0000000000082961
AUTHOR
S. Varisco
Photoluminescence activity in natural silica excited in the vacuum-UV range
Abstract We report an experimental study on the optical absorption and photoluminescence detected in samples of natural silica. Our results show that the two emission bands, β (∼3.1 eV) and α E (∼4.3 eV), have an excitation profile in the vacuum ultraviolet region with a maximum at ∼7.5 eV. This excitation profile indicates that, in terms of energy levels of the luminescent defect, there is a transition from a ground state, S 0 , to a second excited state, S 2 , able to excite PL emission, in addition to the well known transition corresponding to the optical absorption band, B 2β . Our data are in a quantitative agreement with `ab initio' calculations carried out for a two-fold coordinated …
Planar Technology for NDT-Ge X-Ray Microcalorimeters: Absorber Fabrication
We have investigated the electroplating process to deposit thick uniform films of tin on a Ge wafer coated with Spin‐On Glass, in order to fabricate the absorbers for Ge microcalorimeter arrays. Here we discuss some technological details and propose two alternative metal bilayer to be used as seed for the electroplating.
Absorption band at 7.6 eV induced by γ-irradiation in silica glasses
Optical absorption of defects induced by γ-irradiation in both natural and synthetic silica is experimentally investigated in the vacuum-ultraviolet (UV) range. Our results show that γ-rays, in a dose range of 1000 Mrad, induce an absorption band centered at 7.6 eV, the so-called E band, whose growth kinetics is not related to γ-activated precursors but to defects of the glassy matrix directly induced via the breaking of Si–O bonds occurring under γ-irradiation. Moreover, we observe that γ-rays do not bleach the E band present in some silica samples before irradiation, so ruling out that the associated defects can be precursors of the paramagnetic E′ centers, also induced by γ-irradiation.
Chemical Evolution of Interstellar Methanol Ice Analogs upon Ultraviolet Irradiation: The Role of the Substrate
An important issue in the chemistry of interstellar ices is the role of dust materials. In this work, we study the effect of an amorphous water-rich magnesium silicate deposited onto ZnSe windows on the chemical evolution of ultraviolet-irradiated methanol ices. For comparison, we also irradiate similar ices deposited onto bare ZnSe windows. Silicates are produced at relatively low temperatures exploiting a sol-gel technique. The chemical composition of the synthesized material reflects the forsterite stoichiometry. Si-OH groups and magnesium carbonates are incorporated during the process. The results show that the substrate material does affect the chemical evolution of the ice. In particu…
Simbol-X Mirror Module Thermal Shields: I-Design and X-Ray Transmission
The Simbol‐X mission is designed to fly in formation flight configuration. As a consequence, the telescope has both ends open to space, and thermal shielding at telescope entrance and exit is required to maintain temperature uniformity throughout the mirrors. Both mesh and meshless solutions are presently under study for the shields. We discuss the design and the X‐ray transmission.
Experimental evidence of an incomplete thermalization of the energy in an x-ray microcalorimeter with a TaAu absorber.
We have conducted an experimental test at our XACT facility using an x-ray microcalorimeter with Ta∕Au absorber and neutron transmutation doped germanium thermal sensor. The test was aimed at measuring the percentage of energy effectively thermalized after absorption of x-ray photons in superconducting tantalum. Moreover, in general, possible formation of long living quasiparticles implies that by using a superconducting absorber, a fraction of the deposited energy could not be thermalized on the useful time scale of the thermal sensor. To investigate this scenario, we exploited an absorber made of gold, where no energy trapping is expected, with a small piece of superconducting tantalum at…