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McNally B.D.,Xia Llc Inc. | Coleman S.,Xia Llc Inc. | Warburton W.K.,Xia Llc Inc. | Autran J.-L.,Aix - Marseille University | And 4 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

Alpha emissivity measurements are important in the semiconductor industry for assessing the suitability of materials for use in production processes. A recently published round-robin study that circulated the same samples to several alpha counting centers showed wide center-to-center variations in measured alpha emissivity. A separate analysis of these results hypothesized that much of the variation might arise from differences in sample-to-entrance window separations. XIA recently introduced an ultra low background counter, the UltraLo-1800 ("UltraLo"), that operates in a fundamentally different manner from the proportional counters used at most of the centers in the original study. In particular, by placing the sample within the counting volume, it eliminates the sample-to-entrance window separation issue noted above, and so offers an opportunity to test this hypothesis. In this work we briefly review how the UltraLo operates and describe a new round-robin study conducted entirely on UltraLo instruments using a set of standard samples that included two samples used in the original study. This study shows that, for LA ("Low Alpha" between 2 and 50 α/khr-cm2) sample measurements, the only remaining site-to-site variations were due to counting statistics. Variations in ULA ("Ultra-Low Alpha"<2 α/khr-cm2) sample measurements were reduced three-fold, compared to the earlier study, with the measurements suggesting that residual activity variations now primarily arise from site-to-site differences in the cosmogenic background. © 2014 Elsevier B.V.


Warburton W.K.,Xia Llc Inc. | Harris J.T.,Xia Llc Inc. | Friedrich S.,Lawrence Livermore National Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2015

Superconducting tunnel junctions (STJs) are excellent soft x-ray (100-2000 eV) detectors, particularly for synchrotron applications, because of their ability to obtain energy resolutions below 10 eV at count rates approaching 10 kcps. In order to achieve useful solid detection angles with these very small detectors, they are typically deployed in large arrays - currently with 100+ elements, but with 1000 elements being contemplated. In this paper we review a 5-year effort to develop compact, computer controlled low-noise processing electronics for STJ detector arrays, focusing on the major issues encountered and our solutions to them. Of particular interest are our preamplifier design, which can set the STJ operating points under computer control and achieve 2.7 eV energy resolution; our low noise power supply, which produces only 2 nV/√Hz noise at the preamplifier's critical cascode node; our digital processing card that digitizes and digitally processes 32 channels; and an STJ I-V curve scanning algorithm that computes noise as a function of offset voltage, allowing an optimum operating point to be easily selected. With 32 preamplifiers laid out on a custom 3U EuroCard, and the 32 channel digital card in a 3U PXI card format, electronics for a 128 channel array occupy only two small chassis, each the size of a National Instruments 5-slot PXI crate, and allow full array control with simple extensions of existing beam line data collection packages. © 2015 Elsevier B.V. All rights reserved.


Rybka G.,University of Washington | Hotz M.,University of Washington | Rosenberg L.J.,University of Washington | Asztalos S.J.,Lawrence Livermore National Laboratory | And 12 more authors.
Physical Review Letters | Year: 2010

Scalar fields with a "chameleon" property, in which the effective particle mass is a function of its local environment, are common to many theories beyond the standard model and could be responsible for dark energy. If these fields couple weakly to the photon, they could be detectable through the afterglow effect of photon-chameleon-photon transitions. The ADMX experiment was used in the first chameleon search with a microwave cavity to set a new limit on scalar chameleon-photon coupling βγ excluding values between 2×109 and 5×1014 for effective chameleon masses between 1.9510 and 1.9525μeV. © 2010 The American Physical Society.


Paulauskas S.V.,University of Tennessee at Knoxville | Madurga M.,University of Tennessee at Knoxville | Grzywacz R.,University of Tennessee at Knoxville | Grzywacz R.,Oak Ridge National Laboratory | And 3 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

Neutron energy measurements can be achieved using time-of-flight (ToF) techniques. A digital data acquisition system was developed for reliable ToF measurements with subnanosecond timing resolution based on digitizers with 10 ns and 4 ns sampling periods using pulse shape analysis algorithms. A validation procedure was developed to confirm the reliability. The response of the algorithm to photomultiplier signals was studied using a specially designed experimental system based on fast plastic scintillators. The presented developments enabled digital data acquisition systems to instrument the recently developed Versatile Array of Neutron Detectors at Low-Energy (VANDLE). © 2013 Elsevier B.V.


Grant
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2014

The detection and identification of special nuclear materials and nuclear fission by-products is a critically important activity in support of nuclear non-proliferation programs. Gamma-ray spectroscopy is a key tool in this field, but no instrument exists that exploits the intrinsically high energy resolution and detection sensitivity of high purity germanium (HPGe) detectors while operating at high output count rates in the few 100 kcps to 1 Mcps range. The proposed work overcomes the high count-rate technical constraints of standard (high-capacitance) HPGe gamma-ray detectors by developing a multi-contact device with signal electrodes of a few pF capacitance. The technical approach combines the high electric field strength and intrinsically fast rise times of a planar detector with the collection efficiency of a coaxial device. Phase I will employ an electrostatic modeling program to investigate different multi-contact configurations on a 15 mm thick planar HPGe detector to calculate electrode capacitance and charge drift times, and to create a design that optimizes the geometry, contact width and spacing to meet or exceed the required specifications. The efficacy of the charge collection and capacitance model will be checked against measurements on an existing segmented HPGe planar detector. To gain sufficient collection efficiency for gamma-rays in the MeV range, the final detector design will use two back-to-back planar detectors. A second task in Phase I will be to design the detector housing, HPGe crystal mounts and internal connections, and explore options for the FETs and preamplifiers. An analysis of the electronic noise and the detection efficiency at 662 keV will also be made. Phase I will culminate with the design of the complete detector assembly and housing to be fabricated and tested in Phase II. We are in discussions with the leading segmented HPGe detector manufacturer for fabrication and eventual commercialization of the multi-contact detector. When combined with high rate multi-channel spectroscopy electronics, it is expected that the detector system will provide data throughput rates around 300 kcps per channel (at about 1 Mcps input) with electronic noise in the 500-600 eV FWHM range. This will present a significant advance for nuclear safeguards instrumentation with increased speed and accuracy of detection and identification in high count rate applications. As a unique tool for high rate and high resolution gamma spectroscopy, other applications are foreseen in areas such as medical imaging, and materials defect analysis by positron emission spectroscopy.

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