Application of oriented crystals on satellite-borne detectors
Cutini S., Bandiera L., Mazzolari A., Romagnoni M., Sytov A., Haurylavets V., Tikomirov V.
III - Astrofisica
Aula GSSI Ex ISEF - Biblioteca - Venerdì 27 h 15:30 - 19:00
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It has been known since the 1950s that the lattice structure may strongly influence the electromagnetic processes in oriented crystals. In particular, if a beam of electrons or photons is aligned with the crystalline axes or planes, the probability of bremsstrahlung or pair production, respectively, are strongly enhanced. This results in a decrease of the e.m. shower length. The usage of oriented scintillator crystals in calorimeters or in the trackers would permit to reduce the amount of necessary material to build the detector, a possibility from which HEP and astrophysics experiments could benefit from. Recently, our collaborating group in Ferrara extended these studies to high-$Z$ scintillators commonly used in electromagnetic calorimeter. In particular, we measured a huge X0 reduction for 120 GeV electrons interacting with a lead tungstate crystals (PWO), from 8.9 to 1.6 mm in the case of beam alignment with respect to crystal axes. In a satellite with a gamma-ray detector module made of oriented crystals, the e.m. shower created by the incident photon with energy larger than 100 GeV can be completely contained in a quite restrained volume, thus reducing the necessary weight (and therefore the cost) compared to those currently used. If we consider the geometry used for the Fermi-LAT detector in which each of its towers is composed by a tracker and a calorimeter hodoscopic module. In case of pointing, an oriented--crystals-based hodoscopic calorimeter would strongly enhance the sensitivity of the telescope above few GeV, thus containing the electron/positron showers at energies up to TeV and more in a smaller volume as compared to standard detectors. Furthermore, if the W conversion foil is substituted by a crystalline $W$ or high-$Z$ crystal scintillator, the tracker length can be reduced and consequently the multiple scattering, with an improvement of the resolution in the localization of the gamma-ray, thus helping its identification. The required 1 deg alignment precision needed for X0 reduction can be easily satisfied with actual pointing techniques, moreover, such an apparatus would continue to operate in a standard way in the absence of pointing. Several fields of the astrophysics could be explored using the pointing strategy in this energy range, expecially with the birth of the multi-messenger era.