Barlini, S

Bini, M

Bonnet, E

Borderie, B

Bougault, R

Buccola, A

Camaiani, A

Casini, G

Chibli, A

Ciampi, C

Cicerchia, M

Cinausero, M

Dueñas, J A

Fabris, D

Frankland, J

Frosin, C

Gruyer, D

Henri, M

Kordyasz, A

Kozik, Tomasz

LeNeindre, N

Lombardo, I

Lopez, O

Mantovani, G

Marchi, T

Ottanelli, P

Pasquali, G

Piantelli, S

Poggi, G

Quicray, J

Stefanini, A A

Upadhyaya, Sahil

Valdré, S

Verde, G

Vient, E

Vigilante, M

Journal of Physics Conference Series

English

Jagiellonian Univeristy Repository

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing LtdDetection Systems and Techniques in Nuclear and Particle Physics (DeSyT2019)Journal of Physics: Conference Series 1561 (2020) 012003IOP Publishingdoi:10.1088/1742-6596/1561/1/0120031FAZIA: a new performing detector for charged particlesS Barlini*1,2, M Bini1,2, A Buccola1,2, A Camaiani1,2, G Casini2, C Ciampi1,2, C Frosin1,2, P Ottanelli1,2, G Pasquali1,2, S Piantelli2, G Poggi1,2, A A Stefanini1,2, S Valdré2, E Bonnet3, B Borderie4, R Bougault5, A Chibli6, M Cicerchia7,8, M Cinausero9, J A Dueñas10, D Fabris8, J Frankland6, D Gruyer5, M Henri5, A Kordyasz11, T Kozik12, N LeNeindre5, I Lombardo13, O Lopez5, G Mantovani7,8, T Marchi9, J Quicray5, S Upadhyaya12, G Verde13, E Vient5, M Vigilante14,151Dipartimento di Fisica, Università di Firenze, I-50019 Sesto Fiorentino, Italy2INFN-Sezione di Firenze, I-50019 Sesto Fiorentino, Italy                                              3IPNO, CNRS-IN2P3, Univ. Paris-Sud, Université Paris-Saclay, 91406 Orsay, France 4Subatech, EMN-IN2P3/CNRS-Université de Nantes, Namtes; France                          5LPC Caen, Normandie Univ, ENSICAEN, UNICAEN,CNRS/IN2P3, LPC  Caen,1400 Caen, France                                                                                                   6GANIL, CEA/DRF-CNRS/IN2P3, 14076 Caen, France                                                 7Dipartimento di Fisica, Università di Padova, 35131 Padova, Italy                                8INFN –Sezione di Padova, 35131 Padova, Italy                                                             9INFN –Laboratori Nazionali di Legnaro, 35020 Legnaro, Italy                                      10Depto. de Ingeniería Eléctrica y Centro de Estudios Avanzados en Física, Matemáticas y Computación, Universitad de Huelva, 21071 Huelva, Spain                   11Heavy Ion Laboratory, University of Warsaw, 02-093 Warszawa, Poland                   12Faculty of Physics, Astronomy and Applied Computer Science, Jagielloniam University, 30-348 Cracow, Poland                                                                                  13INFN-Laboratori Nazionali del Sud, 95123 Catania, Italy                                             14Dipartimento di Fisica, Università di Napoli, 80126 Napoli, Italy                                15INFN-Sezione di Napoli, 80126 Napoli, Italy*barlini@fi.infn.itAbstract.  The FAZIA apparatus  is  a  new detector  designed for  the Fermi  energydomain for charged particles based on three stages telescopes: Silicon detector (300μm thick),  Silicon detector  (500  μm thick)  and CsI(Tl)  (10 cm).  Using the  ΔE-Etechnique  and  the  Pulse  Shape  Analysis  (PSA)  it  permits  the  charge  and  massdiscrimination up to more than Z=20. In the following, some details about the FAZIAdetectors  and  electronics,  their  performance  and  the  first  experimental  campaignsalready performed will be discussed. Detection Systems and Techniques in Nuclear and Particle Physics (DeSyT2019)Journal of Physics: Conference Series 1561 (2020) 012003IOP Publishingdoi:10.1088/1742-6596/1561/1/01200321.  FAZIA: a first introductionThe FAZIA apparatus has been built within an international collaboration [1] with the aim to obtainthe best as possible charged particles identification in nuclear reaction studies in the domain of theFermi energy. For this reason, an intense R&D phase has been carried out in order to study the bestsolutions in terms of silicon detectors and electronics.        In particular, the collaboration decided to build a modular and versatile apparatus, based on 3 stagestelescopes with the dimension of 2x2 cm, read by a fully digital electronics integrated on board. Thestructure of the telescope is Silicon (300  μm – Si1 in the following) + Silicon (500  μm – Si2) +CsI(Tl) (10 cm). In this way, at Fermi energy (20-80 AMeV) the less energetic or the heaviest chargedfragments can be identified using the Si1 vs Si2 correlation, while the most energetic and the lightestones with the Si2 vs CsI correlation and even, in limiting cases, only using the intrinsic fast-slowmethod for CsI(Tl) scintillators. The 10 cm thickness of the CsI crystals guarantees to stop into thedetector also the most energetic protons (up to 195 MeV) produced in the reaction. To decrease theidentification threshold, the Pulse Shape Analysis is applied to the silicon detectors.  