Radiation Hard Crystals Research Articles

Optical transmission enhancement of ionic crystals via superionic fluoride transfer: Growing VUV-transparent radioactive crystals

The 8−eV first nuclear excited state in Th229 is a candidate for implementing a nuclear clock. Doping Th229 into ionic crystals such as CaF2 is expected to suppress nonradiative decay, enabling nuclear spectroscopy and the realization of a solid-state optical clock. Yet, the inherent radioactivity of Th229 prohibits the growth of high-quality single crystals with high Th229 concentration; radiolysis causes fluoride loss, increasing absorption at 8eV. These radioactively doped crystals are thus a unique material for which a deeper analysis of the physical effects of radioactivity on growth, crystal structure, and electronic properties is presented. Following the analysis, we overcome the increase in absorption at 8eV by annealing Th229-doped CaF2 at 1250∘C in CF4. This technique allows to adjust the fluoride content without crystal melting, preserving its single-crystal structure. Superionic state annealing ensures rapid fluoride distribution, creating fully transparent and radiation-hard crystals. This approach enables control over the charge state of dopants, which can be used in deep-UV optics, laser crystals, scintillators, and nuclear clocks. Published by the American Physical Society 2024

Radiation hardness qualification of PbWO4 scintillation crystals for the CMS Electromagnetic Calorimeter

Ensuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered.

The Electromagnetic Calorimeter of CMS

The electromagnetic calorimeter of CMS at the Large Hadron Collider (LHC) has been designed to measure the energy of electrons and photons with high resolution over a wide energy range. The detector consists of 61200 PBWO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystals for the barrel and 14648 crystals for the endcaps, with a pseudo-rapidity coverage of |eta|les3.0. Preshower detectors are located in front of each endcap. The calorimeter has a pseudo-projective geometry. Great care has been taken in its design to minimize the effects of gaps and cracks in order to ensure the required energy resolution. The detector will operate in a magnetic field of 4 Tesla, and with a bunch crossing rate of 40 MHz. This requires fast and radiation hard crystals, photo-detectors and read-out electronics. An overview of the design, and the status of the construction, will be presented with special consideration given to the challenging goals

BGO crystals grown by a low thermal gradient Czochralski technique

A low thermal gradient version of the Czochralski technique was successfully adopted for growing BGO crystals. Now the technique allows us to grow water transparent, radiation hard crystals of up to 150 mm in diameter and up to 400 mm in length. Results of the application of these crystals in the endcap calorimeter of the CMD-2 detector which consists of 680 BGO crystals with a total weight of about 450 kg are discussed.

Cerium fluoride crystals for calorimetry at LHC

High-resolution homogeneous calorimetry is fully justified for part of the physics program at LHC. In September 1992, two Letters of Intent sent to the LHC Committee proposed CeF 3 crystals for calorimetry. The main design features of calorimeters for LHC are discussed. The severe constraints LHC imposes on detectors make the use of “classical” crystals impossible. Therefore, a large R&D effort has been undertaken by the Crystal Clear Collaboration in order to find new, dense, fast and radiation hard crystals. A good candidate, cerium fluoride, has been identified and studied. It is interesting at this stage to review the specifications of scintillators for LHC and to see how well available data on CeF 3 luminescence, decay time, light yield, optical transmission and resistance to radiation meet them. Milestones to reach before starting a large scale crystal production in view of the eventual construction of a calorimeter, are also discussed.