Proton Capture Research Articles

Evaluation the nonlinear response function of a HPGe detector for 59 keV to 10.7 MeV gamma-rays using a Monte Carlo simulation and comparison with experimental data

Modeling of High Purity Germanium (HPGe) detector on a wide energy range is important in gamma-ray spectroscopy. The precisely modeled detector can be used for proton-induced prompt gamma-ray spectroscopy. In this work, we used both the gamma-rays of calibration sources and prompt gamma-rays emitted in proton capture reactions to model a coaxial p-type HPGe detector using Geant4 Monte Carlo simulation for the gamma-ray energy range of 59–10764 keV. The calibration sources were 137Cs, 241Am, 60Co, 152Eu, and 133Ba, while the prompt gamma-rays were due to the gamma-ray cascades following the 27Al(p,γ)28Si reaction capture at the resonant energies of 992, 1317 and 2483 keV, as well as the 23Na(p,γ)24Mg reaction capture at the resonant energies of 1417 and 1395 keV. According to the results obtained, the presented simulated and experimental spectra show a good agreement. In addition, the mean and maximum relative deviations between experimental and simulated efficiencies corresponding to 27 major peaks are smaller than 5% and 15%, respectively.

Anomalous Beam Transport through Gabor (Plasma) Lens Prototype

An electron plasma lens is a cost-effective, compact, strong-focusing element that can ensure efficient capture of low-energy proton and ion beams from laser-driven sources. A Gabor lens prototype was built for high electron density operation at Imperial College London. The parameters of the stable operation regime of the lens and its performance during a beam test with 1.4 MeV protons are reported here. Narrow pencil beams were imaged on a scintillator screen 67 cm downstream of the lens. The lens converted the pencil beams into rings that show position-dependent shape and intensity modulation that are dependent on the settings of the lens. Characterisation of the focusing effect suggests that the plasma column exhibited an off-axis rotation similar to the m=1 diocotron instability. The association of the instability with the cause of the rings was investigated using particle tracking simulations.

Proton Capture Strategy for Enhancing Electrochemical CO2 Reduction on Atomically Dispersed Metal–Nitrogen Active Sites**

AbstractElectrocatalysts play a key role in accelerating the sluggish electrochemical CO2 reduction (ECR) involving multi‐electron and proton transfer. We now develop a proton capture strategy by accelerating the water dissociation reaction catalyzed by transition‐metal nanoparticles (NPs) adjacent to atomically dispersed and nitrogen‐coordinated single nickel (Ni−Nx) active sites to accelerate proton transfer to the latter for boosting the intermediate protonation step, and thus the whole ECR process. Aberration‐corrected scanning transmission electron microscopy, X‐ray absorption spectroscopy, and calculations reveal that the Ni NPs accelerate the adsorbed H (Had) generation and transfer to the adjacent Ni−Nx sites for boosting the intermediate protonation and the overall ECR processes. This proton capture strategy is universal to design and prepare for various high‐performance catalysts for diverse electrochemical reactions even beyond ECR.

Proton Capture Strategy for Enhancing Electrochemical CO2 Reduction on Atomically Dispersed Metal-Nitrogen Active Sites*.

Electrocatalysts play a key role in accelerating the sluggish electrochemical CO2 reduction (ECR) involving multi-electron and proton transfer. We now develop a proton capture strategy by accelerating the water dissociation reaction catalyzed by transition-metal nanoparticles (NPs) adjacent to atomically dispersed and nitrogen-coordinated single nickel (Ni-Nx ) active sites to accelerate proton transfer to the latter for boosting the intermediate protonation step, and thus the whole ECR process. Aberration-corrected scanning transmission electron microscopy, X-ray absorption spectroscopy, and calculations reveal that the Ni NPs accelerate the adsorbed H (Had ) generation and transfer to the adjacent Ni-Nx sites for boosting the intermediate protonation and the overall ECR processes. This proton capture strategy is universal to design and prepare for various high-performance catalysts for diverse electrochemical reactions even beyond ECR.

