Cristina Plettner

Single-Event-Upset Critical Charge Measurements and Modeling of 65 nm Silicon-on-Insulator Latches and Memory Cells

Experimental and modeling results are presented on the critical charge required to upset exploratory 65 nm silicon-on-insulator (SOI) circuits. Using a mono-energetic, collimated, beam of particles the charge deposition was effectively modulated and modeled

A technique for measuring the energy resolution of low-Z scintillators

Scintillator-based Compton cameras for remote localization and identification of radio nuclides require scatter detectors made of low-Z materials. The energy resolution of such detectors in a range dominated by Compton scattering is a crucial parameter. It has to be known for performance estimates, and it must be quantified and optimized for detector designs to be used in real systems, but it is hard to measure. The Compton Coincidence Technique (CCT) appears to be the best method for reliable and direct measurements, but appropriate facilities are expensive. This paper suggests and investigates a modified CCT which provides less expensive means for qualifying of scatter detectors in a reasonable time frame. The assembly consists of a single HPGe detector, the scatter detector to be investigated, and one or more common gamma sources in close geometry. Pulse height and timing information from both detectors is gathered by multi-parameter data acquisition. Coincidences of both detectors are due to a plurality of Compton scattering angles and corresponding energy transfers. A thorough data analysis then allows extracting the detector resolution as well as the non-linearity as a function of energy from data sets measured within hours. Results obtained for NaI and plastic scatter detectors will be presented and discussed.

A Comparative Study of Silicon Drift Detectors With Photomultipliers, Avalanche Photodiodes and PIN Photodiodes in Gamma Spectrometry With LaBr

The performance of a silicon drift detector (SDD) with an integrated FET, delivered by the company PNSensor, Munich, Germany, was studied in gamma spectrometry at room temperature (23-25degC) with a LaBr3:Ce crystal of 6 mm diameter and 6 mm height. The SDD characteristics were compared with those measured with a Photonis XP5212 photomultiplier, a Large Area Avalanche Photodiode (LAAPD) of Advanced Photonix, Inc., and a Hamamatsu S3590-18 Photodiode (PD). Energy resolution versus gamma ray energies and its components related to the photoelectron/electron-hole pair statistics and dark noise were measured and compared. At low energies, below 100 keV, the light readout by the photomultiplier gives the best results, while for high energies, above 300 keV, the light readout by the SDD delivers superior energy resolution. In particular, the best energy resolution of 2.7% was determined for 662 keV gamma rays from a 137Cs source.

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Non-proportionality of light yield and energy resolution of Compton electrons in three scintillators (LaBr3:Ce, LYSO:Ce and CsI:Tl) were studied in a wide energy range from 10 keV up to 1 MeV. The experimental setup was comprised of a High Purity Germanium detector and tested scintillators coupled to a photomultiplier. Probing the non-proportionality and energy resolution curves at different energies was obtained by changing the position of various radioactive sources with respect to both detectors. The distance between both detectors and source was kept small to make use of Wide Angle Compton Coincidence (WACC) technique, which allowed us to scan large range of scattering angles simultaneously and obtain relatively high coincidence rate of 100 cps using weak sources of about 10 μCi activity. The results are compared with those obtained by direct irradiation of the tested scintillators with gamma-ray sources and fitting the full-energy peaks.

Crystals

A method based on the Compton coincidence technique was applied to study the energy resolution of Compton electrons in wide energy range. The experimental setup was comprised of a High Purity Germanium (HPGe) detector and a LaBr3:Ce scintillator coupled to a photomultiplier. The detectors were set in a face-to-face geometry and the source was placed between them. Thus gating on events backscattered in the scintillator and detected in HPGe allowed one to measure the energy resolution of Compton scattered electrons at an energy corresponding to the Compton edge for a given source. This study confirms the importance of the electron scattering (6-rays) as the main component of the intrinsic resolution in scintillators. The results are particularly important for discussion of the light yield non-proportionality contribution to the energy resolution of scintillators.

