Search

An x-ray microcalorimeter consists of an absorber and a thermometer connected to each other, and to a heat sink, via well defined thermal conductances. The standard theoretical derivation of energy resolution treats the absorber and thermometer as point elements that are internally isothermal. In reality, the finite size and internal diffusivity of the absorber and thermometer prevents these elements from instantly achieving a uniform temperature, leading to a variation in observed pulse shapes as a function of the interaction’s position within the absorber. These variations result in a distortion of the detector response and a subsequent degradation of the energy resolution. This paper presents diffusivity measurements for x-ray microcalorimeters fabricated at the NASA/GSFC. Using a diffusion model we developed, we show quantitatively how a 2 eV Gaussian response is distorted into a non-Gaussian profile roughly 12 eV wide at an energy of 6 keV for an absorber diffusivity of 104 μm2/μs. We then present a method for eliminating the effect of pulse shape variation on the detector energy response with a modified optimal filter approach. [ABSTRACT FROM AUTHOR]

An experimental system has been designed to examine the assembly of nanoparticles in a variety of process engineering applications. These applications include the harvesting from solutions of nanoparticles into green parts, and the subsequent sintering into finished components. The system is based on an x-ray microtomography with a spatial resolution down to 5 μm. The theoretical limitations in x-ray imaging are considered to allow experimental optimization. A standard nondestructive evaluation type apparatus with a small focal-spot x-ray tube, high-resolution complementary metal oxide semiconductor flat-panel pixellated detector, and a mechanical rotational stage is used to image the static systems. Dynamic sintering processes are imaged using the same x-ray source and detector but a custom rotational stage which is contained in an environmental chamber where the temperature, atmospheric pressure, and compaction force can be controlled. Three-dimensional tomographic data sets are presented here for samples from the pharmaceutical, nutraceutical, biotechnology, and nanoparticle handling industries and show the microscopic features and defects which can be resolved with the system. [ABSTRACT FROM AUTHOR]

The performances of the OFFSET3 tracker (Optical Fiber Folded Scintillating Extended Tracker) are presented. It exploits a novel system for particle tracking, designed to achieve real-time particle imaging and tracking, large detection areas, and a high spatial resolution especially suitable for applications in medical diagnostics. The tracker is composed by two 288 \times 288~\mm^2 FOV position detectors stacked by 10 cm, made by 500 micron square scintillating fiber ribbons for both directions. The track position information is extracted in real-time in an innovative way, using a reduced number of readout channels, by means of which it is possible to obtain the large detection area with moderate cost and complexity. The architecture has been patented by the Istituto Nazionale di Fisica Nucleare (INFN). The performances of the tracker were investigated by beta sources, cosmic rays, 60 MeV-250 MeV proton and 400 MeV/A carbon clinical beams. [ABSTRACT FROM PUBLISHER]

In modern particle accelerators, radio frequency (RF) phase detectors have to fulfill high demands on stability and accuracy to meet the goals of state-of-the-art synchronization systems. Especially challenging are those cases where the RF signal phase shift accuracy must be measured with fs accuracy for several hours over the full 2 \pi phase detection range. In these cases special measures on the component’s nonlinearities and RF channel isolation have to be taken. The long-term stability of the phase detector is mostly affected by temperature and humidity variations. To meet the synchronization goals, we have built a phase detector that incorporates a high-speed dual analog-to-digital converter (ADC) with a special circuit for continuous phase drift calibration. In the calibration circuit we successfully combined the RF signal with an RF calibration signal (second tone) to compensate common phase drift that occurs in the microstrip lines, the RF transformers, and the ADC. The second-tone RF signals are directly converted to the digital domain by the fast ADC and, based on signal processing in the field-programmable gate array, are used to calculate the RF signal phase shift correction caused by detector drifts. In this paper, potential error sources of the analog and the digital part of the so-called two-tone calibration technique that limit the phase detector precision are discussed. Finally, the experimental results are presented showing a long-term phase measurement stability better than 0.01\ ^\circ \ pk-\ pk evaluated at an RF frequency of 1.3 GHz over a few days. [ABSTRACT FROM PUBLISHER]

