38 research outputs found
New readout and data-acquisition system in an electron-tracking Compton camera for MeV gamma-ray astronomy (SMILE-II)
For MeV gamma-ray astronomy, we have developed an electron-tracking Compton
camera (ETCC) as a MeV gamma-ray telescope capable of rejecting the radiation
background and attaining the high sensitivity of near 1 mCrab in space. Our
ETCC comprises a gaseous time-projection chamber (TPC) with a micro pattern gas
detector for tracking recoil electrons and a position-sensitive scintillation
camera for detecting scattered gamma rays. After the success of a first balloon
experiment in 2006 with a small ETCC (using a 101015 cm
TPC) for measuring diffuse cosmic and atmospheric sub-MeV gamma rays (Sub-MeV
gamma-ray Imaging Loaded-on-balloon Experiment I; SMILE-I), a (30 cm)
medium-sized ETCC was developed to measure MeV gamma-ray spectra from celestial
sources, such as the Crab Nebula, with single-day balloon flights (SMILE-II).
To achieve this goal, a 100-times-larger detection area compared with that of
SMILE-I is required without changing the weight or power consumption of the
detector system. In addition, the event rate is also expected to dramatically
increase during observation. Here, we describe both the concept and the
performance of the new data-acquisition system with this (30 cm) ETCC to
manage 100 times more data while satisfying the severe restrictions regarding
the weight and power consumption imposed by a balloon-borne observation. In
particular, to improve the detection efficiency of the fine tracks in the TPC
from 10\% to 100\%, we introduce a new data-handling algorithm in
the TPC. Therefore, for efficient management of such large amounts of data, we
developed a data-acquisition system with parallel data flow.Comment: 11 pages, 24 figure
Direction-sensitive dark matter search results in a surface laboratory
We developed a three-dimensional gaseous tracking device and performed a
direction-sensitive dark matter search in a surface laboratory. By using 150
Torr carbon-tetrafluoride (CF_4 gas), we obtained a sky map drawn with the
recoil directions of the carbon and fluorine nuclei, and set the first limit on
the spin-dependent WIMP (Weakly Interacting Massive Particles)-proton cross
section by a direction-sensitive method. Thus, we showed that a WIMP-search
experiment with a gaseous tracking device can actually set limits. Furthermore,
we demonstrated that this method will potentially play a certain role in
revealing the nature of dark matter when a low-background large-volume detector
is developed.Comment: 9 figures, accepted for publication in Phys. Lett.
First observation of MeV gamma-ray universe with bijective imaging spectroscopy using the Electron-Tracking Compton Telescope aboard SMILE-2+
MeV gamma-rays provide a unique window for the direct measurement of line
emissions from radioisotopes, but observations have made little significant
progress after COMPTEL/{\it CGRO}. To observe celestial objects in this band,
we are developing an electron-tracking Compton camera (ETCC), which realizes
both bijective imaging spectroscopy and efficient background reduction gleaned
from the recoil electron track information. The energy spectrum of the
observation target can then be obtained by a simple ON-OFF method using a
correctly defined point spread function on the celestial sphere. The
performance of celestial object observations was validated on the second
balloon SMILE-2+ installed with an ETCC having a gaseous electron tracker with
a volume of 303030 cm. Gamma-rays from the Crab nebula were
detected with a significance of 4.0 in the energy range 0.15--2.1 MeV
with a live time of 5.1 h, as expected before launching. Additionally, the
light curve clarified an enhancement of gamma-ray events generated in the
Galactic center region, indicating that a significant proportion of the final
remaining events are cosmic gamma rays. Independently, the observed intensity
and time variation were consistent with the pre-launch estimates except in the
Galactic center region. The estimates were based on the total background of
extragalactic diffuse, atmospheric, and instrumental gamma-rays after
accounting for the variations in the atmospheric depth and rigidity during the
level flight. The Crab results and light curve strongly support our
understanding of both the detection sensitivity and the background in real
observations. This work promises significant advances in MeV gamma-ray
astronomy
Performance of a Time-Projection-Chamber with a Large-Area Micro-Pixel-Chamber Readout
A micro time-projection-chamber (micro-TPC) with a detection volume of
23*28*31 cm^3 was developed, and its fundamental performance was examined. The
micro-TPC consists of a micro pixel chamber with a detection area of 31*31 cm^2
as a two-dimensional imaging device and a gas electron multiplier with an
effective area of 23*28 cm^2 as a pre-gas-multiplier. The micro-TPC was
operated at a gas gain of 50,000, and energy resolutions and spatial
resolutions were measured.Comment: 4 pages, 7 figures, proceedings of IWORID
First underground results with NEWAGE-0.3a direction-sensitive dark matter detector
A direction-sensitive dark matter search experiment at Kamioka underground
laboratory with the NEWAGE-0.3a detector was performed. The NEWAGE- 0.3a
detector is a gaseous micro-time-projection chamber filled with CF4 gas at 152
Torr. The fiducial volume and target mass are 20*25*31 cm3 and 0.0115 kg,
respectively. With an exposure of 0.524 kgdays, improved spin-dependent weakly
interacting massive particle (WIMP)-proton cross section limits by a
direction-sensitive method were achieved including a new record of 5400 pb for
150 GeV/c2 WIMPs. We studied the remaining background and found that ambient
gamma-rays contributed about one-fifth of the remaining background and
radioactive contaminants inside the gas chamber contributed the rest.Comment: 21 pages, 8 figures, to appear in Physics Letters