M. Gascon

Optimization of Energy Resolution Obtained With CsI(Tl) Crystals for the R3B Calorimeter

Studies with different CsI(Tl) crystals coupled to avalanche photodiodes were performed in the frame of the R+D programme for the design of the R3B calorimeter (CALIFA). The study of the energy resolution has been performed for crystals with lengths varying from 1 to 10 cm and square section (1 times 1 cm2), attending to different optimization of parameters (i.e., crystal wrapping, optical coupling to the avalanche photodiode and the electronic chain). The obtained results with avalanche photo-diodes are very promising and suggest CsI(Tl) as a suitable candidate for at least part of the calorimeter.

Nonproportionality and Scintillation Studies of

The low temperature scintillation properties of 5 atomic % Eu:SrI2 from ambient temperature down to 5 K were studied for the first time. With decreasing temperature, a shift in emission wavelength and a shortening of decay time were observed. Light yield and energy resolution exhibited notable changes with temperature, and were maximized as temperature was decreased. A degradation of light yield proportionality with decreasing temperature was observed.

{\hbox{Eu:}} {\hbox{SrI}}_{\rm 2}

Results are presented from a one-neutron knockout reaction at relativistic energies on 56Ti using the GSI FRS as a two-stage magnetic spectrometer and the Miniball array for gamma-ray detection. Inclusive and exclusive longitudinal momentum distributions and cross-sections were measured enabling the determination of the orbital angular momentum of the populated states. First-time observation of the 955(6) keV -hole state in 55Ti is reported. The measured data for the first time proves that the ground state of 55Ti is a 1/2- state, in agreement with shell-model calculations using the GXPF1A interaction that predict a sizable N=34 gap in 54Ca.

From 295 to 5 K

Studies with different bi-frustum CsI(Tl) crystal samples from several providers, coupled to large area avalanche photodiodes (Hamamatsu S8664-1010 2CH), specifically developed for this project, were performed as part of the R&D program for the design of the R3B calorimeter (CALIFA). Particular attention is given to the energy resolution optimization for CsI(Tl) crystal samples with realistic dimensions. The results obtained with Large Area Avalanche Photo-Diode (LAAPD) are very promising and suggest CsI(Tl) as a suitable candidate for the Barrel part of the calorimeter.

Structure of 55Ti from relativistic one-neutron knockout

Studies with different bi-frustum CsI(Tl) crystal samples from several providers, coupled to large area avalanche photodiodes (Hamamatsu S8664-1010 2CH), specifically developed for this project, were performed as part of the R&D program for the design of the R3B calorimeter (CALIFA). Particular attention is given to the energy resolution optimization for CsI(Tl) crystal samples with realistic dimensions. The results obtained with Large Area Avalanche Photo-Diode (LAAPD) are very promising and suggest CsI(Tl) as a suitable candidate for the barrel of the calorimeter.

Characterization of Large Frustum CsI(Tl) Crystals for the

The low temperature scintillation properties of LSO:Ce from 4.3 to 300 K were systematically studied and temperature-dependent light yield nonproportionality was measured for the first time. Increasing temperature from 4.3 to 300 K led to increased decay times and light output, an improvement in both the total energy resolution and light yield nonproportionality, and a red shift in the emission. Mechanisms were proposed to explain the complex trends observed in these scintillation properties.

{\rm R}^{3}{\rm B}

We describe the design and operation of a unique hydraulic press for the study of scintillator materials under isostatic pressure. This press, capable of developing a pressure of a gigapascal, consists of a large sample chamber pressurized by a two-stage hydraulic amplifier. The optical detection of the scintillation light emitted by the sample is performed, through a large aperture optical port, by a photodetector located outside the pressure vessel. In addition to providing essential pressure-dependent studies on the emission characteristics of radioluminescent materials, this apparatus is being developed to elucidate the mechanisms behind the recently observed dependency of light-yield nonproportionality on electronic band structure. The variation of the light output of a Tl:CsI crystal under 511-keV gamma excitation and hydrostatic pressure is given as an example.

Calorimeter

Among the variety of crystal calorimeters recently designed for several physics facilities, CALIFA (CALorimeter for In-Flight emitted gAmmas and light-charged particles) has especially demanding requirements since it must perform within a very complicated energy domain (gamma-ray energies from 0.1 to 20 MeV and up to 300 MeV protons). As part of the R&D program for the Barrel section of CALIFA, a reduced geometry prototype was constructed. This prototype consisted of a 3 ? 5 array of CsI(Tl) crystals of varying dimensions, coupled to large area avalanche photodiodes. Here reported are the details regarding the construction of the prototype and the experimental results obtained at the NEPTUN tagged gamma beam facility, reconstructing gamma energies up to 10 MeV. Dedicated Monte Carlo simulations of the setup were also performed, enabling a deeper understanding of the experimental data. The experimental results demonstrate the effectiveness of the reconstruction method and helped to establish the most suitable crystal geometry to be employed within the forthcoming calorimeter.

Characterization of large frustum CsI(Tl) crystals for the R3B calorimeter

Several studies with different Large Area Avalanche Photo-Diodes (LAAPDs) coupled to ad-hoc bi-frustum shaped CsI(Tl) crystals have been carried out as a part of the R&D program for the CALIFA R3B/FAIR calorimeter. CALIFA, which is designed for the detection of light charged particles and gamma-rays in a wide energetic domain, has very stringent requirements. We report in this work our studies on the energy resolution for gamma-rays using LAAPDs as photosensors. One of the factors affecting the energy resolution is the matching between the APD active area and the crystal exit face. We present in this paper a procedure for characterizing APDs based on the measurement of their contribution to the energy resolution. The results obtained are very promising and suggest that a solution based on CsI(Tl) crystals coupled to LAAPDs could be suitable for, at least, part of the CALIFA calorimeter.

Nonproportionality and Scintillation Responses of LSO:Ce From 4.3 to 300 K

The nuclei Ca-47 and Ti-55 were populated in one-neutron knock-out reactions at relativistic energies. Momentum distributions of the residual nuclei as well as gamma-ray spectra were measured at the GSI fragment separator (FRS). Preliminary results of the ongoing analysis including cross sections and spin/parity assignments are presented.