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Monolithic CsI(TI) scintillators coupled to a position sensitive photomultiplier tube (PSPMT) have been tested for imaging and environmental performance necessary for hard X-ray astrophysics missions. Using a crossed-wire PSPMT and individual anode-wire readout, a spatial resolution of 1-2 mm rms at 60 keV over the entire photo-cathode imaging surface is obtained out to near the edges of the scintillator. A PSPMT mapping correction was used to obtain an energy resolution close to what is expected from CsI(TI) scintillators. We have also tested pixellated scintillators and find an equivalent spatial resolution but with an energy resolution which is unacceptable for our applications.

Germanium strip detectors combine the excellent energy resolution possible with germanium detectors with fine two-dimensional spatial resolution determined by orthogonal strip electrodes. We are testing a detector with an active volume of 5/spl times/5/spl times/1 cm/sup 3/ and a total of 50 electrodes, 25 on each side with a 2 mm pitch. Potential astrophysics applications include use as a focal plane for a coded-aperture telescope in the energy range /spl sim/5-500 keV, as the focal plane of a grazing-incidence telescope in the /spl sim/5-100 keV band, or in a Compton scatter telescope. The utilization of germanium strip detectors for these applications requires proof of their performance capabilities in terms of energy and spatial resolution, and efficiencies for single and multi-pixel interactions. In this paper, we demonstrate the excellent spectroscopy and imaging performance of a 2 mm pitch strip detector, and report on the results of Monte-Carlo simulations of photopeak efficiencies for single and multi-pixel interactions. These simulations show that 2-pixel interactions are a significant fraction of the photopeak efficiency in the 80-500 keV range. We demonstrate that these interactions can be used to measure linear polarization of a normally incident beam.

We have implemented a capacitive charge-division readout for a germanium 5/spl times/5 orthogonal strip detector. We present measurements of non-linearity, and of energy and position resolution as a function of energy (60 and 662 keV) and of network capacitance. Energy and position non-linearities, which are worse for low capacitance networks, appear in the response along the charge division network, as well as along the length of each detector strip. The nonlinearities can be corrected by using an independent gain calibration for each pixel, allowing for use of a lower capacitance charge division network which provides better position resolution. >

A low-power CMOS peak detecting track and hold circuit optimized for nuclear pulse spectroscopy is presented. The circuit topology eliminates the need for a rectifying diode, reducing the effect of charge injection into the hold capacitor, incorporates a linear gate at the input to prevent pulse pileup, and uses dynamic bias control that minimizes both pedestal and droop. Both positive-going and negative-going pulses are accommodated using a complementary set of track and hold circuits. Full characterization of the design fabricated in 1.2 /spl mu/m CMOS including dynamic range, integral nonlinearity, droop rate, pedestal, and power measurements is presented. The circuit operates with only 250 /spl mu/w for input pulses with 7 /spl mu/s peaking time. Power consumption was increased to 750 /spl mu/w for driving off-chip and test system capacitances. Analysis and design approaches for optimization of operational characteristics are also discussed. >

Germanium strip detectors combine superior spectroscopy typical of germanium detectors with good spatial resolution. Our work has been to develop a 2-dimensional position readout of a 5 × 5 strip X–Y detector. The prototype device uses two capacitive charge division strings. Each string is read out by two 13 bit ADCs, one on each end of the string. The four data channels are stored as an event list for subsequent processing. We form a response map over the detector surface in order to locate the position of each interaction with the spatial resolution of the strip pitch, in our case 9 mm. Cross-talk and non-linearities are removed using the response map. Energy resolution of 5–6 keV FWHM is achieved between 60 and 662 keV across the full surface of the detector.

We have developed a low noise, low power charge sensitive amplifier and pulse shaping circuit. Our application is for a double-sided germanium strip detector, nominally providing 50 independent spectroscopy channels. An array of these detectors would provide significant improvements in imaging, spectroscopy, and sensitivity for space-based gamma-ray astronomy. The key features of these electronics are low noise, very low power, and small footprint per channel. Performance of our first circuit is in good agreement with simulations, with /spl sim/205e noise rms (0 pF), and 3 mW/channel power consumption. Dynamic range is 0-3.3 MeV (germanium) with a linearity of /spl plusmn/0.6%. Performance of this prototype device will be discussed. >

Low temperature detectors promise an order of magnitude improvement over semiconducting devices in energy resolution, spatial resolution and radiation hardness. Within this broad field, bolometers and superconducting tunnel junctions are reviewed and potential applications for accelerator based experiments are examined. Our own experiments using Sn, In, Sn(Sb) and In(Bi) alloy based superconducting grain detectors have demonstrated excellent reproducibility and uniformity.

