Reaction Rate Research Articles

Observation of an order change during the course of a reaction in a kinetic study of the reduction of trans-dicyanodibromoaurate(III) by octacyanotungstate(IV) in an acidic medium

AbstractThe reduction of dibromodicyanoaurate(III) ion by octacyanotungstate(IV) ions was studied under near stoichiometric conditions in an acidic medium. An order change occurred during the course of the reaction. The reaction was first order in Au(CN)2(Br)2– and second order in W(CN)84– for the first half-life, but after ca. 60% conversion became first order in both reactants. The order change is ascribed to two different AuII intermediates that form during the reaction course. A third order rate constant of k3 = 7.80 × 105 M−2 min−1 and a second order rate constant of k2 = 108 M−1 min−1 was found at [H+] = 1.633 × 10–3 M, an ionic strength of I = 0.11 M (NaBr) and at 25.0 ± 0.1 °C for the reaction. The reaction rate decreases with increasing [H+] in the reaction mixture at low pH and an experimental pKa of 1.80 ± 0.03 was found at 25.0 ± 0.1 °C for the deprotonation of HW(CN)83–. The reaction rate is independent of [Br−] and decrease with addition of W(CN)83– in the reaction mixture. Activation parameters have been obtained by a least-squares fit of the temperature data directly to the Eyring equation. Graphical abstract

Oxynitrided Ti-6Al-4V Coatings Deposited by Twin Wire Arc Spray for Protection of Aluminum Die-Casting Molds

Abstract Steel molds used for aluminum die-casting often fail due to excessive wear or cracking phenomena associated with the soldering effect in contact with molten aluminum, which leads to the formation of iron-based intermetallic compounds and causes problems in the cast components. One solution is to apply protective coatings whose composition is less reactive with the molten aluminum and improve its hardness, toughness, wear, and corrosion resistance, thus prolonging its service life. This work evaluates the effectiveness of Ti-6Al-4V coatings deposited by twin wire arc spraying in an air or nitrogen atmosphere. Nitrogen was used as the carrier and shielding gas for the in-flight molten particles. Coatings were deposited by varying the stand-off distance, the nitrogen gas pressures, and the substrate temperature. The microstructure of the coatings is interlayered, one porous layer of dendrites and one highly densified layer. The presence of TiN, TiO2, α-Ti, and β-Ti phases was confirmed by different characterization methods. For instance, x-ray photoelectron spectroscopy measurements confirmed the presence of N-Ti, O-Ti, and N-O bonds, with the oxygen/nitrogen/titanium percentage associated with the formation of a non-stoichiometric (Ti, Al, V)NxOy phase. Finally, the reactivity of selected oxynitrided Ti-6Al-4V coating in contact with molten aluminum showed a low reaction rate compared to the coarse reaction layer suffered by the uncoated steel substrates.

Ammonia and temperature sensing applications using fluorometric and colorimetric microparticles and polymeric films doped with BODIPY-emitters.

Fourfunctionalized BODIPY derivatives(BDP1 to BDP4) were synthesizedand their optical properties investigatedboth in solution and when incorporated into a solid matrix. Recognizing the versatility of BODIPY derivatives and the increasing interest in developing new luminescent organic dyes embedded in polymers, the BODIPY derivatives were dispersed into two types of polymeric matrices: Poly(methyl methacrylate) (PMMA) and Thermoplastic Polyurethane (TPU), both as films and microparticles. This resulted in eight new BODIPY-doped polymer films and eight types of BODIPY-doped polymeric microparticles for use in aqueous solutions. The integration of the BODIPY dyes into the polymeric matrices combines the unique properties of the polymer films, such as porosity, flexibility, and elasticity, with the excellent photophysical characteristics of the BODIPYs. Importantly, the dispersion minimized issues such as aggregation-caused quenching commonly observed in solid-state luminescent materials. The thermometric responses of all polymer films were evaluated by studying their solid-state emission spectra in the 25-200°C temperature range. The reversibility of these temperature-induced changes was also assessed, revealing excellent recovery of luminescence. These promising results suggest these materials could have applications as fluorescent thermometric sensors. Furthermore, we explored the potential of the brominated (BDP3) and chalcogenated (BDP4) BODIPY derivatives as ammonia sensors. The two derivatives produced yellow fluorescent products upon interaction with the analyte. Kinetic studies using solid-state emission spectra of BDP4@TPU and BDP4@PMMA showed significant differences in reaction rates (minutes for BDP4@TPU and hours in the case of BDP4@PMMA) attributable to the higher permeability of TPU when compared with PMMA. Detection and quantification of ammonia concentration were conducted by means of simple photographic analysis, measuring the "R" (red) and "G" (green) components of RGB color parameters. Theresults from the photographic method correlated well with the results from fluorimetric spectroscopy studies. The photographic analysis is straightforward, portable, and does not require expensive equipment. Finally, we successfully applied polymeric microparticles doped with BODIPYs to detect ammonia in water, demonstrating their effectiveness without the need for organic solvents. This highlights their potential for environmental monitoring and other applications requiring sensitive and selective detection methods.

