Thickness and uniformity characterization of thin targets for intense ion beam experiments

The NUMEN Experiment aims to get information on the Nuclear Matrix Elements of the Neutrinoless Double Beta Decay, by measuring heavyion induced Double Charge Exchange (DCE) reactions cross sections. A good energy resolution is needed to clearly distinguish energy states of DCE products. To measure the energy of reaction products with the required resolution, the target must be thin and uniform to minimise dispersion and straggling effects on the ejectile energy. Few hundreds of nanometers of the target isotope are deposited on a Highly Oriented Pyrolytic Graphite substrate a few micrometers thick. The results of the characterisation of the first target prototypes of tin and tellurium are presented. The Scanning Electron Microscopy was used to qualitatively analyse the samples surface. A setup to study Alpha Particle Transmission has been assembled to measure thickness and uniformity of the targets; the thickness results have been verified by the Rutherford Backscattering measurements. To evaluate the effects of the thickness on the resolution of the DCE products energy, a Monte Carlo code has been implemented, using the measured thickness and uniformity as input data for the simulation

Tests of a cooling system for thin targets submitted to intense ion beams for the numen experiment

The NUMEN experiment, hosted at LNS (Catania, Italy), aims to determine the Nuclear Matrix Elements (NMEs) involved in 0β β decay via heavy-ion induced Double Charge Exchange (DCE) reactions. High intensity beams of about 50 μA and of energies ranging from 15 to 60 MeV/u are necessary, due to the low DCE cross sections and the use of very thin targets (several hundreds of nm) needed to reach the required energy resolution. These intense beams produce a considerable amount of heat inside the target, which can be dissipated by depositing the targets on a highly thermally conductive substrate, HOPG (Highly Oriented Pyrolytic Graphite), and coupling it with a suitable designed target-cooler system. The heat transfer from the beam spot to the cold region has been studied by solving numerically the heat equation to determine the evolution in space and time of the temperature inside the target. According to calculations, the temperatures of most of the target isotopes remain under the melting points. Experimental tests with a laser were initiated to validate the whole cooling system and the calculations

Evaluation of target non-uniformity and dispersion effects on energy measurement resolution in NUMEN experiment

In the NUMEN Experiment, Double Charge Exchange (DCE) reactions will be studied to get very precise measurements of their cross sections and final state levels. The interest for these reactions lies in the possibility for some nuclides to have DCE with initial and final states identical to those of the Neutrinoless Double β-Decay. To reach a good precision in the energy measurements, high statistics is needed and severe constraints about the target thickness must be satisfied. A 50 μA intense ion beam will provide the desired statistics, while posing the problem of dissipating the massive heat generated in the target. It is therefore necessary to design a suitable cooling system, which must affect the particles' energy as little as possible. Said energy is already influenced by the current setup. The Superconducting Cyclotron (SC) and the MAGNEX Spectrometer introduce an error on the particles' energy by 1/1000th (FWHM value) of its average energy. In the target, the main sources of error are straggling of projectiles and reaction products, and the dispersion effect. Both closely depend on the target thickness, which must be of the order of few hundred nanometres. In addition, the two effects are worsened if the target thickness is not uniform. The solution to these problems has been found by backing the target isotope with relatively thin substrate of Highly Oriented Pyrolytic Graphite (HOPG). Its thermodynamic properties fit the cooling requirements and can be as thin as 450 μg cm-2. The further straggling suffered by the ejectiles is tolerable, falling within the resolution requirements. Samples are deposited by using Electron Beam Evaporation: results obtained for Sn and Te are checked by Scanning Electron Microscopy (SEM). A quantitative evaluation of the samples' thickness has been performed by Alpha-Particle Transmission (APT) and Rutherford Backscattering Spectrometry (RBS) measurements. A Monte Carlo code has been implemented to estimate the ejectiles energy distribution using the experimental measurements as input. Results from characterization and simulations help in optimizing the target thickness and the energy resolution of reaction products

The NUMEN Project: Toward new experiments with high-intensity beams

The search for neutrinoless double-beta (0νββ) decay is currently a key topic in physics, due to its possible wide implications for nuclear physics, particle physics, and cosmology. The NUMEN project aims to provide experimental information on the nuclear matrix elements (NMEs) that are involved in the expression of 0νββ decay half-life by measuring the cross section of nuclear double-charge exchange (DCE) reactions. NUMEN has already demonstrated the feasibility of measuring these tiny cross sections for some nuclei of interest for the 0νββ using the superconducting cyclotron (CS) and the MAGNEX spectrometer at the Laboratori Nazionali del Sud (LNS.) Catania, Italy. However, since the DCE cross sections are very small and need to be measured with high sensitivity, the systematic exploration of all nuclei of interest requires major upgrade of the facility. R&D for technological tools has been completed. The realization of new radiation-tolerant detectors capable of sustaining high rates while preserving the requested resolution and sensitivity is underway, as well as the upgrade of the CS to deliver beams of higher intensity. Strategies to carry out DCE cross-section measurements with high-intensity beams were developed in order to achieve the challenging sensitivity requested to provide experimental constraints to 0νββ NMEs

