Giovanni Organtini

The L3 lead-scintillating fiber calorimeter

Abstract We report on the construction and test of a lead-scintillating fiber ( spaghetti ) calorimeter built to fill the gap between endcaps and barrel in the L3 BGO detector. Results from test-beam, as well as MC simulations for the prototypes and for the full detector, are presented.

Ordinary and extraordinary complex refractive index of the lead tungstate (PbWO4) crystal

Abstract The ordinary and the extraordinary complex refractive index of PbWO 4 together with the crystal optical axis orientation are determined on the basis of transmittance and reflectance measurements at normal incidence with polarised light and the measurement of the separation angle between the ordinary and the extraordinary ray at various laser wavelengths. The real part of the extraordinary complex refractive index is lower than the ordinary one (i.e. PbWO 4 is a negative uniaxial crystal) and they seem not to be affected by a 30 ppm Nb 5+ doping.

Precise determination of the light yield of scintillating crystals

Abstract A method to determine the photopeak position of the γ absorption spectrum of radioactive sources in low light yield scintillators as lead tungstate is discussed. The method is based on the parametrization of both the Compton and photoelectric contributions to the spectrum and it is proven to be reliable and to give stable and precise results.

Beam tests of lead tungstate crystal matrices and a silicon strip preshower detector for the CMS electromagnetic calorimeter

Tests of lead tungstate crystal matrices carried out in high-energy electron beams in 1996, using new crystals, new APDs and an improved test set-up, confirm that an energy resolution of better than 0.6% at 100 GeV can be obtained when the longitudinal uniformity of the struck crystal is adequate. Light loss measurements under low dose irradiation are reported. It is shown that there is no loss of energy resolution after irradiation and that the calibration change due to light loss can be tracked with a precision monitoring system. Finally, successful tests with a preshower device, equipped with silicon strip detector readout, are described.

An automatic device for the quality control of large-scale crystal's production

Abstract In 1999, the construction of the electromagnetic calorimeter of the Compact Muon Solenoid (CMS) experiment started. Half of the barrel calorimeter made of 61200 lead tungstate (PWO) crystals will be assembled and tested in the Regional Centre of INFN-ENEA in Rome, Italy. Before assembling, all 30600 PWO crystals will be qualified for scintillation and radiation hardness characteristics by a specially built Automatic Crystal Control System. The measuring techniques for crystal qualification and performances of the automatic system will be discussed in this work.

Influence of Gd3+ Concentration on PbWO4:Gd3+ Scintillation Characteristics

The influence of Gd 3+ doping on the optical properties of PbWO 4 has been investigated by radio- and thermoluminescence, photoluminescence time decay, optical absorption and light yield measurements. The samples were grown by the Czochralski method and the concentration of Gd in the melt was in the range 0 to 135 mol. ppm. The results demonstrate that a dopant concentration of around 100 ppm in the crystal appears as the best one in order to optimise the scintillation performance of the material.

Influence of vacuum annealing on properties of PbWO4 crystals

Transmittance and luminescence measurements of Bi-doped and Nb-doped PbWO4 crystals after vacuum annealing were performed. Annealing effect on the optical and scintillation properties of the crystals was detected at various annealing temperatures. The gamma radiation damage is presented at different absorbed doses to investigate radiation resistance after annealing.

Beam test results for a tungsten-cerium fluoride sampling calorimeter with wavelength-shifting fiber readout

A sampling calorimeter using cerium fluoride scintillating crystals as active material, interleaved with heavy absorber plates, and read out by wavelength-shifting (WLS) fibers is being studied as a calorimeter option for detectors at the upgraded High-Luminosity LHC (HL-LHC) collider at CERN. A prototype has been exposed to electron beams of different energies at the INFN Frascati (Italy) Beam Test Facility. This paper presents results from the studies performed on the prototype, such as signal amplitudes, light yield and energy resolution.

Performance of an automatic bench for scintillating crystal light yield measurement

Abstract In this paper, we describe a fully automatic device for the measurement of the light yield and the light collection efficiency of scintillating crystals. We also report the bench performance in terms of resolution and speed.

Detection of photons generated in PbW04 scintillator crystals

This work deals with the optical characterisation of the surface of EG&G and Hamamatsu APDs and performance of an antireflection coating made of Y2O3 and deposited on a PWO test piece. The effect of antireflection treatments of PWO and Si surfaces is evaluated in a simplified and a realistic situation by means of the ratio of “detected to emitted photons”.