Radiation damage from energetic particles at GRad-level of SiO2 fibers of the Large Hadron Collider ATLAS Zero-Degree Calorimeter (ZDC)

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2020-11, Vol.980, Article 164444
• Main Authors: Simos, N., Atoian, G., Bolotnikov, A., Sprouster, D., Tricoli, A., Medvedev, D., Palmer, M., Asner, D., Charitonidis, N., Mokhov, N., Kotsina, Z.
• Format: Article
• Language: English
• Subjects: Energetic protons; Fast neutrons; Quartz fibers; Radiation damage; Transmittance
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2020.164444

Core SiO2 quartz fibers of the Large Hadron Collider (LHC) ATLAS Zero-degree Calorimeter (ZDC) are expected to experience integrated doses of a few giga-Rad (Grad) at their closest position to the LHC beam. An array of fibers was irradiated with 200 MeV protons and spallation-generated mixed spectra (primarily fast neutrons) at the Brookhaven National Laboratory (BNL) Linac. Specifically, 1 mm- and 2 mm-diameter quartz (GE 124) rods of 50 mm length were exposed to direct 200 MeV protons leading to peak integrated dose of ∼28 Grad (∼0.28 GGy). Exposure of 1 mm-diameter SiO2 fibers to a neutron flux was also achieved in the spallation field generated by 128 MeV protons. In the post-irradiation analysis, the quartz fiber transmittance was evaluated as a function of the absorbed dose. Significant degradation of the transmittance and increased radiation damage of the material were observed. Microscopic evaluation of the fibers revealed extensive micro-structural damage and irradiation-induced defects. The measurements revealed that a threshold fluence (∼2.6 1016 p/cm2) or dose of ∼10 Grad (0.1 GGy) appears to exist beyond which light transmittance drops below 10%. Also observed is that fiber transmittance loss increased drastically with SiO2 fiber diameter (1 mm vs. 2 mm diameter). This is attributed, in part, to the earlier lateral leakage from the 1 mm fiber of knock-on electrons and primary protons implying that more damage-inducing protons travel within the bulk of the 50 mm long 2-mm fibers. While Monte Carlo simulations performed tend to support such assumption, future experiments and sensitivity studies are envisioned to address the fiber diameter influence on degradation.