Characterization of optic fiber for the LUCID-3 prototype during gamma irradiation at Calliope facility at ENEA

The luminosity is a fundamental running parameter for collider-based experiments since it is related to the cross section of every process and to the performance of the collider. Therefore its precise measurement is fundamental for every physics program. LUCID-2, the ATLAS main luminometer during Run-2, was able to measure luminosity with a precision of 1.7%. Similar performances are expected also for Run-3 but, starting from Run-4, the current design will not be able to satisfy all of the requirements foreseen by the ATLAS physics program. Therefore a new detector, called LUCID-3, must be built. There are several designs that can be grouped into two categories: fiber based detector and PMT-based detector. For testing purposes, 3 prototypes of LUCID-3 will be installed and tested during Run-3. One of these prototypes is a fiber based detector. For the correct operation of this prototype it is important to study how the fiber behaves when irradiated. Therefore a session of gamma irradiation was performed at the Calliope facility at ENEA. To study how the light transmission changes as a function of the wavelength, various LEDs, going from UV to visible light, were used to inject light into the fibers during the irradiation. As expected, the largest signal losses were observed when using UV light. The relative losses, after an exposure of 705 kGy, were measured as 97%, 94%, 42%, 20% and 27% for deep UV (280 and 340 nm), UV (385 nm) and visible (476 and 525 nm) respectively.