Properties of the CsI(Tl) detector elements of the CALIFA detector

12 pags., 12 figs., 3 tabs. -- Open Access funded by Creative Commons Atribution Licence 4.0In the RB experiment at FAIR, charged particles with energies up to 600 MeV and forward boosted γ-rays with energies up to 20 MeV need to be detected in scattering experiments. Calorimeters for nuclear physics experiments of this kind, using relativistic radioactive ion beams, require high energy resolution and high efficiency for simultaneous detection of strongly Doppler shifted γ-rays and high-energy charged particles. A calorimeter design that can meet these requirements, using CsI(Tl) scintillators, results in detector elements that may exhibit light output variations with crystal depth, which can limit the attainable resolution. In this paper we present results from a systematic study of 478 detector modules of CALIFA, the RB calorimeter, in order to determine and minimize such variations. To facilitate further systematic studies we also present results for the total absorption length of the scintillation light, using spectrophotometry, light crosstalk between adjacent detector modules, and surface topography of the CsI(Tl) crystals from atomic force microscopy.This work was supported by the Swedish research council (VR)grants 2017-03986, 2014-06644, 2013-04178, 2012-04550, BMBF,Germany contracts 05P15WOFNA, 05P19WOFN1, 05P15RDFN1,05P19RDFN1, the TU Darmstadt - GSI cooperation contract and HICfor FAI

Performance recovery of long CsI(Tl) scintillator crystals with APD-based readout

6 pags., 8 figs., 3 tabs.CALIFA is the high efficiency and energy resolution calorimeter for the RB experiment at FAIR, intended for detecting high energy light charged particles and gamma rays in scattering experiments, and is being commissioned during the Phase-0 experiments at FAIR, between 2018 and 2020. It surrounds the reaction target in a segmented configuration with 2432 detection units made of long CsI(Tl) finger-shaped scintillator crystals. CALIFA has a 10 year intended operational lifetime as the RB calorimeter, necessitating measures to be taken to ensure enduring performance. In this paper we present a systematic study of two groups of 6 different detection units of the CALIFA detector after more than four years of operation. The energy resolution and light output yield are evaluated under different conditions. Tests cover the aging of the first detector units assembled and investigates recovery procedures for degraded detection units. A possible reason for the observed degradation is given, pointing to the crystal-APD coupling.This work has been financially supported by the European Union Horizon 2020 research and innovation programme under grants agree-ments No 262010 (ENSAR) and No 654002 (ENSAR2), the Spanish MICCIN grants FPA47831-C2-1P and FPA2015-69640-C2-1-P, by the Plan Galego de Investigación, Innovación e Crecemento (I2C) of Xunta de Galicia, Spain under projects POS-B/2016/015, GRC2013-011 andED431C 2017/54 and by the German BMBF (No. 05P19RDFN1), TUDarmstadt - GSI cooperation contract, HIC for FAIR

Commissioning of the CALIFA Barrel Calorimeter of the R3B Experiment at FAIR

5 pags., 4 figs. -- FAIRNESS2019: FAIR NExt generation ScientistS 20-24 May 2019, Arenzano, Genova, ItalyCALIFA is the high efficiency and energy resolution calorimeter for the R3B experiment at FAIR, intended for detecting high energy charged particles and ¿-rays in inverse kinematics direct reactions. It surrounds the reaction target in a segmented configuration of Barrel and Forward End-Cap pieces. The CALIFA Barrel consists of 1952 detection units made of CsI(Tl) long-shaped scintillator crystals, and it is being commissioned during the Phase0 experiments at FAIR. The first setup for the CALIFA Barrel commissioning is presented here. Results of detector performance with ¿-rays are obtained, and show that the system fulfills the design requirements.The author’s work has been financially supported by the Spanish MICCIN grant FPA2015-69640-C2-1-P

