Yu. I. Davydov

This paper presents a study of gamma irradiation effects on the optical and scintillation properties of pure and yttrium-doped BaF ₂ crystals with yttrium concentrations of 1, 3, and 5 mol%. The optical transmittance, light output, and energy resolution of twenty-four 1×1×1 cm ³ samples were measured before and after ⁶⁰ Co gamma irradiation, with absorbed doses up to 3.56 Mrad. In pure BaF ₂ samples, no noticeable degradation in scintillation properties was observed with increasing absorbed dose. In yttrium-doped samples, a deterioration of scintillation properties is observed, with the fast component of crystal luminescence deteriorating more than the slow one. The correlation between the loss of light output and the radiation-induced decrease of optical transmittance, together with the absence of structural changes in Raman spectra, indicates that the degradation of scintillation properties is primarily due to increased self-absorption, rather than to disruption of the scintillation mechanism.

Based on an unconventional application of commercially available power GaN transistors, a voltage-sensitive amplifier circuit was proposed for a scintillation sandwich-type lead-plastic calorimeter cell using SiPMs, intended for detectors operating under high-radiation conditions. The radiation hardness of the selected GaN transistors under gamma irradiation was investigated. Defect formation in the transistor structures was studied using C-V characteristics. The results demonstrate that GaN transistors can serve as a promising element base for scintillation detectors operating in high-luminosity accelerator environments.

The development and production of the custom Silicon Photomultipliers (SiPMs) for the Mu2e Calorimeter (Mu2e SiPMs) was a complex endeavor, involving meticulous design, procurement, testing, and integration processes. After a thorough analysis of the calorimeter requirements, which translated into detailed technical specifications for the photosensors, a design and pre-production phase was conducted, to evaluate their construction parameters, via an international bidding process with the fabrication contract eventually awarded to Hamamatsu. The production phase, which started in 2018, consisted of manufacturing 3950 Mu2e SiPMs at a rate of 300 units per month, each engineered and quality-controlled to meet the stringent technical requirements. Assembly into the calorimeter disks was completed by December 2023, representing a significant milestone of the Mu2e project. This article offers a comprehensive account of the entire process, from design and procurement to testing and integration.

The Mu2e experiment at Fermilab searches for the neutrino-less conversion of a negative muon into an electron, with a distinctive signature of a mono-energetic electron with energy of 104.967 MeV. The calorimeter is made of two disks of pure CsI crystals, each read out by two custom large area UV-extended SiPMs. It plays a fundamental role in providing excellent particle identification capabilities and an online trigger filter while improving the track reconstruction, requiring better than 10% energy and 500 ps timing resolutions for 100 MeV electrons. In this paper, we present the status of construction and the Quality Control (QC) performed on the produced crystals and photosensors, the development of the rad-hard electronics and the most important results of the irradiation tests. Construction of the mechanics is also reported. Status and plans for the calorimeter assembly and its first commissioning are described.