Kavli Affiliate: Tadayuki Takahashi
| First 5 Authors: Shunsaku Nagasawa, Takahiro Minami, Shin Watanabe, Tadayuki Takahashi,
| Summary:
The fourth flight of the Focusing Optics X-ray Solar Imager sounding rocket
experiment (FOXSI-4) aimed to achieve the first imaging spectroscopic
observations of mid-to-large class ( >= GOES C5 class) solar flares, in
contrast to the previous three flights that targeted relatively quiet regions
of the Sun. To meet the emerging requirements for hard X-ray focal plane
detectors for providing simultaneous diagnostics of spectrally (<1 keV FWHM)
and spatially (<50 um) separated coronal and chromospheric emissions from solar
flares, we developed a new strip-configuration detector called the wide-gap
CdTe semiconductor double-sided strip detector (CdTe-DSD). The wide-gap
CdTe-DSD employs a unique design principle to enhance position resolution. This
enhancement is realized by expanding the gaps between electrodes to induce
charge-sharing across adjacent strip electrodes and using this sharing energy
information for position reconstruction to a level finer than the strip-pitch.
However, the detector response becomes complex and requires consideration of
various factors, such as the charge loss due to wider gaps and the dependence
on the depth of photon interaction. Thus, we developed an energy reconstruction
method that fully leverages the energy information between adjacent strips and
from both the cathode and anode sides, achieving an energy resolution of 0.75
keV (FWHM) at 14 keV. Furthermore, we conducted an X-ray scanning experiment
using a synchrotron beam at Spring-8 to evaluate the detector response with a
fine scale of 10 um. Based on these results, we established a sub-strip
position reconstruction method, demonstrating that X-rays interacting at the
center of the gap can be determined with an accuracy of 20 um, and even those
at the strip center can be determined with an accuracy of 50 um.
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