2.  The FAZIA block: detectors and electronics.The first part of the FAZIA R&D has been devoted to the tests of the single pad silicon detectors,in order to study the effect of the channeling phenomena with respect to the identification capability,the effect of the detector mounting (rear or front mounting), the type of the Pulse Shape (using themaximum of the current signal or the rise-time of the charge signal) and the effect of the dopinghomogeneity  on  the  Pulse  Shape  Analysis.  All  those  different  aspects  have  been  studied  withdedicated experiments, mainly at LNS (Laboratori Nazionali del Sud, Catania, Italy) using differentsetups and configurations.The result is the so called “FAZIA recipe”, which consists in a list  of features that the silicondetectors of the FAZIA apparatus have to respect: "Random" cut  of  the Silicon wafers  which are  tilted with respect  to  the major  crystaldirection in order to avoid as much as possible the channeling effect [2]; Usage of nTD (neutron Transmutation Doped) Silicon detectors (or High Purity Silicon)with good dopant homogeneity (1-3%) to preserve as much as possible the PSA [3]; Reverse mounting configuration of Silicon detectors: the particles enter from the low-fieldside, permitting a better PSA performance without losing any identification capability inthe ΔE-E correlation [4]; An Aluminum layer of about 30 nm on both sides of detectors: negligible sheet resistanceto avoid position-dependence of the signal shapes, that would degrade the PSA consideringthat the FAZIA silicon are single pad 2x2 cm detectors; High thickness uniformity and planarity (around 1um) to preserve the ΔE-E correlation onthe full size of the detector.It is important to stress that the reverse current on the silicon detectors must be controlled. In fact,its variation during the experiment will change the effective applied voltage on the silicon junction,producing a varying electric field into the detector and consequently a different Pulse Shape during theexperiment for the same impinging particles. For such a reason, a monitoring of the reverse current isDetection Systems and Techniques in Nuclear and Particle Physics (DeSyT2019)Journal of Physics: Conference Series 1561 (2020) 012003IOP Publishingdoi:10.1088/1742-6596/1561/1/0120033needed in order to compensate the voltage drop on the bias resistance keeping the voltage on thesilicon junction constant during the whole experiment.After the definition of the elementary telescope, the collaboration focused on the electronics and onthe  mechanics  needed to group a  significant  number  of  single  telescopes.  The  idea was to  buildsomething versatile, easy to mount in different configurations and easy to transport in the differentlaboratories  where  the  FAZIA group aimed  measuring.  This  is  possible  exploiting  the  enormouspotentiality of the fast digital electronics which is mounted as much as possible near to the detectors topreserve as best the signal quality for the PSA.Figure 1. Left panel: a matrix of 2x2 silicon detectors glued in the supporting frame with connection flexible strips. Rightpanel: a FAZIA quartet made of 4 telescopes. The  final  result  of  the  work  is  the  FAZIA block,  which  consists  in  4  quartets  formed  by  4Si+Si+CsI telescopes with all the electronics directly coupled under vacuum in the scattering chamber.The mechanics is designed to minimize as much as possible the dead zone between the telescopes. Aquartet is build using two frames made by Ergal (a light and robust Aluminum alloy) with the electro-erosion method on which 4 silicon detectors are directly glued. Particular care has been dedicated tothe silicon contact which has been realized using kapton strips directly bounded to the silicon chips(see Fig.1, left panel). The two frames are piled and fixed on a cross supporting structure hosting alsothe corresponding four CsI(Tl) crystals (see Fig1, right panel). On top of the structure, a collimator isplaced to avoid border effects on the detectors. Finally, 4 quartets are mounted together on a specificholder which also gives the telescope orientation considering a target distance of 100 cm. Detection Systems and Techniques in Nuclear and Particle Physics (DeSyT2019)Journal of Physics: Conference Series 1561 (2020) 012003IOP Publishingdoi:10.1088/1742-6596/1561/1/0120034Figure 2. A FAZIA block: detectors, FEE and service cards can be easily distinguished. Directly fixed to the same frame of the quartets, there is the digital homemade electronics whichconsists in 8 Front-End Cards (each of them is developed to serve two complete FAZIA telescopes)and three service cards (Block card for the I/O, Half  Bridge and High Voltage to create the lowvoltages needed in the FEE and the HV for the photodiodes of the CsI(Tl) crystals). In Fig.2, a blockof the FAZIA apparatus is shown. The total dimensions are around 80 cm of length. The detectors, theFEE and the service cards are visible. More details  about the electronics can be found in [5],  here we only report  some of the maincharacteristics.  