Lucio Gialanella

Lorentz invariance is a fundamental symmetry underlying both the Standard Model of particle physics and General Relativity. Testing its validity provides a direct means of searching for new physics emerging near the Planck scale. A search for isotropic Lorentz invariance violation using 5828 selected atmospheric-neutrino candidate events is presented. The data were collected over 1.4 years with a partial configuration of the KM3NeT/ORCA detector comprising six detection units. No evidence for such violation is found; thus, competitive constraints are set on off-diagonal isotropic Lorentz-invariance-violating coefficients of mass dimension 3. In addition, the first direct constraints on isotropic flavour-diagonal coefficient differences between the muon and tau sectors are obtained for mass dimensions 3 to 8.

This work explores the possibility of using 4H-SiC PIN diodes to provide a high electric field able to induce the Stark effect in ⁷Be atoms implanted in the diode space charge region, modifying the ⁷Be radioactive decay time. A set of PIN diodes of area ranging between 2.12 × 10⁻³ cm² and 9.88 × 10⁻³ cm² was designed and fabricated to reach breakdown voltages up to 1000 V. Be ions were implanted in the epitaxial layer, and then the devices were reverse biased at about 75% of the theoretical breakdown voltage for durations exceeding 100 days, long enough for a precise measurement of the ⁷Be radioactive decay time. Electrical characterization in the pristine state, after Be ion implantation, and after long reverse bias allowed us to verify the suitability of 4H-SiC PIN diodes by assessing both the agreement between simulated and measured performance and the stability of the electric field. Be ion implantation-related defects induced both an increase in the reverse current generation and a decrease in the junction capacitance, though not affecting the breakdown voltage. Comparison with test devices implanted with the stable isotope ⁹Be indicates that any defects introduced by the ⁷Be radioactive decay are below the detection limit of the employed characterization techniques and have a negligible impact on the reverse-blocking characteristics of the diodes. Device simulations allowed us to conclude that the electric field remains close to its theoretical value throughout the experiment duration, confirming the suitability of 4H-SiC diodes for both induction and measurement of ⁷Be lifetime variations.

This study presents the design, fabrication, and electrical characterization of 4H-SiC PIN diodes employed to provide a high electric field able to induce Stark effect in ⁷ Be atoms implanted in the space charge region. Indeed, a variation in the half-life of the ⁷ Be radioactive decay is expected to be achieved by applying an electric field of the order of 10 ⁶ V/cm, which can be produced by reverse-biasing 4H-SiC diodes close to the breakdown voltage. A set of diodes of area ranging between 2.12×10 ^-3 cm ² and 9.88×10 ³ cm ² was designed and fabricated to reach breakdown voltages up to 1000 V. When tested under reverse current limitation set equal to 300 nA, over 50% out of 24 devices could withstand reverse bias exceeding 800 V. This work reports on the characteristics of one diode of 9.88×10 ³ cm ² area, implanted with ⁷ Be and subject to continuous reverse-bias at 750 V for 107 days. Electrical characterization conducted before, during, and after long-term polarization highlighted an increase in the reverse current generation due to implantation-related defects, which however does not affect the breakdown voltage. These considerations lead to the conclusion that the electric field acting on the implanted ⁷Be remains stable over time, confirming the suitability of 4H-SiC diodes for both induction and measurement of ⁷ Be lifetime variations.

The rapid neutron capture process (r-process) is responsible for producing about half of the elements heavier than iron in the Universe through cataclysmic events such as core-collapse supernovae and neutron star mergers (NSMs). Despite extensive research, the exact astrophysical sites of the r-process remain one of the unanswered questions in science. The well-known supernova-produced radioisotope ⁶⁰Fe has been detected in terrestrial reservoirs, providing evidence that material from a nearby supernova reached Earth approximately 2 million years (Ma) ago. Our study reports the detection of ²⁴⁴Pu in fossilized stromatolite samples that are 2.0 Ma old, collected from palustrine–lacustrine stratigraphic layers dating back to approximately 5 Ma located at the margins of the present-day Lake Turkana Basin in northern Kenya. We demonstrate that stromatolites can mass-concentrate actinides in the range of 10²–10³. Using accelerator mass spectrometry, we isolate ²⁴⁴Pu and eliminate the anthropogenic contribution. From our findings, we evaluate a terrestrial fluence between 0.2 and 4.7 × 10³ at ​​​​cm⁻², in relative agreement with previous studies. The detection of the r-process ²⁴⁴Pu around 2 Ma ago raises the possibility of a common supernova origin with ⁶⁰Fe; however, alternative scenarios, such as the production of ²⁴⁴Pu in NSMs or other cosmic events and its transport to Earth alongside ⁶⁰Fe via interstellar debris, cannot be ruled out, highlighting the need to consider multiple mechanisms for isotopic transport in the cosmos.

The KM3NeT Collaboration is building an underwater neutrino observatory at the bottom of the Mediterranean Sea, consisting of two neutrino telescopes, both composed of a three-dimensional array of light detectors, known as digital optical modules. Each digital optical module contains a set of 31 three-inch photomultiplier tubes distributed over the surface of a 0.44 m diameter pressure-resistant glass sphere. The module also includes calibration instruments and electronics for power, readout, and data acquisition. The power board was developed to supply power to all the elements of the digital optical module. The design of the power board began in 2013, and ten prototypes were produced and tested. After an exhaustive validation process in various laboratories within the KM3NeT Collaboration, a mass production batch began, resulting in the construction of over 1200 power boards so far. These boards were integrated in the digital optical modules that have already been produced and deployed, which total 828 as of October 2023. In 2017, an upgrade of the power board, to increase reliability and efficiency, was initiated. The validation of a pre-production series has been completed, and a production batch of 800 upgraded boards is currently underway. This paper describes the design, architecture, upgrade, validation, and production of the power board, including the reliability studies and tests conducted to ensure safe operation at the bottom of the Mediterranean Sea throughout the observatory’s lifespan.

For more than two decades, the ERNA collaboration has investigated nuclear processes of astrophysical interest through the direct measurement of cross sections or the identification of the nucleosynthesis effects. Measurements of cross-section, reported in this publication, of radiative capture reactions have been mainly conducted using the ERNA Recoil Mass Separator, and more recently with an array of charged particle detector telescopes designed for nuclear astrophysics measurements. Some results achieved with ERNA will be reviewed, with a focus on the results most relevant for nucleosynthesis in AGB and advanced burning phases.

Positron Emission Tomography is a non-disruptive and high-sensitive digital imaging technique which allows to measure in-vivo and non invasively the changes of metabolic and transport mechanisms in plants. When it comes to the early assessment of stress-induced alterations of plant functions, plant PET has the potential of a major breakthrough. The development of dedicated plant PET systems faces a series of technological and experimental difficulties, which make conventional clinical and preclinical PET systems not fully suitable to agronomy. First, the functional and metabolic mechanisms of plants depend on environmental conditions, which can be controlled during the experiment if the scanner is transported into the growing chamber. Second, plants need to be imaged vertically, thus requiring a proper Field Of View. Third, the transverse Field of View needs to adapt to the different plant shapes, according to the species and the experimental protocols. In this paper, we perform a simulation study, proposing a novel design of dedicated plant PET scanners specifically conceived to address these agronomic issues. We estimate their expected sensitivity, count rate performance and spatial resolution, and we identify these specific features, which need to be investigated when realizing a plant PET scanner. Finally, we propose a novel approach to the measurement and verification of the performance of plant PET systems, including the design of dedicated plant phantoms, in order to provide a standard evaluation procedure for this emerging digital imaging agronomic technology.