Impact of Antibiotic on Efficacy and Adverse Reactions of Chemoimmunotherapy in Non‐small Cell Lung Cancer Patients: A Retrospective Cohort Study

ABSTRACTBackgroundThis study aimed to evaluate the impact of antibiotic exposure on efficacy and adverse reactions in non‐small cell lung cancer (NSCLC) patients receiving chemoimmunotherapy, and to explore any specific associations on the basis of antibiotic class.MethodsA retrospective study was conducted on NSCLC patients who received chemoimmunotherapy in two Shandong hospitals between January 2018 and October 2023. The association between antibiotic exposure and progression‐free survival (PFS), overall survival (OS), objective response rate (ORR) and incidence of immune related adverse reactions (irAE) of patients were evaluated.ResultsOf the 316 patients, 134 (42.41%) received antibiotics (ATB group), and 182 (57.59%) did not (N‐ATB group). There was no significant difference in PFS (aHR = 1.009, 95% CI: 0.770–1.323; p = 0.946) or OS (aHR = 1.420, 95% CI: 0.986–2.047; p = 0.060) between ATB and N‐ATB groups. The impact on efficacy was related to the type of antibiotic. β‐Lactams (aHR = 1.737, 95% CI: 1.148–2.629; p = 0.009), in particular β‐lactam/β‐lactamase inhibitor combinations (BLBLIs) (aHR = 1.885, 95% CI: 1.207–2.944, p = 0.005) were associated with poorer OS. However, quinolones (aHR = 1.192, 95% CI: 0.861–1.650; p = 0.291) were not associated with OS. The incidence of irAEs was not significantly different between ATB and N‐ATB groups (p = 0.073), but was higher with BLBLIs (p = 0.013).ConclusionsIn NSCLC patients receiving chemoimmunotherapy, no significant difference was observed in efficacy and incidence of irAEs between the ATB and the n‐ATB groups. In antibiotic class analysis, β‐lactams and specifically BLBLIs were observed to be associated with worse OS.

Determining reaction rate parameters for an energetic material through inverse multi-scale analysis of shock-to-detonation transition

Determining reaction rate parameters for an energetic material through inverse multi-scale analysis of shock-to-detonation transition

Valorization of marble sludge waste in biodiesel production using a central composite design.

This work addresses the scarcity of energy resources and environmental issues by concentrating on the synthesis of biodiesel by the transesterification of waste cooking oil with methanol. Marble sludge (MS), a novel heterogeneous catalyst, was used to speed up the rate of reaction. The catalyst's physical and chemical characteristics were thoroughly examined using a variety of methods, including X-ray diffraction, X-ray Fluorescence, SEM, particle size distribution, and BET analysis. Using the MS catalyst, the study investigated the impact of important parameters on the yield of biodiesel from waste cooking oil with the aid of response surface methodology using Design-Expert version 13 software. These parameters included temperature (50-70℃), reaction time (1-4h), catalyst concentration (1-5 wt%), and methanol-to-oil molar ratio (5-20mol/mol). Optimization of the parameters was performed for economic targets to lower the production cost of biodiesel. The results showed that a methanol-to-oil molar ratio of 20:1, a catalyst of 5 wt%, and a reaction time of 1h at 57℃ were the ideal parameters for obtaining a biodiesel yield of 93.5%. The resultant biodiesel revealed promising characteristics, such as a flash point of 160℃, a kinematic viscosity of 4 mm2/s, and a density of 0.871g/cm3. The study demonstrates the significant consequences and real-world advantages of using rational engineering methods to use MS as a very effective, stable, and easily recoverable catalyst for the long-term, sustainable generation of biodiesel from waste cooking oil.

