Raman studies of amorphous nanocarbon obtained by laser sputtering

The structural properties of amorphous nanocarbon films fabricated by laser sputtering of a graphite target are investigated by means of Raman spectroscopy. Analysis of the spectral features in the region of 100–3600 cm-1 allowed us to determine the allotrope composition of the films and the degree of disorder in terms of average crystallite size. The results obtained are important for application of such films in the field of electrode coatings.

Tribological characterization of graphene oxide by laser ablation as a grease additive

In this work, the structural and tribological behavior of graphene oxide samples as a grease addi-tive was studied. By Nd:YAG laser ablation system and using graphite target at two laser energy of 0.3 W and 0.6 W, graphene oxide (GO) samples were successfully prepared. GO samples were characterized using Raman spectroscopy, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray spectroscopy (EDAX). Also, tribological behaviors of the lubricating grease, with and without the graphene oxide in grease, by the pin-on disc tribometer were determined. The Raman spectroscopy measurements showed D and G bound, which confirmed the successful synthesis of the graphene oxide sample and also the I D/I G, decreased by increasing laser power due to decreasing disorder in graphene oxide structure. FESEM images show that by ablating carbon atoms from graphite target in water, particles assemble to form a GO micro-cluster due to thermodynamically agglomeration with average size of about 3–4 µm, which the size of them depends on the laser pulse energy. Based on FTIR and EDAX analysis, GO sample which prepared at lower laser energy possessed the highest content of oxygen and oxygen functional groups. In addition, the results of tribological behavior showed that the friction-reducing ability and antiwear property of the grease can be improved effectively with the addition of GO. However, it is revealed that the small size GO has a better lubricating performance and therefore cluster size appears to play a role in the degree of wear protection due to its impact on the physical and chemical properties. The results of this study indicate that the GO sample prepared at lower laser energy (0.3 W) has a smaller size and the higher the oxygen content therefore provide better friction-reducing and anti-wear effect. Also, additive of graphene oxide in lubricating grease decreases coefficient of friction as well as wear. Based on our results, the application of GO as an additive in grease leads to increased performance of the lubricated kinematic machine.

The Meson Production Targets in the high energy beamline of HIPA at PSI

Two target stations in the 590 MeV proton beamline of the High Intensity Proton Accelerator (HIPA) at the Paul Scherrer Institut (PSI) produce pions and muons for seven secondary beamlines, leading to several experimental stations. The two target stations are 18 m apart. Target M is a graphite target with an effective thickness of 5 mm, Target E is a graphite wheel with a thickness of 40 mm or 60 mm. Due to the spreading of the beam in the thick target, a high power collimator system is needed to shape the beam for further transport. The beam is then transported to either the SINQ target, a neutron spallation source, or stopped in the beam dump, where about 450 kW beam power is dissipated. Targets, collimators and beam dumps are described.

Fluorescent Nanodiamonds Synthesized in One-Step by Pulsed Laser Ablation of Graphite in Liquid-Nitrogen

In this work, we present a relevant upgrade to the technique of pulsed laser ablation of fluorescent nanodiamonds (NDs), relying on an automatized graphite-target movement maintaining a constant level of liquid nitrogen over its surface during hours of deposition. Around 60 mg of NDs nanopowder was synthesized and optomagnetically characterized to assess its optical quality. Chemical purification of the ablated nanopowders, which removes the graphitic byproducts, permits to obtain pure fluorescent NDs with an efficiency of 7 ± 1% with respect to the total nanopowder mass. This value compares positively with the efficiency of other commercial NDs synthesis techniques such as detonation, cavitation, and high pressure–high temperature.

Luminescent Carbon Dots Synthesized by the Laser Ablation of Graphite in Polyethylenimine and Ethylenediamine

Fluorescent carbon dots (CDs) synthesized by pulsed laser ablation in liquid (PLAL) are still interesting materials due to their possible applications. However, unlike CDs produced by the hydrothermal method, CDs produced the synthesis products by the PLAL method were never separated by dialysis, which differentiates the synthesis products and allows the identification of the main source of fluorescence. In this work, the synthesis of fluorescent carbon dots (CDs) was performed by nanosecond laser ablation of a graphite target immersed in polyethyleneimine (PEI) and ethylenediamine (EDA), and the synthesis products were separated by dialysis. The results of optical measurements showed that the main source of luminescence of the obtained nanostructures are fluorescent particles or quasi-molecular fluorophores created in the ablation process. In the case of ablation in PEI, most of the produced molecular fluorophores are associated with carbogenic nanostructures, while in the case of EDA, free fluorescent molecules dominate.

