Preliminary Results from in Situ Quartz Fiber Neutron Irradiations

Optical transmission characteristics of multi-mode synthetic silica-core fibers between 325 nm and 800 nm were studied in situ while irradiated with neutrons. In one case, fiber samples were placed in the core of a 10-kWatt reactor; in the other, fast neutrons generated by p ( 18 MeV) + Be reaction in a cyclotron, irradiated the fibers. The neutron fluence in both studies totaled ~10^15 n/cm2. Both of these initial studies indicate that in the sensitivity region of bialkiline PMTs, the irradiation induced loss is ~1dB/m. These initial experiments are aimed at establishing a fiber testing methodology for assessing the expected degradation of the CMS forward calorimeter at the LHC due to large neutron backgrounds.