Thick Pb Research Articles

Photon and neutron dose evaluation at the Beam Test Facility of the INFN - National Laboratory of Frascati

Dose evaluation and direct measurements are fundamental for radiation protection in non-conventional accelerator facilities, both before and after the primary and secondary shielding. In this paper, we will report about the experimental setup, data acquisition and analysis, together with FLUKA modeling, of the dose measurements test carried out in the Beam Test Facility (BTF) of the INFN - Frascati’s National Laboratories (LNF), where an intense mixed field is produced and measured with thermoluminescent dosimeters. BTF is an extraction and transport line of DAΦNE LINAC (Buonomo et al. 2021; Mazzitelli et al. 2003). It is optimized for electrons and positrons production in a wide range of intensity, energy (30 MeV–800 MeV), beam spot dimensions and divergence, using both primary and secondary beam of the DAΦNE LINAC. Through the years, the BTF has gained an important role in particle detectors test and development with electron/positron beam. A small fraction of the BTF’s shifts have been dedicated to radiation damage test using LINAC electron primary beam up to 5×1010 e-/s. As radiation protection group of the LNF, we evaluated the dose when electrons impinging on a Pb target from: (i) photon Bremsstrahlung production; (ii) photoneutron production. Three dedicated tests with 503 MeV electrons impinging on a ∼16 cm thick Pb target have been carried out in February, June 2022 and in January 2023, using TLD700 and TLD600, measuring doses at several charge intervals. The aim of this study focuses on evaluating dosimetric quantities produced by the mixed field, air kerma for the photon component, and ambient dose equivalent for the neutron one, using thermoluminescence dosimeters calibrated with low-energy standards: Cs-137 and Am-Be. The approach adopted involves the use of Monte Carlo simulations of the experiment, both to benchmark against experimental measurements and to validate the results obtained for energies higher than those of calibration. The results of this comparison show excellent agreement between measured and simulated quantities in the forward direction, allowing us to conclude and confirm the validity of the calibrations themselves.

Alumina Nanoparticle Interfacial Buffer Layer for Low‐Bandgap Lead‐Tin Perovskite Solar Cells

AbstractMixed lead‐tin (Pb:Sn) halide perovskites are promising absorbers with narrow‐bandgaps (1.25–1.4 eV) suitable for high‐efficiency all‐perovskite tandem solar cells. However, solution processing of optimally thick Pb:Sn perovskite films is notoriously difficult in comparison with their neat‐Pb counterparts. This is partly due to the rapid crystallization of Sn‐based perovskites, resulting in films that have a high degree of roughness. Rougher films are harder to coat conformally with subsequent layers using solution‐based processing techniques leading to contact between the absorber and the top metal electrode in completed devices, resulting in a loss of VOC, fill factor, efficiency, and stability. Herein, this study employs a non‐continuous layer of alumina nanoparticles distributed on the surface of rough Pb:Sn perovskite films. Using this approach, the conformality of the subsequent electron‐transport layer, which is only tens of nanometres in thickness is improved. The overall maximum‐power‐point‐tracked efficiency improves by 65% and the steady‐state VOC improves by 28%. Application of the alumina nanoparticles as an interfacial buffer layer also results in highly reproducible Pb:Sn solar cell devices while simultaneously improving device stability at 65 °C under full spectrum simulated solar irradiance. Aged devices show a six‐fold improvement in stability over pristine Pb:Sn devices, increasing their lifetime to 120 h.

Enhanced performance on piezoelectric MEMS vibration energy harvester by dynamic magnifier under impulsive force

Vibration energy harvesters that use resonance phenomena exhibit a high output power density for constant frequency vibrations, but they suffer from a significant drop in performance for non-steady-state vibrations, which are important for practical applications. In this work, we demonstrate that the output power under an impulsive force can be increased significantly by placing a U-shaped metal component, called a dynamic magnifier (DM), under an MEMS piezoelectric vibration energy harvester (MEMS-pVEH) with a 6 mm long cantilever using a 3 μm thick Pb(Zr,Ti)O3 film. Based on the results of numerical calculations using a model of pVEH with a two-degree-of-freedom (2DOF) system, the DM was designed to have the same resonant frequency as the MEMS-pVEH and a high mechanical quality factor (Qm). The waveforms of the output voltage of the fabricated 2DOF-pVEHs were measured for impulsive forces with various duration times, and the output power was calculated by integrating the waveforms over time. The output power of the MEMS-pVEH placed on the DM with a Qm of 56 showed a gradual change according to the duration of applying an impulsive force and a maximum of 19 nJ/G2 (G: gravitational acceleration) when the duration of the impulsive force was 3.8 ms. This result was about 90 times greater than the output power of the MEMS-pVEH without a DM. While it is not easy to fabricate pVEHs with a complex 2DOF structure using only the MEMS process, we have demonstrated that the output power can be significantly improved by adding a spring structure to a simple MEMS-pVEH.