Design and test of an innovative static thin target for intense ion beams

In the present work an innovative design for thin target suited for high intensity beam is proposed, which consists in the deposition of the target material on a substrate of pyrolytic graphite, whose in-plane thermal conductivity allows a quick dissipation into a heat sink. Such a target cooling system has been designed for the NUMEN experiment (hosted at LNS-INFN, Catania), which will use targets of particular isotopes under highly intense ion beams. The time evolution and the spatial distribution of the temperature have been numerically calculated. Results of these calculations show that the target/graphite system can tolerate ion beams with intensities of about 50 eμA and energy of 15 MeV/u. A significant nonuniformity in the target thickness would limit the energy resolution of the reaction products. A technique, based on the α-particle transmission, is used for measuring the thickness and uniformity of the target. Preliminary results from tests with this technique applied to the graphite substrate are shown

Association of MC1R Variants and host phenotypes with melanoma risk in CDKN2A mutation carriers: a GenoMEL study

<p><b>Background</b> Carrying the cyclin-dependent kinase inhibitor 2A (CDKN2A) germline mutations is associated with a high risk for melanoma. Penetrance of CDKN2A mutations is modified by pigmentation characteristics, nevus phenotypes, and some variants of the melanocortin-1 receptor gene (MC1R), which is known to have a role in the pigmentation process. However, investigation of the associations of both MC1R variants and host phenotypes with melanoma risk has been limited.</p> <p><b>Methods</b> We included 815 CDKN2A mutation carriers (473 affected, and 342 unaffected, with melanoma) from 186 families from 15 centers in Europe, North America, and Australia who participated in the Melanoma Genetics Consortium. In this family-based study, we assessed the associations of the four most frequent MC1R variants (V60L, V92M, R151C, and R160W) and the number of variants (1, ≥2 variants), alone or jointly with the host phenotypes (hair color, propensity to sunburn, and number of nevi), with melanoma risk in CDKN2A mutation carriers. These associations were estimated and tested using generalized estimating equations. All statistical tests were two-sided.</p> <p><b>Results</b> Carrying any one of the four most frequent MC1R variants (V60L, V92M, R151C, R160W) in CDKN2A mutation carriers was associated with a statistically significantly increased risk for melanoma across all continents (1.24 × 10−6 ≤ P ≤ .0007). A consistent pattern of increase in melanoma risk was also associated with increase in number of MC1R variants. The risk of melanoma associated with at least two MC1R variants was 2.6-fold higher than the risk associated with only one variant (odds ratio = 5.83 [95% confidence interval = 3.60 to 9.46] vs 2.25 [95% confidence interval = 1.44 to 3.52]; Ptrend = 1.86 × 10−8). The joint analysis of MC1R variants and host phenotypes showed statistically significant associations of melanoma risk, together with MC1R variants (.0001 ≤ P ≤ .04), hair color (.006 ≤ P ≤ .06), and number of nevi (6.9 × 10−6 ≤ P ≤ .02).</p> <p><b>Conclusion</b> Results show that MC1R variants, hair color, and number of nevi were jointly associated with melanoma risk in CDKN2A mutation carriers. This joint association may have important consequences for risk assessments in familial settings.</p&gt

The NUMEN heavy ion multidetector for a complementary approach to the neutrinoless 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 NUMEN heavy ion multidetector for a complementary approach to the neutrinoless 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

Cross-section measurement of two-photon annihilation in-flight of positrons at s=20\sqrt{s}=20 MeV with the PADME detector

The inclusive cross-section of annihilation in flight $e^+e^-\rightarrow\gamma\gamma$ of 430 MeV positrons with atomic electrons of a thin diamond target has been measured with the PADME detector at the Laboratori Nazionali di Frascati. The two photons produced in the process were detected by an electromagnetic calorimeter made of BGO crystals. This measurement is the first one based on the direct detection of the photon pair and one of the most precise for positron energies below 1 GeV. This measurement represents a necessary step to search for dark sector particles and mediators weakly coupled to photons and/or electrons with masses ranging from 1 MeV to 20 MeV with PADME. The measurement agrees with the Next to Leading Order QED prediction within the overall 6% uncertainty.Comment: Submitted to PR

One-proton transfer reaction for the O 18 + Ti 48 system at 275 MeV

Single-nucleon transfer reactions are processes that selectively probe single-particle components of the populated many-body nuclear states. In this context, recent efforts have been made to build a unified description of the rich nuclear spectroscopy accessible in heavy-ion collisions. An example of this multichannel approach is the study of the competition between successive nucleon transfer and charge exchange reactions, the latter being of particular interest in the context of single and double beta decay studies. To this extent, the one-proton pickup reaction Ti48(O18,F19)Sc47 at 275 MeV was measured for the first time, under the NUMEN experimental campaign. Differential cross-section angular distribution measurements for the F19 ejectiles were performed at INFN-LNS in Catania by using the MAGNEX large acceptance magnetic spectrometer. The data were analyzed within the distorted-wave and coupled-channels Born approximation frameworks. The initial and final-state interactions were described adopting the São Paulo potential, whereas the spectroscopic amplitudes for the projectile and target overlaps were derived from shell-model calculations. The theoretical cross sections are found to be in very good agreement with the experimental data, suggesting the validity of the optical potentials and the shell-model description of the involved nuclear states within the adopted model space