CHIMERA (Charged Heavy-Ion Mass and Energy Resolving Array) is a multidetector operating at Laboratori Nazionali del Sud since the new millennium, in its complete 4π configuration [1,2]. It is made of 1192 detection units, each one consisting of a Silicon first stage detector (300 µm), followed by CsI(Tl) crystal, which thickness ranges from 12 to 3 cm, depending on the angle, coupled to a photodiode as second stage. 688 telescopes are arranged in 18 rings covering the polar angles between 1 ° and 30 ° (forward part). These telescopes are placed at a large distance from the target in order to have an enough base of flight and a good solid angle segmentation. In 1999 was conducted the first experiment, the REVERSE experiment, using 688 telescopes installed in the CICLOPE scattering chamber at LNS, for the investigation of reactions in inverse kinematic [3,4,5]. The remaining 504 telescopes are arranged to form a sphere, with a radius of 40 cm, covering polar angle from 30° to 176°. Figure 1 shows a photo of the CHIMERA multidetector inside the dedicated vacuum chamber. The different identification methods used in CHIMERA and displayed in Figure 2 (ΔE-E, E-TOF, Pulse shape discrimination on both silicon and CsI (Tl) detectors) allow a complete detection of charged particles, emitted in nuclear collisions, and a direct measure of the velocity for Z>≈2. Moreover, the detection and identification of gamma-rays, and in some cases of neutrons, is possible thanks to the use of CsI(Tl) scintillators, even if with low efficiency. Recently, the CHI-NEXT Collaboration has started an R&D phase for the neutron detection, using dedicated plastic scintillators of new generation, such as the EJ276, with the aim to detect the neutron signals [6,7]. Fig. 3 (top) shows a fast-slow correlation obtained using a EJ 299-33 scintillators irradiated with neutron and gamma sources. Fig. 3 (bottom) shows the projection of the slow component for a range of values of the fast component. Furthermore, the collaboration is working on an upgrade of electronics of CHIMERA multidetector.
Figure 1: Photo of CHIMERA multidetector inside the vacuum chamber
Figure 2: Identification methods used in CHIMERA [1,2,22].
Figure 3: Top: fast-slow correlation obtained using a EJ 299-33 scintillator, irradiatated with a neutron and gamma source. Bottom: projection of the slow component for a range of values of the fast component [6,7].
FARCOS
The FARCOS (Femtoscope ARray for COrrelations and Spectroscopy) correlator is a new detector developed by the collaboration for the study of correlations, femtoscopy, spectroscopy, and their related applications [23,24]. FARCOS is a compact detection system which, compared to CHIMERA, covers a small solid angle; its main features are high angular and energy resolutions, along with modularity. The basic detection module is a telescope consisting of two Silicon detectors with thicknesses of 300 and 1500 μm, featuring an area segmentation of 64×64 mm2 into 32 strips along both the horizontal and vertical directions, followed by four 6-cm-thick CsI(Tl) scintillators. By positioning the FARCOS telescopes at about 1 m from the reaction target, it is possible to achieve a precision of approximately 0.1° in measuring the emission angle of the products. Furthermore, pairs of particles emitted at small relative angles/momenta can be measured with high resolution. Since each telescope requires 132 readout channels, the Politecnico di Milano has developed, within the collaboration, compact high-channel-density preamplifiers based on ASIC integrated technology [25]. A new, dedicated working-voltage distribution system and signal filtering/coupling boards for the GET digital readout system were also developed. During the CHIFAR experiment, carried out at LNS in November 2019, 10 FARCOS telescopes were used in coupling with the CHIMERA multi-detector. The identification methods used are both the ΔE-E technique, which can be applied either as ΔESil300 vs ESil1500 or as ΔESil1500 vs ECsI, and the pulse shape analysis of the CsI(Tl) signals to discriminate light particles. In 2020, it was possible to operate FARCOS in its final configuration consisting of 20 modules. FARCOS has already been successfully used in experiments on the decay of the Pygmy Dipole Resonance in $^{68}$Ni [19], and for the study of cluster effects both in exotic nuclei, such as 10Be and 16C, and in stable alpha-conjugated nuclei, such as 28Si [18].
Figure 4: 10 telescopes of the FARCOS correlator in the configuration used for the CHIFAR experiment at INFN-LNS (November 2019).
|
Figure 5: Scheme of a FARCOS telescope and of the new preamplifiers. |
Figure 6: DE-E plot obtained with the FARCOS array during the SIKO experiment [18].
GET Electronics
Due to the extremely high number of detection channels required for the new CHIMERA plus FARCOS configuration, using standard Front-End electronics proves to be costly and poorly compact. For this reason, the signals from FARCOS and the CsI(Tl) of the CHIMERA sphere are now read out and digitized using the GET electronics [26]. To this end, the Catania division has developed specific adaptation modules to interface the CHIMERA signals with the GET electronics; in order to overcome the limitation of the GET electronics' narrow dynamic range, these modules produce two copies of the input signal at different gains, thus allowing the digitization of the signals on two different scales [24]. The acquisition system currently in use, based on the NARVAL system, allows for the parallel acquisition of events encoded by the traditional VME-standard-based CHIMERA electronics, as well as events encoded by the GET digital readout system [27]. 
