Self-supporting Targets Research Articles

Measurement of differential cross sections for proton elastic scattering on natO at Ep= 4-6 MeV, suitable for EBS

In this study we present the experimental differential cross sections of natO(p,p0) elastic scattering, determined via the relative measurement technique, in the proton beam energy range Elab=4-6 MeV with a varying step (from 5-15 keV), at six backscattering detector angles between 120o and 170o (every 10o). A thin, self-supporting target manufactured in the lab was used in this experiment and the determination of its stoichiometry was carried out according to the currently existing evaluation, which has also been benchmarked recently. The measurements were performed using the Van de Graaff Tandem 5.5 MV Accelerator of N.C.S.R. “Demokritos” in Athens, Greece. The differential cross-section datasets obtained in the present work and already existing ones in literature for this extended proton beam energy range are shown and the observed peculiarities and discrepancies are discussed and analyzed.

Measurement, evaluation and benchmarking of differential cross sections for proton elastic scattering on natO in the energy range E = 4–6 MeV, suitable for EBS

In this study we present the experimental differential cross sections of the natO(p,p0) elastic scattering, determined via the relative measurement technique, in the proton beam energy range Elab = 4–6 MeV with a varying step (from 5 to 15 keV), at six backscattering detector angles between 120° and 170° (every 10°). A thin, self-supporting target manufactured was used in this experiment and the determination of its stoichiometry was carried out according to the currently existing evaluation at lower energy, which has also been benchmarked recently. The measurements were performed using the Van de Graaff Tandem 5.5 MV Accelerator of N.C.S.R. “Demokritos” in Athens, Greece. Theoretical calculations leading to the extension of the existing evaluation up to Ep,lab ∼ 6 MeV have also been performed and the obtained results seem to reproduce well not only the differential cross-section datasets obtained in the present work, but also already existing ones in literature for this extended proton beam energy range. The observed peculiarities and discrepancies are discussed and analyzed, while the theoretical differential cross sections are validated via an accurate benchmarking experiment carried out at RUBION, Ruhr University Bochum, using a thick Bi2O3 target.

Simultaneous assessment of energy, charge state and angular distribution for medium energy ions interacting with ultra-thin self-supporting targets: A time-of-flight approach

We demonstrate simultaneous measurements of the charge state, energy and angular distribution of keV ions in transmission experiments through self-supporting foils. Using a time-of-flight approach we have introduced an electrostatic deflection apparatus as an extension to existing medium energy ion scattering (MEIS) instrumentation. Different positive, neutral and negative charge states have been discriminated and quantified for initially singly charged beams of He, N, O and Ne in the energy range from 25 to 250 keV. In parallel, the ion energy after interaction with the target has been assessed for all detected particles, while particles can be discriminated by deflection angle. Self-supporting thin carbon foils were used as samples to benchmark our experiments with literature data where available.

Effects of molecular axis orientation of MeV diatomic projectiles on secondary ion emission from biomolecular targets

We report first experimental results on the orientation effect of fast diatomic molecular projectiles on secondary ion emission processes for 3.6-MeV C2+ traversing a self-supporting target of phenylalanine (Phe) film evaporated on a carbon foil. Coincidence measurements were performed on the image of fragments resulting from the Coulomb explosion of C2+ projectiles and the time-of-flight mass spectrometry of secondary ions emitted from the Phe film. We compared the secondary ion yield for C2+ projectiles with parallel and perpendicular orientations to the beam direction. The parallel orientation was found to enhance the secondary ion yield by a factor of approximately 1.1 compared with that for the perpendicular orientation. This enhancement corresponds to an increase in the average charge of Coulomb-exploded fragments. This finding implies that there is a linear correlation between the electronic energy deposition causing secondary ion production and the effective charge number of the incident molecular ions which interact with biomolecular targets.