Trapping a magnetic field of 17.89 T in stacked coated conductors by suppression of flux jumps

We have successfully trapped a field of 17.89 T at 6.5 K at the center of a compact coated-conductor (CC) stacks (13 12 11.7 mm3) within 75 min by suppressing flux jumps. The CC stack consists of 200 sheets of EuBa2Cu3O7 CCs with BaHfO3 nanorods to increase the critical current density at high fields and low temperatures. To enhance thermomagnetic stability, the central 50 CCs are coated with 1 µm thick Pb with large specific heat at low temperatures. Numerical calculations based on the actual J c–H characteristics reproduces the trapped field quantitatively. New directions for achieving even higher trapped field at higher temperatures and making use of the trapped field are discussed.

32 Element Piezoelectric Micromachined Ultrasound Transducer (PMUT) Phased Array for Neuromodulation

Interest in utilizing ultrasound (US) transducers for non-invasive neuromodulation treatment, including for low intensity transcranial focused ultrasound stimulation (tFUS), has grown rapidly. The most widely demonstrated US transducers for tFUS are either bulk piezoelectric transducers or capacitive micromachine transducers (CMUT) which require high voltage excitation to operate. In order to advance the development of the US transducers towards small, portable devices for safe tFUS at large scale, a low voltage array of US transducers with beam focusing and steering capability is of interest. This work presents the design methodology, fabrication, and characterization of 32-element phased array piezoelectric micromachined ultrasound transducers (PMUT) using 1.5 μm thick Pb(Zr0.52 Ti0.48)O3 films doped with 2 mol% Nb. The electrode/piezoelectric/electrode stack was deposited on a silicon on insulator (SOI) wafer with a 2 μm silicon device layer that serves as the passive elastic layer for bending-mode vibration. The fabricated 32-element PMUT has a central frequency at 1.4 MHz. Ultrasound beam focusing and steering (through beamforming) was demonstrated where the array was driven with 14.6 V square unipolar pulses. The PMUT generated a maximum peak-to-peak focused acoustic pressure output of 0.44 MPa at a focal distance of 20 mm with a 9.2 mm and 1 mm axial and lateral resolution, respectively. The maximum pressure is equivalent to a spatial-peak pulse-average intensity of 1.29 W/cm2, which is suitable for tFUS application.

Estimates of upper limit of neutron yield in experiments with Z-pinch dynamic hohlraums at 8-MA pulsed power facility

In ongoing attempts to generate thermonuclear neutrons with the Z-pinch dynamic hohlraum concept at an 8-MA pulsed power facility, it has become possible to determine an upper limit for the neutron yield. The neutron time-of-flight diagnostic uses thick Pb shields and a specifically formulated fast liquid scintillator coupled to gated photomultiplier tubes to mitigate the hard bremsstrahlung x-ray (HXR) background that would otherwise overwhelm a potential neutron signal, and its suppression gives an upper-limit estimation for the neutron yield. A slow-neutron detector in the form of a BF3 counting system suggests a lower limit to the neutron yield although the early HXR pulse interference requires further confirmation as to whether the subsequent multiple pulses are induced by neutrons. Together, these measurements suggest a neutron-yield upper limit of 1.1×107.

A simulation study on beam property of 124Sb–Be isotope-based neutron for BNCT

The 9Be(γ,n) neutrons with the energies at 21–24 keV generated by 1.691 MeV photons from 124Sb was investigated as a source of epithermal neutrons for BNCT, using PHITS code. A beam shaping assembly composed of 13 mm thick Be target, a gamma ray shield made of 30 cm thick Bi, and a reflector of 30 cm thick Pb satisfied the beam requirements of IAEA-TECDOC-1223. The needed 124Sb activity was estimated in the order of 1016–1017 Bq. Feasibility of BNCT using 124Sb–Be neutrons would be influenced by the capability of periodic supply of short-lived 124Sb (half-life: 60 days) with such high activity.