Three-dimensional (3D) photodiode detectors offer advantages over standard planar photodiodes in a range of applications, including X-ray detection for synchrotrons and medical imaging. The principal advantage of these sensors for X-ray imaging is their low charge sharing between adjacent pixels, which could improve spatial and spectral resolution. A 'double-sided' 3D detector has been bonded to a Medipix2 single-photon-counting readout chip, and tested in a monochromatic X-ray beam at the Diamond synchrotron. Tests of the 3D detector's response spectrum and its Line Spread Function have shown that it has substantially lower charge sharing than a standard planar Medipix2 sensor. Additionally, the 3D detector was used to image diffraction rings produced by a powdered silicon sample, demonstrating the detector's use in a standard synchrotron experiment. [ABSTRACT FROM AUTHOR]

A highly sensitive detection system for magnetic contaminants using a High-Tc superconducting quantum interference device (SQUID) was developed. Finding ultra-small metallic contaminants is a big issue for manufacturers producing commercial products such as lithium ion batteries. When the contamination does occur, the manufacturer of the product suffers a great loss to recall the tainted products. The outer dimension of metallic particles less than 100 microns can not be detected by X-ray imaging, which is commonly used as the inspection method. Inmost cases, the matrix of industrial products is magnetized and the magnetic signal from the matrix is large enough to mask the signal from contaminants. We developed a detection system based on a high-Tc SQUID gradiometer. A specially designed low noise planar gradiometer for the system was developed. The flux white noise level of the SQUID gradiometer was 8-16μø0/Hz1/2 at 1 kHz. Use of the gradiometer and horizontal magnetization could solve problem above. We tested the performances of the system and found that small iron particles as small as 50 μm × 50 μm on the electrode of the lithium ion battery could be clearly detect. This detection level is difficult to achieve using other methods. [ABSTRACT FROM AUTHOR]

In cone beam industrial computed tomography (ICT), it is often required to inspect the large object using flat detector. If traditional helical scanning is used, the field of view (FOV) is limited due to the size of flat detector. As an alternative, a dual helical cone-beam scanning is proposed in this paper. Before each helical scanning, x-ray source and flat detector are horizontally translated a given distance, and part of the object is covered by x-ray at each view angle. Then the object function is reconstructed by use of the improved helical FDK algorithm, which does not rebin projection data. Simulations validate that the images, which are reconstructed by proposed scanning mode and improved algorithm with small flat detector, are similar to those from the conventional helical scanning and FDK algorithm with large flat detector. The improved FDK algorithm is not sensitive to translation step. Furthermore, the proposed scanning mode can extend the radius of FOV up to at least 1.7 times. [ABSTRACT FROM AUTHOR]

The National Space Institute, of the Technical University of Denmark is responsible for the selection and characterization of the CZT detector crystals for the X- and Gamma-ray instrument, MXGS, onboard ESA's Atmospheric Space Interaction Monitor (ASIM) mission. The first CZT pixel detector modules for MXGS have recently been delivered by Redlen. Measurements at the University of Bergen demonstrate that the detectors exhibit the expected spectral performance; however, it was also found that the detector modules showed unexplained pixel-to-pixel count rate variations. At The National Space Institute a series of measurements were initiated focusing on the pixel-to-pixel count rate variations. Collimated monochromatic X-ray beams were used to scan a number of Redlen pixel detectors. The main conclusion of these measurements is that the pixel-to-pixel count rate variations are correlated with variations in the effective pixel areas. These variations are likely related to non-uniformity of the internal electric detector field. [ABSTRACT FROM AUTHOR]

