Development of a 30 cm-cube Electron-Tracking Compton Camera for the SMILE-II Experiment

Abstract

To explore the sub-MeV/MeV gamma-ray window for astronomy, we have developed the Electron-Tracking Compton Camera (ETCC), and carried out the first performance test in laboratory conditions using several gamma-ray sources in the sub-MeV energy band. Using a simple track analysis for a quick first test of the performance, the gamma-ray imaging capability was demonstrated with clear images and 5.3 degrees of angular resolution measure (ARM) measured at 662 keV. As the greatest impact of this work, a gamma-ray detection efficiency on the order of 10 −4 was achieved at the sub-MeV gamma-ray band, which is one order of magnitude higher than our previous experiment. This angular resolution and detection efficiency enables us to detect the Crab Nebula at the 5σ level with several hours observation at balloon altitude in middle latitude. Furthermore, good consistency of efficiencies between this performance test and simulation including only physical processes is very important; it means we achieve nearly 100% detection of Compton recoil electrons and means that our predictions of performance enhancement resulting from future upgrades are more realistic. We are planning to confirm the imaging capability of the ETCC by observation of celestial objects in the SMILE-II (Sub-MeV gamma ray Imaging Loadedon-balloon Experiment II). The SMILE-II and following SMILE-III project will be an important key of sub-MeV/MeV gamma-ray astronomy.

Gaseous and dual-phase time projection chambers for imaging rare processes

“…Other TPCs that emphasize image reconstruction, in astronomy and applied science, involve x-ray polarimetry through the accurate reconstruction of the photoelectron (e.g. [413][414][415][416]), γ-ray polarimetry through pair production [77], Compton Cameras [417] and thermal neutron detectors [418]. They are particularly synergetic with many TPCs described in this review.…”

Active targets for the study of nuclei far from stability

“…The µ-PIC are read out via 512 electronic channels: 256 anode strips and 256 cathode strips. The electronic signals collected by these strips are amplified and discriminated using EF2009bal chips originally developed for the compton camera experiment at Kyoto university [90]. The information is afterwards registered using VME memory modules.…”

New readout and data-acquisition system in an electron-tracking Compton camera for MeV gamma-ray astronomy (SMILE-II)

“…For this purpose, a medium-sized ETCC having approximately 100 times larger effective area than that of SMILE-I with the angular resolution of <10 degrees at 662 keV is necessary to observe these targets during single-day balloon flights where the observation time is between 4 and 8 h [21]. Hence, we developed the medium-sized ETCC with a (30 cm) 3 TPC and 108 PSAs (6912 GSO pixel scintillators) for SMILE-II [22]. The SMILE-II ETCC also benefited from more efficient tracking of recoil electrons compared with that of SMILE-I: the ∼10% efficiency of SMILE-I [19] was improved to ∼100% efficiency by improving the readout electronics and the algorithm for finding tracks in the TPC [23].…”