Study on X-ray Emission Using Ultrashort Pulsed Lasers in Materials Processing

The interaction of ultrashort pulsed laser radiation with intensities of 10¹³ W cm⁻² and above with materials often results in an unexpected high X-ray photon flux. It has been shown so far, on the one hand, that X-ray photon emissions increase proportionally with higher laser power and the accumulated X-ray dose rates can cause serious health risks for the laser operators. On the other hand, there is clear evidence that little variations of the operational conditions can considerably affect the spectral X-ray photon flux and X-ray emissions dose. In order to enhance the knowledge in this field, four ultrashort pulse laser systems for providing different complementary beam characteristics were employed in this study on laser-induced X-ray emissions, including peak intensities between 8 × 10¹² W∙cm⁻² < I₀ < 5.2 × 10¹⁶ W∙cm⁻², up to 72.2 W average laser power as well as burst/bi-burst processing mode. By the example of AISI 304 stainless steel, it was verified that X-ray emission dose rates as high as H˙′(0.07) > 45 mSv h⁻¹ can be produced when low-intensity ultrashort pulses irradiate at a small 1 µm intra-line pulse distance during laser beam scanning and megahertz pulse repetition frequencies. For burst and bi-burst pulses, the second intra-burst pulse was found to significantly enhance the X-ray emission potentially induced by laser pulse and plasma interaction.     

Enhanced X-ray Emissions Arising from High Pulse Repetition Frequency Ultrashort Pulse Laser Materials Processing

The ongoing trend in the development of powerful ultrashort pulse lasers has attracted increasing attention for this technology to be applied in large-scale surface engineering and modern microfabrication. However, the emission of undesired X-ray photon radiation was recently reported even for industrially relevant laser irradiation regimes, causing serious health risks for laser operators. In the meantime, more than twenty influencing factors have been identified with substantial effects on X-ray photon emission released by ultrashort pulse laser processes. The presented study on enhanced X-ray emission arising from high pulse repetition frequency ultrashort pulse laser processing provides new insights into the interrelation of the highest-contributing parameters. It is verified by the example of AISI 304 substrates that X-ray photon emission can considerably exceed the legal dose rate limit when ultrashort laser pulses with peak intensities below 1 × 10¹³ W/cm² irradiate at a 0.5 MHz pulse repetition frequency. The peak intensity threshold value for X-ray emissions decreases with larger laser spot sizes and longer pulse durations. Another key finding of this study is that the suction flow conditions in the laser processing area can affect the released X-ray emission dose rate. The presented results support the development of effective X-ray protection strategies for safe and risk-free ultrashort pulse laser operation in industrial and academic research applications.     

Influence of Pulse Duration on X-ray Emission during Industrial Ultrafast Laser Processing

Soft X-ray emissions during the processing of industrial materials with ultrafast lasers are of major interest, especially against the background of legal regulations. Potentially hazardous soft X-rays, with photon energies of >5 keV, originate from the fraction of hot electrons in plasma, the temperature of which depends on laser irradiance. The interaction of a laser with the plasma intensifies with growing plasma expansion during the laser pulse, and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, pulse duration is one of the dominant laser parameters that determines the soft X-ray emission. An existing analytical model, in which the fraction of hot electrons was treated as a constant, was therefore extended to include the influence of the duration of laser pulses on the fraction of hot electrons in the generated plasma. This extended model was validated with measurements of H (0.07) dose rates as a function of the pulse duration for a constant irradiance of about 3.5 × 10¹⁴ W/cm², a laser wavelength of 800 nm, and a pulse repetition rate of 1 kHz, as well as for varying irradiance at the laser wavelength of 1030 nm and pulse repetition rates of 50 kHz and 200 kHz. The experimental data clearly verified the predictions of the model and confirmed that significantly decreased dose rates are generated with a decreasing pulse duration when the irradiance is kept constant.     

