John F. Krizmanic

The Absolute Flux of Protons and Helium at the Top of the Atmosphere Using IMAX

The cosmic-ray proton and helium spectra from 0.2 GeV nucleon^(-1) to about 200 GeV nucleon^(-1) have been measured with the balloon-borne experiment Isotope Matter-Antimatter Experiment (IMAX) launched from Lynn Lake, Manitoba, Canada, in 1992. IMAX was designed to search for antiprotons and light isotopes using a superconducting magnet spectrometer together with scintillators, a time-of-flight system, and Cherenkov detectors. Using redundant detectors, an extensive examination of the instrument efficiency was carried out. We present here the absolute spectra of protons and helium corrected to the top of the atmosphere and to interstellar space. If demodulated with a solar modulation parameter of Φ = 750 MV, the measured interstellar spectra between 20 and 200 GV can be represented by a power law in rigidity, with (1.42 ± 0.21) × 10^4R^(-2.71±0.04) (m^2 GV s sr)^(-1) for protons and (3.15 ± 1.03) × 10^3R^(-2.79±0.08) (m^2 GV s sr)^(-1) for helium.

Development of a deep silicon phase Fresnel lens using Gray-scale lithography and deep reactive ion etching

We report the first fabrication and development of a deep phase Fresnel lens (PFL) in silicon through the use of gray-scale lithography and deep-reactive ion etching (DRIE). A Gaussian tail approximation is introduced as a method of predicting the height of photoresist gray levels given the relative amount of transmitted light through a gray-scale optical mask. Device mask design is accomplished through command-line scripting in a CAD tool to precisely define the millions of pixels required to generate the appropriate profile in photoresist. Etch selectivity during DRIE pattern transfer is accurately controlled to produce the desired scaling factor between the photoresist and silicon profiles. As a demonstration of this technology, a 1.6-mm diameter PFL is etched 43 /spl mu/m into silicon with each grating profile designed to focus 8.4 keV photons a distance of 118 m.

Observing the Ultrahigh Energy Universe with OWL Eyes

The goal of the Orbiting Wide-field Light-collectors ( OWL ) mission is to study the origin and physics of the highest energy particles known in nature, the ultrahigh energy cosmic rays (UHECRs). The OWL mission consists of telescopes with UV sensitive cameras on two satellites operating in tandem to view in stereo the development of the giant particle showers induced in the Earths atmosphere by UHECRs. This paper discusses the characteristics of the OWL mission.

The Milli-Arc-Second Structure Imager, MASSIM: A New Concept for a High Angular Resolution X-ray Telescope

MASSIM, the Milli-Arc-Second Structure Imager, is a mission that has been proposed for study within the context of NASAs Astrophysics Strategic Mission Concept Studies program. It uses a set of achromatic diffractive-refractive Fresnel lenses on an optics spacecraft to focus 5-11 keV X-rays onto detectors on a second spacecraft flying in formation 1000 km away. It will have a point-source sensitivity comparable with that of the current generation of major X-ray observatories (Chandra, XMM-Newton) but an angular resolution some three orders of magnitude better. MASSIM is optimized for the study of jets and other phenomena that occur in the immediate vicinity of black holes and neutron stars. It can also be used for studying other astrophysical phenomena on the milli-arc-second scale, such as those involving proto-stars, the surfaces and surroundings of nearby active stars and interacting winds. We describe the MASSIM mission concept, scientific objectives and the trade-offs within the X-ray optics design. The anticipated performance of the mission and possible future developments using the diffractive-refractive optics approach to imaging at X-ray and gamma-ray energies are discussed.

Radiation damage and activation of CdZnTe by intermediate energy neutrons

We exposed a CdZnTe detector to MeV neutrons from a 252Cf source and found no performance degradation for fluences below 1010 neutrons cm-2. Detector resolution did show significant degradation at higher neutron fluences. There is evidence of room temperature annealing of the radiation effects over time. Activation lines were observed and the responsible isotopes were identified by the energy and half-life of the lines. These radiation damage studies allow evaluation of the robustness of CdZnTe detectors in high neutron and radiation environments.