In  each  FEE  card,  we  have  a  first  pre-amplification  stage  with  six  channels  (2telescopes), then we have 6 ADCs at 14 bits for each telescope and an FPGA to perform on-boardcalculation and trigger.  Then,  the FEE card hosts  also the circuits  to  produce the HV for  silicondetectors, which include the monitoring of the reverse current with an automatic check in order tokeep constant the HV on the silicon junction. The 6 ADCs are needed because we have 3 differentelectronic channels for Si1 (charge output with 4 GeV range sampled at 100 MHz, charge output with250 MeV range sampled at 250 MHz, current signal sampled at 250 MHz derived analogically fromthe charge output), 2 channels for Si2 (charge at 4 GeV and current signals) and finally a channel forthe CsI (only charge signal). The use of the current signal is needed to perform the maximum of thecurrent signal which is used in the PSA. The FEE contains also a pulse generator useful to test theelectronics stability during the experiment. All the blocks are connected by optical fiber to a Regional Board (RB) which is located out of thescattering chamber. In the RB the main trigger is generated starting from the local triggers created inthe various FEE with a fast shaping. Each local trigger is an OR-combination of logic signals fromeach detector of the telescopes, while the global trigger is a trigger of multiplicity of the previous ones.A different scaling factor can be introduced in the RB for each multiplicity trigger. The acquisition isconnected to the RG by mean of an Ethernet link. Detection Systems and Techniques in Nuclear and Particle Physics (DeSyT2019)Journal of Physics: Conference Series 1561 (2020) 012003IOP Publishingdoi:10.1088/1742-6596/1561/1/0120035Figure 3. A chart of Nuclides built with particles coming from the reaction 48Ca+48Ca@35AMeV fully identified by FAZIA.Each single FAZIA block can work alone, and the only connections needed are two optical fibers(one for input and one for output) and a power 48 V link from which all the low voltages needed bythe FEE and the HV for CsI(Tl) photodiodes are created in the service cards. Of course, consideringthat a part from the RB all the FAZIA electronics is under vacuum, the cooling is a very importantissue taking into account that the power consumption of each FEE is around 25 W. For this reason, theelectronic cards are mounted on a cold copper plate with particular attention in order to guarantee thebest thermal contact. In the copper plate, a mixture of water and alcohol is circulating and kept at fixedtemperature using an external chiller to dissipate the heat created in the electronics. At regime, thetemperature of the FEE controlled in various hot spots, stays normally below 50-60°C. With a single RB up to 36 FAZIA blocks could be connected. The installation of the blocks andtheir connection is quite easy: for each block (it means 16 telescopes), three connections are needed,i.e 2 optical fibers, a 48 V cable and the cooling system. In this sense the purpose to have a versatileand easy movable set-up is fully accomplished by the FAZIA apparatus. Thanks to the big effort of the collaboration to have the best performance from the detectors andthe electronics, the identification capability in terms of charge and mass identification of the chargedfragments reached by the FAZIA apparatus fears no rivals: a complete identification (mass and charge)up to more than Calcium ions for all the fragments that punch-through the first silicon layer, as onecan see in Fig.3. Some identification in charge and mass is moreover achievable using the PSA appliedto the first layer. A global evaluation of the identification threshold and capability is given in the Fig.4taken from [6] using the system 40,48Ca+40,48Ca@35 AMeV. One should consider that there are somefluctuations between the detectors due to a different noise level or aging, and that for this particularDetection Systems and Techniques in Nuclear and Particle Physics (DeSyT2019)Journal of Physics: Conference Series 1561 (2020) 012003IOP Publishingdoi:10.1088/1742-6596/1561/1/0120036experiment  the  statistics  of  particles  detected  with  charge  more  than  20  is  lower.  Using  heavierprojectiles (as Kr and Xe), better results have been reached for some telescopes in terms of massseparation (up to charge around 24-25) [7].    Figure 4. Performances and identification regions for the  40,48Ca+40,48Ca@35 AMeV reactions. 3.  The physics items investigated with the FAZIA blocks.The excellent identification capability of the FAZIA apparatus can be used to investigate differentphysics items. It has been designed mainly to approach the study of the isospin transport in nuclearreactions, which is connected to the study of the Nuclear Equation of State for the Asymmetric matter,but  it  can  be  used as  particle  correlator  and in  general  in  all  the  experiments  where  an  isotopicidentification is important.  