Stellar Thermonuclear Reaction Rates of Proton Radiative Capture by Closed Light Shell Isotopes

Light isotopes, especially closed shell nuclei, have significance in thermonuclear reactions of the Carbon-Nitrogen-Oxygen (CNO) cycle in stars. In this research, 12C(p, γ) 13N and 14N(p, γ) 15O reactions have been calculated by means of Matlab codes to find the reaction rate across a temperature range of 0.006 to 10 GK using non-resonant parts, as well as the astrophysical S- factor S(E) at low energies. It was concluded that the high binding energy of 12C and 14N nuclei make the reaction less probable thus enabling other competitive processes to develop, which enhances the probability of other competitive proton reactions in the CNO cycle.

Maximizing Oxygen Evolution Performance of NiFeOx Semitransparent Electrocatalysts Applicable to Photoelectrochemical Water Splitting Device

In photoelectrochemical (PEC) water splitting, semiconductor‐based photoelectrodes can improve reaction rates and durability by incorporating cocatalysts that serve as active sites for the water splitting process. However, achieving both high light transmittance and efficient catalytic activity is essential for these cocatalysts. This study aimed to optimize the surface loading of semitransparent NiFeOx thin‐film electrocatalysts to enhance the oxygen evolution reaction (OER) rates while maintaining high light transmittance. NiFeOx thin films were deposited on fluorine‐doped SnO2 (FTO) transparent conductive substrates, and the relationship between the NiFeOx loading amount (Γ) and the OER rate was examined using electrochemical techniques. The OER rate of NiFeOx on FTO (NiFeOx/FTO) was the highest at a Γ value of 0.20 μmol cm‐2. To further explore the connection between this optimized Γ and PEC activity, the impact of Γ on the PEC OER performance of visible‐light‐absorbing α‐Fe2O3 semitransparent photoanodes was evaluated as a model system. Applying the optimized Γ of NiFeOx to modify the α‐Fe2O3 surface also led to enhanced PEC OER performance. These findings highlight the critical role of surface design, specifically the optimization of cocatalyst loading and electrocatalytic activity, in improving PEC water splitting efficiency, providing valuable guidelines for future semitransparent photoelectrode development.

Cavity induced modulation of intramolecular vibrational energy flow pathways.

Recent experiments in polariton chemistry indicate that reaction rates can be significantly enhanced or suppressed inside an optical cavity. One possible explanation for the rate modulation involves the cavity mode altering the intramolecular vibrational energy redistribution (IVR) pathways by coupling to specific molecular vibrations in the vibrational strong coupling (VSC) regime. However, the mechanism for such a cavity-mediated modulation of IVR is yet to be understood. In a recent study, Ahn et al. [Science 380, 1165 (2023)] observed that the rate of alcoholysis of phenyl isocyanate (PHI) is considerably suppressed when the cavity mode is tuned to be resonant with the isocyanate (NCO) stretching mode of PHI. Here, we analyze the quantum and classical IVR dynamics of a model effective Hamiltonian for PHI involving the high-frequency NCO-stretch mode and two of the key low-frequency phenyl ring modes. We compute various indicators of the extent of IVR in the cavity-molecule system and show that tuning the cavity frequency to the NCO-stretching mode strongly perturbs the cavity-free IVR pathways. Subsequent IVR dynamics involving the cavity and the molecular anharmonic resonances lead to efficient scrambling of an initial NCO-stretching overtone state over the molecular quantum number space. We also show that the hybrid light-matter states of the effective Hamiltonian undergo a localization-delocalization transition in the VSC regime.

Learning reaction-transport coupling from thermal waves.

Although thermal waves are ubiquitous in nature and engineering, the development of diagnostic tools capable of elucidating the roles of reaction and transport remains an unmet need. This limits our comprehension of the physics and ability to predict wave dynamics. Here we demonstrate that thermal properties and chemical kinetics can be learned directly from observing thermal wave dynamics, using partial differential equation-constrained optimization. This enables the determination of unobserved reaction rates without the need for a comprehensive measurement of all state variables, given the model space constrained by governing equations. Examples include steady planar waves and unsteady pulsating waves of which dynamics are commonly observed in nature. We show successful learning of thermal properties and chemical kinetics and reconstruction of wave dynamics with the inferred properties, which enables the comprehension of the intricate reaction-transport coupling from thermal data.

