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Marco Ripani

Publications and source records attributed to Marco Ripani.

6 recordsLinked to original sources
arXiv2025

Measurement of photo- and radio-luminescence of thin ThF4 films

We conducted measurements on the photo- and radio-luminescence of thin ThF$_4$ films in both the UV and visible ranges. In the UV range, we found that both luminescences are at a similar level as the internal dark counting noise of the photo-multiplier-tube (PMT). Our results suggest that thin ThF$_4$ crystals could be used as a target for the search for $^{229m}$Th and as a medium for the future nuclear clock. The measurements indicate that using a small and thin ThF$_4$ film can reduce background noise while maintaining the signal at the same level, achieved by increasing the $^{229}$Th enrichment. Our developed apparatus is now ready for direct measurements of $^{229m}$Th excitation and decay in ThF$_4$.

physics.ins-det↗
arXiv2024

New Spin Structure Constraints on Hyperfine Splitting and Proton Size

The 1S hyperfine splitting in hydrogen is measured to an impressive ppt precision and will soon be measured to ppm precision in muonic hydrogen. The latter measurement will rely on theoretical predictions, which are limited by knowledge of the proton polarizability effect $\Delta_\text{pol}$. Data-driven evaluations of $\Delta_\text{pol}$ have long been in significant tension with baryon chiral perturbation theory. Here we present improved results for $\Delta_\text{pol}$ driven by new spin structure data, reducing the long-standing tension between theory and experiment and halving the dominating uncertainty in hyperfine splitting calculations.

nucl-ex↗
arXiv2023

Characterization of LAPPD timing at CERN PS testbeam

Large Area Picosecond PhotoDetectors (LAPPDs) are photosensors based on microchannel plate technology with about 400 cm$^2$ sensitive area. The external readout plane of a capacitively coupled LAPPD can be segmented into pads providing a spatial resolution down to 1 mm scale. The LAPPD signals have about 0.5 ns risetime followed by a slightly longer falltime and their amplitude reaches a few dozens of mV per single photoelectron. In this article, we report on the measurement of the time resolution of an LAPPD prototype in a test beam exercise at CERN PS. Most of the previous measurements of LAPPD time resolution had been performed with laser sources. In this article we report time resolution measurements obtained through the detection of Cherenkov radiation emitted by high energy hadrons. Our approach has been demonstrated capable of measuring time resolutions as fine as 25-30 ps. The available prototype had performance limitations, which prevented us from applying the optimal high voltage setting. The measured time resolution for single photoelectrons is about 80 ps r.m.s.

physics.ins-det↗
arXiv2016

Influence of reflector materials and core coolant on the characteristics of accelerator driven systems

In this paper we simulated the behavior of a simple ADS model, based on MOX fuel embedded in solid lead, in terms of multiplication coefficient keff, thermal power and absolute neutron spectra. In the first part of the paper, we report on the results obtained when modifying the reflector surrounding the fission core, by replacing pure lead with a layered graphite/lead structure. We found that, by appropriately choosing position and thickness of the graphite and lead layers, it is possible to obtain a hybrid system where the neutron spectrum in the core still exhibits a fast character, while the spectrum in the graphite layer is considerably softer, becoming thermal in the most peripheral positions. In order to obtain such a modulation of the neutron spectra from the center of the system to the periphery, a careful choice of the materials has to be made in order to avoid large variations of the local power at the core boundary. However, the smoothness of the power distribution is obtained at the expense of lower values of keff and the total power of the system. In the second part of the paper, we explored the option of adopting light water as coolant, instead of the helium gas assumed in the initial design. We found that this produces an increase in keff and thermal power, without significantly perturbing the fast character of the system and without introducing spatial power excursions in any place within the core. The characteristics obtained may allow to design a system where fast, mixed and thermal spectra can be used to expand the use of the ADS as an irradiation facility.

physics.comp-ph↗
arXiv2016

An alternative observable to estimate keff in fast ADS

In this paper we examine an alternative method for determining the neutron multiplication factor keff in fast subcritical reactors, based on the observable obtained by calculating the ratio between the ``fast`` component of the neutron flux (in this case by fast we mean neutrons with kinetic energy above 0.5 MeV) and the whole flux at all energies. The assumption behind the present study was that the above mentioned observable would be only sensitive to keff, provided a peripheral fuel rod is considered (i.e. far from the neutron source in subcritical systems) and keff is sufficiently high. Indeed, our results show that, for keff> 0.7, the ratio calculated for LFR or GFR models turns out to show a quite similar trend well approximated by a straight line, while a different slope is observed for a sodium reactor. In our opinion, the results obtained show that such observable, after appropriate calibrations on the real systems under consideration, may be used for determining keff in all operational conditions, in particular for subcritical systems with different types of neutron source and different values of the beam current.

physics.ins-det↗