Coulomb Barrier Research Articles

Compact dwarfs made of light-quark nuggets

Utilizing an equiparticle model with both linear confinement and leading-order perturbative interactions, we obtain systematically the properties of strangelets and nonstrange quark matter (udQM) nuggets at various baryon (A) and charge (Z) numbers, where the detailed single-quark-energy levels are fixed by solving Dirac equations in mean-field approximation. We then examine the structures of compact dwarfs made of light strangelets or udQM nuggets forming body-centered cubic lattices in a uniform electron background. Despite that the strangelets and udQM nuggets generally become more stable at larger A, the compact dwarfs are still stable since the fusion reactions between those objects do not take place in the presence of a Coulomb barrier, which is similar to the cases of light nuclei in normal white dwarfs. If udQM dwarfs or strangelet dwarfs are covered with normal matter, their masses and radii become larger but do not exceed those of ordinary white dwarfs. Finally, we investigate the radial oscillation frequencies of udQM dwarfs and strangelet dwarfs and find that their frequencies are typically higher than traditional white dwarfs. The stability of compact dwarfs are then analyzed by examining radial oscillation frequencies of the fundamental mode, where compact dwarfs covered by normal matter are still stable. Published by the American Physical Society 2024

Electron Screening in Laboratory Nuclear Reactions

A thorough understanding of nuclear reaction rates at low energies is essential for improving our understanding of energy generation in stars and primordial and stellar nucleosynthesis. At low energies, fusion reactions between charged particles are strongly suppressed by the presence of the Coulomb barrier, which classically inhibits the penetration of one nucleus into another. The barrier penetration causes the cross section to have a steep energy dependence at low energies, making cross section measurements very challenging. Furthermore, little is known about the impact of surrounding electrons in stellar plasmas that are currently beyond the reach of experiments. As a result, measuring the bare cross sections as accurately as possible is essential. Reaction rate measurements at very low energies have been made possible in recent years by the development of high-current low-energy accelerators as well as enhanced target and detection methods. Nevertheless, the presence of atomic electrons, which alter the Coulomb barrier by screening the nuclear charge and increase the cross section at low energies compared to the case of bare nuclei, complicates these observations. A review of the experimental and corresponding theoretical work on laboratory electron screening performed so far will be presented.

Formation of Doubly and Triply Charged Fullerene Dimers in Superfluid Helium Nanodroplets.

Sequential ionization of fullerene cluster ions (C_{60})_{n}^{+} within multiply charged helium nanodroplets leads to the intriguing phenomenon of forming and stabilizing doubly and triply charged fullerene oligomers. While the formation of doubly charged dimers (C_{60})_{2}^{2+} has been predicted in earlier studies, the observation of even triply charged ones (C_{60})_{2}^{3+} is highly surprising. This remarkable resilience against Coulomb explosion is achieved through efficient cooling within the superfluid environment of helium nanodroplets and a sequential ionization scheme that populates covalently bound or physisorbed fullerene dimers. Calculations support the stability of four differently bonded (C_{60})_{2}^{2+} and (C_{60})_{2}^{3+} isomers and predict a low Coulomb barrier (<0.4 eV) preventing even dissociation of cold van der Waals complexes.

Critical Examination of Gamow's Theory of Alpha Particle Decay

Gamow’s Theory of Alpha Particle Decay was initially formulated for a limited set of nuclei. In this study, the researchers extend the scope and assessed the applicability of the theory to a broader range of nuclides especially those with different proton and neutron compositions. Three objectives were formulated to undertake the research. The researcher utilized one-dimensional WKB approximation to calculate the probability of tunneling through the potential barrier, which is a simplification compared to other formulas. The Geiger-Nuttall law, which describes a dependence of the disintegration constant on the range of α-particles, was deduced using the Gamow theory describing the passage of the α-particles through the Coulomb barrier by the quantum mechanical tunneling effect. Ground-to-ground state α-transitions for α-active nuclides were analyzed based on their half-lives and their dependence on various factors. The study revealed that all α-active nuclides whose Z ranges between 70 to100 undergoes similar alpha decay processes.