A Pseudo‐catalytic Network Motif for Thiol‐based Chemical Reaction Networks

AbstractThe construction of chemical reaction networks (CRNs) is a formidable challenge because of their holistic and nonlinear nature. One approach to constructing CRNs involves combining fragments with distinctive properties, known as network motifs. Thiol chemistry is widely used in the construction of CRNs, with motifs available for positive and negative feedback loops. However, a simple catalytic motif has been lacking. Here, we developed a pseudo‐catalytic motif using the reaction between cystamine and organic thiocyanates, which operates through a nucleophilic chain mechanism. Although similar to thiol autocatalytic systems, this reaction does not involve a doubling of the number of thiol species at any stage. The reaction is high‐yielding and produces 2‐amino‐2‐thiazoline. Its pseudo‐catalytic nature manifests itself in the nearly linear relationship between the reaction rate and the amount of free thiols added at the beginning of the reaction. We demonstrated that this reaction can be regulated by external, time‐dependent thiol signals and integrated into larger CRNs. We believe that this system will be a valuable addition to thiol chemistry, enabling the construction of CRNs with interesting functionalities.

Factors Inducing Cutaneous Adverse Reactions in Cancer Patients Treated with PD-1 and PD-L1 Inhibitors: A Machine-Learning Algorithm Approach

Immune checkpoint inhibitors (ICIs) show promise in cancer treatment but can lead to immune-related adverse events (irAEs), notably affecting the skin. Understanding the factors behind these skin reactions is crucial for effective management during treatment. Hence, the aim of this study was to uncover associations between patient characteristics and cutaneous adverse reactions among cancer patients undergoing ICI treatment. The study involved 209 cancer patients receiving ICIs. Statistical methods, including the chi-square test, Fisher's exact test, and multivariable logistic regression, were employed to analyze variables such as hypertension, antihistamine use, cancer metastasis, diabetes, and opioid usage. Additionally, machine learning techniques, including logistic regression, elastic net, random forest, and support vector machines (SVM), were utilized to develop predictive models anticipating skin-related adverse events. Results highlighted significant associations between specific patient attributes and the incidence of skin reactions post-ICI treatment. Notably, patients using antihistamines or with cancer metastasis exhibited higher rates of skin adverse reactions, while those with diabetes or using opioids displayed lower incidence rates. Robust performance in forecasting these adverse events was observed, particularly in the predictive models employing logistic regression and elastic net. This pioneering study contributes crucial insights into predictive modeling for ICI-induced skin reactions, emphasizing the importance of personalized treatment strategies. By identifying risk factors and utilizing tailored predictive models, healthcare providers can proactively manage adverse events, optimizing the benefits of ICIs while mitigating potential side effects.

2-O-α-D-glucosyl glycerol production by whole-cell biocatalyst of lactobacilli encapsulating sucrose phosphorylase with improved glycerol affinity and conversion rate.

2-O-α-D-glucosyl glycerol (2-αGG) is a valuable ingredient in cosmetics, health-care and food fields. Sucrose phosphorylase (SPase) is a favorable choice for biosynthesis of 2-αGG, while its glucosyl-acceptor affinity and thermodynamic feature remain largely unknown, limiting 2-αGG manufacturing. Here, three SPases were obtained from lactobacilli and bifidobacteria, and the one encoded by Lb. reuteri SDMCC050455 (LrSP) had the best transglucosylation ability, with 2-αGG accounting for 86.01% in the total product. However, the LrSP exhibited an initial forward reaction rate of 11.83/s and reached equilibrium of 56.90% at 110h, indicating low glycerol affinity and conversion rate. To improve catalytic efficiency, the LrSP was overexpressed in Lb. paracasei BL-SP, of which the intracellular SPase activity increased by 6.67-fold compared with Lb. reuteri SDMCC050455. After chemically permeabilized with Triton X-100, the whole-cell biocatalysis of Lb. paracasei BL-SP was prepared and showed the highest activity, with the initial forward reaction rate improved to 50.17/s and conversion rate risen to 80.79% within 17h. Using the whole-cell biocatalyst, the final yield of 2-αGG was 203.21g/L from 1M sucrose and 1M glycerol. The food grade strain Lb. paracasei was used for the first time as cell factory to recombinantly express the LrSP and construct a whole-cell biocatalyst for the production of 2-αGG. After condition optimization and cell permeabilization, the whole-cell biocatalyst exhibited 23.89% higher equilibrium conversion and 9.10-fold of productivity compared with the pure enzyme catalytic system. This work would provide a reference for large-scale bioprocess of 2-αGG.