Starting from 2015, at least 4 blocks up to a maximum of 6 blocks of the FAZIA apparatus havebeen used for different experiments all performed at the LNS with a “wall” or “belt” configuration,depending on the cases. In particular, the following experiments have been performed:  80Kr+40,48Ca@35  AMeV  and  40,48Ca+40,48Ca@35  AMeV  focusing  on  the  exited  Quasi-Projectile decay and the Isospin transport mechanism. It is important to note that using theCa beam the fission fragments from the Quasi-Projectile breakup are fully identifiable interms of  charge and mass  by the FAZIA apparatus,  if  they are  inside the geometricalacceptance. The same occurs also for the great part of the Kr* fissions. This is not usual insuch type of studies, where usually only one of the two fragments is fully identified by amagnetic spectrometer (no coincidences),  while for most other multi-detectors there arelimitations in mass separation typically beyond oxygen.  20Ne,32S+12C@25,45 AMeV where the particle correlation technique is applied to study thein-medium effects in the decay of fragments created in the nuclear reactions. Note thatthanks to the identification capability of FAZIA, also correlation between Light ChargedParticles (Z=1,2) and Intermediate Mass Fragments (Z between 6 and 10) can be detectedand analysed.  Detection Systems and Techniques in Nuclear and Particle Physics (DeSyT2019)Journal of Physics: Conference Series 1561 (2020) 012003IOP Publishingdoi:10.1088/1742-6596/1561/1/0120037 40,48Ca+12Ca@20,40 AMeV where the question of the Isospin mechanism versus the beamenergy is approached to study how the possible appearance of a preferential neutron pre-equilibrium emission  can  decrease  the  initial  isospin  difference  between projectile  andtarget 12C+12C@62 AMeV (in  collaboration  with  the  Beihang University)  to  test  the  FAZIAblocks for cross section measurements at zero degrees with very low current beams. Thetest  was  performed on  a  rather  well  known system,  but  the  final  goal  concerns  crosssections of reactions with exotic ions,  using selected fragmentation beams at  cyclotronfacilities. The analysis of those experiments is in some cases still in progress, while results from the first twoexperiments are near to be published.  Presently, 12 blocks of FAZIA are coupled to the INDRA 4π detector [8] at GANIL; they cover theangular range between 1.5°≤θ≤14° to detect with precision mainly the QP decay products, while theINDRA  detector  covers  a  large  part  of  the  rest  of  the  solid  angle  thus  allowing  for  a  goodcharacterization of the reaction mechanism. A big effort has been devoted to couple together those twodetectors, a task complicated by the fact that INDRA is based on old analog electronics. During the2019,  an  experimental  campaign  about  the  isospin  transport  mechanism  has  been  performedmeasuring the systems 58,64Ni+58,64Ni@32,52 AMeV. About 30 Million of events for each combinationof projectile, target and energy have been collected and the analysis is now in progress. 4.  ConclusionsThe FAZIA apparatus represents one of the best detectors for charged particles in the range between20-60 MeV/n in term of identification capability with reasonable energy threshold. It can be used fordifferent purposes, mainly connected to isospin transport in nuclear collisions by accurately detectingQuasi-Projectile and their emission particles for which a complete isotopic characterization is crucial,but not only. At present, 12 blocks are coupled to the INDRA detector at GANIL, while 4 blocks willbe available for different experiments also in other laboratories.  AcknowledgmentsAuthors wish to remember here the colleague Prof. Mauro Bruno from the University of Bologna(Italy)  deceased in  2019.  He  dedicated his  carrier  to  study heavy-ion reactions  with  passion  andcompetence, becoming a point of reference for all the students of the Bologna University interested inthe nuclear physics and for his colleagues during his entire professional life.    References[1] More information on http://fazia.in2p3.fr[2] Bardelli L et al. 2009 Nucl. Instr. and Meth. A 605  353Bardelli L et al. 2011 Nucl. Instr. and Meth. A 654  272[3] LeNeindre N et al. 2013 Nucl. Instr. and Meth. A 701 (2013) 145[4] Valdré S et al. 2019 Nucl. Instr. and Meth. A 930 27[5] Camaiani A, Ph.D Thesis, University of Florence[6] Carboni S et al. 2012 Nucl. Instr. and Meth. A 664 251[7] Pouthas J et al. 1995 Nucl. Instr. and Meth. A 357(2-3) 418

FAZIA : a new performing detector for charged particles

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FAZIA : a new performing detector for charged particles

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