Fabrication of thin targets for nuclear reaction studies at IUAC

Thin, durable, uniform, isotopic targets of 193Ir, 187Re, 182W, 181Ta, 175Lu and 169Tm of thicknesses ∼80 μg/cm2, 60 μg/cm2, 70 μg/cm2, 175 μg/cm2, 110 μg/cm2 and 270 μg/cm2, respectively, have been fabricated on carbon backing by physical vapor deposition technique for nuclear reaction studies at Inter University Accelerator Centre (IUAC), New Delhi. Preparation of very thin self-supporting targets of these elements is non-reproducible. A carbon backing thickness of ∼22 μg/cm2 was achieved. For the targets of refractory metals (193Ir, 187Re, 182W, 181Ta) e-gun evaporation was used. The lanthanide targets (175Lu, 169Tm) were fabricated using: (a) e-gun (for natC backing), (b) resistive heating (for source material deposition) and (c) e-gun evaporation (for natC capping) methods successively, without breaking the vacuum. Fabrication details of these targets, with actions taken against the challenges (peeling off, heat damage etc.) experienced during fabrication, are reported. No high Z contamination is found in any of the targets by RBS and XRF analysis.

Use of freezing techniques for increasing the output of ultralow density laser targets

Self-supporting ultralow density laser targets with an apparent density as low as 1 mg/cm3, a porous layer thickness of 60–500 μm, and a window diameter of 2.5 mm were prepared by thermally induced gelation of cellulose acetate solution in a mixture solvent between two glass slides using the mold casting method. In view of the low mechanical gel strength at a concentration of <0.2 wt %, supercritical drying of molded targets is carried out without separating the glass slides. For the target output to be radically increased, a new procedure has been developed based on rapid freezing of the solution on a metal brick from room temperature to–60°C and lower, down to–190°C, without initial gelation.

Recent target development activities at Inter-University Accelerator Centre

The target development laboratory at Inter-University Accelerator Centre (IUAC) is one of the main facilities for the fabrication of nuclear physics targets in India. Vacuum evaporation and cold rolling technique are mainly used for the production of isotopically pure targets at IUAC. Targets of Gd, Pt, W, Mo, Ta, Ni, Ag and Sn have been developed in the form of self-supporting targets and with thin carbon backing. Recent progress in target development laboratory at IUAC will be discussed in the report.

Fabrication of self-supporting targets of lead (206,208Pb) using evaporation technique

The self-supporting 206,208Pb enriched isotopic targets of thicknesses varying from 500μg/cm2 to 800μg/cm2 have been prepared in the high vacuum environment at the target laboratory of Inter University Accelerator Centre (IUAC), by using the resistive heating method. The limited amount of the target material, selection of the parting agent, highly oxidizing tendency of the Pb in the atmosphere and the separation of the lead film from the glass slides were the few major challenges faced in the fabrication of the targets. A limited amount of isotopic material (100mg) was utilized for the preparation of more than 20 thick self-supporting targets of 206Pb and 208Pb isotopes. Several attempts were made to overcome the difficulty of finding a suitable parting agent to avoid direct contact of water with the target material are discussed, along with the methods adopted for the fabrication of the targets. Further Energy Dispersive X-ray (EDX) analysis was performed to check the elemental purity of the foils. These targets have been successfully used for several nuclear physics experiments using the neutron detector setup known as National Array of Neutron Detectors (NAND) at IUAC, New Delhi.

Optimization of Actinide Quantification by Electron Probe Microanalysis

Conventional quantitative electron probe microanalysis of actinides requires the use of reference standard samples. However, for such elements, standards are generally not available. To overcome this difficulty, standardless methods of analysis are used, in which the x-ray intensity emitted by the standard is calculated. To be reliable, such calculations require accurate knowledge of physical data such as the x-ray production cross section. However, experimental data of this quantity are not always available for actinide elements. In the present work, experimental L and M x-ray production cross sections were measured for elements uranium and lead. Measurements were performed with two electron microprobes using wavelength-dispersive spectrometers using thin self-supporting targets. Experimental results are compared with calculated cross sections obtained from different analytical formulae, and, whenever possible, with experimental data obtained from the literature.

