Tested: 15 types of LEDs (blue, green); quartz fibers with core diameters of 300µm and 50µm. Proposal: Blue LEDs rather than green: + : larger signal, because of higher QE + : less radiation damage in quartz fibers - : maybe more attenuation in the 40 cm piece of clear fiber than for Y11 light For inner region – fibers with a core diameter of at least 100µm, to have large enough amplitude (super rad. hard also available) HV=650V, Max. signal ~ 1200 ADC counts; For middle and outer regions – 50µm fibers is enough (super rad. hard ) HV=850V, Max. signal ~ 1200 ADC counts.

Radiation hardness of quartz fibers Quartz fibers as active elements in detectors for particle physics Nural Akchurin and Richard Wigmans Citation: Rev. Sci. Instrum. 74, 2955 (2003); doi: / View online: View Table of Contents: Published by the American Institute of Physics.

The OH − (hydroxide ion) content of the core affects the optical transmission and it is formulated at the preform stage. Low OH − fibers have very low attenuation throughout the infrared range from 700 to 1800 nm, except for a small absorption band at 1380 nm. On the other hand, fibers with a high-OH − core perform significantly better in the near ultraviolet region and are more radiation resistant.

Figure. 24 shows a typical radiation-induced attenuation profile for a high- OH − QP fiber when irradiated with 500 MeV electrons. There is enhanced absorption for wavelengths <380 nm, so-called UV tail, a relatively shallow dip around 450 nm, and a strong absorption peak around 610 nm. For most quartz fibers, the optical transmission loss at 450 nm amounts to 20%–40% for an absorbed dose of 1 MGy. This wavelength is of particular importance, since most generic photomultiplier tubes have a good quantum efficiency in this region. Interestingly, the wavelength range where PMTs are most sensitive is at the same time the most radiation hard spectral region of these quartz fibers. This is a very fortunate coincidence indeed. The radiation-induced attenuation (A) depends both on the accumulated dose (D) and on the wavelength (λ). This dependence is usually expressed in the form of a power law: A(λ,D)=α(λ)*(D/D0) β(λ), Where α and β are parameters that describe the radiation hardness properties of a given type of fiber, and D0 is the reference dose. For convenience, we will chose D0 to be 1 MGy, so that at that value, α represents the induced attenuation. When similar high- OH − quartz fibers were irradiated, α values were found to range from 1.3 to 1.6 (dB/m) at 450nm. The β parameter varied between 0.2 and 0.4. In the case of the dose of 2 Mrad: A(λ,D)=0.21 (dB/m) or 5%/m attenuation.

FIG. The induced in situ attenuation profile measurement for a high- OH − QP fiber at 0.54 MGy shows enhanced attenuation in the shorter wavelengths and a strong absorption peak around 610 nm.

dB/100m

Bend Radius for core/cladding/coating (105µm/125µm/250µm)

-105/125µm fibre (pure-silica core/Fluorine doped cladding) + acrylate coating. -100/170µm fibre with Fluorine doped core / Fluorine doped cladding + acrylate coating. -standard PCS fibre (200/230/500µm) Fiber samples from DRAKA