21 research outputs found
Improving Photoelectron Counting and Particle Identification in Scintillation Detectors with Bayesian Techniques
Many current and future dark matter and neutrino detectors are designed to
measure scintillation light with a large array of photomultiplier tubes (PMTs).
The energy resolution and particle identification capabilities of these
detectors depend in part on the ability to accurately identify individual
photoelectrons in PMT waveforms despite large variability in pulse amplitudes
and pulse pileup. We describe a Bayesian technique that can identify the times
of individual photoelectrons in a sampled PMT waveform without deconvolution,
even when pileup is present. To demonstrate the technique, we apply it to the
general problem of particle identification in single-phase liquid argon dark
matter detectors. Using the output of the Bayesian photoelectron counting
algorithm described in this paper, we construct several test statistics for
rejection of backgrounds for dark matter searches in argon. Compared to simpler
methods based on either observed charge or peak finding, the photoelectron
counting technique improves both energy resolution and particle identification
of low energy events in calibration data from the DEAP-1 detector and
simulation of the larger MiniCLEAN dark matter detector.Comment: 16 pages, 16 figure
Radon backgrounds in the DEAP-1 liquid-argon-based Dark Matter detector
The DEAP-1 \SI{7}{kg} single phase liquid argon scintillation detector was
operated underground at SNOLAB in order to test the techniques and measure the
backgrounds inherent to single phase detection, in support of the
\mbox{DEAP-3600} Dark Matter detector. Backgrounds in DEAP are controlled
through material selection, construction techniques, pulse shape discrimination
and event reconstruction. This report details the analysis of background events
observed in three iterations of the DEAP-1 detector, and the measures taken to
reduce them.
The Rn decay rate in the liquid argon was measured to be between 16
and \SI{26}{\micro\becquerel\per\kilogram}. We found that the background
spectrum near the region of interest for Dark Matter detection in the DEAP-1
detector can be described considering events from three sources: radon
daughters decaying on the surface of the active volume, the expected rate of
electromagnetic events misidentified as nuclear recoils due to inefficiencies
in the pulse shape discrimination, and leakage of events from outside the
fiducial volume due to imperfect position reconstruction. These backgrounds
statistically account for all observed events, and they will be strongly
reduced in the DEAP-3600 detector due to its higher light yield and simpler
geometry
Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy beta and nuclear recoils in liquid argon with DEAP-1
The DEAP-1 low-background liquid argon detector was used to measure
scintillation pulse shapes of electron and nuclear recoil events and to
demonstrate the feasibility of pulse-shape discrimination (PSD) down to an
electron-equivalent energy of 20 keV.
In the surface dataset using a triple-coincidence tag we found the fraction
of beta events that are misidentified as nuclear recoils to be (90% C.L.) for energies between 43-86 keVee and for a nuclear recoil
acceptance of at least 90%, with 4% systematic uncertainty on the absolute
energy scale. The discrimination measurement on surface was limited by nuclear
recoils induced by cosmic-ray generated neutrons. This was improved by moving
the detector to the SNOLAB underground laboratory, where the reduced background
rate allowed the same measurement with only a double-coincidence tag.
The combined data set contains events. One of those, in the
underground data set, is in the nuclear-recoil region of interest. Taking into
account the expected background of 0.48 events coming from random pileup, the
resulting upper limit on the electronic recoil contamination is
(90% C.L.) between 44-89 keVee and for a nuclear recoil
acceptance of at least 90%, with 6% systematic uncertainty on the absolute
energy scale.