北京大学超小型激光加速器系统研究进展

When ultra short and intense laser interacts with plasma, the accelerating field gradient can be three order of magnitude higher than the conventional accelerator, which can accelerate the ion more efficiently. So the accelerator scale and cost can be reduced greatly. Among the various acceleration mechanisms, target normal sheath acceleration (TNSA) and radiation pressure acceleration (RPA) are the two main mechanisms widely studied. The RPA mechanism can produce energetic ion with higher energy, narrower energy spectrum and higher acceleration efficiency than TNSA. Peking University proposed RPA mechanism in phase stable regime and is building a Compact laser plasma accelerator (CLAPA) basded on this mechanism. This paper presents the progress of laser acceleration research and the development of laser accelerator including theoretical simulation, proof of principle experiments, self-supporting ultra-thin target fabrication and preliminary design of beam line.

Preparation of isotopic antimony targets

Thin self-supporting 123Sb targets were needed for studies using GAMMASPHERE investigating transverse wobbling in the highly-deformed triaxial nucleus 135Pr. The experiment was carried out using the 123Sb(16O,4n)135Pr reaction with the 80 MeV 16O beam provided by the ATLAS accelerator facility. In particle–particle coincidence measurements 121Sb targets were irradiated with a 332 MeV 28Si beam from ATLAS to measure evaporation residues and fission. The antimony targets were prepared self-supporting by the method of physical vapor deposition onto polished glass substrates or on various backing materials. Target thicknesses on the order of 500–1,000 μg/cm2 were obtained and used for the experiments. Details of the target production and performance in beam will be discussed.

Ultra-thin polymer foils for laser-ion acceleration

We report on the development of new materials for laser-ion acceleration applicable for the advanced mechanism of radiation-pressure-acceleration. These targets are ultra-thin with thicknesses of just a few nm. For several years, diamond-like carbon foils in this thickness range can be produced. An alternative material containing more than one ion-species has the potential to further improve the acceleration mechanism. The fabrication and characterization of self-supporting polymer-based targets will be described in this paper. Furthermore, we show the significant influence on a radiation-pressure induced acceleration process by experimental data.

Phenomenological and semi-microscopic analysis for 16O and 12C elastically scattering on the nucleus of 16O and 12C at Energies near the Coulomb barrier

The nuclear burning process proceeds from the conservation of the most abundant element hydrogen to helium, then from helium to carbon and oxygen, and then from these to heavier elements. Some of the key reactions for the carbon and oxygen burning stages of the nucleosynthesis are 12C+12C and 16O+16O leading to all possible final states. This paper contains the experimental measurements of 12C+12C and 16O+16O angular distributions performed at the cyclotron DC-60 in Astana, Kazakhstan. The extracted beam of 16O and 12C was accelerated up to two energies 1.75 and 1.5 MeV/n and then directed to an Al2O3 target of thickness 20 μg/cm2 and a carbon self-supporting target of thickness 17.4 μg/cm2. The angular distribution calculations were performed using both the phenomenological optical potential (SPI-GENOA) code and the double folding potential (FRESCO) code.

Preparation of self-supporting nickel targets from 58Ni, 60Ni and 61Ni

The investigation of the distribution of the fusion-barrier height by heavy-ion collisions requires thin self-supporting targets. To increase the accuracy of the measurement the thickness and homogeneity has to be known as precisely as possible.We prepared the self-supporting nickel foils out of the isotopes 58Ni, 60Ni and 61Ni. The resulting targets were between 75 and 105μg/cm² thick. The foils were produced on copper backing by electron-beam gun evaporation and by extracted ion-beam sputtering, both in high vacuum. To obtain self-supporting nickel foils the copper was removed by etching. We will discuss and compare both methods.