A Theoretical Study of the Possibility of Obtaining the Radioisotope 13N for Medical Applications Using Dense Plasma Focus Device

The aim of this research is to study the possibility of obtaining the short-lived radioisotope 13N by colliding with a deuterium ion beam emitted by an NX2 dense plasma focus device with a graphite target, as a technique alternative to the traditional technique for getting short-lived radioisotope (SLR) accelerators. Lee code was used to study the properties of the plasma pinch, which is the source of deuterium ion beams. Then, a function of distributing the beam energy and stopping power was found within the graphite using SRIM program. The reaction cross-section was also found from an EXFOR database and the radiative yield of the reaction was calculated. The radioactivity of 13N was calculated and found to be equal to A = 4.14×103 Bq. The effect of the change in deuterium gas pressure on the radioactivity was studied and it was found that the best value for the pressure is 3 Torr, where the number of deuterium ions is the greatest amounting to 3.12×1011 ions and thus the radioactivity increased to 5.616 ×103 Bq. The effects of repetition rate of the studied dense plasma focus device and the exposure time of the graphite target to deuterium ions were studied. The radioactivity was calculated at repetition rates (1,5,10,16 ) Hz and exposure times (30,60,600) sec., where we noticed an increase in the value of radioactivity at a repetition rate of 16 Hz and an exposure time of 600 sec., reaching to 28791 × 103 Bq. To obtain a radioactivity value for 13N suitable for use in PET technique, the radioactivity value was calculated at high repetition rates (50,100,500) Hz and exposure times (30,60,600) sec. We obtained the value of radioactivity 527 ×106 Bq at a repetition rate of 500 Hz and an exposure time of 300 sec. and this value is suitable for use in PET technique. However, there are technical difficulties in the studied dense plasma focus device to obtain a high repetition rate of this value. The radioactivity of 13N was calculated at very high times of exposure of the graphite target to deuterium ions (1000, 1500, 2000, 2500, 3000) sec. at the repetition rates of the device studied. The highest radioactivity value obtained was 55.79 ×106 Bq at an exposure time of 3000 sec. and this value is less than the required value for the required use in PET technique. Keywords: Dense plasma focus device NX2, Lee code, Radioactivity.

VOLUMES OF WORTH—DELIMITING THE SAMPLE SIZE FOR RADIOCARBON DATING OF PARCHMENT

ABSTRACT Medieval manuscripts are invaluable archives of the written history of our past. Manuscripts can be dated and localized paleographically, but this method has its limitations. The Fragmenta membranea manuscript collection at the National Library of Finland has proved difficult to date using paleographic methods. Radiocarbon dating has been applied to manuscripts of parchment before, but a systematic protocol for radiocarbon dating of parchment has not been established with a minimally destructive sampling strategy. In this work, we have established a radiocarbon dating procedure for parchments combining a clean-room based chemical pretreatment process, elemental analyzer combustion, automatic graphitization and accelerator mass spectrometry (AMS) measurements to reduce the AMS target size from a typical 1 mg of carbon. Prolonged acid treatment resulted in improved dating accuracy, since this is consistent with the manufacturing process of medieval parchment involving a lime bath. Two different combustion processes were compared. The traditional closed tube combustion (CTC) method provided a well-established though labor-intensive way to produce 1 mg AMS targets. The Elemental Analyzer-based process (EA-HASE, Elemental Analyzer Helsinki Adaptive Sample prEparation line), is designed for fast combustion and smaller sample sizes. The EA-HASE process was capable of reproducing the simulated radiocarbon ages of known-age samples with AMS graphite target sizes of 0.3 mg of carbon, corresponding to a 3 mm2 area of a typical medieval parchment. The full potential of the process to go down to as little as 50 μg will be further explored in the future in parallel to studies of sample-specific contamination issues.