Quantum Chemistry Study on Cl-Initiated Reactions of 2-Chloropropane and 2-Methylpropanoyl Halogen (Cl, Br, F): Mechanism, Kinetics, and Atmospheric Implications.

Halogenated volatile organic compounds (HVOCs) pose significant bioaccumulative and toxicological risks, necessitating effective strategies for their removal. Here, we show, through a computational study employing density functional theory and coupled cluster methods, the detailed mechanism and kinetic properties of Cl-initiated degradation reactions of 2-chloropropane (2-CP, (CH3)2CHCl) and 2-methylpropanoyl halide ((CH3)2CHCOX, X = Cl, Br, F). The reaction rate constants of all the channels were calculated by the canonical variational transition state theory (CVT) with the correction of the small curvature tunneling effect (SCT) at 200-1000 K. The subsequent transformation pathways of the major radical products of (CH3)2CHCl and (CH3)2CHCOCl in the presence of O2, NO, and HO2 radical were investigated. The results elucidate the reaction pathways and rate constants, which are in excellent agreement with the experimental data at 296 K. We further explore the atmospheric implications of these reactions by assessing the atmospheric lifetime (τ) and ozone depletion potential (ODP). Additionally, we delve into the aquatic toxicity and bioaccumulation potential of the reactants and their transformation products. This study not only advances our knowledge of the atmospheric fate of halogenated hydrocarbons but also underscores the importance of considering the environmental and toxicological impacts in the development of HVOC mitigation strategies.

Safety and immunogenicity of freeze-dried human rabies vaccines: A phase 3 clinical trial of Zagreb and Essen regimes

ABSTRACT Recently optimized freeze-dried rabies vaccines (Vero cell) are promising for rabies prevention; however, comparisons of Essen 5-dose and Zagreb 4-dose regimens are needed for clinical applications. This phase III clinical trial aimed to assess the safety and immunogenicity of candidate freeze-dried rabies vaccines developed for human use by Shandong Yeedo Biotechnology (Registration No.: CTR20182016, http://www.chinadrugtrials.org.cn/index.html). In total, 40 participants in stage I and 1797 subjects in stage II with an age range of 10–60 years were recruited. Both 4-dose and 5-dose experimental vaccines were well-tolerated in stage 1, with similar overall adverse event (AE) rates. In stage 2, systemic fever (35.39%) and local pain (48.91%) were common, and the rate of Grade 3 AEs was approximately 2.5%. Rates of local reactions and unsolicited AEs differed among groups (p = .045 and 0.011). Immunogenicity analyses showed higher antibody levels, seroconversion rates, and pre-immune seroconversion rates in the 4-dose experimental group versus the 5-dose group (p < .001) on day 7 post-first dose, with similar GMCs (geometric mean concentrations) by day 14. Pre-immune negative subjects had comparable antibody levels in the 4-dose and 5-dose experimental groups, outperforming the 5-dose control group (p = .039). The rate difference (95% CI) for first-dose seroconversion at 14 days post-vaccination among pre-immune antibody-negative subjects indicated non-inferiority between the 5-dose experimental and control groups. Overall, the Shandong Yeedo rabies vaccine demonstrated satisfactory safety and efficacy, offering a new option for rabies prevention.

Modulating the band structure of two-dimensional black phosphorus via electronic effects of organic functional groups for enhanced hydrogen production activity.

Electronic effects of organic functional groups play a fundamental role in determining the rate and/or direction of organic chemical reactions. The implementation of this concept in selective organic catalysis is achieved by tuning the electronic effects of organic functional groups to alter the corresponding reactivity. However, this approach has hardly been applied to modulate the band structure of inorganic materials. Here, we show that modulating the electronic band structure of two-dimensional black phosphorus (BP) is possible via the electronic effects of organic functional groups covalently modified on its surface. Organic functional group can either donate or withdraw charge density from BP surface, which will alter the bonding/anti-binding orbitals occupancy and thus shift the band-edge positions of functionalized BP downward/upward. Therefore, the valence-band maxima and the conduction-band minima of functionalized BP can be continuously tuned by changing the binding group with different Hammett parameters. Finally, unexpectedly high hydrogen evolution reaction rates under visible light are achieved using functionalized BP heterojunctions as photocatalysts. This work underscores the significant role of electronic effects in chemically controlling BP's band structure, offering greater flexibility and affordability beyond physical method limits.