Quantitative measurement of oxygen content in Si targets

Enriched self-supporting targets of 28,29,30Si are often used in the field of high resolution nuclear physics experiments. The Si targets were prepared by the thermal evaporation deposition or reduction–deposition methods. The targets, however, are always contaminated by oxygen as Si-material is easily oxidised. These contaminated targets lead to poor data with low S/N ratio. Thus it is very useful if one can estimate the amount of oxygen in the target quantitatively before experiments.In this work we have developed a method to estimate the amount of oxygen in the Si target. We used α-ray and β-ray thickness gauges, which have different sensitivity to oxygen atoms. Namely, the α-ray gauge is more sensitive to light elements such as oxygen compared to the β-ray gauge. Thus one can deduce the amount of oxygen by comparing the oxygen thickness measured by α-ray gauge with that of the β-ray gauge.Accuracy of a few percents can be obtained for the oxygen content in Si targets with a thickness of 1mg/cm2. The present method can also be applied to heavy elements such as Ta2O5.

Preparation of self-supporting targets with thickness

Preparation techniques are described for self-supporting targets with thickness of less than 100 μg/cm 2 by means of vacuum evaporation and focused heavy-ion beam sputtering. With a visible light photo spectrometer optical transmittance as a function of thickness was calibrated for several metal films of different elements. These data were used for thickness determination of self-supporting targets of those materials.

Self-supporting elemental sulfur target for charged particle irradiation

A self-supporting target made of elemental sulfur has been developed for use in vacuum in high energy-resolution measurements at 0° using charged particle beams. The sulfur target is placed on a target ladder that is cooled by liquid nitrogen to minimize its sublimation due to heating by the energy loss of the beam in the target. Sulfur sheets with areal densities of 6–60 mg/cm 2 and size of 2 × 2 cm 2 are prepared. An energy resolution of 29 keV (FWHM) in the 32 S ( p , p ′ ) experiment at 0° is achieved using a 295 MeV proton beam. The target thickness is stable within ±5% during irradiation with a beam energy loss of 0.2 mW in the target. A windowless sulfur target was used successfully for the first time.

First results of target preparation by the HIVIPP method in pressures higher than one bar

We recently developed a new variation for the deposition method named HIVIPP (HIgh energy VIbrational Powder Plating), which is based on the high-energy vibrational motion of powder in the high electric field between parallel electrodes at room temperature and in vacuum. The HIVIPP method is very simple and does not require any complicated mechanisms to prepare both supported (backed) and self-supporting targets. The motivation for the present work was a desire to explore whether it could be done successfully with pressures higher than one bar, with reactive gases or inert gases, and without a vacuum-pumping system. The first successful results are reported for depositions of metallic chromium and non-metallic silicon powders in nitrogen, oxygen, and air at >1 bar.

Production of stable tellurium evaporated targets

Due to the low melting point of tellurium metal, self-supporting Te targets degrade quickly when exposed to particle beams. This situation is greatly improved if the tellurium material is evaporated onto C foil backings. Elastic scattering in target and backing layers broadens the Te peak, making measurements difficult, while too little material reduces the reaction rate. Therefore, it is necessary to optimize the target thickness. Evaporated metallic and oxide Te targets were prepared at Argonne National Laboratory by vacuum deposition from a resistively heated source boat. The stability of the targets was then tested by exposing them to a varying intensity alpha beam with an energy range from 17 to 27 MeV using the FN Tandem Van de Graaff accelerator at the University of Notre Dame. Optimal target thicknesses and beam currents were then obtained for p-process experiments. A description of the apparatus and production method will be presented.

Study of 7Be+d reactions for Standard Big Bang Nucleosynthesis

The recent WMAP results tightly constrain the baryon density in the universe, which in turn constrains the light element abundance predicted in Standard Big Bang Nucleosynthesis (SBBN). There is a discrepance in the Li-7 abundance which cannot be explained by uncertainties in the main reactions included in the SBBN. Up to now, the influence of the reaction Be-7(d,p)2 alpha has been neglected. We have investigated this reaction at SBBN energies using a radioactive Be-7 beam and a (CD2)(n) self-supporting target at the CYCLONE RIB facility at Louvain-la-Neuve. The experimental method is briefly described. Preliminary results and consequences for primordial nucleosynthesis are discussed.