X-ray Dose Rate and Spectral Measurements during Ultrafast Laser Machining Using a Calibrated (High-Sensitivity) Novel X-ray Detector

Ultrashort pulse laser machining is subject to increase the processing speeds by scaling average power and pulse repetition rate, accompanied with higher dose rates of X-ray emission generated during laser–matter interaction. In particular, the X-ray energy range below 10 keV is rarely studied in a quantitative approach. We present measurements with a novel calibrated X-ray detector in the detection range of 2–20 keV and show the dependence of X-ray radiation dose rates and the spectral emissions for different laser parameters from frequently used metals, alloys, and ceramics for ultrafast laser machining. Our investigations include the dose rate dependence on various laser parameters available in ultrafast laser laboratories as well as on industrial laser systems. The measured X-ray dose rates for high repetition rate lasers with different materials definitely exceed the legal limitations in the absence of radiation shielding.     

Observation of femtosecond X-ray interactions with matter using an X-ray–X-ray pump–probe scheme

Resolution in the X-ray structure determination of noncrystalline samples has been limited to several tens of nanometers, because deep X-ray irradiation required for enhanced resolution causes radiation damage to samples. However, theoretical studies predict that the femtosecond (fs) durations of X-ray free-electron laser (XFEL) pulses make it possible to record scattering signals before the initiation of X-ray damage processes; thus, an ultraintense X-ray beam can be used beyond the conventional limit of radiation dose. Here, we verify this scenario by directly observing femtosecond X-ray damage processes in diamond irradiated with extraordinarily intense (∼10¹⁹ W/cm²) XFEL pulses. An X-ray pump–probe diffraction scheme was developed in this study; tightly focused double–5-fs XFEL pulses with time separations ranging from sub-fs to 80 fs were used to excite (i.e., pump) the diamond and characterize (i.e., probe) the temporal changes of the crystalline structures through Bragg reflection. It was found that the pump and probe diffraction intensities remain almost constant for shorter time separations of the double pulse, whereas the probe diffraction intensities decreased after 20 fs following pump pulse irradiation due to the X-ray–induced atomic displacement. This result indicates that sub-10-fs XFEL pulses enable conductions of damageless structural determinations and supports the validity of the theoretical predictions of ultraintense X-ray–matter interactions. The X-ray pump–probe scheme demonstrated here would be effective for understanding ultraintense X-ray–matter interactions, which will greatly stimulate advanced XFEL applications, such as atomic structure determination of a single molecule and generation of exotic matters with high energy densities.Since W. C. Röntgen discovered X-rays emitted from vacuum tube equipment in 1895, scientists have continuously endeavored to develop brighter X-ray sources throughout the 20th century. One of the most remarkable breakthroughs was the emergence of synchrotron light sources, which were much more brilliant than the early lab-based X-ray sources. Such dramatic increase in X-ray brilliance provided a pathway to obtain high-quality X-ray scattering data. This, in turn, enabled one to solve the structures of complex systems such as proteins, functional units of living organisms, and viruses. However, the increase in the brilliance is also accompanied by a severe problem of X-ray radiation damage to the samples being examined (1). X-rays ionize atoms and generate highly activated radicals that break chemical bonds and cause changes in the structures of the samples. To achieve structure determination precisely, a sufficient scattering signal should be recorded before the samples are severely damaged. Radiation damage was considered to be an intrinsic problem associated with X-ray scattering experiments, which imposed a fundamental limit on the resolution in X-ray structure determination (2).The recent advent of X-ray free-electron lasers (XFELs) (3–5), which emit ultraintense X-ray pulses with durations of several femtoseconds, may totally avoid the problem of radiation damage. The irradiation of intense XFEL pulses generates highly ionized atoms, and the strong Coulomb repulsive force leads to evaporation of the samples. Meanwhile, it has been predicted theoretically (6) that atoms do not change their positions before the termination of the femtosecond X-ray pulse owing to inertia, thus enabling the use of X-ray radiations beyond the conventional X-ray dose limit. This innovative concept, called a “diffraction-before-destruction” scheme (6, 7), has paved a clear way to high-resolution structure determinations of weak scattering objects, including nanometer-sized protein crystals (8), noncrystalline biological particles (9), and damage-sensitive protein crystals (10).Despite the potential impact of XFELs, detailed understanding of the ultrafast XFEL damage processes has been missing. As a pioneering work, Barty et al. (11) measured the diffraction intensities of protein nanocrystals by changing the XFEL pulse durations from 70 to 300 fs at intensities of ∼10¹⁷ W/cm². They found that the diffraction intensities greatly decrease for longer durations, clearly indicating sign of structural damage, i.e., X-ray–induced atomic displacements within the XFEL pulse durations. For further understanding of ultraintense X-ray interactions with matter, we need to directly measure the temporal changes of the structural damage. In particular, measuring the ignition time of the atomic displacements is crucial for realizing advanced applications with greatly intense XFELs. Although improving our knowledge of the X-ray damage processes is essential for all aspects of XFEL science, the experimental verifications have been missing because of the extreme difficulty in observation with ultrahigh resolutions in space (ångstrom) and time (femtosecond).As a new approach to investigate the femtosecond X-ray damage processes, we here propose an X-ray–X-ray pump–probe experiment using double X-ray pulses; a pump X-ray pulse excites a sample and a probe X-ray pulse with a well-controlled time delay characterizes the change in the sample. In this approach, it is highly useful to exploit two-color double pulses with tunable temporal separations (12–15), which have been developed at SPring-8 Angstrom Compact free-electron LAser (SACLA) (4) and Linac Coherent Light Source (3). In this article, we measured the X-ray damage processes of diamond by using an X-ray–X-ray pump–probe diffraction experiment at SACLA. As the carbon–carbon bond is one of the most fundamental bonds in biomolecules, our results should provide a benchmark for XFEL-induced damage to practical samples.     

