The perturbed angular correlation (PAC) technique was used to study the hyperfine interactions in the antiferromagnetic and paramagnetic regions of the distorted perovskites ${\mathrm{LaCrO}}_3$ and ${\mathrm{LaFeO}}_3.$ The dilute ${}^{111}{\overrightarrow{\mathrm{In}}}^{111}\mathrm{Cd}$ nuclear probes were introduced into the samples through a chemical process. The present measurements cover the temperature ranges from 15 to 848 K for ${\mathrm{LaCrO}}_3$ and 77 to 1324 K for ${\mathrm{LaFeO}}_3.$ Two distinct electric-quadrupole interactions were observed in each compound. The lower quadrupole frequency was assigned to the transition-metal atom site while the higher frequency was attributed to the lanthanum site in both cases. Temperature dependence of the electric-quadrupole interaction parameters indicated structural phase transitions at around 512 and 1223 K, respectively, in ${\mathrm{LaCrO}}_3$ and ${\mathrm{LaFeO}}_3.$ The phase transitions were associated with the change from an orthorhombic to rhombohedral structure and characterized by a sudden increase in the electric field gradient $V_{\mathrm{zz}}$ and a decrease in the asymmetry parameter $\eta$ for both sites. PAC spectra measured below the Néel temperature revealed that at 0 K the supertransferred magnetic hyperfine field on ${}^{111}\mathrm{Cd}$ at the Cr site in ${\mathrm{LaCrO}}_3$ (2.4 T) is much smaller than at the Fe site in ${\mathrm{LaFeO}}_3$ (19.4 T). The magnetic field on ${}^{111}\mathrm{Cd}$ at La sites in both compounds is of the order of 0.3 T. Additional measurements were made to determine the magnetic hyperfine field using the probe nucleus ${}^{140}{\overrightarrow{\mathrm{La}}}^{140}\mathrm{Ce}.$ The result reconfirmed that a relatively weak hyperfine field is supertransferred to the probe atoms at La sites.

Background: Double charge exchange (DCE) nuclear reactions have recently attracted much interest as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-$\beta$ decay. In this framework, a good description of the reaction mechanism and a complete knowledge of the initial and final-state interactions are mandatory. Presently, not enough is known about the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for future DCE studies. Among these, the ${}^{20}\mathrm{Ne}+{}^{76}\mathrm{Ge}$ DCE reaction is particularly relevant due to its connection with ${}^{76}\mathrm{Ge}$ double-$\beta$ decay.

Neutrinos are so far the most elusive known particles, and in the last decades many sophisticated experiments have been set up in order to clarify several questions about their intrinsic nature, in particular their masses, mass hierarchy, intrinsic nature of Majorana or Dirac particles. Evidence of the Neutrinoless Double-Beta Decay (NDBD) would prove that neutrinos are Majorana particles, thus improving the understanding of the universe itself. Besides the search for several large underground experiments for the direct experimental detection of NDBD, the NUMEN experiment proposes the investigation of a nuclear mechanism strongly linked to this decay: the Double Charge Exchange reactions (DCE). As such reactions share with the NDBD the same initial and final nuclear states, they could shed light on the determination of the Nuclear Matrix Elements (NMEs), which play a relevant role in the decay. The physics of DCE is described elsewhere in this issue, while the focus of this paper will be on the challenging experimental apparatus currently under construction in order to fulfil the requirements of the NUMEN experiment. The overall structure of the technological improvement to the cyclotron, along with the newly developed detection systems required for tracking and identifying the reaction products and their final excitation level are described.

The goal of NUMEN project is to access experimentally driven information on Nuclear Matrix Elements (NME) involved in the neutrinoless double beta decay (0νββ) by accurate measurements of the cross sections of heavy-ion induced double charge-exchange reactions. In particular, the (¹⁸O,¹⁸Ne) and (²⁰Ne,²⁰O) reactions are adopted as tools for β⁺β⁺and β⁻β⁻decays, respectively. The experiments are performed at INFN–Laboratory Nazionali del Sud (LNS) in Catania using the Superconducting Cyclotron to accelerate the beams and the MAGNEX magnetic spectrometer to detect the reaction products. The measured cross sections are very low, limiting the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. In order to make feasible a systematic study of all the candidate nuclei, a major upgrade of the LNS facility is foreseen to increase the experimental yield by more than two orders of magnitude. To this purpose, frontier technologies are being developed for both the accelerator and the detection systems. An update description of the NUMEN project is presented here, focusing on recent achievements from the R&D activity.