This paper considers the problem of container inspection at a port-of-entry. Containers are inspected through a specific sequence to detect the presence of nuclear materials, biological and chemical agents, and other illegal shipments. The threshold levels of sensors at inspection stations of the port-of-entry affect the probabilities of incorrectly accepting or rejecting a container. In this paper, we present several optimization approaches for determining the optimum sensor threshold levels, while considering misclassification errors, total cost of inspection, and budget constraints. In contrast to previous work which determines threshold levels and sequence separately, we consider an integrated system and determine them simultaneously. Examples applying the approaches in different sensor arrangements are demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: High-Tc superconducting quantum interference device (SQUID) is an ultra-sensitive magnetic sensor. Since the performance of the SQUID is improved and stabilized, now it is ready for application. One strong candidate for application is a detection system of magnetic foreign matters in industrial products or beverages. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. If this happens, the manufacturer of the product suffers a great loss recalling products. The outer dimension of metallic particles less than 100μm cannot be detected by an X-ray imaging, which is commonly used for the inspection. Ionization of the material is also a big issue for beverages in the case of the X-ray imaging. Therefore a highly sensitive and safety detection system for small foreign matters is required. We developed detection systems based on high-Tc SQUID with a high-performance magnetic shield. We could successfully measure small iron particles of 100μm on a belt conveyer and stainless steel balls of 300μm in water. These detection levels were hard to be achieved by a conventional X-ray detection or other methods. [Copyright &y& Elsevier]

Abstract: A new charge coupled device (CCD)-based X-ray detector, which uses a high-gain microchannel plate image intensifier for upfront optical gain, is proposed. The intensifier is directly coupled with the photosensitive surface of a CCD by a fiber optic taper and acts as both a converter and intensifier. Experimental results for the detector in X-ray imaging show that the detector currently has an intrinsic resolution of approximately 83μm (12lp/mm). [Copyright &y& Elsevier]

A CMOS charge readout ASIC (SD7110) for flat-panel X-ray detectors was designed and tested. This ASIC contains 128 readout channels, with each channel consisting of a charge sensitive amplifier, a correlated double sampler, and a track-and-hold circuit. Channel outputs are read out via a 128:1 analog multiplexer and fed into an external 16-bit A/D converter. Conversion gain can be selected from 0.25 V/pC to 8 V/pC. The ASIC operates using a +5.0 V single power supply, with power dissipation of 1.8 mW/channel. The equivalent noise charge (ENC) measured was 400 + 18.9 e-/pF. [ABSTRACT FROM AUTHOR]

This work addresses the fabrication by X-ray lithography of building block structures for integrated microfluidics. In particular, we demonstrate the realization of a closed microfluidic channel based on a multiple tilted X-ray exposure scheme without the need for registration steps. This scheme is exploited also for the fabrication of metallic 2D vertical gratings that can be used as sieves or electrical detectors in microfluidic channels. Finally, we describe a new process based on the combination of X-ray and e-beam lithography for the realization of flyover channel connecting vertical micro-tank structures. [Copyright &y& Elsevier]

Abstract: A new X-ray detector using surface plasmon resonance (SPR) is proposed. The detector consists of a prism coated with a thin metal film and semiconductor film. Optical laser pulse induces SPR condition on the metal surface, and synchronized X-ray pulse which is absorbed into the semiconductor film can be detected by measuring the change of the resonance condition of the surface plasmon. The expected time and spatial resolution of this detector is better than that of conventional X-ray detectors by combining this SPR measurement with ultra-short laser pulse as the probe beam. Our preliminary investigation using Au and ZnSe coated prism implies this scheme works well as the detector for the ultra-short X-ray pulse. [Copyright &y& Elsevier]

An x-ray streak camera with high resolution in both temporal and spatial dimensions has been developed. It is achieved by using extraction-mesh acceleration and a large opening aperture magnetic solenoid lens design. High resolutions in the temporal and spatial dimensions can be retained in a wide 53 ps time window. A temporal resolution of 233 fs and a spatial resolution of 10 μm have been demonstrated using a Au photocathode. [ABSTRACT FROM AUTHOR]