High-Resolution Mapping of Local Photoluminescence Properties in CuO/Cu2O Semiconductor Bi-Layers by Using Synchrotron Radiation

The quality of a semiconductor, which strongly affects its performance, can be estimated by its photoluminescence, which closely relates to the defect and impurity energy levels. In light of this, it is necessary to have a measurement method for photoluminescence properties with spatial resolution at the sub-micron or nanoscale. In this study, a mapping method for local photoluminescence properties was developed using a focused synchrotron radiation X-ray beam to evaluate localized photoluminescence in bi-layered semiconductors. CuO/Cu₂O/ZnO semiconductors were prepared on F:SnO₂/soda-lime glass substrates by means of electrodeposition. The synchrotron radiation experiment was conducted at the beamline 20XU in the Japanese synchrotron radiation facility, SPring-8. By mounting the high-sensitivity spectrum analyzer near the edge of the CuO/Cu₂O/ZnO devices, luminescence maps of the semiconductor were obtained with unit sizes of 0.3 μm × 0.3 μm. The devices were scanned in 2D. Light emission 2D maps were created by classifying the obtained spectra based on emission energy already reported by M. Izaki, et al. Band-like structures corresponding to the stacking layers of CuO/Cu₂O/ZnO were visualized. The intensities of emissions at different energies at each position can be associated with localized photovoltaic properties. This result suggests the validity of the method for investigation of localized photoluminescence related to the semiconductor quality.     

Kudzu (Pueraria montana) invasion doubles emissions of nitric oxide and increases ozone pollution

The nitrogen-fixing legume kudzu (Pueraria montana) is a widespread invasive plant in the southeastern United States with physiological traits that may lead to important impacts on ecosystems and the atmosphere. Its spread has the potential to raise ozone levels in the region by increasing nitric oxide (NO) emissions from soils as a consequence of increasing nitrogen (N) inputs and cycling in soils. We studied the effects of kudzu invasions on soils and trace N gas emissions at three sites in Madison County, Georgia in 2007 and used the results to model the effects of kudzu invasion on regional air quality. We found that rates of net N mineralization increased by up to 1,000%, and net nitrification increased by up to 500% in invaded soils in Georgia. Nitric oxide emissions from invaded soils were more than 100% higher (2.81 vs. 1.24 ng NO-N cm⁻² h⁻¹). We used the GEOS-Chem chemical transport model to evaluate the potential impact of kudzu invasion on regional atmospheric chemistry and air quality. In an extreme scenario, extensive kudzu invasion leads directly to an increase in the number of high ozone events (above 70 ppb) of up to 7 days each summer in some areas, up from 10 to 20 days in a control scenario with no kudzu invasion. These results establish a quantitative link between a biological invasion and ozone formation and suggest that in this extreme scenario, kudzu invasion can overcome some of the air quality benefits of legislative control.     

