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Register a new userSound and light from fractures in scintillators
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Added by
Philippe Di Stefano
Publication date
2013
fields
Physics
and research's language is
English
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Prompted by intriguing events observed in certain particle-physics searches for rare events, we study light and acoustic emission simultaneously in some inorganic scintillators subject to mechanical stress. We observe mechanoluminescence in ${Bi}_4{Ge}_{3}{O}_{12}$, ${CdWO}_{4}$ and ${ZnWO}_{4}$, in various mechanical configurations at room temperature and ambient pressure. We analyze how the light emission is correlated to acoustic emission during fracture. For ${Bi}_4{Ge}_{3}{O}_{12}$, we set a lower bound on the energy of the emitted light, and deduce that the fraction of elastic energy converted to light is at least $3 times 10^{-5}$.
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To investigate fractoluminescence in scintillating crystals used for particle detection, we have developed a multi-channel setup built around samples of double-cleavage drilled compression (DCDC) geometry in a controllable atmosphere. The setup allows the continuous digitization over hours of various parameters, including the applied load, and the compressive strain of the sample, as well as the acoustic emission. Emitted visible light is recorded with nanosecond resolution, and crack propagation is monitored using infrared lighting and camera. An example of application to Bi4Ge3O12 (BGO) is provided.
During a winter thunderstorm on November 24, 2017, a downward terrestrial gamma-ray flash took place and triggered photonuclear reactions with atmospheric nitrogen and oxygen nuclei, coincident with a lightning discharge at the Kashiwazaki-Kariwa nuclear power station in Japan. We directly detected neutrons produced by the photonuclear reactions with gadolinium orthosilicate scintillation crystals installed at sea level. Two gadolinium isotopes included in the scintillation crystals, $^{155}$Gd and $^{157}$Gd, have large cross-sections of neutron captures to thermal neutrons such as $^{155}$Gd(n,$gamma$)$^{156}$Gd and $^{157}$Gd(n,$gamma$)$^{158}$Gd. De-excitation gamma rays from $^{156}$Gd and $^{158}$Gd are self-absorbed in the scintillation crystals, and make spectral-line features which can be distinguished from other non-neutron signals. The neutron burst lasted for $sim$100~ms, and neutron fluences are estimated to be $>$52 and $>$31~neutrons~cm$^{-2}$ at two observation points inside the power plant. Gadolinium orthosilicate scintillators work as valid detectors for thermal neutrons in lightning.
The radioactive contamination of ZnWO4 crystal scintillators has been measured deep underground at the Gran Sasso National Laboratory (LNGS) of the INFN in Italy with a total exposure 3197 kg x h. Monte Carlo simulation, time-amplitude and pulse-shape analyses of the data have been applied to estimate the radioactive contamination of the ZnWO4 samples. One of the ZnWO4 crystals has also been tested by ultra-low background gamma spectrometry. The radioactive contaminations of the ZnWO4 samples do not exceed 0.002 -- 0.8 mBq/kg (depending on the radionuclide), the total alpha activity is in the range: 0.2 - 2 mBq/kg. Particular radioactivity, beta active 65Zn and alpha active 180W, has been detected. The effect of the re-crystallization on the radiopurity of the ZnWO4 crystal has been studied. The radioactive contamination of samples of the ceramic details of the set-ups used in the crystals growth has been checked by low background gamma spectrometry. A project scheme on further improvement of the radiopurity level of the ZnWO4 crystal scintillators is briefly addressed.
Energy spectra of backscattered and transmitted ions with primary energies of 50 keV and 100 keV interacting with self-supporting foils were recorded with a Time-of-Flight Medium-Energy Ion Scattering setup in a single experiment. Self-supporting Au and W foils without backing material were used. For He ions transmitted through Au the spectrum of detected particles shows two distinct components corresponding to different energy losses in the film, whereas for protons no such phenomenon was observed. To determine the origin of these different contributions, measurements for different angles of incidence and scattering angles have been evaluated. The results suggest that the two components in the spectrum of transmitted He ions could be attributed to impact parameter dependent energy loss, being more prominent for He ions than for protons. The main origin of the necessary impact parameter selection along the different ion trajectories is expected to be texture in the Au-foils.
Competitive mechanisms contribute to image contrast from dislocations in annular dark field scanning transmission electron microscopy ADF STEM. A clear theoretical understanding of the mechanisms underlying the ADF STEM contrast is therefore essential for correct interpretation of dislocation images. This paper reports on a systematic study of the ADF STEM contrast from dislocations in a GaN specimen, both experimentally and computationally. Systematic experimental ADF STEM images of the edge character dislocations revealed a number of characteristic contrast features that are shown to depend on both the angular detection range and specific position of the dislocation in the sample. A theoretical model based on electron channelling and Bloch wave scattering theories, supported by multislice simulations using Grillo s strain channelling equation, is proposed to elucidate the physical origin of such complex contrast phenomena.
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