End-point Energy Research Articles

Measurement of flux-weighted average cross-section in the photo-neutron reactions of Nb at the bremsstrahlung end-point energies of 20 MeV and 67 MeV

The photo-neutron flux-weighted average cross-sections for 93Nb(γ,xn) reactions at the bremsstrahlung end-point energies of 20 MeV and 67 MeV have been measured by the activation technique using the electron linear accelerator LUE-75 located at the A.I. Alikhanyan National Science Laboratory (AANL). Furthermore, the isomeric cross-section ratio has been determined for the 89m,gNb isomeric pair. TALYS 1.96 and EMPIRE 3.2 nuclear codes were used to calculate the 93Nb(γ,xn) reaction cross-sections and isomeric ratio as functions of bremsstrahlung end-point energy. The energy distribution of bremsstrahlung photons has been calculated by GEANT4. The measured experimental data has been compared with currently available literature data as well as with the values based on theoretical calculations.

An analytical approach to optimization of isotope production by bremsstrahlung radiation

Based on analytical description of isotope production by bremsstrahlung (X-ray) radiation, an algorithm is proposed for calculating the optimal dimensions of a cylindrical target of given mass positioned at a given distance from a bremsstrahlung converter to ensure the maximum yield of the isotope product. The expressions are derived for the total activity and its distribution along the target axis. A technique of γ-spectrometric measuring the activity of a thick production target is proposed. The novel approach is validated by the 100Mo(γ,n)99Mo reaction induced in a natural molybdenum target by mass in the range 10–100g with the X-ray photons at an end-point energy of 40 MeV. The analytical predictions are in good agreement with the results of Monte-Carlo simulations and experiment.

Photonuclear reactions on 59Co at bremsstrahlung end-point energies of 40–130 MeV* *Supported in part by the Ministry of Science and Higher Education of the Russian Federation (075-15-2021-1360), and by the project of the National Center for Physics and Mathematics (NCPM) No. 6 ''Nuclear and Radiation Physics,'' direction 6.5.1

Relative yields were measured in the 40−130 MeV bremsstrahlung induced reactions of 59Co. The experiments were performed with the beam from the electron linear accelerator LINAC-200 using the activation and off-line γ-ray spectrometric techniques. The bremsstrahlung photon flux was calculated with the Geant4 program. The cross sections were calculated by using the computer code TALYS-1.96 with different models and were found to be in good agreement with the experimental data.

A Benchmark Test of High-Throughput Atomistic Modeling for Octa-Acid Host–Guest Complexes

Years of massive applications of high-throughput atomistic modeling tools such as molecular docking and end-point free energy calculations in the drug industry and academic exploration have made them indispensable parts of hierarchical screening. While the similarities between host–guest and protein–ligand complexes lead to the direct extension of techniques for protein–ligand screening to host–guest systems, the practical performance of these hit identification tools remains unclear in host-–-guest binding. Recent reports on specific host–guest complexes suggest that the experience on the accuracy ladder accumulated from protein–ligand cases could be invalid in host–guest complexes, which makes it an urgent need to perform a systematic benchmark to secure solid numerical supports and guidance of practical setups. Concerning molecular docking, there still lacks a comprehensive benchmark considering popular docking programs. As for end-point reranking, quantitative and rigorous free energy estimation via end-point formulism requires establishing statistically meaningful measurements of uncertainties due to finite sampling, which is neglected or underestimated by a significant portion in almost all main-stream applications. Further, a face-to-face comparison between different screening tools is required for the design of a hierarchical workflow. To fill the above-mentioned critical gaps, in this work, using a dataset containing tens of host–guest complexes involving basket-like macromolecular hosts from the octa acid family, we extensively benchmark seven academic docking protocols and perform post-docking end-point rescoring with twenty protocols. The resulting comprehensive benchmark provides conclusive pictures of the practical value of docking and end-point screening in OA host–guest binding.