Study of Micro/Nano Structuring and Mechanical Properties of KrF Excimer Laser Irradiated Al for Aerospace Industry and Surface Engineering Applications

Micro/nano structuring of KrF Excimer laser-irradiated Aluminum (Al) has been correlated with laser-produced structural and mechanical changes. The effect of non-reactive Argon (Ar) and reactive Oxygen (O₂) environments on the surface, structural and mechanical characteristics of nano-second pulsed laser-ablated Aluminum (Al) has been revealed. KrF Excimer laser with pulse duration 20 ns, central wavelength of 248 nm and repetition rate of was utilized for this purpose. Exposure of targets has been carried out for 0.86, 1, 1.13 and 1.27 J^·cm⁻² laser fluences in non-reactive (Ar) and reactive (O₂) ambient environments at a pressure of 100 torr. A variety of characteristics of the irradiated targets like the morphology of the surface, chemical composition, crystallinity and nano hardness were investigated by using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffractometer (XRD), Raman spectroscopy and Nanohardness tester techniques, respectively. The nature (reactive or non-reactive) and pressure of gas played an important role in modification of materials. In this study, a strong correlation is observed between the surface structuring, chemical composition, residual stress variation and the variation in hardness of Al surface after ablation in both ambient (Ar, O₂). In the case of reactive environment (O₂), the interplay among the deposition of laser energy and species of plasma of ambient gas enhances chemical reactivity, which causes the formation of oxides of aluminum (AlO, Al₂O₃) with high mechanical strength. That makes it useful in the field of process and aerospace industry as well as in surface engineering.     

Conventional endoscopic retrograde cholangiopancreaticography vs the Olympus V-scope system

AIM: To compare the new Olympus V-scope (VS) to conventional endoscopic retrograde cholangiopancreati-cography (ERCP). METHODS: Forty-nine patients with previous endoscopic papillotomy who were admitted for interventional ERCP for one of several reasons were included in this single-centre, prospective randomized study. Consecutive patients were randomized to either the VS group or to the conventional ERCP group. ERCP-nave patients who had not undergone papillotomy were excluded. The main study parameters were interventional examination time, X-ray time and dose, and premedication dose (all given below as the median, range) and were investigated in addition to each patient’s clinical outcome and complications. Subjective scores to assess each procedure were also provided by the physicians and endoscopy assistants who carried out the procedures. A statistical analysis was carried out using the Wilcoxon rank-sum test.RESULTS: Twenty-five patients with 50 interventions were examined with the VS ERCP technique, and 24 patients with 47 interventions were examined using the conventional ERCP technique. There were no significant differences between the two groups regarding the age, sex, indications, degree of ERCP difficulty, or interventions performed. The main study parameters in the VS group showed a nonsignificant trend towards a shorter interventional examination time (29 min, 5-50 min vs 31 min, 7-90 min, P = 0.28), shorter X-ray time (5.8 min, 0.6-14.1 min vs 6.1 min, 1.6-18.8 min, P = 0.48), and lower X-ray dose (1351 cGy/m2 , 159-5039 cGy/m2 vs 1296 cGy/m2 , 202.2-6421 cGy/m 2 , P = 0.34). A nonsignificant trend towards fewer adverse events occurred in the VS group as compared with the conventional ERCP group (cholangitis: 12% vs 16%, P = 0.12; pain: 4% vs 12.5%, P = 0.33; post-ERCP pancreatitis: 4% vs 12.5%, P = 0.14). In addition, there were no statistically significant differences in assessment by the physicians and endoscopy assistants using subjective questionnaires.CONCLUSION: ERCP using the short-gu     

Endoscopic enhancement of the healing of high-risk colon anastomoses by low-power helium-neon laser

Recent studies suggest that helium-neon (He-Ne) lasers at low energy can enhance wound healing in intestinal anastomoses. In this experimental study, we tested the strength and collagen concentration of high-risk anastomoses of the rat colon after endoscopic irradiation by helium-neon laser. Our results show that repeated helium-neon laser irradiation (1.9 J/cm ²)increases the bursting strength of the anastomoses by almost 100% on the fourth postoperative day. This effect is not observed by increasing the radiation dose (6.4 J/cm ²).Differences in collagen (hydroxyproline) concentration did not reach statistical significance.     