Deducing primary γ -ray intensities and the dipole strength function in Mo94 via radiative proton capture

Background: The nucleosynthesis of heavy nuclei is affected by the reaction rates of radiative capture reactions. Many of the astrophysical relevant rates cannot be obtained from experiments but are obtained from theoretical models. The $\ensuremath{\gamma}$-decay widths that are derived from radiative strength functions are one of the key nuclear physics input parameters in those calculations. The explicit study of $\ensuremath{\gamma}$-ray strength functions has been thoroughly addressed in the last decade and various methods have been established to extract the dipole strength in atomic nuclei.Purpose: The investigation of primary $\ensuremath{\gamma}$-ray transitions from the $^{93}\mathrm{Nb}(p,\ensuremath{\gamma})^{94}\mathrm{Mo}$ reaction allows deducing the $\ensuremath{\gamma}$-ray strength function in $^{94}\mathrm{Mo}$. The results are compared to results obtained using other techniques and the impact of level densities, excitation mechanism, and excitation energy will be thoroughly investigated.Method: The proton beam was delivered by the 10 MV FN-Tandem accelerator located at the Institute for Nuclear Physics at the University of Cologne, Germany. By means of in-beam $\ensuremath{\gamma}$-ray spectroscopy the intensity of primary $\ensuremath{\gamma}$ rays is determined. Additionally, the first generation $\ensuremath{\gamma}$-ray intensity is deduced from the secondary $\ensuremath{\gamma}$ rays using their branching and the coincidence detection efficiency. Absolute $\ensuremath{\gamma}$-ray strength function values as well as relative values using the ratio method will be extracted.Results: Numerous states in $^{94}\mathrm{Mo}$ at excitation energies above 3 MeV have been identified for the first time and their decay behavior has been studied. We disentangled the effects of $M1$ and $E1$ radiation for the $\ensuremath{\gamma}$-ray emission channel in $^{94}\mathrm{Mo}$ and extracted strength function curves for both radiation types. Our results are in good agreement with experimental results using the Oslo method and photoinduced experiments as well as with recent theoretical quasiparticle random-phase approximation (QRPA) calculations. An enhancement of the $\ensuremath{\gamma}$-ray strength below the neutron separation energy was found that is most likely of $E1$ character. In addition, a significant increase of the dipole strength at low $\ensuremath{\gamma}$-ray energies was found which is most likely due to $M1$ strength.Conclusion: Radiative proton capture reactions are a well-suited tool to study the $\ensuremath{\gamma}$-ray strength function in atomic nuclei. From the intensity of primary $\ensuremath{\gamma}$-ray transitions as well as from secondary $\ensuremath{\gamma}$-rays, information about the radiative dipole strength can be extracted. The $\ensuremath{\gamma}$-ray emission seems to be independent of the excitation energy in the studied mass and energy range. Detailed knowledge about the intrinsic properties of the nuclear states is very important and their uncertainties affect the uncertainty of the extracted $\ensuremath{\gamma}$-ray strength functions heavily.

The astrophysical S-factor of proton radiative capture on triton

The proton capture on 3H is important to understand various physical and astrophysical processes. In this study, the cross section and astrophysical S-factor of the proton radiative capture on triton were taken into account at low energies. The 3H(p,γ)4He reaction was studied using the E1 transition. The gamma-ray transition is dominated by the E1 multipolarity and by incoming p-waves. The non-resonant astrophysical S-factors for the E1 transition were calculated using the potential model. The results were satisfactorily in good agreement with the corresponding experimental data.

Three-dimensional Supernova Models Provide New Insights into the Origins of Stardust

Abstract We present the isotope yields of two post-explosion, three-dimensional 15 core-collapse supernova models, 15S and 15A, and compare them to the carbon, nitrogen, silicon, aluminum, sulfur, calcium, titanium, iron, and nickel isotopic compositions of SiC stardust. We find that these core-collapse supernova models predict similar carbon and nitrogen compositions to SiC X grains and grains with 12C/13C < 20 and 14N/15N < 60, which we will hereafter refer to as SiC ‘D’ grains. Material from the interior of a 15 explosion reaches high enough temperatures shortly after core collapse to produce the large enrichments of 13C and 15N necessary to replicate the compositions of SiC D grains. The innermost ejecta in a core-collapse supernova is operating in the neutrino-driven regime and undergoes fast proton capture after being heated by the supernova shockwave. Both 3D models predict 0.3 Al/27Al < 1.5, comparable to the ratios seen in SiC X, C, and D grains. Models 15S and 15A, in general, predict very large anomalies in calcium isotopes but do compare qualitatively with the SiC X grain measurements that show 44Ca and 43Ca excesses. The titanium isotopic compositions of SiC X grains are well reproduced. The models predict 57Fe excesses and depletions that are observed in SiC X grains, and in addition predict accurately the 60Ni/58Ni, 61Ni/58Ni, and 62Ni/58Ni ratios in SiC X grains, as a result of fast neutron captures initiated by the propagation of the supernova shockwave. Finally, symmetry has a noticeable effect on the production of silicon, sulfur, and iron isotopes in the SN ejecta.