|
Figure 7: Photo of the dual-gain board (left) and its connection to an ASAD board of the GET system (right). |
Figure 8: Block diagram view of the coupling between GET and VME acquisition systems
SiC
The characterization of SiC detectors for fast timing applications is an important topic within the collaboration. The main goal is to develop a tagging system for the event-by-event identification of radioactive ion beams (RIBs) using the ΔE-TOF method. This tagging system will be employed at the FRAISE facility, currently under construction at INFN-LNS, but it is designed to be versatile enough for use at other facilities worldwide. Over the years, we have carried out an extensive characterization of SiC detectors, including the detailed analysis of several tests and experiments performed with radioactive sources and beams. These studies were conducted using the first SiC prototypes and commercial electronics, also benefiting from the synergy with the SAMOTHRACE ecosystem. The results are very promising in terms of both energy and timing resolution: an energy resolution of about 1% at 5 MeV and a timing resolution below 200 ps in the energy region around 10 MeV have been achieved. The main results have been published in [28]. In parallel, significant work has been carried out in Milan to develop fast front-end electronics. The first experiment coupling SiC detectors with this fast-front end electronics was performed in June 2025: the T-INSIDE experiment (spokespersons N.S. Martorana and E. Geraci) at the HIL laboratory, Warsaw. Another important experiment was performed in November in Prague, (spokes G. D’Agata, N. S. Martorana, and A. Barbon). In this case, an alpha micro-beam at 3 and 6 MeV was used to scan the SiC detectors along both the X and Y directions. To learn more about this topic please read [28-43].
References
[1] A. Pagano et al., Nucl. Phys. A 681, 331 (2001).
[2] A. Pagano et al., Nucl. Phys. A 734, 504c (2004).
[3] E. Geraci et al., Nucl. Phys. A 732, 173 (2004).
[4] E. De Filippo and Pagano A. Eur. Phys. Jour. A 50 (2014) 32.
[5] A. Pagano, Nuclear Physics News International, 22:1 (2012)25.
[6] E.V. Pagano et al., Nucl. Instr. and Methods A 889, 83 (2018).
[7] E.V. Pagano et al, Nucl. Instr. and Methods A 905, 47 (2018).
[8] E. De Filippo et al., Phys. Rev. C 71, 044602 (2005).
[9] E. De Filippo et al., Phys. Rev. C 71, 064604 (2005).
[10] F. Amorini et al., Phys. Rev. Lett. 102, 112701 (2009).
[11] G. Cardella et al., Phys. Rev. C 85, 012093 (2012).
[12] S. Pirrone et al., Eur. Phys. Jour. A 55, 22 (2019).
[13] E. De Filippo et al., Phys. Rev. C 86, 014610 (2012).
[14] P. Russotto et al. Phys. Rev. C 94, 034608 (2016).
[15] M. Papa et al. Phys. Rev. C 91, 041601(R) (2015).
[16] D. Dell'aquila et al, Phys. Rev. C 93, 024611c(2016).
[17] Ad.R. Raduta et al., Physics Letters B 705 (2011); B.Borderie et al., Phys. Lett. B 755 (2016).
[18] J. Bishop et al., Phys Rev. C 100, 034320 (2019).
[19] N.S. Martorana et al., Phys. Lett. B782 (2018) 112.
[20] G. Cardella et al., EPJ Web of Conf. 165, 01009 (2017).
[21] A. Trzcinska et al., Acta Phys. Pol. B 49, 393 (2018).
[22] A. Pagano et al., Eur. Phys. J. A 56, 102 (2020).
[23] E.V. Pagano et al., Eur. Phys. J. Web of Conf. 117 (2016) 10008.
[24] L. Acosta et al., Nucl. Instr. and Methods A in preparation.
[25] A. Castoldi et al., Il Nuovo Cimento C 41 C (2018) 168; A. Castoldi et al., IEEE Trans. Nucl. Sci., vol. 64, no. 10, October 2017, pp. 2678-2682.
[26] E. Pollacco, Nucl. Instr. and Methods A 887, 81 (2018).
[27] E. De Filippo et al, IOP Conf. Series: Journal of Physics, 1014, 012003 (2018).
[28] N. S. Martorana et al., Nuclear Instruments and Methods in Physics Research A, 171356 (2026).
[29] N. S. Martorana et al., 2025 JINST 20 C07064.
[30] A. Barbon et al., 2025 JINST 20 C07058.
[31] G. D'Agata et al., 2025 JINST 20 C09015.
[32] G. D’Agata et al., IL NUOVO CIMENTO 48 C (2025) 72.
[33] A. Barbon et al., IL NUOVO CIMENTO 48 C (2025) 72.
[34] N.S. Martorana et al., IL NUOVO CIMENTO 48 C (2025) 62.
[35] N.S. Martorana et al., IL NUOVO CIMENTO 47 C (2024) 56.
[36] N.S. Martorana et al., Frontiers in Physics, 10 (2022).
[37] F. Risitano, IL NUOVO CIMENTO 45 C (2022) 68.
[38] L. Acosta et al., 2022 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), Italy, 2022, pp. 1-4.
[39] N.S. Martorana et al., IL NUOVO CIMENTO 45 C (2022) 63.
[40] N.S. Martorana et al., IL NUOVO CIMENTO 44 C (2021) 1.
[41] C. Altana et al., IEEE Nuclear Science Symposium and Medical Imaging Conference 390 (NSS/MIC) (2021), 1–4.
[42] A. Russo et al., NIM B 463 (2020) 359 418 – 420.
[43] P. Russotto et al., J. Physics: Conf. Ser., 1014 (2018) 012016.