New measurements of the 19F(p, α 0)16O and 19F(p, α π )16O* reaction cross sections close to the Coulomb barrier

New absolute cross section measurements of the 19F(p, α 0)16O and 19F(p, α π )16O* reactions at energies close to the Coulomb barrier are reported. The availability of high-resolution and low-noise energy spectra obtained in the experiment allowed to resolve the 6.05–6.13 MeV doublet in 16O. In particular, the α π channel cross section was measured in the poorly-known 1.3 MeV bombarding energy region, and the α 0 channel was investigated in the 1.6 MeV region, where a strong discrepancy between previous data-sets is present. A comprehensive R-matrix fit, including the new data, was performed and the structure of the states ranging in the 14–15 MeV region is discussed.

Elastic and inelastic scattering measurements for the $$^{13}$$C+$$^{208}$$Pb system at close to the Coulomb barrier energies

Elastic and inelastic scattering measurements for the $$^{13}$$C+$$^{208}$$Pb system at close to the Coulomb barrier energies

Study on the reaction channels in the 6Li+89Y system with multi-angular proton and deutron-γ coincidence analysis

The 6Li+89Y experiment was conducted at the Legnaro National Laboratory in Italy to explore the influence of breakup and transfer reactions on the fusion process induced by the weakly bound projectiles. Due to the competition between neutron and proton evaporation, complete and incomplete fusion might produce identical residues, leading to the difficulties in identification of different reaction process. In this work, the High-Purity-Germanium (HPGe) detector array (GALILEO) was employed to measure γ rays, and the silicon detector array (EUCLIDES) was utilized to capture light charged particles. Exclusive measurements of prompt γ rays from residuals with various light charged particles at an energy near the Coulomb barrier are reported. In the p−γ coincident measurements, observed 91Nb, 92Nb, and 93Nb is considered from neutron evaporation channel in complete fusion reaction, and 90Y is generated through 1n stripping reaction. A two-step, breakup followed by fusion, in case of the capture of α is inferred to be the dominant mechanism to yield the 92Nb and 91Nb in the deutron coincident exclusive measurement.

Magnetoresistance and Magnetocapacitance Effect in Magnetic Tunnel Junction with Perpendicular Anisotropy of Magnetic Electrodes Tb22−δCo5Fe73/Pr6O11/Tb19−δCo5Fe76

This paper presents the results of studies of the effects of magnetoresistance and magnetocapacitance in magnetic tunnel junctions [Formula: see text]Co5[Formula: see text]/Pr6[Formula: see text]/[Formula: see text]Co5[Formula: see text] with perpendicular anisotropy of magnetic electrodes and a paramagnetic barrier layer. Experimentally measured values of tunnel magnetic resistance and tunnel magnetic capacitance in such contacts exceed 100% at room temperature. The paper analyzes the effect of magnetization reversal of one of the electrodes on the conductivity of magnetic tunnel junctions with electrodes that have perpendicular anisotropy. It is shown that significant changes in tunnel magnetic resistance and tunnel magnetic capacity in such contacts can be explained by the separation of electrons with major and minor spin polarization in the inverse nanolayer in the interface region. The separation of polarized electrons is caused by the magnetomotive force acting on the electron spin in a strongly gradient magnetic field. Such a magnetomotive force occurs with antiparallel magnetization of the magnetic electrodes and it has opposite directions for major and minor polarized electrons. As a result of the spatial separation of polarized electrons in the inversion layer, an inhomogeneous distribution of the electron density along the direction of magnetization of the magnetic contacts occurs. As a result, an additional Coulomb barrier between the magnetic electrodes and the dielectric nanolayer appears in the tunnel contacts and an additional spin capacitance appears.