Non-Proportionality of Electron Response and Energy Resolution of Compton Electrons in Scintillators

The concept of a two-plane planar Compton camera, consisting of scintillation detector elements, is presented. Several materials as C<inf>9</inf>H<inf>10</inf>, CaF<inf>2</inf>, YAlO<inf>3</inf>, NaI, and LaBr<inf>3</inf> are considered for operation in the scatter and/or absorption plane. The performance of the Compton camera is optimized by means of Monte Carlo simulations to meet the requirements for Homeland Security applications. For a low-threshold detector system we propose to utilize C<inf>9</inf>H<inf>10</inf> or CaF<inf>2</inf> for the scatter plane and NaI or LaBr<inf>3</inf> for the absorption plane. Particular effort must be focused to achieve low energy thresholds in particular for the detectors of the scatter plane if photons of incident energies below 200 keV are to be detected with reasonable efficiencies.

Energy Resolution of Compton Electrons in LaBr

This paper describes techniques for mitigating single event upsets in master-slave flip-flop latches in 65 nm SOI device technology. Techniques are explained, modeled, and measured with hardware experiments.

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A novel concept for improving gamma ray spectroscopy in compact instruments is presented. The dual-range photon detector (DRPD) consists of a silicon drift detector (SDD) which is optically coupled with a LaBr3(Ce3+) crystal. In contrast to similar configurations investigated so far the SDD points to the radiation source. Pulse shape discrimination allows separating the distinct detection mechanisms which correspond to gamma absorption in the SDD or in the scintillator, respectively. This arrangement combines for the first time the excellent performance of an SDD as X-ray detector on its own with the striking energy resolution of a LaBr3(Ce3+) scintillator read out by an SDD. The concept was successfully demonstrated with two experimental SDD-LaBr3(Ce3+) systems. An energy resolution (FWHM) of 2.7% and 2.9% at 662 keV was measured with the two distinct systems operated in scintillator mode whereas scintillator-photomultiplier combinations with the same crystals yielded only 3.3% and 3.1%, respectively. The SDD mode provided an energy resolution surpassing the scintillator resolution by about one order of magnitude in the limited energy range up to 100 keV. Measurements with various radioactive sources demonstrated that this mode uncovers line structures which could never be resolved with scintillators or CZT detectors. Homeland security programs could profit from the proposed detector concept.

:Ce Scintillator

Compton cameras are of general interest in various fields of operation. Because of the ability to locate and identify remote sources, homeland security supports the development of such devices in a rugged and reliable form. The decisions upon appropriate materials for the scatter- and absorber plane depend on performance and economical trade-offs. In order to estimate the expected performance of the Compton camera, simulations are necessary. Certain experimentally determined parameters have to be fed into simulations, such as the energy resolution of the detector. Two materials with low effective atomic number (Zeff), CaF2 and plastic, promise to be good candidates for the scattering plane. Those scintillators are known for quite some time, but not very well characterized with respect of energy resolution and nonlinearity. A modified Compton coincidence technique using a high purity Germanium (HPGe) detector in coincidence with the investigated scintillator is discussed in this paper: The wide-angle Compton-coincidence (WACC) setup provides a fast and reliable means for characterization of low-Z scintillators. For quality control purposes, the actual scatter detector can be monitored in-house using the WACC technique. This work presents results of different scintillator materials and sizes for validation and exploration of this method.

Concept study of a two-plane Compton camera designed for location and nuclide identification of remote radiation sources

Performance of a He-3 counter and a B-10 loaded liquid scintillator EJ309B5 has been studied in terms of neutron detection efficiency. The measurements were carried out in a mixed field of neutron and gamma radiation from an intense ( ~ 106 neutrons/s/4π)252Cf source. The response of both detectors to background and high intensity gamma radiation ( ~ 100 μSv/h at a detector) from a 60Co source has been measured to establish background count rate and gamma rays cut-off point, respectively. The analysis showed that the properties of a He-3 counter are significantly better than that of EJ309B5. However, it has been pointed out how to improve the performance of a liquid scintillator in order to reduce gamma radiation sensitivity.