Effect of Pb(Zr0.52Ti0.48)O3 thin films on electron transport at the LaAlO3/SrTiO3 interface by surface acoustic waves

Surface acoustic waves (SAWs) are capable tools for providing mechanical control over the electronic properties of functional materials. Coupling SAWs with the LaAlO3/SrTiO3 (LAO/STO) conducting interface is particularly interesting as this interface exhibits extraordinary features, such as high mobility at low temperature, ferromagnetism, and superconductivity below 200 mK. For SAW generation, piezoelectricity is indispensable, and due to lack of that in the LAO/STO system, a 200 nm thick Pb(Zr0.52Ti0.48)O3 (PZT) film was grown on top of LAO. SAW excitation and propagation was demonstrated on a PZT/LAO/STO multilayer structure. We further employed SAWs in order to transport free electrons confined to the LAO/STO interface, detected as an acoustoelectric voltage at room temperature. Electrical characterization of the interface was carried out by Van der Pauw measurements. We found that having a PZT layer on top of LAO/STO considerably degraded the interfacial conductivity. The degradation became more pronounced at low temperatures. We attribute these effects to the filling of oxygen vacancies due to interlayer oxygen migration, combined with carrier freeze-out at low temperatures.

Measurements of L-subshell x-ray production cross sections and M-shell x-ray yields of Pb by low-energy electron impact using the thick-target method

The Lα, Lβ, and Lγ x-ray production cross sections and M-shell x-ray yields by 5–29 keV electrons bombarding a thick Pb target were measured. The effects of multiple-scattered electrons, from the bremsstrahlung and other secondary particles within the thick sample were corrected using the Monte Carlo simulations. The experimental results are compared with the DWBA predictions of Bote et al., and also with the experimental data from the literature. The results indicate that the measurements of the production cross sections for the L subshells of the elements with higher atomic numbers using the thick-target method are feasible and reliable.

Nonuniform Quantum-Confined States and Visualization of Hidden Defects in Pb(111) Films

The spatial distribution of the differential conductance for ultrathin Pb films grown on Si(111)7x7 substrate is studied by means of low-temperature scanning tunneling microscopy and spectroscopy. The formation of the quantum--confined states for conduction electrons and, correspondingly, the appearance of local maxima of the differential tunneling conductance are typical for Pb films; the energy of such states is determined mainly by the local thickness of Pb film. We demonstrate that the magnitude of the tunneling conductivity within atomically flat terraces can be spatially nonuniform and the period of the small-scale modulation coincides with the period of Si(111)7x7 reconstruction. For relatively thick Pb films we observe large-scale inhomogeneities of the tunneling conductance, which reveal itself as a gradual shift of the quantized levels at a value of the order of 50 meV at distances of the order of 100 nm. We believe that such large-scale variations of the tunneling conductance and, respectively, local density of states in Pb films can be related to presence of internal defects of crystalline structure, for instance, local electrical potentials and stresses.

Preliminary Experimentation of Fast Neutron Radiography with D-T Neutron Generator at BARC

An experimental study on fast neutron radiography (FNR) has been carried out using a laboratory based D-T neutron generator facility at Bhabha Atomic Research Centre (BARC) and initial results are presented. The aim was to develop an FNR system with a moderate intensity neutron source for imaging of specimen containing mixed low-Z and high-Z materials. The experimental set-up consists of a D-T neutron generator, collimator and an EMCCD camera based imaging system. Experiments were carried out with the neutron generator having a source strength of about 2 × 109 n/s and source spot size of 20 mm. To obtain optimum image quality with such a moderate neutron yield, a collimator has been designed having an inlet aperture of 10 mm and an L/D of 43. The imaging system was kept at an optimum distance from the collimator and various test samples of materials ranging from low Z to high Z were imaged. Thick samples in step wedge form, hole features in step wedge of polyethylene, mild steel and lead were imaged and analysed. Also a test sample of a low Z material (HDPE) with a hole placed behind a thick Pb was imaged to study the effect of thickness of high Z material on image quality with fast neutrons. The initial results emphasizes that a moderate yield D-T neutron generator based fast neutron radiography system with EMCCD camera could be deployed for field applications yielding moderate image quality to obtain first hand information of the investigated samples.