Neutron-transfer induced breakup of the Borromean nucleus 9Be

We address the problem of evaluating neutron-transfer induced breakup cross sections caused by the Borromean nucleus 9Be, using the reaction 197Au(9Be,8Be)198Au as a test case. This reaction was recently measured over a wide range of incident energies around the Coulomb barrier. To deal with the high density of 198Au states that can be potentially populated in this reaction, we employ the Ichimura, Austern, Vicent model, in which the spectrum of physical states for this system is replaced by the solutions of a complex n+197Au potential, accounting effectively for the fragmentation of single-particle states into physical states. Furthermore, to account for the unbound nature of the emitted 8Be system, we employ a three-body model of 9Be. The calculated stripping cross sections are found to be in good agreement with existing data over a wide range of incident energies. The importance of taking into account the energy spread of the single-particle strength of the outgoing 8Be and the target-like residual nucleus is discussed.

Exploring fission and quasi-fission in 31Al + 197Au: probing energies near and beyond Coulomb barrier

An idea to understand the fragmentation of a formed nuclear entity (i.e. compound nucleus), induced via heavy-ion reactions, is an interesting task especially at incident energies near, above and far away from the Coulomb barrier. In the present work, we are studying the decay dynamics of a formed nuclear entity i.e. 228U* compound nucleus (CN), via the radioactive beam of Aluminium-31 (31Al) striking on the stable Gold-197 (197Au) target nucleus, for incident energies E c.m. = 106.2–163.2 MeV. A comprehensive knowledge regarding the probable decaying fragments from 228U* has been accumulated using the collective clusterization approach of the Dynamical Cluster-decay Model (DCM) in terms of mass and charge dispersion, which built up on the Quantum Mechanical Fragmentation Theory (QMFT). Through both of these dispersion cases, we have identified the decaying fragments in the fission and heavy-mass regions, at different scale of incident energies. Further, the fission cross-sections ( σfisTheo ) have been obtained for 31Al + 197Au → 228U* reaction at the above said E c.m. (MeV) and compared with the experimental data. This study has been carried out using two different sets of Skyrme force parameters (SIII and SSk), which are employed within the semiclassical approach of Skyrme Energy Density Formalism. Unlike for energies below and near the barrier, a significant difference has been observed between calculated ( σfisTheo ) and experimental ( σfisExpt ) cross-sections for above barrier energies, with independent choice of Skyrme forces. Such discrepancy noticed has been addressed with the presence of quasi-fission (QF) event. Similar phenomena has also been seen for 19F-induced reaction forming the same CN (228U*).

Fusion and one-neutron stripping process for 6Li + 94Zr system around the Coulomb Barrier* *This research is supported by the National Nature Science Foundation of China (U2167204, 11975040, 1832130, 12375130), the Director's Foundation of Department of Nuclear Physics, China Institute of Atomic Energy 12SZJJ-202305. The Brazilian authors are grateful to the partial support from financial agencies FAPERJ, CNPq, and INTC-FNA

The complete and incomplete fusion cross section as well as one-neutron stripping process of 6Li + 94Zr system were measured at the energies around the Coulomb barrier by online γ-ray method. In addition to a 30% suppression factor when compared with the measured total fusion process, the complete fusion cross section in 6Li + 94Zr system was observed to be significantly lower than those in the nearby 6Li + 90, 96Zr system. The new experimental result implies that the coupling with breakup channel in the 6Li-induced fusion processes can be affected by the inner structure of the target, which is still not clear in any available model calculation. For the one-neutron stripping process, the direct production cross sections for each level in 95Zr were extracted and compared with the coupled reaction channel calculation, offering a unique opportunity to examine the single-particle nature of the produced excited states. Given the fact that an overall overestimation of the production cross section for 954-keV and 1618-keV levels was observed in the comparison, further investigation is highly demanded in order to understand the full reaction mechanism for the one-neutron stripping process induced by 6Li.