We present an instrument concept called GIPSI that uses germanium strip detectors in an imaging system to provide narrow line sensitivity less than 8.0 multiplied by 10-6 gamma cm-2s-1 at 100 keV in a 2 week exposure (3 sigma), and which has a point spread function (spatial resolution of approximately 20 arc minutes rms. The germanium strip detectors also make an excellent polarimeter by capitalizing on the angular dependence of the Compton scattering cross section. Gamma-ray polarimetry in the energy band around 60 - 300 keV is an interesting area of high energy astrophysics where observations have not been possible with the technologies employed in current and past space missions. We have tested a prototype detector with polarized beams and have measured a modulation factor of approximately 0.8 at 100 keV. A sensitive instrument can be realized on a modest space mission or a long duration balloon flight. Linear polarization can be detected in sources such as the Crab Pulsar, Cen A, Cyg X-1, and solar flares down to less than 5% of the source flux. The proposed instrument would have a collecting area of 400 cm2.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new balloon instrument, the advanced thin ionization calorimeter (ATIC), is currently under development by an international collaboration involving researchers in the U.S., Germany, Korea, Russia and the Ukraine. The instrument will be used, in a series of long duration balloon flights, to investigate the charge composition and energy spectra of primary cosmic rays over the energy range from about 1010 to 1014 eV. The ATIC instrument is designed around a new technology, fully active Bismuth Germanate (BGO) ionization calorimeter that is used to measure the energy deposited by the cascades formed by particles interacting in an approximately 1 proton interaction length thick carbon target. The charge module comprises a highly segmented, triply redundant set of detectors (scintillator, silicon matrix and Cherenkov) that together give good incident charge resolution plus rejection of the 'backscattered' particles from the interaction. Trajectory information is obtained both from scintillator layers and from the cascade profile throughout the BGO calorimeter. This instrument is specifically designed to take advantage of the existing NASA long duration balloon flight capability in Antarctica and/or the Northern Hemisphere. The ATIC instrumentation is presented here, while a companion paper at this conference discusses the expected performance.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Burst locations with an arc second telescope (BLAST) is a new mission concept being studied for NASA's medium explorer (MIDEX) mission opportunities. The principal scientific objectives of the BLAST mission are (1) to localize gamma- ray burst (GRB) positions to arcsec accuracy; (2) to search for enhancements in the rate of GRBs toward M31; and (3) to conduct the most sensitive sky survey to date of x-ray sources in the 7 - 200 keV regime. These objectives are achieved using a large array of position-sensitive scintillation detectors with a total area of 17,000 cm2. This array is combined with a large field of view telescope (greater than 1 steradian) comprising two separate imaging systems. A coded aperture telescope provides arcminute source localization. For low energy x-rays (less than 50 keV), the aperture is also defined by phase modulation grids with provide complementary arcsecond information. The grid system consists of two aperture planes with 'checker board' patterns of slightly different pitch. The beating between the two grid pitches casts a broad interference pattern on the detector plane. Determining the phase of this interference pattern in both coordinates gives the location of a point source source in the sky, with aliased positions at approximately 1 arcmin spacing. The arcmin ambiguity is resolved by the coded aperture image. BLAST has a sensitivity to bursts of 0.03 photons cm-2 s-1, almost ten times more sensitive than BATSE. We expect to position 20 bursts per year to better than 2 arcsec accuracy and 35 bursts per year to better than 5 arcsec. BLAST will provide an all sky survey in hard x-rays with a sensitivity of 0.2 milliCrab at low energies.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We describe the use of position sensitive planar germanium detectors in a Compton telescope/camera. This Compton telescope achieves the very good energy resolution (/spl Delta/Etotal

Germanium strip detectors combine both the excellent energy resolution typical of germanium detectors and fine spatial resolution possible in a strip detector. They are applicable to sensitive, high spectral resolution γ-ray detectors using coded-aperture or Compton telescope techniques. Our first detector is in a planar geometry with orthogonal strips on the upper and lower detector surfaces, providing 9 mm spatial resolution. The detector has 5 strips on each surface and an active volume of 45 x 45 x 12 mm. Good spatial and energy resolution are demonstrated.

We investigate the characteristics of imaging systems in the 20 keV - 10 MeV energy band which incorporate the high spatial and spectral resolution of planar germanium strip detectors. A Compton scatter telescope provides sensitivity above approximately 250 keV; a coded aperture positioned above the top germanium detector plane of the Compton telescope forms a coded-aperture telescope with sensitivity in the 20 – 250 keV band. The high spectral resolution and spatial resolution of germanium strip detectors provides a Compton telescope with dramatically improved energy resolution, angular resolution, and sensitivity compared with previous Compton instruments. Such a system has excellent angular response for point source identification and spectroscopy and also provides response to high energy diffuse emissions such as the Galactic 511 keV line emission and 26A1 emission. Monte Carlo simulations of the concept and estimates of the sensitivity shall be presented.

The exceptionally short Ginzburg-Landau coherence length of the high temperature superconductor YBa 2 Cu 3 O 7−δ makes possible the observation of fluctuation effects near the transition from the normal to the superconducting state. At the time of this writing, observations of fluctuation contributions to the electrical conductivity,1 magnetic susceptibility2 and thermopower3 have been reported. Excess contributions to the heat capacity (C fl ) due to thermal fluctuations, though far more difficult to observe, have been noted by several researchers.4 The heat capacity measurements are of particular interest, as a comparison of C fl above and below T c may elucidate the number of components of the Ginzburg-Landau (GL) order parameter and hence the nature of the pairing. The behavior of the heat capacity in an applied magnetic field is distinctly different from that of an ordinary superconductor.5 We summarize here our results on heat capacity measurements in zero field and in an applied magnetic field.

An Advanced Thin Ionization Calorimeter (ATIC) will be used to investigate the charge composition and energy spectra of primary cosmic rays over the energy range from about 10 10 to >10 14 eV in a series of long-duration balloon flights. The totally active BGO calorimeter, 22 radiation length thick, will measure the electromagnetic energy ensuing from nuclear interactions in a one interaction length thick carbon target. Trajectory information will be obtained from the location of the cascade axis in the BGO calorimeter and in the segmented scintillator layers of the upstream carbon target. The highly segmented charge module comprised of scintillator strips, a silicon matrix, and a Cherenkov array will minimize the effect of backscattered particles on primary charge measurements. While obtaining new high priority scientific results, the ATIC balloon payload can also serve as a proof of concept, or engineering model, for a BGO calorimeter-based instrument on the International Space Station. We examine the added advantage of locating such an experiment for long durations on a platform such as the Space Station.