Exploiting Isospin Symmetry to Study the Role of Isomers in Stellar Environments.

Proton capture on the excited isomeric state of ^{26}Al strongly influences the abundance of ^{26}Mg ejected in explosive astronomical events and, as such, plays a critical role in determining the initial content of radiogenic ^{26}Al in presolar grains. This reaction also affects the temperature range for thermal equilibrium between the ground and isomeric levels. We present a novel technique, which exploits the isospin symmetry of the nuclear force, to address the long-standing challenge of determining proton-capture rates on excited nuclear levels. Such a technique has in-built tests that strongly support its veracity and, for the first time, we have experimentally constrained the strengths of resonances that dominate the astrophysical ^{26m}Al(p,γ)^{27}Si reaction. These constraints demonstrate that the rate is at least a factor ∼8 lower than previously expected, indicating an increase in the stellar production of ^{26}Mg and a possible need to reinvestigate sensitivity studies involving the thermal equilibration of ^{26}Al.

Front Cover: Synthesis, Characterization and Electrochemical Reductive Properties of Complexes [Fe2(CO)4(κ2‐PPh2NR2)(μ‐dithiolato)] Related to the H‐Cluster of [FeFe]‐H2ases (Eur. J. Inorg. Chem. 3/2021)

The Front Cover shows the fate of protons at a diiron site inspired by the H-cluster of [FeFe]-H2ases. Different conformations favor the capture of protons and their transfer to the diiron core, thus generating a suitable proton channel. Finding the right combinations of ligands for the design of efficient diiron electrocatalysts for proton reduction is like a 3D combination puzzle involving concerted electronic and steric effects through the choice of ligands around the dinuclear site. More information can be found in the Full Paper by C. Elleouet, P. Schollhammer and co-workers.

Re-examination of astrophysical S-factor of proton capture [formula omitted] in stellar matter

The astrophysical S-factor for proton capture on 9Be at astrophysical is considered in this work by using a modified potential model approach. The total cross-section is taken as the sum of both direct and resonance transitions. Based on the computed total astrophysical S-factor we calculate the nuclear reaction rates within the selected range of temperatures. The calculated values of S-factor and nuclear reaction rates are in good agreement with the measured data. Our modified potential model based astrophysical S-factor at zero energy shows a satisfactory agreement with the previously published results.

New measurements of cross sections and S-factors for $$d(p,\gamma )^{3}\text{He}$$ reaction at BBN energies

This communication is a summary of our measurements of cross sections and astrophysical S-factors for radiative proton capture on deuteron. The measurements are a part of a new program to study light-ion induced nuclear capture and inelastic scattering reactions relevant to nucleosynthesis and astrophysics. We are primarily interested in the capture reactions relevant to primordial or Big Bang Nucleosynthesis (BBN). Section 1 provides a brief and general overview of nuclear astrophysics and the primary experimental challenges in the measurements of cross sections and S-factors for reactions relevant to nuclear astrophysics. The next section discusses the significance of the $$d(p,\gamma )^{3}\text{He}$$ reaction in context of BBN and the need for generating a more precise data in the relevant energy window. The subsequent section is devoted to the experiment and results of measurements of cross sections and astrophysical S-factors for the $$d(p,\gamma )^{3}\text{He}$$ reaction at three new BBN energies. One salient features of the measurements is the use of large volume LaBr $$_{3}$$ :Ce scintillation detector for measurement of the capture $$\gamma $$ -rays. To the best of our knowledge, capture $$\gamma $$ -rays for this reaction had so far been measured with NaI(Tl) or HPGe detectors only. The detection efficiency of the detector has been measured experimentally for different monochromatic $$\gamma $$ -ray energies. In addition, realistic GEANT4 Monte Carlo simulations have been carried out to generate the response of the detector for $$\gamma $$ -ray energies of interest. The measured cross section and astrophysical S(E)-factor for the three incident proton energies are found to be in agreement with the overall trend of the global data set for the BBN region, reported in the literature. The measured S-factors are also found to be in agreement with recent microscopic calculations of Marcucci et al. (2016).