HSADab: A comprehensive database for human serum albumin

Human Serum Albumin (HSA), the most abundant protein in human body fluids, plays a crucial role in the transportation, absorption, metabolism, distribution, and excretion of drugs, significantly influencing their therapeutic efficacy. Despite the importance of HSA as a drug target, the available data on its interactions with external agents, such as drug-like molecules and antibodies, are limited, posing challenges for molecular modeling investigations and the development of empirical scoring functions or machine learning predictors for this target. Furthermore, the reported entries in existing databases often contain major inconsistencies due to varied experiments and conditions, raising concerns about data quality. To address these issues, a pioneering database, HSADab, was established through an extensive review of >30,000 scientific publications published between 1987 and 2023. The database encompasses over 5000 affinity data points at multiple temperatures and >130 crystal structures, including both ligand-bound and apo forms. The current HSADab resource (www.hsadab.cn) serves as a reliable foundation for validating molecular simulation protocols, such as traditional virtual screening workflows using docking, end-point, and al-chemical free energy techniques. Additionally, it provides a valuable data source for the implementation of machine learning predictors, including plasma protein binding models and plasma protein-based drug design models.

89Zr production with electron accelerators by irradiating molybdenum

89Zr is a promising radionuclide for high-resolution PET imaging with radiolabelled monoclonal antibodies. In the present study, the possibility of 89Zr production from molybdenum targets was investigated using electron accelerators. The 89Zr activity yields were determined experimentally for bremsstrahlung with endpoint energies of 20 and 55 MeV. The amount of radioactive impurities and stable zirconium isotopes associated with the 89Zr produced was estimated using experimental results and the TALYS 1.96 code. The conditions for achieving a minimum level of zirconium by-product isotopes to meet the expected clinical requirements are discussed in the article. The reaction 92Mo (γ, p2n)89Nb→89Zr was found to be the most promising for photonuclear production. It can provide the highest purity of zirconium radionuclide and the lowest amount of zirconium stable isotopes. A major advantage of the proposed method will be the ability to use natural molybdenum targets.

Identification of material by X-ray fluorescence analysis with a pyroelectric X-ray generator

By changing the temperature of Lithium Tantalate (LiTaO3) single crystal at moderate vacuum conditions leads to generation of strong electric field. The uncompensated polarization during the heating or cooling of the crystal causes the ejection of electrons from either the dielectric layer on the surface of the crystal or from a metal target depending on the polarity. The electrons are accelerated and gain energy of up to 100 keV. The energy of these electrons can be determined by measuring the end-point energy of the X-ray spectrum that resulted from the electron interactions with the target. The conception of a pyroelectric accelerator enabled us to develop compact (portable) electron source, which does not require an external high-voltage and the use of hazardous materials. The compact and portable nature of pyroelectric-driven particle sources holds significant promise for applications in materials science, particularly for materials analysis methodologies. The research demonstrates the feasibility of utilizing the X-ray signal generated by irradiation with electrons to identify elements in each sample. It is revealed that employing only the electron beam enables the successful acquisition of quantitative information regarding the sample structure through pyroelectric driven PD-PIXE analysis. These findings set the stage for the development of a compact and versatile apparatus for elemental analysis of materials based on a pyroelectric source.

Formation of medical radioisotope 111In in photonuclear reactions

The possibility of photonuclear production of 111In radioisotope has been investigated. The enriched target 112Sn was irradiated at the linear electron accelerator LUE-75 of A. Alikhanian National Science Laboratory (Yerevan, Armenia) at the bremsstrahlung endpoint energy Eγmax = 55 MeV. The cross section per equivalent quantum for reactions 112Sn(γ,x)111In, 112Sn(γ,n)111Sn, 112Sn(γ,2n)110Sn, 112Sn(γ,3n)109Sn,112 Sn(γ,pn)110mIn, 112Sn(γ,pn)110g110In, 112Sn(γ,p2n)109In have been measured via the method of activation and off-line γ-ray spectrometric technique. The cross section per equivalent quantum of the 111In in photonuclear reaction was compared with its cross section in proton induced reaction on cadmium targets and other possible 111In production routes. It is shown that the photonuclear method can be used for the production of 111In.

