A new scenario is presented for the cause of magnetospheric relativistic electron decreases (REDs) and potential effects in the atmosphere and on climate. High‐density solar wind heliospheric ...plasmasheet (HPS) events impinge onto the magnetosphere, compressing it along with remnant noon‐sector outer‐zone magnetospheric ~10‐100 keV protons. The betatron accelerated protons generate coherent electromagnetic ion cyclotron (EMIC) waves through a temperature anisotropy (T⊥/T|| > 1) instability. The waves in turn interact with relativistic electrons and cause the rapid loss of these particles to a small region of the atmosphere. A peak total energy deposition of ~3 × 1020 ergs is derived for the precipitating electrons. Maximum energy deposition and creation of electron‐ion pairs at 30‐50 km and at < 30 km altitude are quantified. We focus the readers' attention on the relevance of this present work to two climate change mechanisms. Wilcox et al. (1973) noted a correlation between solar wind heliospheric current sheet (HCS) crossings and high atmospheric vorticity centers at 300 mb altitude. Tinsley et al. () has constructed a global circuit model which depends on particle precipitation into the atmosphere. Other possible scenarios potentially affecting weather/climate change are also discussed.
Key Points
Heliospheric plasmasheet impingements on the magnetosphere lead to relativistic electron losses
Compressing the magnetosphere causes generation of coherent EMIC waves which confine electron losses to small region of dayside ionosphere
Energy deposition and ionization at low altitudes may cause Wilcox effect and Tinsley effect
ABSTRACT Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which originate from incompleteness in determining the physical parameters of ...Compton scattering in detection, e.g., lack of the directional information of the recoil electrons. The recent major mission/instrument in the MeV band, Compton Gamma Ray Observatory/COMPTEL, which was Compton Camera (CC), detected a mere ∼30 persistent sources. It is in stark contrast with the ∼2000 sources in the GeV band. Here we report the performance of an Electron-Tracking Compton Camera (ETCC), and prove that it has a good potential to break through this stagnation in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3D recoil electron tracks; then the Scatter Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx), which CCs cannot measure, is also obtained, and is found to be helpful to reduce the background under conditions similar to those in space. Accordingly, the significance in gamma detection is improved severalfold. On the other hand, SPD is essential to determine the point-spread function (PSF) quantitatively. The SPD resolution is improved close to the theoretical limit for multiple scattering of recoil electrons. With such a well-determined PSF, we demonstrate for the first time that it is possible to provide reliable sensitivity in Compton imaging without utilizing an optimization algorithm. As such, this study highlights the fundamental weak-points of CCs. In contrast we demonstrate the possibility of ETCC reaching the sensitivity below 1 × 10−12 erg cm−2 s−1 at 1 MeV.
X-ray and gamma-ray polarimetry is a promising tool to study the geometry and the magnetic configuration of various celestial objects, such as binary black holes or gamma-ray bursts (GRBs). However, ...statistically significant polarizations have been detected in few of the brightest objects. Even though future polarimeters using X-ray telescopes are expected to observe weak persistent sources, there are no effective approaches to survey transient and serendipitous sources with a wide field of view (FoV). Here we present an electron-tracking Compton camera (ETCC) as a highly sensitive gamma-ray imaging polarimeter. The ETCC provides powerful background rejection and a high modulation factor over an FoV of up to 2π sr thanks to its excellent imaging based on a well-defined point-spread function. Importantly, we demonstrated for the first time the stability of the modulation factor under realistic conditions of off-axis incidence and huge backgrounds using the SPring-8 polarized X-ray beam. The measured modulation factor of the ETCC was 0.65 0.01 at 150 keV for an off-axis incidence with an oblique angle of 30° and was not degraded compared to the 0.58 0.02 at 130 keV for on-axis incidence. These measured results are consistent with the simulation results. Consequently, we found that the satellite-ETCC proposed in Tanimori et al. would provide all-sky surveys of weak persistent sources of 13 mCrab with 10% polarization for a 107 s exposure and over 20 GRBs down to a 6 × 10−6 erg cm−2 fluence and 10% polarization during a one-year observation.
Performance test of the MAIKo active target Furuno, T.; Kawabata, T.; Ong, H.J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2018, Letnik:
908
Journal Article
Recenzirano
Odprti dostop
A new active target named MAIKo (Mu-PIC based Active target for Inverse Kinematics∘) has been developed at Kyoto University and Research Center for Nuclear Physics (RCNP), Osaka University. MAIKo is ...suited for missing-mass spectroscopy of unstable nuclei at forward scattering angles in inverse kinematics. MAIKo consists of a time projection chamber (TPC), which incorporates a micro-pixel chamber (μ-PIC) as the electron multiplication and collection system. In MAIKo, the medium gas also plays the role of a reaction target, thus allowing detection of low-energy recoil particles with high position resolution. The MAIKo TPC was commissioned with He(93%)+iso-C4H10(7%) and He(93%)+CO2(7%) mixture gasses at 430 hPa. The gas gain and the angular resolution of MAIKo were evaluated with an alpha source and a 4He beam at 56 MeV. The TPC was stably operated up to 1000-kcps beam intensity. A tracking algorithm using the Hough transform method has been developed to analyze scattering events. An angular resolution of 1.3°was achieved for scattered 4He particles.
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 1mCrab 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 10×10×15cm3 TPC) for measuring diffuse cosmic and atmospheric sub-MeV gamma rays (Sub-MeV gamma-ray Imaging Loaded-on-balloon Experiment I; SMILE-I), a (30cm)3 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 (30cm)3 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.
Micro pixel chambers (μ-PICs), which are a type of the micro-pattern gas chambers, are usually manufactured using the printed-circuit-board (PCB) technology. However, recent application projects have ...begun to require higher gas gains and finer position resolution than those obtainable with current μ-PICs. It is difficult to improve the electrode structure to achieve these improvements because PCB technology limits the precision of electrode fabrication and the thickness of the substrate. We have therefore adopted micro-electro-mechanical-systems (MEMS) technology and developed the first prototype of a through-glass-via (TGV) μ-PIC. This prototype TGV μ-PIC worked well, achieving a maximum gain of approximately 20,000 and an energy resolution of 20.6% (FWHM) at 5.9 keV over the whole 5 × 5 cm2 detection area.
Micro pixel chambers (
μ
-PIC) are gaseous two-dimensional imaging detectors originally manufactured using printed circuit board (PCB) technology. They are used in MeV gamma-ray astronomy, ...medicalimaging, neutron imaging, the search for dark matter, and dose monitoring. The position resolution of the present
μ
-PIC is approximately 120
μ
m (RMS), however some applications require a fine position resolution of less than 100
μ
m. To this end, we have started to develop a
μ
-PIC based on micro electro mechanical system (MEMS) technology, which provides better manufacturing accuracy than PCB technology. Our simulation predicted the gains of MEMS
μ
-PICs to be twice those of PCB
μ
-PICs at the same anode voltage. We manufactured two MEMS
μ
-PICs and tested them to study their behavior. In these experiments, we successfully operated the fabricatedMEMS
μ
-PICs and we achieved a maximum gain of approximately 7×10
3
and collected their energy spectra under irradiation of X-rays from
55
Fe. However, the measured gains of the MEMS
μ
-PICs were less than half of the values predicted in the simulations. We postulated that the gains of the MEMS
μ
-PICs are diminished by the effect of the silicon used as a semiconducting substrate.
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