CdZnTe strip detector for arcsecond imaging and spectroscopy

A CdZnTe strip detector array with capabilities for arc second imaging and spectroscopy is being developed for a space flight gamma-ray burst instrument. Two dimensional strip detectors with 100 micrometers pitch have been fabricated and wire bonded to readout electronics to demonstrate the ability to localize 22 to 122 keV photons to less than 100 micrometers. In addition, good spectral resolution has been achieved. The uniformity of response and relative efficiency of the strip detector will be discussed. Results form electrical characterization which include strip leakage current and strip capacitance will be presented.

CALET UPPER LIMITS on X-RAY and GAMMA-RAY COUNTERPARTS of GW151226

We present upper limits in the hard X-ray and gamma-ray bands at the time of the LIGO gravitational-wave event GW 151226 derived from the CALorimetric Electron Telescope (CALET) observation. The main instrument of CALET, CALorimeter (CAL), observes gamma-rays from ~1 GeV up to 10 TeV with a field of view of ~2 sr. The CALET gamma-ray burst monitor (CGBM) views ~3 sr and ~2pi sr of the sky in the 7 keV - 1 MeV and the 40 keV - 20 MeV bands, respectively, by using two different scintillator-based instruments. The CGBM covered 32.5% and 49.1% of the GW 151226 sky localization probability in the 7 keV - 1 MeV and 40 keV - 20 MeV bands respectively. We place a 90% upper limit of 2 x 10^{-7} erg cm-2 s-1 in the 1 - 100 GeV band where CAL reaches 15% of the integrated LIGO probability (~1.1 sr). The CGBM 7 sigma upper limits are 1.0 x 10^{-6} erg cm-2 s-1 (7-500 keV) and 1.8 x 10^{-6} erg cm-2 s-1 (50-1000 keV) for one second exposure. Those upper limits correspond to the luminosity of 3-5 x 10^{49} erg s-1 which is significantly lower than typical short GRBs.

CdZnTe strip detectors for astrophysical arc second imaging and spectroscopy: detector performance and radiation effects

CdZnTe strip detectors have been fabricated and tested to show the ability for arc second imaging and spectroscopy. Two dimensional CdZnTe strip detectors with 100 micron pitch have been fabricated and wire bonded to readout electronics to demonstrate the ability to localize 22 to 122 keV photons to less than 100 microns. Good spectral resolution has also been achieved. The uniformity and relative efficiency of the strip detector are discussed. Radiation damage effects by intermediate energy neutrons and low energy protons on the surface and bulk performance of CdZnTe devices have been investigated and are presented. Activation and annealing of radiation effects have been seen and are discussed.

Development of ground-testable phase fresnel lenses in silicon

Diffractive optics, such as Phase Fresnel Lenses (PFLs), offer the potential to achieve excellent imaging performance in the x-ray and gamma-ray photon regimes. In principle, the angular resolution obtained with these devices can be diffraction limited. Furthermore, improvements in signal sensitivity can be achieved as virtually the entire flux incident on a lens can be concentrated onto a small detector area. In order to verify experimentally the imaging performance, we have fabricated PFLs in silicon using gray-scale lithography to produce the required Fresnel profile. These devices are to be evaluated in the recently constructed 600-meter x-ray interferometry testbed at NASA/GSFC. Profile measurements of the Fresnel structures in fabricated PFLs have been performed and have been used to obtain initial characterization of the expected PFL imaging efficiencies.

XA readout chip characteristics and CdZnTe spectral measurements

The authors report on the performance of a CdZnTe (CZT) array readout by an XA (X-ray imaging chip produced at the AMS foundry) application specific readout chip (ASIC). The array was designed and fabricated at NASA/Goddard Space Flight Center (GSFC) as a prototype for the Burst Arc-Second Imaging and Spectroscopy gamma-ray instrument. The XA ASIC was obtained from Integrated Detector and Electronics (IDE), in Norway. Performance characteristics and spectral data for /sup 241/Am are presented both at room temperature and at -20/spl deg/C. The measured noise (/spl sigma/) was 2.5 keV at 60 keV at room temperature. This paper represents a progress report on work with the XA ASIC and CZT detectors. Work is continuing and in particular, larger arrays are planned for future NASA missions.