Virtual screening of cucurbituril host-guest complexes: Large-scale benchmark of end-point protocols under MM and QM Hamiltonians

The similarity of protein–ligand and host–guest complexes leads to the direct extension of end-point free energy techniques to virtual screening of the latter. Despite the massive application of end-point calculations in modelling and predictions of host–guest binding, it still lacks a large-scale benchmark test with sufficient sizes, sampling length and diverse coverages of chemical spaces to get rid of many disturbing factors and provide an unbiased statistical perspective of practical performance and value of end-point screening. Cucurbiturils as one of the main-stream macrocycles are quite popular in pharmaceutical research and industrial applications as drug reservoirs and carriers. In this work, we gather a large dataset of ∼150 host–guest complexes involving cucurbiturils with varying numbers of repeating units, extensively sample the conformational space in physical end states with both the single- and three-trajectory protocols, and extract the affinity estimates with a variety of MM and QM/GBSA Hamiltonians with implicit solvents. The diversity of chemical compositions, the quality of configurational sampling, and the comprehensiveness of parameter combinations are unprecedently high, enabling us to deduce conclusive pictures of the end-point performance in host–guest binding. Unlike previous reports on improved performance due to the incorporation of the QM treatment, shifting to QM/GBSA treatments deteriorates both the reproduction of absolute affinities and the prediction of affinity ranks in our large-scale end-point benchmark, regardless of the employed sampling protocol (i.e., single- and three-trajectory realization). Overall, in the end-point screening of cucurbituril host–guest complexes, we recommend sticking to the original MM/GBSA Hamiltonians in both sampling and free energy estimation. The best/recommended selection with high accuracy and robustness among all end-point protocols benchmarked in this work is the three-trajectory GAFF + GBOBC-I regime, which achieves top performances for both the reproduction of absolute affinities and ranking different host–guest pairs. Docking estimates with seven main-stream protocols have been observed as a promising tool for host–guest binding, but their ranking powers in the current large host–guest dataset does not surpass end-point tools, validating the value of post-docking end-point screening.

CROSS-SECTIONS OF PHOTONEUTRON REACTION natMo(γ,xn)93mMo AT THE BREMSSTRAHLUNG ENERGY UP TO 95 MeV

The photoproduction of the 93mMo nucleus on natural molybdenum was studied using the electron beam of the LUE-40 linac RDC “Accelerator” NSC KIPT. Measurements were performed using the activation method and off-line γ-ray spectrometric technique. For the natMo(γ,xn)93mMo reaction the experimental flux-averaged cross-sectionϭ(Eγmax)m at the bremsstrahlung end-point energy range of 38…93 MeV was first time determined. The theoretical values of the yields Ym,g(Eγmax) and flux-averaged cross-sections(Eγmax)m,g for the natMo(γ,xn)93m,gMo reactions were calculated using the cross-sections ϭ(Eγ) from the TALYS1.96 code for different gamma strength functions and level density models. The comparison showed strong discrepancies between the experimental values and the theoretical results of (Eγmax)m.

Measurement of effective 98Mo(n,γ)99 Mo reaction cross-section in the epi-cadmium neutron flux produced by 10 MeV electron LINAC with Ta-BeO assembly

An experiment was carried out to study the feasibility of 99Mo production using an electron accelerator based epi-cadmium neutron source. The neutrons were produced by the interaction of bremsstrahlung end-point energy of 10 MeV with BeO blocks and the neutrons thus produced were moderated using High Density Polyethylene blocks. Effective cross-section of 98Mo(n,γ)99Mo reaction was measured using foil activation method. An enhancement in the effective cross-section due to resonances in the epi-cadmium region was observed. The photons and neutron production/transport in the experimental set-up were simulated using the FLUKA Monte Carlo code. The simulations were found to be in good agreement with the experimental findings.

