William K. Warburton

A MODULE FOR ENERGY AND PULSE SHAPE DATA ACQUISITION

Abstract This paper describes a 4-channel data acquisition module designed for use with multi-electrode semiconductor detectors of X-ray and γ-rays. It combines high-speed waveform sampling with digital filtering to acquire accurate energy spectra at high rates and, at the same time, capture and store precisely measured waveforms.

Single-channel beta-gamma coincidence detection of radioactive xenon using digital pulse shape analysis of phoswich detector signals

Monitoring radioactive xenon in the atmosphere is one of several methods used to detect nuclear weapons testing. To increase sensitivity, monitoring stations use a complex system of separate beta and gamma detectors to detect beta-gamma coincidences from the Xe isotopes of interest, which is effective but requires such careful gain matching and calibration that it is difficult to operate in the field. To simplify the system, a phoswich detector has been designed, consisting of optically coupled plastic and CsI scintillators to absorb beta particles and gamma rays, respectively. Digital pulse shape analysis (PSA) of the detector signal is used to determine if radiation interacted in either or both parts of the detector and to measure the energy deposited in each part, thus using only a single channel of readout electronics to detect beta-gamma coincidences and to measure both energies. Experiments with a prototype detector show that the technique can clearly separate event types, does not degrade the energy resolution, and has an error rate for detecting coincidences of less than 0.1%. Monte Carlo simulations of radiation transport and light collection in the proposed detector were performed to obtain optimum values for its design parameters and an estimate of the coincidence detection efficiency (82%-92%) and the background rejection rate (better than 99%).

Position resolution in a Ge-strip detector

We have investigated, both experimentally and theoretically, how to reconstruct in 3D the interaction positions for (gamma) -rays penetrating into a double-sized Ge cross trip detector. We found that when a suitable geometry is used, the 3D-reconstruction problem can be reduced to three 1D ones, which greatly simplifies the task. We report measurements on a 10mm thick detector with 2mm strip pitch, showing that at least 2mm position resolution can easily be achieved perpendicular to the detector plane. While the in- plane resolution is presently limited to the strip pitch we present work on progress in developing algorithms to improve this. This includes in particular the expected effects of the electronics and the interstrip capacitance on the signal shapes. Finally, we present captured waveforms that indicate the possibility of reconstructing more complex events such as Compton scattering.

An Evaluation of An Ultralow Background Alpha-Particle Detector

XIA has provided IBM with a prototype ultralow background alpha particle counter for evaluation. Results show a significant decrease in background compared to other commercial counters allowing for rapid measurement of low-emissivity materials.

The HgI2 array detector development project

Abstract There are various areas of synchrotron radiation research, particularly EXAFS on dilute solutions and anomalous scattering, which would strongly benefit from the availability of energy dispersive detector arrays having energy resolution of better than 300 eV at 6 keV and spatial resolution of 1 mm or better. The goal of this development project is to produce a robust ten-element submodule which possesses these characteristics and can be aggregated into larger arrays of 100–400 elements and arbitrary geometric shape. We report here on the projects current status. Major effort has occurred in several areas. We have developed techniques for producing multielement arrays on HgI 2 and constructed a testing system to evaluate our initial ideas for miniaturizing the array processing electronics. We have combined fiber optics with pulsed optical resetting in a novel way in order to be able to employ this reset scheme in the physically dense array environment. We present the results of crosstalk testing using this new scheme, as well as electronic-noise and energy-resolution results on a recently fabricated HgI 2 detector array. Finally, we describe our current progress in eliminating charge division between neighboring detector elements through the use of entrance window masking.

Alpha-Particle Emission Energy Spectra From Materials Used for Solder Bumps

The emitted alpha particle energy distribution from solder bumps can show substantial surface emission which has a large impact on the modeled SEU rate. State-of-the art alpha-particle detectors are required to measure the low emissivity and energy distribution.

Development of mercuric iodide detectors for XAS and XRD measurements

Abstract A prototype element for an energy dispersive detector (EDD) array was constructed using a mercuric iodide detector. Both detector and front end FET could be thermoelectrically cooled. Tested at SSRL, the detector had 250 eV electronic noise and 315 eV resolution at 5.9 keV. K line fluorescence spectra were collected for selected elements between Cl (2622 eV) and Zn (8638 eV). Count rate capability to 60 000 cps was demonstrated. Several detector parameters were measured, including energy linearity, resolution vs shaping time, and detector dead time. An EXAFS (extended X-ray absorption fine structure) spectrum was recorded and compared to simultaneously collected transmission data.

Study of silicon detectors for high resolution radioxenon measurements

Measurement of radioactive xenon in the atmosphere is one of several techniques to detect nuclear weapons testing, typically using either scintillator based coincidence beta/gamma detectors or germanium based gamma only detectors. Silicon detectors have a number of potential advantages over these detectors (high resolution, low background, sensitive to photons and electrons) and are explored in this work as a possible alternative. Using energy resolutions from measurements and detection efficiencies from simulations of characteristic electron and photon energies, the minimum detectable concentration for Xe isotopes was estimated for several possible detector geometries. Test coincidence spectra were acquired with a prototype detector.

Development of mercuric iodide energy dispersive X-ray array detectors

The authors consider that various areas of synchrotron radiation research, particularly extended X-ray absorption fine structure (EXAFS) on dilute solutions and anomalous scattering, would greatly benefit from the availability of energy-dispersive detector arrays with high-energy resolution and good spatial resolution. Mercuric iodide (HgI/sub 2/) detector submodules developed to meet this need are described. These submodules can be grouped into larger arrays of 100-400 elements. A prototype five-element HgI/sub 2/ array detector has been constructed and tested. Each element is 7.3 mm*0.7 mm. An energy resolution of 335 eV (FWHM) for Mn-K/sub alpha / at 5.9 keV has been introduced into the charge preamplifiers in order to minimize electronic crosstalk between channels. >

Development of Ta-Based Superconducting Tunnel Junction X-Ray Detector Arrays

We are developing new Ta-based superconducting tunnel junction (STJ) X-ray detectors for high-resolution soft X-ray spectroscopy at synchrotrons. STJ detectors combine the high-energy resolution of cryogenic detectors with the high count rate capabilities of athermal devices and the high efficiencies of solid state detectors, which increases the sensitivity for material analysis by fluorescence-detected X-ray absorption spectroscopy. Our STJ detectors are fabricated using thick, high-Z Ta absorber films that enhance quantum efficiency and spectral purity, and extend operational range to several keV compared with earlier Nb-based STJs. They offer an energy resolution of ~ 5 to 10 eV FWHM for soft X-rays up to ~1 keV, and count rates of several 1000 counts/s per detector pixel. For increased solid angle coverage, we have fabricated 36- and 112-pixel Ta-based STJ detector arrays with total areas of 1.4 and 4.5 mm2, respectively. The 208 × 208 μm2 pixels have an energy resolution between 6.8 and 7.6 eV FWHM at 525 eV with a low-energy shoulder, and their responsivity is uniform to within 2% across the array. Here we discuss the performance of the array in the context of synchrotron science.