens the way for a rigorous process for upscaling based on thermodynamic models.

https://www.pnas.org/content/pnas/110/10/3755.full.pdf

Real-time 3D imaging of Haines jumps in porous media flow

IEEE Nuclear Science Symposium Conference Record

Using the photomultiplier-quadrant-sharing (PQS) technique, we designed pentagonal detector blocks with high resolution (2.0 mm) and high sensitivity for a rodent research PET (RRPET). In order to reduce the cost, 8 /spl times/ 8 Bismuth germinate (BGO) crystal array and 19-mm regular round PMTs were used in this research. The average detector pitch was about 2.0 /spl times/ 2.0 mm and 10 mm deep. To minimize the depth-of-interaction effect due to the "panelization" of the detectors, we modified the original cubical block for panelized PQS detector into a pentagon shape with the ends tapered, so that each pentagonal block acted as a facet of the polygonal detector ring. This tapered-pentagon-PQS design provides a very high packing-fraction (96%) for a ring-type PET. We fully exploited the flexibility of our latest PQS fabrication method, i.e., using partially painted reflective windows between crystals, in the pentagonal block development, this fabrication method allowed the fine tuning of the scintillation light distribution inside the block for optimal decoding. The effect of block geometry on PQS design was examined by developing cubical and pentagonal block directly coupled to four PMTs and decoding by pileup-recovery electronics. Two-dimensional crystal decoding maps and pulse-height spectra of the individual crystals with their corresponding energy resolutions were acquired. Each crystal was clearly decoded and the average individual crystal energy resolution was found to be 21% and 22.3% for cubical and pentagon block, respectively. The pentagon-PQS design is an alternative to the prevailing small animal PET detector assembly of lutetium oxyorthosilicate (LSO) or gadolinium oxyorthosilicate (GSO), optical-fiber or light-guide with PS-PMT.

A pentagon photomultiplier-quadrant-sharing BGO detector for a rodent research PET (RRPET)

We have developed a high-resolution transformable positron emission tomography (PET) camera that can be configured into either a whole-body mode (83-cm detector ring diameter, 13-cm axial field-of-view (AFOV)) or a brain/breast/axilla (54-cm detector ring diameter, 21-cm AFOV) mode. The camera has 12 rectangular detector modules, and the detector gap between adjacent modules is very small and remains constant for each configuration. Each module has a large detection area (13 cm times 21 cm) and 38016 bismuth germanate (BGO) detector crystals of 2.7 times 2.7 times 18 mm3 with built-in front-end electronics. To improve spatial sampling, the gantry on which the camera is mounted can be rotated 30deg with a fine step size of 1deg, and the high-speed electronics and detector modules also rotate along with the gantry. This system uses only 924 photomultiplier tubes (PMT) by applying a low-cost high-resolution PMT-quadrant-sharing detector design. To compensate for the slower scintillation timing of BGO detectors, the camera is equipped with the "HYPER", high-yield pile-up event recovery front-end electronics. A fast light-emitting diode (LED) cross-reference PMT tuning method is used to maintain the PMT gain balance. The system has been constructed and tested for preliminary imaging characteristics. The system sensitivity is 4.2% for whole-body and 9.2% for brain/breast/axilla mode measured with Na-22 at center of field of view (FOV). For brain/breast/axilla modes, the transaxial image resolutions at 0 and 10 cm were found to be 2.7 and 4.0 mm, respectively, while for whole-body mode, the image resolutions were 3.3 and 3.9 mm. The slice thickness resolution ranged from 2.6 to 3.3 mm for middle 7 detector rings in brain/breast/axilla modes. High quality Hoffman brain phantom images were obtained in both brain and whole-body modes.

