Equipment and methods for rapid analysis of PWO full-sized scintillation crystal radiation hardness during mass production

Abstract

Abstract-The mass production of lead tungstate crystals (PWO) for the Compact Muon Solenoid (CMS) Project at CERN began at the Bogoroditsk Techno-Chemical Plant (BTCP, TulaRegion, Russia) in 2000. Mass production technology, developed in recent years, is based on a set of methods and instrumentation for crystal growth and machining, as well as quality control and certification of crystals. One of the most crucial categories of tolerances is the radiation hardness of crystals. Control of the PWO radiation hardness during the mass production phase requires a reliable, easy-to-use measuring tool with high productivity. A semiautomatic spectrometric setup for PWO radiation hardness monitoring was developed and tested at CERN. After final crosschecks, the setup was put into operation at BTCP.Index Terms-Certification, electromagnetic calorimeters, radiation hardness, scintillation crystals. I. REQUIREMENTS FOR PWO CRYSTAL RADIATION HARDNESST HE requirements on radiation tolerance, set by the specification for the preproduction phase, are intended to provide the best possible compromise between electromagnetic calorimeter barrel performance and crystal production yield [1]. As is stated in the specification, the required level of PWO radiation hardness is defined by three parameters: 1) induced absorption of fully saturated crystal, laterally irradiated by Co with a total absorbed dose 500 Gy at a dose rate 100 Gy/h at 420 nm is m (measured within 40 min after irradiation, T C); 2) a light yield loss 6% after frontal Co irradiation for a total absorbed dose of 2 Gy and a dose rate of 0.15 Gy/h corresponding to the large hadron collider (LHC) irradiation environment (measured periodically during irradiation, T C); 3) no recovery time constant shorter than 1 h. During the optimization of the lead tungstate production technology, numerous irradiation tests were performed to measure PWO crystal behavior in the irradiation environment similar to one of LHC and to tune the specification of the crystals. Besides the specification tuning, these tests provided valuable feedback to crystal technology development. Although various irradiation methods gave results differing by a factor of about two [2] and the information return to the producer was rather slow, in the end the technology of radiation-hard PWO crystal production was achieved [3]- [5]. After this, the stabilization of the level of technology reached becomes crucial, requiring development of adequate methods and equipment for fast control of crystal quality during mass production. From this point of view, the crystal producer has all the needed instrumentation for crystal geometry and optical property control, namely, an automatic crystal control system (ACCOS), which includes a three-dimensional machine [6]. However, the organization of a reliable control of radiation hardness met some obstacles. First of all, such measurements require a long time. Taking into account the total quantity of crystals under production, it is impossible to measure the radiation hardness...

PWO-II scintillation crystals for the PANDA electromagnetic calorimeter

“…All crystals were tested at room temperature (T=+18°C). The radiation induced coefficient at 420 nm wavelength (luminescence maximum of PWD) was measured with the so-called "RGB box" [5] using a 6OCo "(-source with a total absorbed dose of 50 Gy. The light yield was measured with a photomultiplier with bialkali photocathode.…”

On the Mechanism of Radiation Damage of Optical Transmission in Lead Tungstate Crystal

“…Moreover, thermally stimulated luminescence (TSL) data obtained with a variety of synthetic lead tungstate crystals grown under different technological conditions as well as data obtained with measurements using the combination of TSL, photo-stimulated EPR, and optically detected magnetic resonance (ODMR) methods were taken into account [6][7][8][9]. Also, the data of transmission recovery after saturating irradiation and low dose irradiation at different facilities [10,11] were analysed.…”