An analytic description of electron thermalization in kilonovae ejecta

ABSTRACT A simple analytic description is provided of the rate of energy deposition by β-decay electrons in the homologously expanding radioactive plasma ejected in neutron star mergers, valid for a wide range of ejecta parameters – initial entropy, electron fraction {s0, Ye}, and scaled (time-independent) density ρt3. The formulae are derived using detailed numerical calculations following the time-dependent composition and β-decay emission spectra (including the effect of delayed deposition). The deposition efficiency depends mainly on ρt3 and only weakly on {s0, Ye}. The time te at which the ratio between the rates of electron energy deposition and energy production drops to 1 − e−1, is given by $t_e=t_{0e}\Big (\frac{\rho t^3}{0.5(\rho t^3)_0}\Big)^a$, where $(\rho t^3)_0=\frac{0.05\, {\rm M}_{\odot }}{4\pi (0.2c)^3}$, t0e(s0, Ye) ≈ 17 d, and 0.4 ≤ a(s0, Ye) ≤ 0.5. The fractional uncertainty in te due to nuclear physics uncertainties is $\approx 10~{{\ \rm per\ cent}}$. The result a ≤ 0.5 reflects the fact that the characteristic β-decay electron energies do not decrease with time (largely due to ‘inverted decay chains’ in which a slowly decaying isotope decays to a rapidly decaying isotope with higher end-point energy). We provide an analytic approximation for the time-dependent electron energy deposition rate, reproducing the numerical results to better than 50 per cent (typically $\lt 30~{{\ \rm per\ cent}}$, well within the energy production rate uncertainty due to nuclear physics uncertainties) over a 3–4 orders-of-magnitude deposition rate decrease with time. Our results may be easily incorporated in calculations of kilonovae light curves (with general density and composition structures), eliminating the need to numerically follow the time-dependent electron spectra. Identifying te, e.g. in the bolometric light curve, will constrain the ejecta density distribution.

A method of determining the bremsstrahlung flux-weighted average photonuclear cross section

Based on a developed analytical model, a method is proposed for measuring the photonuclear cross section averaged over bremsstrahlung flux without application of additional target-monitor of photon flux. The method involves the use of a thin isotopic target, that completely overlaps the photon beam (a photonuclear converter), as well as an algorithm for processing the data on the yield of a reaction under study in such a target. The novel technique was validated on the reactions 100Mo(γ,n)99Mo and 58Ni(γ,n)57Ni in the range of photon end-point energy of 40.7–93.9 MeV. The photon flux-weighted average cross sections of the reactions measured experimentally are in good agreement with Monte Carlo simulations and TALYS predictions on their excitation functions.

Novel epoxy-bPBD-BisMSB composite plastic scintillator for alpha, beta and gamma radiation detection

A composite plastic scintillator is prepared by uniform dispersion of organic fluorophores 2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (b-PBD) and 1,4-bis(2-methylstyryl) benzene (Bis-MSB) in epoxy resin followed by curing at room temperature. The developed scintillator is strong blue emitter (425 nm), confirmed by 365 nm UV excited Photo luminescence and beta particle (90Sr-90Y) excited Radio-luminescence characterizations. The developed scintillator is highly transparent (~ 70%) to emitted light wavelength. Moreover, the scintillator’s blue emission is appropriate for photomultiplier tube (PMT) based scintillation measurement due to its maximum peak spectral response in blue region. Alpha, beta and gamma radiation detection were performed on PMT coupled scintillators of sizes Ø50 mm × 1 mm, Ø50 mm × 5 mm and Ø50 mm × 25 mm respectively. Pulse height spectra were recorded using 1 k Multichannel analyser (MCA) using various reference radiation sources. All scintillators demonstrated promising response to the respective radiations. Absolute detection efficiency of alpha scintillator is obtained as 32% (241Am), 86% of that of standard plastic scintillator EJ-212. Beta endpoint energy and gamma Compton edges showed linear variation w.r.t. corresponding channel numbers. Detection efficiency of beta and gamma scintillator is found to be 35.7% (90Sr-90Y) and 6.7% (136Cs) respectively. The developed scintillator has potential to be used for radioactivity contamination & gamma dose rate measurement applications.

