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CryoFree Final Report

Description: CryoFree, a gamma-ray spectrometer, has been built and successfully tested. This instrument is based on a planar germanium semiconductor detector and is optimized for high-resolution spectroscopy in the range of a 30 keV to a few hundred keV to detect U and Pu. The spectrometer is cooled with a mechanical cryocooler that obviates the need for liquid cryogen. Furthermore, the instrument is battery powered. The combination of mechanical cooling and battery operation allows high-resolution spectroscopy in a highly-portable field instrument. A description of the instrument along with its performance is given.
Date: November 7, 2006
Creator: Burks, M
Partner: UNT Libraries Government Documents Department

A Compton-Vetoed Germanium Detector with Increased Sensitivity at Low Energies

Description: The difficulty to directly detect plutonium in spent nuclear fuel due to the high Compton background of the fission products motivates the design of a Gamma detector with improved sensitivity at low energies. We have built such a detector by operating a thin high-purity Ge detector with a large scintillator Compton veto directly behind it. The Ge detector is thin to absorb just the low-energy Pu radiation of interest while minimizing Compton scattering of high energy radiation from the fission products. The subsequent scintillator is large so that forward scattered photons from the Ge detector interact in it at least once to provide an anti-coincidence veto for the Ge detector. For highest sensitivity, additional material in the line-of-sight is minimized, the radioactive sample is kept thin, and its radiation is collimated. We will discuss the instrument design, and demonstrate the feasibility of the approach with a prototype that employs two large CsI scintillator vetoes. Initial spectra of a thin Cs-137 calibration source show a background suppression of a factor of {approx}2.5 at {approx}100 keV, limited by an unexpectedly thick 4 mm dead layer in the Ge detector.
Date: March 29, 2012
Creator: Friedrich, S; Bates, C; Drury, O B; Burks, M & DiPrete, D
Partner: UNT Libraries Government Documents Department

Methods for increasing the efficiency of Compton imagers

Description: A Compton scatter camera based on position sensitive, planar Ge and Si(Li) detectors with segmented electrodes is being developed at LLNL. This paper presents various methods that were developed to increase the position resolution of the detectors, the granularity and capability to reconstruct the scattering sequence of the gamma-ray within the detectors. All these methods help to increase the efficiency of the imager, by accepting more photons in the final image. The initial extent and diffusion of charge-carrier clouds inside the semiconductor detectors are found to affect profoundly the fraction of interactions that deposit charge in multiple adjacent electrodes. An accurate identification of these charge-shared interactions is a key factor in correctly reconstructing the position of interactions in the detector.
Date: November 15, 2005
Creator: Mihailescu, L; Vetter, K; Burks, M; Chivers, D; Cunningham, M; Gunter, D et al.
Partner: UNT Libraries Government Documents Department

An ionization chamber shower detector for the LHC Luminosity Monitor

Description: The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the Large Hadron Collider (LHC) each absorb approximately 1.8 TeV of forward collision products on average per pp interaction (~;;235W at design luminosity 1034cm-2s-1). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. A novel segmented, multi-gap, pressurized gas ionization chamber is being developed for sampling the energy deposited near the maxima of the hadronic/ electromagnetic showers in these absorbers. The system design choices have been strongly influenced by optimization of signal to noise ratio and by the very high radiation environment. The ionization chambers are instrumented with low noise, fast, pulse shaping electronics to be capable of resolving individual bunch crossings at 40 MHz. Data on each bunch are to be separately accumulated over multiple bunch crossings until the desired statistical accuracy is obtained. At design luminosity approximately 2x103 bunch crossings will suffice for a 1percent luminosity measurement. In this paper we report the first experimental results of the ionization chamber and analog electronics. Single 450GeV protons from the SPS at CERN are used to simulate the hadronic/electromagnetic showers produced by the forward collision products from the interaction regions of the LHC.
Date: October 1, 2000
Creator: Speziali, V.; Beche, J.F.; Burks, M.T.; Datte, P.S.; Haguenauer, M.; manfredi, P.F. et al.
Partner: UNT Libraries Government Documents Department

Imaging Performance of the Si/Ge Hybrid Compton Imager

Description: The point spread function (PSF) of a fully-instrumented silicon/germanium Compton telescope has been measured as a function of energy and angle. Overall, the resolution ranged from 3{sup o} to 4{sup o} FWHM over most of the energy range and field of view. The various contributions to the resolution have been quantified. These contributions include the energy uncertainty and position uncertainty of the detector; source energy; Doppler broadening; and the 1/r broadening characteristic of Compton back-projection. Furthermore, a distortion of the PSF is observed for sources imaged off-axis from the detector. These contributions are discussed and compared to theory and simulations.
Date: November 10, 2005
Creator: Burks, M; Chivers, D; Cork, C; Cunningham, M; Fabris, L; Gunter, D et al.
Partner: UNT Libraries Government Documents Department

First-Generation Hybrid Compact Compton Imager

Description: At Lawrence Livermore National Laboratory, we are pursuing the development of a gamma-ray imaging system using the Compton effect. We have built our first generation hybrid Compton imaging system, and we have conducted initial calibration and image measurements using this system. In this paper, we present the details of the hybrid Compton imaging system and initial calibration and image measurements.
Date: November 7, 2005
Creator: Cunningham, M; Burks, M; Chivers, D; Cork, C; Fabris, L; Gunter, D et al.
Partner: UNT Libraries Government Documents Department

Development of a detector for bunch by bunch measurement and optimization of luminosity in the LHC

Description: The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the LHC each absorb approximately 1.8TeV of forward collision products on average per pp interaction ({approximately}235W at design luminosity 1034cm-2s-1). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. Novel segmented, multi-gap, pressurized gas ionization chambers are proposed for sampling the energy deposited near the maxima of the hadronic/ electromagnetic showers in these absorbers. The system design choices have been strongly influenced by optimization of signal to noise ratio and by the very high radiation environment. The ionization chambers are instrumented with state of the art low noise, fast, pulse shaping electronics capable of resolving individual bunch crossings at 40 MHz. Data on each bunch are separately accumulated over multiple bunch crossings until the desired statistical accuracy is obtained. At design luminosity approximately 2x103 bunch crossings suffice for a 1% luminosity measurement.
Date: May 19, 2000
Creator: Turner, W.C.; Burks, M.T.; Datte, P.S.; Manfredi, P.F.; Millaud, J.E.; Mokhov, N.V. et al.
Partner: UNT Libraries Government Documents Department