Re-examination of proton capture 13N(p, γ)14O in stellar matter

Radiative capture p + 13N → 14O + γ at energies bearing astrophysical importance is one of the key processes in the hot CNO cycle. The transition from normal CNO to hot CNO takes place when the proton capture rates on 13N are higher than the β decay rates of 13N. The hot CNO cycle initiates at stellar temperature T ≥ 0.11 ×109 K. Within the frame work of potential model, we calculate the nuclear reaction rates and astrophysical S-factor for the reaction 13N(p, γ)14O. It is to be noted that the nuclear cross-section is calculated for the first resonance of p–13N system within the proton energy range (0–1) MeV, where the E1 transition plays a dominant role. Our calculated radiative capture rates are in nice comparison with the existing data. Based on the radiative capture rates we further estimate the temperature at which the normal CNO turns into a hot CNO cycle

Calculation of electron capture probability of energetic protons colliding with rare-gas atoms: A comparison study on four methods

We calculate the probability of electron capture of energetic protons colliding with rare-gas atoms, comparing four methods based on time-dependent density-functional theory (TDDFT). By approximating the pair-correlation function of the system with an explicit dependence on the fractional number of bound electrons, a new effective model of pair-correlation function is built up. Benchmark calculations are given over a wide range of impact energy, demonstrating that the new designed read-out functional reproduces quite accurately the single-electron capture cross sections and the double-electron capture features which were not properly described by previous TDDFT calculations.

Intensity of a weak 519-keV γ ray following β decay of the superallowed emitter Ar34 determined via the S33 ( p,γ ) Cl34 reaction

The predominant branch in the $\ensuremath{\beta}$ decay of $^{34}\mathrm{Ar}$ is the superallowed ${0}^{+}\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}{0}^{+}$ transition to the ground state of $^{34}\mathrm{Cl}$. To determine its important branching ratio one must first establish the ratios for the competing Gamow-Teller branches based on the measured intensities of $\ensuremath{\gamma}$ rays subsequently emitted from the excited states they populate in $^{34}\mathrm{Cl}$. The strongest of these branches populates the ${1}^{+}$ state at 666 keV in $^{34}\mathrm{Cl}$, which has three possible $\ensuremath{\gamma}$-decay paths. We report here a measurement of the decay of this state, which we populated via resonant proton capture in the reaction $^{33}\mathrm{S}$($p,\ensuremath{\gamma}$)$^{34}\mathrm{Cl}$. We find that the intensity of the 519-keV $\ensuremath{\gamma}$-ray path is 1.46(19)% relative to that of the 666-keV path. This result is critical to new precise measurements of the superallowed decay of $^{34}\mathrm{Ar}$.

Extracting capture from transfer reactions

Indirect reaction techniques are very important in astrophysics as they provide information that is complementary to direct measurements or that otherwise cannot be obtained directly. It is then critical to have a reliable reaction theory that can connect the reaction measurement with the astrophysical information desired. This is a brief report on the progress made in the theory for transfer reactions when used to determine neutron capture rates for r-process and proton capture for rp-process nuclei. We will discuss the different types of experiments and their connection to astrophysics. An overview of the current status of the theory will be provided, with emphasis on several recent theory developments, including transfer to continuum, the improvement of the optical potential and uncertainty quantification. Applications to a couple of neutron rich and proton rich cases will be discussed.