We developed a general mathematical framework to describe PSD parameter
distributions and used it to build an analytical model of the distributions
observed in DEAP-1. Using this model, we project a misidentification fraction
of approx. for an electron-equivalent energy threshold of 15 keV for
a detector with 8 PE/keVee light yield. This reduction enables a search for
spin-independent scattering of WIMPs from 1000 kg of liquid argon with a
WIMP-nucleon cross-section sensitivity of cm, assuming
negligible contribution from nuclear recoil backgrounds.Comment: Accepted for publication in Astroparticle Physic
Physical design for reliability of solder joint interconnections for application in aerospace electronics
The problem and the challenge of the physical (mechanical) design for reliability of solder joint interconnections (SJIs) for aerospace electronics is addressed and some practically useful solutions to this problem are suggested and discussed in detail. The considered problem includes: 1) the possibility of avoiding inelastic strains in the solder material; 2) quantification, on the probabilistic basis, the expected lifetime of the SJI of interest; and 3) possible replacement of the temperature cycling accelerated testing with a more physically meaningful, less costly and less time-and labor consuming low-temperature/random-vibration bias. The general concepts are illustrated by numerical examples
Semiconductor Film Grown on a Circular Substrate: Predictive Modeling of Lattice-Misfit Stresses
Power core (PC) embedding a plurality of IC devices and sandwiched between two dissimilar insulated metal substrates (IMSâ): predicted thermal stresses
Assessed Interfacial Strength and Elastic Moduli of the Bonding Material From Shear-Off Test Data
A simple and physically meaningful analytical stress model is developed in application to shear-off testing with an objective to evaluate the interfacial shearing stress in the bonding material from the measured shear off force. The model can be used also for the evaluation of the shear modulus of the bonding material, if the interfacial displacement is also measured. The general concept is illustrated by a numerical example. In the authorsâ opinion, the suggested methodology, based on the concept of the interfacial compliance, suggested by the first author in his 1986 ASME J. Appl. Mech. paper, could become a basis for a new effective experimental method for assessing the interfacial shearing strength and elastic moduli of the bonding material in electronics. The methodology can be used particularly in application to the recently suggested sintered silver bonding materials to evaluate their bonding strength from the measured force-at-failure and shear modulus from the measured shearing force and displacement
Time dependent and temperature dependent properties of the forward voltage characteristic of InGaN high power LEDs
Estimating the junction temperature and its dynamic behavior in dependence of various operating conditions is an important issue, since these properties influence the optical characteristics as well as the aging processes of a light-emitting diode (LED). Particularly for high-power LEDs and pulsed operation, the dynamic behavior and the resulting thermal cycles are of interest. The forward voltage method relies on the existence of a time-independent unique triple of forward-voltage, forward-current, and junction temperature. These three figures should as well uniquely define the optical output power and spectrum, as well as the loss power of the LED, which is responsible for an increase of the junction temperature. From transient FEM-simulations one may expect an increase of the temperature of the active semiconductor layer of some 1/10 K within the first 10 ÎŒs. Most of the well-established techniques for junction temperature measurement via forward voltage method evaluate the measurement data several dozens of microseconds after switching on or switching off and estimate the junction temperature by extrapolation towards the time of switching. In contrast, the authors developed a measurement procedure with the focus on the first microseconds after switching. Besides a fast data acquisition system, a precise control of the switching process is required, i.e. a precisely defined current pulse amplitude with fast rise-time and negligible transient by-effects. We start with a short description of the measurement setup and the newly developed control algorithm for the generation of short current pulses. The thermal characterization of the LED chip during the measurement procedures is accomplished by an IR thermography system and transient finite element simulations. The same experimental setup is used to investigate the optical properties of the LED in an Ulbricht-sphere. Our experiments are performed on InGaN LED chips mounted on an Al based insulated metal substrate (IMS), giving a comprehensive picture of the transient behavior of the forward voltage of this type of high power LED
Thermal benchmark of a classic and novel embedded high-power 3-phase inverter Bridge
A 3-phase high power inverter bridge for a 500 W PEDELEC motor fabricated using a novel embedding technology was benchmarked against a classically designed module using MOSFETs in a B6 Bridge. By operating each MOSFET individually in reverse mode and measuring the forward voltage during high current operation and after switching to a measuring current of 50 mA the junction temperature has been measured. Equivalent thermal resistances used for comparison have been calculated. By reverse modelling the thermal behaviour of the entire module including the MOSFETs' junction temperatures at full operation has been established. The study is extended to an embedded 50kW-demonstrator design for electric vehicle applications where the thermal resistances were studied and the maximum allowable boundary conditions predicted by simulation