Monte Carlo simulation of biological shielding parameters in PGNAA

A prompt γ neutron activation analysis (PGNAA) facility based on a 252 Cf spontaneous fission neutron was performed with the final goal of obtaining various optimised radiation protection design parameters. MCNP Monte Carlo code was used to simulate the lead (Pb) shield thickness on two sides of the sample chamber, and B4 C, B2O3, LiOH, LiF, and borax were selected as neutron-absorbing materials that were simulated to determine optimal parameters for the optimal design of a biological multilayer composite shield. A series of calculations performed with the MCNP code indicated that the 5 cm thick Pb innermost layer of a biological shield rapidly reduced fast neutrons, and a moderation layer of 25 cm thick paraffin, 20 mm thick borax, and 2 mm thick B4 C were selected as neutron-absorbing materials. The calculated biological shield protection parameters satisfied the requirements of the PGNAA facility used in the experiment.

Significant enhancement of bond strength in the roll bonding process using Pb particles

Abstract Composite materials and layered alloys have become an interesting topic in materials development. The roll bonding (RB) process as a solid phase method of bonding has been widely used in the manufacturing of layered strips. The poor bond strength is one of the major drawbacks of the RB process. In the present study, Pb particles were used to enhance the bond strength between aluminum strips as filler material. AA1050 particle-reinforced sheets with different contents of interlayer Pb particles were fabricated at various rolling temperatures and thickness reduction ratios. Effects of roll bonding parameters that create successful bonds such as amount of Pb particle content, plastic strain from rolling process and rolling temperature were investigated. The bond strength was evaluated by the peeling test. It was found that by increasing the rolling temperature, thickness reduction ratio and Pb content, successful bonds with higher strength were created. Scanning electron microscopy was utilized to characterize the peeled surface of AA1050/Pb samples.

Magnetic-Field-Induced Superconductivity in Ultrathin Pb Films with Magnetic Impurities.

It is well known that external magnetic fields and magnetic moments of impurities both suppress superconductivity. Here, we demonstrate that their combined effect enhances the superconductivity of a few atomic layer thick Pb films grown on a cleaved GaAs(110) surface. A Ce-doped film, where superconductivity is totally suppressed at a zero field, actually turns superconducting when an external magnetic field is applied parallel to the conducting plane. For films with Mn adatoms, the screening of the magnetic moment by conduction electrons, i.e., the Kondo singlet formation, becomes important. We found that the degree of screening can be reduced by capping the Pb film with a Au layer, and observed the positive magnetic field dependence of the superconducting transition temperature.

Huge gain in pyroelectric energy conversion through epitaxy for integrated self-powered nanodevices

Polycrystalline (textured) and epitaxial 500nm thick Pb(Zr0.52Ti0.48)O3 (PZT) layers have been monolithically integrated in metal-insulator-metal structure on silicon in order to compare their pyroelectric properties, both statically (under stabilized temperatures) and dynamically (when submitted to temperature transient as a pyroelectric device should work). The films have roughly the same out-of-plane orientation, and thus a similar out-of-plane remnant ferroelectric polarization around 12μC/cm2. Whereas their static pyroelectric coefficients are similar (around −470μCm−2 K−1), the dynamic pyroelectric coefficient of the epitaxial layer is about one order of magnitude larger than that of the polycrystalline layer (−230 vs −30μCm−2K−1). This causes an important difference on the densities of converted pyroelectric energy by almost two orders of magnitude (1 vs 1.5 10−2mJ/cm3 per cycle for temperature variations of ∼6K). This difference is explained here by the counterbalanced extrinsic pyroelectric contribution arising from the domain walls motion in the dynamical measurements. Extrinsic pyroelectric contribution appears almost twice larger on polycrystalline layer than on epitaxial layer (+430 vs +250μCm−2K−1). These results are crucial for further design of advanced integrated pyroelectric-based nanodevices.

31-mode piezoelectric micromachined ultrasonic transducer with PZT thick film by granule spraying in vacuum process

A piezoelectric micromachined ultrasonic transducer (pMUT) is an ideal device for portable medical diagnosis systems, intravascular ultrasound systems, and ultrasonic cameras because of its favorable characteristics including small size, acoustic impedance matching with the body, low power consumption, and simple integration with the systems. Despite these advantages, practical applications are limited because of insufficient acoustic pressure of the pMUT caused by the thin active piezoelectric layer. Here, we report the fabrication of a thick piezoelectric Pb(Zr,Ti)O3 (PZT) film-based pMUT device having high deflection at low driving voltage using the granule spraying in vacuum (GSV) process. Pre-patterned high-density thick (exceeding 8 μm) PZT films were grown on 6-inch-diameter Si/SiO2/Ti/Pt silicon-on-insulator wafers at room temperature at a high deposition rate of ∼5 μm min−1. The fabrication process using the proposed GSV process was simple and fast, and the deflection of the pMUT exhibited a high value of 0.8 μm.