Research on natAg(γ,xn)103-106Ag reaction cross sections with the bremsstrahlung end-point energy of 70 and 75 MeV

The flux-weighted average cross sections of natAg(γ,xn)103-106Ag reactions were measured with the bremsstrahlung end-point energy of 70 and 75 MeV using an activation and off-line γ-ray spectrometric technique. The GEANT4 code was used for the simulation of the bremsstrahlung spectra. The cross sections of natAg(γ,xn) 103-106Ag reactions as a function of mono-energetic photons were theoretically calculated by using the TALYS-1.96 code. The data of the present work and literature at different bremsstrahlung end-point energy are found to be in agreement with the theoretical values within the uncertainty limit. It can be seen that the flux-weighted average cross sections of the natAg(γ,xn)105.106Ag reactions increase with bremsstrahlung energy up to the Giant Dipole Resonance region. Thereafter, a small decrease trend with the bremsstrahlung energy was seen due to the opening of another reaction channel.

Evaluation of 180mTa formation cross-sections in photoneutron reactions

Determining the relative production cross-sections of the short-lived (ground) and long- lived (metastable) states of 180Ta is integral in nuclear physics research. However, direct measurement of these cross-sections is challenging. In this study, we proposed a method for estimating the total flux-weighted average formation cross-section of 180m+gTa based on GEANT4 modeling to evaluate the short-lived (ground) and long-lived (metastable) states of 180Ta. A Ta target was irradiated by a bremsstrahlung photon beam (maximum electron energy: 20 MeV) obtained from the linear electron accelerator LUE-75 at the A.I. Alikhanyan National Science Laboratory (AANL), Armenia. The experiment was performed using the activation technique, and the proposed GEANT4 simulation-based method was employed to evaluate the flux-weighted average formation cross-section of 180mTa. In addition, the isomeric cross-section ratio for the 180m,gTa isomeric pair was calculated. The theoretical results obtained using the TALYS 1.96 and EMPIRE 3.2 codes were consistent with the experimental ones. To the best of the authors’ knowledge, this paper reports the estimated flux-weighted average formation cross-section of 180mTa and isomer ratio for the 180m,gTa isomeric pair, induced by the irradiation of a bremsstrahlung beam with an end-point energy of 20 MeV, for the first time. This study opens new avenues for determining the relative production cross-sections of the ground and metastable states of 180Ta, which is widely studied as a natural isomeric target in various fields, including nuclear transformation reactions, fission dynamics, etc.

The influence of patients’ nutritional risk, nutritional status, and energy density in MEDPass versus conventional administration of oral nutritional supplements – A secondary analysis of a randomized controlled trial

ObjectivesThe clinical influence of nutritional risk, nutritional status, and energy density of oral nutritional supplements (ONS) in MEDPass versus conventional administration of ONS is currently unknown. The aim of this analysis was to examine whether these variables have an impact on clinical outcomes. MethodsSecondary analysis of the intention to treat dataset of the randomized controlled MEDPass Trial in geriatric and medical inpatients. Patients in the intervention group received 4 × 50 ml ONS during the medication rounds (MEDPass mode), while those in the control group received ONS in a non-standardized manner. The examined endpoints included energy and protein coverage, ONS intake, handgrip strength (HGS), weight, appetite nausea and 30-day mortality. Three subgroup analyses for NRS 2002 total score (3, 4 or 5−7 points), NRS 2002 impaired nutritional status score (0, 1, 2 or 3 points) and energy density of the ONS (1.5 kcal/mL or 2 kcal/mL) were performed using linear and logistic regression with interaction and mixed effect models. ResultsThe data of 202 patients (103 women and 99 men) at nutritional risk (NRS total 2002 score ≥3), mean (SD) age 82.2 (6.5) years were included. There was no significant difference between the groups in the primary endpoint energy coverage in all three subgroup analyses. There were also no significant differences between the groups in the secondary endpoints of protein coverage, ONS intake, HGS, weight, appetite, nausea, and 30-day mortality. ConclusionThe MEDPass mode of ONS administration was not superior to the conventional mode of administration in this study. ONS with high energy density (≥2 kcal/mL) should be offered since current evidence shows a tendency towards improved appetite, increased ONS and increased energy intake.

Assessing the performance of MM/PBSA and MM/GBSA methods. 10. Prediction reliability of binding affinities and binding poses for RNA-ligand complexes.