Assessment of feasibility and efficacy of Class IV laser therapy for postoperative pain relief in off-pump coronary artery bypass surgery patients: A pilot study

Background:

Laser therapy, for its established analgesic properties with minimal side effects, has been used for the treatment of chronic pain. However, it has not been used for the treatment of acute postoperative pain. This pilot study was designed to assess the feasibility and efficacy of Class IV laser on postoperative pain relief following off-pump coronary artery bypass graft (OPCABG) surgery, as a component of multimodal analgesia (MMA) technique.

Methods:

This open observational prospective study comprised of 100 adult patients (84 male, 16 female) who underwent OPCABG through sternotomy. For postoperative analgesia, they were subjected to laser therapy subjected to laser therapy in addition to the standard institutional pain management protocol comprising of IV infusion/bolus of tramadol and paracetamol and fentanyl bolus as rescue analgesic. Pain intensity was measured by Verbal Rating Scale (VRS). The laser therapy was scheduled as once a day regime for three consecutive postoperative days (PODs) starting on POD 1, 30 min following tracheal extubation. The subsequent laser applications were also scheduled at the same time of the day as on day 1 if VRS was ≥5. 10 W Class IV laser was applied over 150 cm² sternal wound area for 150 s. VRS was used to assess pain severity and was recorded for statistical analysis using Friedman Test.

Results:

The mean (standard deviation [SD]) VRS of all the 100 patients just before application of the first dose of laser was 7.31 (0.94) while on MMT; the same fell to 4.0 (1.279) and 3.40 (2.697) at 1 h and 24 h respectively following first dose of laser. The change of VRS over first 24 h among all the 100 patients was statistically significant (P = 0.000). Laser was re-applied in 40 patients whose VRS was ≥5 (mean [SD] – 6.38 [0.868]) at 24^th h. After receiving the 2^nd dose of laser the VRS scores fell significantly (P = 0.000) and became 0 at 54^th h. No patients required 3^rd dose of the laser. No patient required rescue analgesic while on laser therapy.

Conclusion:

Class IV laser can be an effective technique for postoperative analgesia following OPCABG surgery through sternotomy when included as a component of MMA technique.     

Enhancement of Bentonite Materials with Cement for Gamma-Ray Shielding Capability

The gamma-ray shielding ability of various Bentonite–Cement mixed materials from northeast Egypt have been examined by determining their theoretical and experimental mass attenuation coefficients, μ_m (cm²g⁻¹), at photon energies of 59.6, 121.78, 344.28, 661.66, 964.13, 1173.23, 1332.5 and 1408.01 keV emitted from ²⁴¹Am, ¹³⁷Cs, ¹⁵²Eu and ⁶⁰Co point sources. The μ_m was theoretically calculated using the chemical compositions obtained by Energy Dispersive X-ray Analysis (EDX), while a NaI (Tl) scintillation detector was used to experimentally determine the μ_m (cm²g⁻¹) of the mixed samples. The theoretical values are in acceptable agreement with the experimental calculations of the XCom software. The linear attenuation coefficient (μ), mean free path (MFP), half-value layer (HVL) and the exposure buildup factor (EBF) were also calculated by knowing the μ_m values of the examined samples. The gamma-radiation shielding ability of the selected Bentonite–Cement mixed samples have been studied against other puplished shielding materials. Knowledge of various factors such as thermo-chemical stability, availability and water holding capacity of the bentonite–cement mixed samples can be analyzed to determine the effectiveness of the materials to shield gamma rays.     