Modulating the band structure of two‐dimensional black phosphorus via electronic effects of organic functional groups for enhanced hydrogen production activity

Electronic effects of organic functional groups play a fundamental role in determining the rate and/or direction of organic chemical reactions. The implementation of this concept in selective organic catalysis is achieved by tuning the electronic effects of organic functional groups to alter the corresponding reactivity. However, this approach has hardly been applied to modulate the band structure of inorganic materials. Here, we show that modulating the electronic band structure of two‐dimensional black phosphorus (BP) is possible via the electronic effects of organic functional groups covalently modified on its surface. Organic functional group can either donate or withdraw charge density from BP surface, which will alter the bonding/anti‐binding orbitals occupancy and thus shift the band‐edge positions of functionalized BP downward/upward. Therefore, the valence‐band maxima and the conduction‐band minima of functionalized BP can be continuously tuned by changing the binding group with different Hammett parameters. Finally, unexpectedly high hydrogen evolution reaction rates under visible light are achieved using functionalized BP heterojunctions as photocatalysts. This work underscores the significant role of electronic effects in chemically controlling BP’s band structure, offering greater flexibility and affordability beyond physical method limits.

Influence of Ultrasound on the Rheological Properties, Color, Carotenoid Content, and Other Physical Characteristics of Carrot Puree

This study aimed to investigate the effect of ultrasonic frequencies (21 and 35 kHz) on the physical properties of carrot puree at different concentrations (9, 12, and 21 °Brix). The viscosity, total soluble content, density, color, and β-carotene content were tested. It was found that the viscosity of the puree, determined with respect to shear rate, concentration, and the use of ultrasonic treatment, indicates that the purees should be defined as shear thinning fluids. Moreover, a decrease in activation energy was observed with the increase in extract and ultrasonic treatment, which may cause changes in the rate of reactions occurring in the tested material. A significant effect of this may be the observed change in the color of the puree after ultrasonic treatment; the increase in frequency from 21 to 35 kHz caused an increase in redness and yellowness and a decrease in lightness, independently of concentration. The most significant color difference was noted in the puree with a 21 °Brix concentration, where a ΔE value of 21 was recorded. In contrast, the ΔE values for the other purees post-treatment remained below 5. The content of carotenoids did not change after sonication, independently of the concentration of carrot puree.

Eco-Friendly TiO2 Nanoparticles: Harnessing Aloe Vera for Superior Photocatalytic Degradation of Methylene Blue

In recent years, the contamination of aquatic environments by organic chemicals, including dyes such as methylene blue (MB), Congo red, and crystal violet, has become an increasing concern, as has their treatment. In this work, titanium dioxide nanoparticles (TiO2 NPs) were studied for their photocatalytic performance by measuring the degradation of MB under UV light. TiO2 NPs were synthesized using two synthetic processes optimized in this study: a green method, namely leveraging the natural properties of Aloe vera leaf extract; and a conventional approach. The resulting NPs were thoroughly characterized using X-rays Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), UV–Vis and ζ-potential analysis. The TiO2 NPs synthesized by the green method demonstrated a degradation efficiency of (50 ± 3)% after 180 minutes, which was significantly higher than the (16 ± 3)% achieved by NPs synthesized through the conventional route. Moreover, the reaction rate constant for the green-synthesized TiO2 NPs was found to be approximately five times greater than that of the conventionally synthesized NPs. These results open up a new scenario in the pollution removal strategy research, using resources accessible in nature to synthesize NPs with high photocatalytic activity, which could also be useful for other applications, such as hydrogen production.

Assessment of photon and proton-induced activation in particles accelerators.

Nuclear activation affects all operating, future, or dismantled particle accelerators used in various fields, from medical applications to industrial applications. This work is concerned with the study of the radioactivity induced in various materials (Sc, Cu, Tb, Ta, W, Au) irradiated by hard Bremsstrahlung photons from an electron beam and by secondary neutrons induced by a proton beam. In both cases, the primary beam features an 18 MeV kinetic energy. We have performed Monte Carlo simulations with MCNP, GEANT4, FLUKA, and PHITS, coupled with the analytical codes CINDER'90 or FISPACT-II, to estimate the threshold reaction rates and the induced radioactivity in the samples. We compared the simulations with experimental activation measurements performed by high-resolution gamma spectrometry at a decommissioned medical LINAC and around the CYRCé cyclotron. We also used CR-39 solid-state nuclear track detectors to characterize the thermal and fast neutron components of the secondary fields.