Ribonucleic acid (RNA)-ligand interactions play a pivotal role in a wide spectrum of biological processes, ranging from protein biosynthesis to cellular reproduction. This recognition has prompted the broader acceptance of RNA as a viable candidate for drug targets. Delving into the atomic-scale understanding of RNA-ligand interactions holds paramount importance in unraveling intricate molecular mechanisms and further contributing to RNA-based drug discovery. Computational approaches, particularly molecular docking, offer an efficient way of predicting the interactions between RNA and small molecules. However, the accuracy and reliability of these predictions heavily depend on the performance of scoring functions (SFs). In contrast to the majority of SFs used in RNA-ligand docking, the end-point binding free energy calculation methods, such as molecular mechanics/generalized Born surface area (MM/GBSA) and molecular mechanics/Poisson Boltzmann surface area (MM/PBSA), stand as theoretically more rigorous approaches. Yet, the evaluation of their effectiveness in predicting both binding affinities and binding poses within RNA-ligand systems remains unexplored. This study first reported the performance of MM/PBSA and MM/GBSA with diverse solvation models, interior dielectric constants (εin) and force fields in the context of binding affinity prediction for 29 RNA-ligand complexes. MM/GBSA is based on short (5 ns) molecular dynamics (MD) simulations in an explicit solvent with the YIL force field; the GBGBn2 model with higher interior dielectric constant (εin = 12, 16 or 20) yields the best correlation (Rp = -0.513), which outperforms the best correlation (Rp = -0.317, rDock) offered by various docking programs. Then, the efficacy of MM/GBSA in identifying the near-native binding poses from the decoys was assessed based on 56 RNA-ligand complexes. However, it is evident that MM/GBSA has limitations in accurately predicting binding poses for RNA-ligand systems, particularly compared with notably proficient docking programs like rDock and PLANTS. The best top-1 success rate achieved by MM/GBSA rescoring is 39.3%, which falls below the best results given by docking programs (50%, PLNATS). This study represents the first evaluation of MM/PBSA and MM/GBSA for RNA-ligand systems and is expected to provide valuable insights into their successful application to RNA targets.

Measurement of the flux-weighted average cross section for the \(^{186}\)W\((\gamma,p)^{185}\)Ta reaction at the bremsstrahlung end-point energy of 70 MeV

Abstract. The flux-weighted average cross section for the 186W(γ,p)185Ta reaction induced with 70 MeV bremsstrahlung end-point energy was measured using the activation method in combination with off-line gamma activity measurement. The 27Al(γ,2pn)24Na monitor reaction was used for the determination of the bremsstrahlung flux. The bremsstrahlung photons used to produce the photonuclear reactions were generated from a thin tungsten (W) converter by bombardment with a 70 MeV electron beam. The experimental flux-weighted average cross section is compared with the theoretical prediction, for which the absolute cross section was calculated using the TALYS 1.95 code and the bremsstrahlung spectrum was simulated using the computer program MCNPX. The present experiment was carried out at the 100 MeV electron linac of the Pohang Accelerator Laboratory, POSTECH, Pohang, Korea.

STUDY THE ISOMERIC RATIOS IN PHOTONUCLEAR EXPERIMENTS ON THE LUE-40 LINAC RDC “ACCELERATOR” NSC KIPT

The results of photoproduction of isomeric pairs from the (γ,xn) and (γ,pxn) reactions on nuclei from Zr up to Ta at the bremsstrahlung end-point energy range 30…100 MeV are systematized. Measurements were performed at the electron beam of the LUE-40 linac RDC “Accelerator” NSC KIPT using the activation method and off-line γ-ray spectrometric technique. The theoretical isomeric ratios IR for the nuclei-products of studied reactions were calculated using the cross-sections σ(E) from the TALYS1.95 code for six different level density models. The data from the international databases were additionally used to compare experimental results and theoretical predictions. The obtained results let us make conclusions about trends of values and energy dependence of IR in studied photonuclear reactions. Further directions of experimental research in the RDC “Accelerator” NSC KIPT are discussed.