The roles of long-range proton-coupled electron transfer in the directionality and efficiency of [FeFe]-hydrogenases

As paradigms for proton-coupled electron transfer in enzymes and benchmarks for a fully renewable H2 technology, [FeFe]-hydrogenases behave as highly reversible electrocatalysts when immobilized on an electrode, operating in both catalytic directions with minimal overpotential requirement. Using the [FeFe]-hydrogenases from Clostridium pasteurianum (CpI) and Chlamydomonas reinhardtii (CrHydA1) we have conducted site-directed mutagenesis and protein film electrochemistry to determine how efficient catalysis depends on the long-range coupling of electron and proton transfer steps. Importantly, the electron and proton transfer pathways in [FeFe]-hydrogenases are well separated from each other in space. Variants with conservative substitutions (glutamate to aspartate) in either of two positions in the proton-transfer pathway retain significant activity and reveal the consequences of slowing down proton transfer for both catalytic directions over a wide range of pH and potential values. Proton reduction in the variants is impaired mainly by limiting the turnover rate, which drops sharply as the pH is raised, showing that proton capture from bulk solvent becomes critical. In contrast, hydrogen oxidation is affected in two ways: by limiting the turnover rate and by a large overpotential requirement that increases as the pH is raised, consistent with the accumulation of a reduced and protonated intermediate. A unique observation having fundamental significance is made under conditions where the variants still retain sufficient catalytic activity in both directions: An inflection appears as the catalytic current switches direction at the 2H+/H2 thermodynamic potential, clearly signaling a departure from electrocatalytic reversibility as electron and proton transfers begin to be decoupled.

Proton capture resonant state ofO15at 7556 keV

The slowest reaction in the CNO cycle 14N(p, gamma)15O has been studied by populating the E^lab_p =278 keV (E^r_c.m.=259 keV) proton capture resonant state of ^{15}O at 7556 keV. The strength of the resonance has been determined from the experimental data. The level lifetime of the sub-threshold resonant state at Ex=6792 keV, as well as the lifetimes of the 5181 keV and 6172 keV states, have been measured using the Doppler shift attenuation method (DSAM). The structural properties of the nucleus ^{15}O, such as, the level energies, transition strengths, level lifetimes, and spectroscopic factors, have been calculated theoretically by using the large basis shell model, which agrees reasonably well with the present as well as the previous experimental data.

Astrophysical S-factor for radiative capture of proton by 13C at low energy

Radiative capture p + 13C → 14N + γ at energies of astrophysical interest is one of the important process in the CNO cycle. We focus the reader’s attention on the possibility of describing this reaction within the framework of a single-particle potential model even when the reaction has a resonant characteristic. The partial components of the astrophysical S-factor are calculated for electric dipole transition. The calculated value of S-factor is in good agreement with experimental data both at low and high energy from the resonance position.

GIANT M1 RESONANCE ON THE GROUND AND EXCITED STATES IN 2s1d-SHELL NUCLEI

The gamma decay of the resonance-like structures observed in the reaction of radiative capture of protons by the nuclei 22Ne, 26Mg, 30Si, 34,36S, and 38Ar in the region of excitation energies of 7…12 MeV was studied. The excitation functions of this reaction were measured. The resonance strengths in the energy range of the accelerated protons Ep = 1.0…3.0 MeV were determined. The obtained discrete distributions of the magnetic dipole γ-transitions on the ground and excited states for the nuclei of the 2s1d-shell have resonance character. Giant M1 resonance on the ground and excited states in the 23Na, 27Al, 31P, 35.37Cl, and 39K nuclei has been identified. The position of the M1 resonance on excited states coincides with that predicted by the Brink-Axel hypothesis for nuclei that are at the beginning of the subshell.

Radiative capture of proton by $^{13}\mbox{C}$ at low energy

Radiative capture $p + {}^{13}\mathrm{C}\rightarrow {}^{14}\mathrm{N}+\gamma $ at energies bearing astrophysical consequences is one of the important processes in the CNO cycle. We focus on the possibility of describing the main contribution to the total cross section of the radiative capture process in the framework of the single-particle potential model without separation into direct and resonant transitions. In case where the single-particle potential model fails to describe other partial components, we use the R-matrix approach. The partial components of the astrophysical S-factor are calculated for all possible electric dipole transitions. The calculated value of the total S-factor at zero energy is in good agreement with earlier reported values. Based on the value of total astrophysical S-factor depending on the collision energy, we calculate the nuclear reaction rates for ${p} + {^{13}\mathrm{C}} \rightarrow {^{14}\mathrm{{N}}}+\gamma $ .