Space radiation induced displacement damage effects on the performance of the silicon drift detector onboard chandrayaan-2 mission
The space radiation induced displacement damage effects on the performance of the Silicon Drift Detector (SDD) based X-ray spectrometer has been studied using X-ray (Fe-55) and gamma ray (Co-60) radiations. The spectroscopic performance of the SDD based spectrometer degrades due to radiation damage during the transit and in-orbit operations. Silicon detectors are sensitive to displacement damage which is due to the non ionizing energy loss of the incident radiation. The displacement damage increases the leakage current of the SDD and hence the energy resolution. The X-ray irradiation is to quantify the X-ray fluence level up to which the SDD provides stable energy resolution. After X-ray irradiation tests, it is observed that there is no change in the leakage current and the energy resolution for dose up to 64 krad. The gamma ray irradiation test is to quantify the space radiation damage effects on the SDD and shown that the energy resolution degrades from ~160 eV at 5.9 keV to ~210 eV for the detector operating temperature of ~-40°C for the gamma ray dose of ~10 Krad. It is observed that the increase in the leakage current due to displacement damage is ~0.15 pA and its contribution to the degradation in the energy resolution is insignificant. The degradation in the energy resolution is attributed to the radiation damage of the electronic components inside the SDD module and meets the Chandrayaan-2 requirement of <; 250 eV for the mission life of 2 years.
The new Athena alpha particle X‐ray spectrometer for the Mars Exploration Rovers
[1] The new alpha particle X-ray spectrometer (APXS) is part of the Athena payload of the two Mars Exploration Rovers (MER). The APXS sensor head is attached to the turret of the instrument deployment device (IDD) of the rover. The APXS is a very light-weight instrument for determining the major and minor elemental composition of Martian soils, rocks, and other geological materials at the MER landing sites. The sensor head has simply to be docked by the IDD on the surface of the selected sample. X-ray radiation, excited by alpha particles and X rays of the radioactive sources, is recorded by a high-resolution X-ray detector. The X-ray spectra show elements starting from sodium up to yttrium, depending on their concentrations. The backscattered alpha spectra, measured by a ring of detectors, provide additional data on carbon and oxygen. By means of a proper calibration, the elemental concentrations are derived. Together with data from the two other Athena instruments mounted on the IDD, the samples under investigation can be fully characterized. Key APXS objectives are the determination of the chemistry of crustal rocks and soils and the examination of water-related deposits, sediments, or evaporates. Using the rock abrasion tool attached to the IDD, issues of weathering can be addressed by measuring natural and abraded surfaces of rocks.
DEPFET based focal plane instrumentation for X-ray imaging spectroscopy in space
The combined Detector-Amplifier structure DEPFET (Depleted P-channel FET) is a promising new building block for large area silicon detector devices, e.g. in X-ray astronomy and high energy physics. The DEPFET structure combines excellent energy resolution, high speed readout and low power consumption with the attractive features of random accessibility of pixels and on-demand readout. In addition, it features all advantages of a sideways depleted device in terms of fill factor and quantum efficiency. Finally, the newly introduced combination of a DEPFET structure and a silicon drift diode (SDD) like drift ring structure to form a so-called macropixel device allows for large flexibility in terms of pixel size. Presently, focal plane instrumentation for X-ray imaging spectroscopy based on DEPFET arrays is being developed for a variety of space experiments with very different requirements. The next European X-ray Observatory XEUS is going to have a wide field imager covering the full FOV, which consists of a large-area DEPFET array. The concept for the French-Italian X-ray Astronomy mission SIMBOL-X includes a focal plane array based on DEPFET macropixels, and, finally, the MIXS (Mercury Imaging X-ray Spectrometer) instrument on the European Mercury exploration mission BepiColombo also contains two DEPFET macropixel based focal plane arrays. While for XEUS and SIMBOL-X excellent energy resolution and quantum efficiency in the low energy range are mandatory, radiation hardness is imperative for MIXS. A first production of DEPFET prototype arrays showed very promising results. More sophisticated prototype devices for SIMBOL-X and XEUS with a large sensitive area as well as flight grade devices for the MIXS instrument have been produced at the MPI semiconductor laboratory in Munich/Germany. The strategies to meet the respective requirements by an appropriate design of the focal plane instrumentation are shown as well as first results of the new production.