Tl concentration and its variation in a CsI(Tl) crystal for the CALIFA detector

9 pags., 6 figs.One of the factors that can contribute to the resolution of long, doped inorganic scintillators used for nuclear spectroscopy is the variation of the dopant concentration over the length the detector crystal. In this work an investigation of such potential variations in one of the CsI(Tl) scintillators used in the calorimeter, CALIFA, of the RB experiment at FAIR, has been performed using particle induced X-ray emission. No statistically significant gradient in doping level was found along the long axis of the investigated sample crystal and the mean value of the Tl concentration was measured to be 0.0839(38)% by weight. This corresponds to a light output of 97.3 % relative to the maximum attainable light output according to previously published work. By taking the ±1σ bounds, the 3% statistical spread in the relative light output provides a good reference value of the minimum light-output non-uniformity observed for the CALIFA crystals. If the relative light output is estimated pointwise from a set of Tl concentration measurements a light-output non-uniformity of 4.6(2.4)% results. For a γ-ray energy of 662 keV the deduced variation in Tl concentration contributes with 0.48(6)% to the typical resolution of 7.74(6)% measured with a collimated source along the crystal main axis. The result is of interest for the characterization of the detector system performance and for realistic simulations of the light collection process in detector systems that are used for nuclear spectroscopy and calorimetry.This work was supported by the Swedish research council (VR) grants 2017-03986, 2014-06644, 2013-04178, 2012-04550, BMBF contracts 05P15WOFNA, 05P19WOFN1, 05P15RDFN1, 05P19RDFN1, the TU Darmstadt – GSI cooperation contract HIC for FAIR, by the Spanish National Research Council, Spain grants FPA02015-64969-P (MINDECO/FEDER/EU), FPA2015-69640-C2-1-P, PGC2018-099746-B-C21, MDM-2016.0692 (MINECO/FEDER/EU) and by GRC, Germany ED431C 2017/54 (Xunta de Galicia/FEDER/EU)

Simulations of light collection in long tapered CsI(Tl) scintillators using real crystal surface data and comparisons to measurement

10 pags., 9 figs., 2 tabs.Simulation results for light transport in long tapered CsI(Tl) crystals using look-up tables (LUTs) are presented. The LUTs were derived from the topography of a polished and a lapped surface of a CsI(Tl) crystal measured with atomic force microscopy. Simulations with different combinations of polished and lapped surfaces were performed, to extract the non-uniformity of light collection depending on the interaction point, and compared to experimental results. The simulations reproduce the general trend given by the measurements, and show that more homogeneous light collection is attained when all lateral sides of the crystal are lapped. For the lapped crystal the simulation model is most sensitive to the reflectivity of the enhanced specular reflector (ESR) foil surrounding the crystal, which is one of several properties influencing the light transport examined in this study. The sensitivity of the light-output non-uniformity to variations in the absorption length observed in a batch of CsI(Tl) crystals in a previous study is also discussed. Residual differences between the simulation and the measurements can potentially be attributed to the scattering of scintillation photons inside the materials used. Additional measurements to further advance the construction of the simulation model are suggested.This work was supported by the Swedish research council (VR) grants 2017-03986, 2014-06644, 2013-04178, 2012-04550, BMBF contracts 05P15WOFNA, 05P19WOFN1, 05P15RDFN1, 05P19RDFN1, the TU Darmstadt – GSI cooperation contract HIC for FAIR, by the Spanish research council grants FPA02015-64969-P (MINDECO/FEDER/EU), FPA2015-69640-C2-1-P, PGC2018-099746-B-C21, MDM-2016.0692 (MINECO/FEDER/EU) and by ED431C-2017/54 and EDB481-2017/002 (Xunta de Galicia/FEDER/EU).Peer reviewe

\u27Take a deep breath’: how recreational SCUBA divers negotiate in-water constraints

A significant body of work now exists on what constrains people\u27s leisure. While early theorizations of constraints focused on what prevented individuals from participating in leisure, the literature has expanded to include discussions on how constraints may be negotiated, overcome or substituted. This article explores constraints negotiation in the context of adventurous leisure. This study considers how leisure constraints are negotiated in the in-situ experience of recreational scuba diving. In-depth interviews were conducted with 27 recreational divers. Analysis revealed three interrelated negotiation strategies used to deal with in-situ constraints, namely consolidate, co-operate, or cancel. These negotiation techniques were influenced by factors including divers\u27 histories, perceptions of the severity of the constraint and in-water experience. Findings support the recognition of in-situ constraints negotiation in adventurous leisure. Results highlight the need to reflect on how individuals negotiate constraints during leisure, particularly in difficult environments which can present unpredictable and dangerous risks