ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

The Madrid group has in 2010-11 developed, in collaboration with the company Mesytec a Temperature and Biascontrol of the preamplifier stage in order to cope with the very sensitive LAPD light collection diodes. The preamphas been further adapted to handle the huge dynamic energy range to be covered using the Time-Over-Thresholdmethod. The full system has been designed to fit with the specific crystal encapsulation and the boards modified sothat the preamplifiers with the temp and bias stabilisation are directly fitted onto the crystals.In the design of CALIFA's forward end cap an innovative solution using two scintillators crystals stacked together,one after the other, in a so called Phoswich configuration with a common readout is being considered, see the 2010annual report. The experiments using this first LaBr-LaCl Phoswich detector are now fully analysed and the resultfits perfect with the GEANT4 simulations we have performed, a NIM article, “A high ResolutionPhoswich:LaBr 3 (Ce) coupled with LaCl 3 (Ce)” is in preparation. Based on these results we have simulated, designedand constructed a CEPA demonstrator consisting 2x2 crystal cluster of 4 cm long LaBr 3 (Ce) coupled with 6cm longLaCl 3 (Ce) crystals in Phoswich configuration. This detector was delivered in December 2011, and is now beingmounted in a specially designed support structure, see the figure. During 2012 a full characterization and evaluationof this Phoswich approach will be performed.The CEPA(CALIFA Endcap Phoswich Assembly) detector mounted on a methacrylate table support for itscharacterization in the laboratory. On the right, a zoom of the pieces that contitutes CEPA. As seen the detector ismounted on a vacuum flange so it can be used together with our particle detectors.Focusing on the end-cap, IEM group has been working on the overall design of the end cap to obtain a perfectadaption to the CALIFA barrel. This design is independent of the final choice of crystal material. This design ismade so that the front-end cap, CEPA, can work as a stand-alone detector and on the same time be fully integratedinto the Barrel. The design goal is a perfect adaption to the barrel, with minimum dead material and a minimumnumber of overall crystals (each crystal ad an electronic chain) as well as a minimum number of crystal types (foreach type of crystal one will have to pay for the “mask/design” to the company). As the end cap is the lid of thebarrel it has the shape of a circular disc. In its present design it is formed by 750 crystals grouped in 10 equal“packages” of 75 crystals separated into 5 alveoli of 15 crystals. Further, as the crystal size along the polar anglehas to match with the effect of the Lorenz boost on the gamma rays emitted in flight, it is natural to divide the discinto ring segments. Every ring has a different polar direction depending on the energy resolution decided (k=3.75%). The geometry of the crystals are rectangular pyramids with truncated bases with their edges dependent on thepolar angular change (frustrum-shaped crystals), so that it is adapted to the energy uncertainty associated to the γLorentz transformation characteristic of relativistic velocities of the gamma radiation. The total dead volume(including wrapping) is 15 %.BEAM DIAGNOSTICS STUDIES FOR HIE-ISOLDEThe Dr. Francesca Zocca, sponsored by the Consolider CPAN project, is working in beam diagnostics developmentsthat are carried out on the framework of the R&D program for the HIE-ISOLDE superconducting (SC) upgrade ofthe REX-ISOLDE linear accelerator at CERN. In particular, a silicon monitor prototype has been developed andsuccessfully tested to be located downstream the cryogenic SC modules, for beam energy and timing measurementsaimed at the SC cavities phase tuning. The energy measurements performed at REX allowed for beam spectroscopyand ion identification with a resolution of 1.4 to 0.5 % rms in the REX energy range from 300 keV/u to 3 MeV/u.The time profile of the beam, characterized by a bunch period of 9.87 ns, has been measured with a resolution betterthan 200 ps rms. The achieved resolutions are suited for a fast phase tuning of the cavities, which has beendemonstrated at REX while using both energy and time-of-flight measurements.59