Effect of the charge asymmetry and orbital angular momentum in the entrance channel on the hindrance to complete fusion

The hindrance to complete fusion is studied as a function of the charge asymmetry of colliding nuclei and orbital angular momentum of the collision. The formation and evolution of a dinuclear system (DNS) in the heavy-ion collisions at energies near the Coulomb barrier is calculated in the framework of the DNS model. The DNS evolution is considered as nucleon transfer between its fragments. The results prove that a hindrance at formation of a compound nucleus (CN) is related with the quasifission process, which is breakup of the DNS into products instead to reach the equilibrated state of the CN. The role of the angular momentum in the charge (mass) distribution of the reaction products for the given mass asymmetry of the colliding nuclei has been demonstrated. The results of this work have been compared with the measured data for the quasifission yields in the C12+Pb204 and Ca48+Er168 reactions to show the role of the mass asymmetry of the entrance channel. Published by the American Physical Society 2024

Some of the History Surrounding the Oliphant et al. Discovery of dd Fusion and an Inference of the d(d,p)t Cross Section from This 1934 Paper

A review of the flurry of papers involving deuteron beams in 1933 and 1934 reveals some aspects of historical significance. A team led by Lawrence saw several mega-electron-volt protons and neutrons from deuteron-plus-deuteron (dd) fusion in 1933 before the discovery of this process by Oliphant et al. in 1934. However, Lawrence et al. failed to notice deuteron contamination in their targets, and instead incorrectly concluded that the protons and neutrons were being emitted back to back from the breakup of the deuterons in the relevant center-of-mass frame. By observing disintegrations induced by deuteron beams incident on deuterated targets, Oliphant et al. correctly identified dd fusion proceeding through an intermediate excited 4He nucleus that broke up into either back-to-back protons and tritons or back-to-back neutrons and 3He nuclei. Here we use Oliphant et al.’s proton production rates to infer d(d,p) cross sections that are twice the known modern values. This discrepancy is likely due to our lack of knowledge of some key aspects of Oliphant et al.’s 1934 experimental setup. However, the deuterium beam energy dependence of Oliphant et al.’s d(d,p) proton production rate is clearly consistent with the quantum mechanical tunneling through the Coulomb barrier associated with the fusion of two hydrogen isotopes.

Microscopic study of deformation and orientation effects in heavy-ion reactions above the Coulomb barrier using the Boltzmann-Uehling-Uhlenbeck model

Microscopic study of deformation and orientation effects in heavy-ion reactions above the Coulomb barrier using the Boltzmann-Uehling-Uhlenbeck model

Further investigation on the fusion of 6Li with 209Bi target at near-barrier energies

Abstract The complete and incomplete fusion cross sections for 6Li+209Bi were measured via the in-beam γ-ray method around the Coulomb barrier. The cross sections of (deuteron captured) incomplete fusion (ICF) products were re-quantified experimentally for this reaction system. The results reveal that the ICF cross section is equivalent to that of complete fusion (CF) above the Coulomb barrier and dominant near or below the barrier. A theoretical calculation based on the Continuum Discretized Coupled Channel (CDCC) method is performed for the aforementioned CF and ICF cross sections, and the result is consistent with the experimental ones. The universal fusion function (UFF) is also compared with the measured CF cross section with different barrier parameters, demonstrating that the CF suppression factor is quite sensitive to the choice of potential, which can reflect both dynamic and static effects of breakup on the fusion process.