The Engineering and Initial Results of a Transformable Low-cost Ultra-high Resolution PET Camera

The goal of this study is to develop lower-cost ultrahigh resolution detectors for PET systems, using the PMT-quadrant-sharing (PQS) decoding technology on L(Y)SO scintillation crystals. For this work, L(Y)SO PQS block detectors for both animal and human PET cameras were developed and studied. Both simulation and experimental detector design studies were carried out to achieve efficient light distribution and crystal decoding. The effects of crystal finishes and reflector patterns on light distribution, light output and energy resolution were investigated and used to derive the highest resolution PQS-L(YSO) block-detector. The PQS-L(Y)SO detector performance was measured on the best performing blocks. For performance evaluation, list-mode data from the detectors were acquired and analyzed to extract light-collection efficiency, energy-resolution distribution, and pulse height distribution for individual crystals. The potential PET imaging resolution performance was investigated using Monte Carlo simulation studies with the GEANT4/GATE software for both detectors developed for small animal PET and human PET applications. From these studies, we have the following findings: 1) For light distribution studies on the crystal surface finish, 4 mum lapping was found to be the preferred finish for achieving the best position decoding together with good overall light output for all the crystals in both, the human and animal detector arrays; 2) Intricate reflector patterns between crystals can be made from the ESR mirror film (3M Inc.) for optimally controlling the light sharing between crystals and to the four decoding PMT's, with high packing fractions on the PQS-blocks; 3) For the PQS-LYSO detector block for animal PET systems, using 19-mm circular photomultipliers (PMT), we achieved decoding a 14 times 14 arrays with a crystal pitch of 1.27 times 1.27 mm2. This animal detector has a packing fraction of 95.6%, an energy resolution ranging between 12.9%~15.8% for individual crystals (average energy resolution of 14%), the pulse height for the least favorable crystal is 63.5% of the most favorable crystal; 4) For PQS-LSO detector block for human PET systems using very large circular 51-mm PMT, we achieved decoding a 15 times 15 array with a crystal pitch of 3.25 times 3.25 mm2. The human PET detector has packing fraction of 98.2%, an energy resolution range 12.9%~15.8% (average energy resolution 14%). The pulse height of least favorable crystals is 80% of the most favorable crystal. 5) From Monte Carlo simulations for LSO small animal PET, a spatial resolution of 1.1-1.2 mm may potentially be achieved using low cost 19-mm circular PMT. For human PET systems, 3-mm spatial resolution may potentially be achieved using very large 51-mm circular PMT for cost reduction.

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Ultrahigh-Resolution L(Y)SO Detectors Using PMT-Quadrant-Sharing for Human & Animal PET Cameras

The goal of this work is to develop a novel, accurate, real-time digital baseline restorer using online statistical processing for a high count-rate digital system such as positron emission tomography (PET). In high count-rate nuclear instrumentation applications, analog signals are DC-coupled for better performance. However, the detectors, pre-amplifiers and other front-end electronics would cause a signal baseline drift in a DC-coupling system, which will degrade the performance of energy resolution and positioning accuracy. Event pileups normally exist in a high-count rate system and the baseline drift will create errors in the event pileup-correction. Hence, a baseline restorer (BLR) is required in a high count-rate system to remove the DC drift ahead of the pileup correction. Many methods have been reported for BLR from classic analog methods to digital filter solutions. However a single channel BLR with analog method can only work under 500 kcps count-rate, and normally an analog front-end application-specific integrated circuits (ASIC) is required for the application involved hundreds BLR such as a PET camera. We have developed a simple statistics-based online baseline restorer (SOBLR) for a high count-rate fully digital system. In this method, we acquire additional samples, excluding the real gamma pulses, from the existing free-running ADC in the digital system, and perform online statistical processing to generate a baseline value. This baseline value will be subtracted from the digitized waveform to retrieve its original pulse with zero-baseline drift. This method can self-track the baseline without a micro-controller involved. The circuit consists of two digital counter/timers, one comparator, one register and one subtraction unit. Simulation shows a single channel works at 30 Mcps count-rate with pileup condition. 336 baseline restorer circuits have been implemented into 12 field-programmable-gate-arrays (FPGA) for our new fully digital PET system.

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Rocio Ramirez

Papers

IEEE Nuclear Science Symposium Conference Record

A pentagon photomultiplier-quadrant-sharing BGO detector for a rodent research PET (RRPET)

The Engineering and Initial Results of a Transformable Low-cost Ultra-high Resolution PET Camera

Ultrahigh-Resolution L(Y)SO Detectors Using PMT-Quadrant-Sharing for Human & Animal PET Cameras

A new statistics-based online baseline restorer (SOBLR) for a high count-rate fully digital system