Nonresonant femtosecond laser vaporization of aqueous protein preserves folded structure

Femtosecond laser vaporization-based mass spectrometry can be used to measure protein conformation in vitro at atmospheric pressure. Cytochrome c and lysozyme are vaporized from the condensed phase into the gas phase intact when exposed to an intense (10¹³ W/cm²), nonresonant (800 nm), ultrafast (75 fs) laser pulse. Electrospray postionization time-of-flight mass spectrometry reveals that the vaporized protein maintains the solution-phase conformation through measurement of the charge-state distribution and the collision-induced dissociation channels.     

Improving Gamma Ray Shielding Behaviors of Polypropylene Using PbO Nanoparticles: An Experimental Study

Recently, polymers have entered into many medical and industrial applications. This work aimed to intensively study polypropylene samples (PP) embedded with micro and nanoparticles of PbO for their application in radiation shielding. Samples were prepared by adding 10%, 30%, and 50% by weight of PbO microparticles (mPbO) and adding 10% and 50% PbO nanoparticles (nPbO), in addition to the control sample (pure polypropylene). The morphology of the prepared samples was tested; on the other hand, the shielding efficiency of gamma rays was tested for different sources with different energies. The experimental linear attenuation coefficient (LAC) was determined using a NaI scintillation detector, the experimental results were compared with NIST-XCOM results, and a good agreement was noticed. The LAC was 0.8005 cm⁻¹ for PP-10%nPbO and 0.6283 cm⁻¹ for PP-10%mPbO while was 5.8793 cm⁻¹ for PP-50%nPbO and 3.9268 cm⁻¹ for PP-50%mPbO at 0.060 MeV. The LAC values have been converted to some specific values, such as half value layer (HVL), mean free path (MFP), tenth value layer (TVL), and radiation protection efficiency (RPE) which are useful for discussing the shielding capabilities for gamma-rays. The results of shielding parameters reveal that the PP embedded with nPbO gives better attenuation than its counterpart pp embedded with mPbO at all studied energies.     

The inhomogeneous structure of water at ambient conditions

Small-angle X-ray scattering (SAXS) is used to demonstrate the presence of density fluctuations in ambient water on a physical length-scale of ≈1 nm; this is retained with decreasing temperature while the magnitude is enhanced. In contrast, the magnitude of fluctuations in a normal liquid, such as CCl₄, exhibits no enhancement with decreasing temperature, as is also the case for water from molecular dynamics simulations under ambient conditions. Based on X-ray emission spectroscopy and X-ray Raman scattering data we propose that the density difference contrast in SAXS is due to fluctuations between tetrahedral-like and hydrogen-bond distorted structures related to, respectively, low and high density water. We combine our experimental observations to propose a model of water as a temperature-dependent, fluctuating equilibrium between the two types of local structures driven by incommensurate requirements for minimizing enthalpy (strong near-tetrahedral hydrogen-bonds) and maximizing entropy (nondirectional H-bonds and disorder). The present results provide experimental evidence that the extreme differences anticipated in the hydrogen-bonding environment in the deeply supercooled regime surprisingly remain in bulk water even at conditions ranging from ambient up to close to the boiling point.     

Free jet excitation and emission spectra of diphenylbutadiene

Highly resolved emission and one-photon fluorescence excitation spectra for 1,4-diphenyl-1,3-butadiene seeded in a supersonic expansion of helium have been measured. The spectra show a long-lived (52.8 nsec for excitation at the 0-0) state at 29,652.5 cm^-1, approximately 1,150 cm^-1 below the well-characterized ¹B_u state, which is assigned as ¹A_g—i.e., we have directly observed a polyene ¹A_g state in the gas phase. Emission spectra and decay times for the ¹A_g state were measured at a number of different excitation energies. These data clarify the ordering of excited singlet states and the photophysical behavior of diphenylbutadiene.     

Carbon Nanotube Electron Emitter for X-ray Imaging

The carbon nanotube field emitter array was grown on silicon substrate through a resist-assisted patterning (RAP) process. The shape of the carbon nanotube array is elliptical with 2.0 × 0.5 mm² for an isotropic focal spot size at anode target. The field emission properties with triode electrodes show a gate turn-on field of 3 V/µm at an anode emission current of 0.1 mA. The author demonstrated the X-ray source with triode electrode structure utilizing the carbon nanotube emitter, and the transmitted X-ray image was of high resolution.     