Investigation of reaction and α production cross sections with 9Be projectile

In order to investigate the contribution of α production in the reaction cross sections, measurements of elastic scattering and inclusive α particle angular distributions have been carried out with the 9Be projectile on 89Y, 124Sn, 159Tb, 198Pt, and 209Bi targets over a wide angular range at energies near the Coulomb barrier. The measured elastic scattering angular distributions were fitted with optical model calculations, and reaction cross sections were extracted. The same data were also analyzed using both global optical model potentials (Global OMP) and microscopic São Paulo potentials (SPP), to obtain the reaction cross sections. The data available in the literature for 9Be projectile includes the elastic scattering angular distributions, α production cross sections, and complete fusion cross sections on these and other targets at several energies are also utilized for comparative studies. The reaction cross section extracted from the three potentials (Best Fit, Global OMP and SPP) are in reasonable agreement for all the targets except for the energies below the barrier where the results from SPP deviate by 30-50%. Inclusive α particle production cross sections were also extracted by integrating the α particle angular distributions. The present data and data available from literature of reaction and α-particle production cross sections were utilized to make systematic studies. Systematics of reaction and α-particle production cross sections revealed their universal behavior. The ratio of complete fusion (CF), inclusive α cross sections, and their sum (CF+α) to reaction cross sections show that at sub-barrier energies inclusive α dominates and above barrier CF dominates, and cumulative of these two processes almost explains the reaction cross section at all energies over a wide range of target mass. A comparative study of α production with other weakly bound projectiles is also performed and a clear distinction between projectile types is observed, which is found to correlate well with α separation energies of the projectiles.

Study of $$^{9}$$Be fusion in $$^{93}$$Nb near the Coulomb barrier

Study of $$^{9}$$Be fusion in $$^{93}$$Nb near the Coulomb barrier

A study the 16 O + 166 E R , 16 O + 197 Au Systems Using Calculations of Quasi-elastic Scattering

Specific systematic studies on the nuclear potential parameter for the heavy-ion reactions which includes the systems have been achieved by using large-angle quasi elastic scattering at deep sub-barrier energies close to the Coulomb barrier height. The elastic scattering barrier distribution Dqelas a function of energy has also been calculated in this theoretical study. The single-channel (SC) and coupled-channels calculations have been carried out to elicit the nuclear potential. The chi-square method X2 has been used find the best value of the nuclear potential in comparison with the experimental data. The best values of the nuclear potential were found from the calculations of the single channels for systems: 16O+166ER , 16O+197Au, which are equal to (60.5, 100) MeV, respectively.

TALYS calculation and a short review of the experimental status of proton capture studies on p-nuclei: A guide to future investigation* *The present study was funded by DST, Govt. of India, under the WOS-A scheme (Reference No.: SR/WOS-A/PM-68/2017)

TALYS calculations were performed to obtain the theoretical proton capture cross-sections on the p-nuclei. A short review on the status of related experimental studies was also conducted. Some basic properties such as Q-values, Coulomb barrier, Gamow peak, Gamow Window, and decay properties of the parent and daughter nuclei were studied. Various experimental parameters, e.g., beam energy, beam current, targets, and detectors, used in experimental investigations reported in the literature, were tabulated. The results of the TALYS calculations in the Gamow region were compared with the corresponding experimental values wherever available. This study is expected to facilitate the planning of future experiments.

Quantum field stabilization of the di-neutron enabling low energy deuterium fusion

The free space di-proton (1p1p) and di-neutron (onon) are not bound and are non-existent. However, the latter can and does exist as a 1So entity in the confines of a quantum field of a nearby nucleus. Igor Kadenko et al. have shown that when a single low energy neutron approaches within femtometers of a Tb or Au nucleus, on actually sequesters a neutron from the nuclear skin to form the di-neutron (on↓on↑) residing in the quantum field (QF) of the heavy nucleus. This product can be expressed as [Φn1⊗Φn2]⊗ΦNuc (a three-body problem), leaving the di-neutron free to fuse with the nearby nucleus leading to useful transmutation products. During Fleischmann-Pons heat effect (FPHE) electrolysis experiments, the di-neutron is also formed via deuteron-electron capture; Φe-⊗ΦD+ (for a near relativistic electron) suggests a positive scattering length (electron penetration below the Bohr radius) and di-neutron formation. Since the uncharged onon can freely pass through the Coulomb barrier of the deuteron (2D+), the resulting hydrogen-4 can undergo electro-weak decay to 4He. The di-neutron provides a mechanism for the FPHE observed during the electrolysis of palladium deuteride in D2O, which has now been confirmed and reproduced by M. R. Staker.