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We developed wide-gap CdTe Double-sided Strip Detectors (CdTe-DSDs) for the hard X-ray focal plane detector, which achieved an energy resolution of 1 keV (FWHM) and a high position resolution of 30 Μm with high detection efficiency. We also developed a new onboard data acquisition (DAQ) system with a Raspberry Pi, an FPGA board SPMU-001, and a SpaceWire interface for controlling all CdTe-DSDs and realizing fast readout of the observation data whose counting rate is estimated to be 5000 counts per second. The observation data is written in a 128 MB data ring buffer region for temporary storage. The software in the Raspberry Pi controls each detector by the commands from a ground-based computer and simultaneously reads the data at 0.6 Mbps for storage in the DAQ. Some essential data for operation, for example, light curves, energy spectrum, and the status of the DAQ system, is sent to the ground-based computer through the onboard control system.
The Focusing Optics X-ray Solar Imager (FOXSI ) sounding rockets are the first solar-dedicated direct-focusing hard X-ray (HXR) instruments. FOXSI rockets use Wolter-1 style HXR optics and solid state double-sided strip detectors. FOXSI images of solar HXR sources are influenced by the point spread function of the optics, the 2D segmentation of the detector into strip intersections, and noise in the detector readout. For FOXSI-4, new high-resolution optics will cause the instrument angular resolution to be limited by the minimum strip pitch of its CdTe detectors (60 μm).
FOXSI images are also affected by charge sharing in the detector, when one incident photon causes signals in multiple adjacent strips. Charge sharing is more likely the closer a photon is incident to a strip boundary, making it a sub-strip-position-dependent effect. Tests of a FOXSI-3 CdTe detector (with 60 μm strip pitch) at a synchrotron beamline (the Advanced Light Source) have allowed for characterization of charge shared events. This knowledge is used to develop new methods for achieving sub-strip resolution in FOXSI detectors (0.6-3", depending on incident photon position), applicable in the future to the FOXSI-4 detectors (or other similar systems).
To evaluate the performance of these methods, a model has been developed combining the FOXSI-3 optical and detector response, the latter incorporating lab-measured properties of charge sharing in the system. Using this model, generated sources are convolved with the FOXSI-3 system to simulate FOXSI data. A corresponding deconvolution process then extracts a reconstructed source from the simulated data using the new imaging methods, and the original and reconstructed sources can be compared. We show that the reconstructed source approximates the original with higher spatial resolution than that which results from using strip-based position knowledge only. Notably, we demonstrate a new ability to resolve independent sources located only one strip pitch apart.
Vibration isolation system for cryocoolers of Soft X-ray Spectrometer (SXS) onboard ASTRO-H (Hitomi)
But the challenge of fabricating truly aspheric Wolter type molding dies, which are capable of highly accurate angular resolution (below 5 arcs), remains very expensive and time consuming. In this paper, three methods for producing X-ray optic molding dies are presented. Each method uses a different substrate material and process chain, as follows: electroless nickel plated aluminum (first diamond turned then correctively polished), fused silica (first precision ground then correctively polished), and CVD silicon carbide (which can be finished entirely with a newly developed Shape Adaptive Grinding process). The process chains employed for each method are explained in details, and their relative merits discussed. A way forward for the next generation of X-ray telescopes after ASTRO-H is then drawn out.
Monte Carlo simulation study of in-orbit background for the soft gamma-ray detector on-board ASTRO-H
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