Infrared reflection spectra of the films of topological insulator Pb1-xSnxSe on the substrates ZnTe/GaAs

Infrared reflectivity spectra of the 700 nm thick topological insulator Pb 1-x Sn x Se films grown by the molecular beam epitaxy technique on ZnTe/GaAs substrates were studied. Using dispersion analysis of reflectivity spectra plasmon and phonon parameters for the samples under study were obtained.

Free-standing and flexible graphene papers as disposable non-enzymatic electrochemical sensors

We have explored AuNPs (13nm) both as a catalyst and as a core for synthesizing water-dispersible and highly stable core–shell structural gold@Prussian blue (Au@PB) nanoparticles (NPs). Systematic characterization by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) disclosed AuNPs coated uniformly by a 5nm thick PB layer. Au@PB NPs were attached to single-layer graphene oxide (GO) to form Au@PB decorated GO sheets. The resulting hybrid material was filtered layer-by-layer into flexible and free-standing GO paper, which was further converted into conductive reduced GO (RGO)/Au@PB paper via hydrazine vapour reduction. High-resolution TEM images suggested that RGO papers are multiply sandwich-like structures functionalized with core–shell NPs. Resulting sandwich functionalized graphene papers have high conductivity, sufficient flexibility, and robust mechanical strength, which can be cut into free-standing electrodes. Such electrodes, used as non-enzymatic electrochemical sensors, were tested systematically for electrocatalytic sensing of hydrogen peroxide. The high performance was indicated by some of the key parameters, for example the linear H2O2 concentration response range (1–30μM), the detection limit (100nM), and the high amperometric sensitivity (5Acm−2M−1). With the advantages of low cost and scalable production capacity, such graphene supported functional papers are of particular interest in the use as flexible disposable sensors.

Orientation control of epitaxial tetragonal Pb(ZrxTi1−x)O3 thin films grown on (100)KTaO3 substrates by tuning the Zr/(Zr + Ti) ratio

Pulsed metal organic chemical vapor deposition is used to epitaxially grow 30-nm thick tetragonal Pb(ZrxTi1−x)O3 thin films on (100) KTaO3 single crystal substrates. The in-plane misfit strain, which is controlled by the Zr/(Zr+Ti) ratio of Pb(ZrxTi1−x)O3 thin films, tunes the film orientation. When Zr/(Zr+Ti) = 0, which leads to the tensile strain from the substrate, a perfectly (100)-oriented film is formed, whereas when Zr/(Zr+Ti) = 0.45, which leads to the compressive strain from the substrate, a completely (001)-oriented film is realized. The volume fraction of the (001)-oriented domain almost linearly increases as the Zr/(Zr+Ti) ratio increases for films with (100) and (001) mixed orientations; this change in the volume fraction can be explained by considering the average lattice parameter matching between the Pb(ZrxTi1−x)O3 thin film and the KTaO3 substrate. These results demonstrate a method to systematically control the film orientation using the Zr/(Zr+Ti) ratio to tune the in-plane strain of Pb(ZrxTi1−x)O3 films grown on (100) KTaO3 single crystal substrates.

Vortices in a wedge made of a type-I superconductor

Using the time-dependent Ginzburg–Landau approach, we analyze vortex states and vortex dynamics in type-I superconductor films with a thickness gradient in one direction. In the thinnest part of the structures under consideration, the equilibrium states manifest the typical type-II vortex patterns with only singly-quantized vortices. At the same time, in the regions with larger thickness the singly-quantized and giant vortices coexist, in a qualitative agreement with our scanning Hall probe microscopy measurements on relatively thick Pb films. In the presence of an external current applied perpendicularly to the thickness gradient direction, the singly-quantized vortices, which enter the wedge through its thinnest edge, merge into giant vortices when propagating to the thicker parts of the structure. Remarkably, the results of our simulations imply that at moderate external current densities a regime is possible where the winding number of giant vortices, formed as a result of vortex coalescence, takes preferentially (or even exclusively) the values given by positive integer powers of two.