Design and Gamma-Ray Attenuation Features of New Concrete Materials for Low- and Moderate-Photons Energy Protection Applications

We aimed, in this investigation, to prepare novel concretes which can be used in gamma-ray shielding applications. The experimental approach was performed using a NaI (Tl) detector to measure the concrete’s shielding features for different energies, ranging from 0.081 MeV to 1.408 MeV. The density of the fabricated concretes decreased with increasing W/C ratio, where the density decreased by 2.680 g/cm³, 2.614 g/cm³, and 2.564 g/cm³ for concretes A, B, and C, respectively, with increases in the W/C ratio of 0.4, 0.6, and 0.8, respectively. When the energy was elevated between 0.08 MeV and 1.408 MeV, the highest values were attained for concrete A, with values ranging between 0.451 cm⁻¹ and 0.179 cm⁻¹. The lowest half-value layer (Δ_0.5) values were achieved for concrete C, where the Δ_0.5 values varied between 1.53 cm and 3.86 cm between 0.08 MeV and 1.408 MeV. The highest Δ_0.5 values were achieved for concrete A, where the Δ_0.5 varied between 1.77 cm and 4.67 cm between 0.08 MeV and 1.408 MeV. According to this investigation, concrete A has the highest promise in radiation shielding purposes because it has the most desirable properties of the concretes studied.     

Low-Power Laser Powder Bed Fusion Processing of Scalmalloy®

Among recently developed high-strength and lightweight alloys, the high-performance Scalmalloy^® certainly stands out for laser powder bed fusion (LPBF) production. The primary goal of this study was to optimize the Scalmalloy^® LPBF process parameters by setting power values suitable for the use of lab-scale machines. Despite that these LPBF machines are commonly characterized by considerably lower maximum power values (around 100 W) compared to industrial-scale machines (up to 480 W), they are widely used when quick setup and short processing time are needed and a limited amount of powder is available. In order to obtain the optimal process parameters, the influence of volumetric energy density (VED) on the sample porosity, microstructure and mechanical properties was accurately studied. The obtained results reveal the stability of the microstructural and mechanical behaviour of the alloy for VEDs higher than 175 Jmm⁻³. In this way, an energy-and-time-saving choice at low VEDs can be taken for the LPBF production of Scalmalloy^®. After identifying the low-power optimized process parameters, the effects of the heat treatment on the microstructural and mechanical properties were investigated. The results prove that low-VED heat-treated samples produced with an LPBF lab-scale machine can achieve outstanding mechanical performance compared with the results of energy-intensive industrial production.     

The Vital Role of La2O3 on the La2O3-CaO-B2O3-SiO2 Glass System for Shielding Some Common Gamma Ray Radioactive Sources

The role La₂O₃ on the radiation shielding properties of La₂O₃-CaO-B₂O₃-SiO₂ glass systems was investigated. The energies were selected between 0.284 and 1.275 MeV and Phy-X software was used for the calculations. BLa10 glass had the least linear attenuation coefficient (LAC) at all the tested energies, while BLa30 had the greatest, which indicated that increasing the content of La₂O₃ in the BLa-X glasses enhances the shielding performance of these glasses. The mass attenuation coefficient (MAC) of BLa15 decreases from 0.150 cm²/g to 0.054 cm²/g at energies of 0.284 MeV and 1.275 MeV, respectively, while the MAC of BLa25 decreases from 0.164 cm²/g to 0.053 cm²/g for the same energies, respectively. At all energies, the effective atomic number (Z_eff) values follow the trend BLa10 < BLa15 < BLa20 < BLa25 < BLa30. The half value thickness (HVL) of the BLa-X glass shields were also investigated. The minimum HVL values are found at 0.284 MeV. The HVL results demonstrated that BLa30 is the most space-efficient shield. The tenth value layer (TVL) results demonstrated that the glasses are more effective attenuators at lower energies, while decreasing in ability at greater energies. These mean free path results proved that increasing the density of the glasses, by increasing the amount of La₂O₃ content, lowers MFP, and increases attenuation, which means that BLa30, the glass with the greatest density, absorbs the most amount of radiation.