Alpha-particle Cluster Research Articles

Alpha-particle clustering in self-conjugate nuclei from the experimental side

Alpha-particle clustering in self-conjugate nuclei from the experimental side

Probing Cluster Transfer in Peripheral Collisions of 40Ar on 64Ni at 15 MeV/nucleon

This work focuses on the study of the yields and momentum distributions of projectile-like fragments from 40Ar collisions with target 64Ni at 15 MeV/nucleon, using experimental data obtained in previous work with the MARS spectrometer at the Cyclotron Institute at Texas A&M University. Motivated by the current activity on clustering, we focused our attention on the channel corresponding to the production of the 36S ejectile, which may have resulted from the removal of an alpha particle cluster from the 40Ar projectile. The experimental distributions were compared with two dynamical models, the deep-inelastic transfer (DIT) model and the constrained molecular dynamics (CoMD) model, followed by the de-excitation code GEMINI. The observed discrepancies potentially indicate direct cluster transfer in quasi-elastic peripheral collisions. By comparing our experimental data with appropriate models, we hope to gain valuable insight into the mechanisms governing clustering and cluster transfer in peripheral collisions in the Fermi energy regime.

Stopping power of high-density alpha-particle clusters in partially degenerated deuterium–tritium fuels

The state of burning plasma had been achieved in inertial confinement fusion (ICF), which was regarded as a great milestone for high-gain laser fusion energy. In the burning plasma, alpha particles incident on the cryogenic (warm dense) fuels cannot be simply regarded as single particles, and the new physics brought about by the density effects of alpha particles should be considered. In this work, the collective interaction between them has been considered, namely, the effect of the superposition of wake waves. The stopping power of alpha-particle clusters, i.e., the rate of energy loss per unit distance traveled has been calculated using both analytical and simulation approaches. In theory, we obtain the stopping power of alpha clusters in cryogenic (warm dense) fuel by the dielectric function method, which illustrates the importance of the effective interaction between particles. Simulation results using the LAPINS code show that the collective stopping power of the alpha cluster is indeed increased via coherent superposition of excitation fields (the excitation of high-amplitude wake waves). However, the comparison between simulation and theoretical results also illustrates a coherent–decoherent transition of the stopping power of the cluster. The initial conditions with various sizes and densities of the alpha clusters have been considered to verify the condition of decoherence transition. Our work provides a theoretical description of the transport properties of high-density alpha particles in warm dense cryogenic fuel and might give some theoretical guidance for the design of actual fusion processes.

Competition between alpha and heavy cluster decay in superheavy element 296Og

Systematic study of superheavy nuclei 296 Og and its possibilities to emit alpha particle and heavier clusters are studied using Modified Generalized Liquid Drop Model (MGLDM) with Q value dependent preformation factor. Half-lives and branching ratio of all possible cluster emission of 296 Og is checked and only those cluster which are within the experimental half-lives limit (less than 10 30 s) and branching ratio limit (down to 10 -19 ) are considered. Among this, 88 Kr is found to be the most probable heavy cluster, leading to doubly magic 208 Pb daughter nuclei, with half-lives comparable with alpha decay half-lives. Thus the role of doubly magic daughter nuclei in cluster decay is highlighted here. Again the decay modes of 296 Og are also studied by comparing alpha decay half-lives using MGLDM with spontaneous fission half-lives proposed by Bao et al. , and from this, it is found that for superheavy element 296 Og, decays by 3 alpha chains followed by spontaneous fission. We hope that this study would help when this emission is experimentally detected in near future.

Dependence of Multiparticle Processes on the Interaction-Region Size in Collisions of High-Energy Protons and Nuclei

The problem of the dependence of multiparticle reaction-product formation on the interactionregion size is considered both at cosmic-ray and accelerator energies. In cosmic rays, a comparative analysis of interactions induced by protons and light nuclei was performed on the basis of data obtained by the Stratosphere Collaboration. At accelerator energies, the problem was studied by employing data of the EMU Collaboration. The results revealed a substantial distinction between the production processes in these event groups. An analysis of interactions between light nuclei, (C, O, Ne) + (C/N/O); between intermediate and light nuclei, (Si, S) + (C/N/O); and between heavy nuclei, (Au, Pb) + (Ag/Br), showed that there is a sizable enhancement of fluctuations as the size of the interaction region becomes smaller. A sharp growth of multiplicity and pseudorapidity correlations in the most central interactions, (C, O, Ne) + (C/N/O), is interpreted as a manifestation of internal virtual alpha-particle clustering of light nuclei.

Alpha-particle clustering in excited alpha-conjugate nuclei

The nuclear reaction 40Ca+12C at 25 MeV per nucleon incident energy was used to produce excited alpha-conjugate fragments from projectile fragmentation mechanism. From a careful selection provided by a complete detection and from comparisons with models of sequential and simultaneous decays, evidence in favor of α-particle clustering from excited light alpha-conjugate nuclei is reported.

Alpha-particle clustering in excited expanding self-conjugate nuclei

The fragmentation of quasi-projectiles from the nuclear reaction 40Ca + 12C at 25 MeV/nucleon was used to produce alpha-emission sources. From a careful selection of these sources provided by a complete detection and from comparisons with models of sequential and simultaneous decays, strong indications in favour of $\alpha$-particle clustering in excited 16O, 20Ne and 24}Mg are reported.

Z dependence of the (γ, α) reaction yield

Reactions induced by photons may be used as a probe for bonds and correlations of nucleons inside a heavy target nucleus. In contrast to strongly interacting particles, electromagnetic radiation perturbs nucleons only slightly. The yield of (γ, α) reactions could be used to test theoretical models that assume complete alpha-particle clustering or the presence of multiquark objects in heavy nuclei. The relative yields of (γ, n), (γ, p), and (γ, α) reactions were measured at the bremsstrahlung endpoint energy of 23 MeV for several targets. A much lower probability of (γ, α) in relation to (γ, p) reactions was proved despite very close threshold and spin factors for the two reaction types being considered. Therefore, alpha-particle clustering in heavy targets was not confirmed. The mechanism of particle release in nuclear reactions is discussed, and some details are clarified.

Determining the statistical weight of multicluster wave functions for light nuclei in a parametrized phase analysis

The experimental angular distributions of light alpha-cluster nuclei are described. Based on fitting, we find that the experimental angular distribution splits into two diffraction modes: the first has a short oscillation period on the nucleus as a whole, and the second has long oscillation periods on the alpha-cluster substructures. Fitting also reveals that the cross sections rising above the Rutherford level for light nuclei is explained by the additivity (modulation) of the alpha-particle mode of elastic scattering (the scattering of alpha particles on alpha-particle clusters).

Structural properties of the 10Be and 10C four-cluster nuclei

The structure functions for the 10Be and 10C nuclei are studied in a four-particle approximation (two alpha-particle clusters plus two nucleons). New versions of the αα interaction potential are constructed. Together with the nα, pα, and NN potentials proposed previously, they make it possible to describe the binding energies and radii of the nuclei being considered, along with the S-wave twocluster phase shifts at low energies. General properties of four-particle wave functions are studied, and two basic configurations of the cross and tetrahedron types are revealed in the 10Be and 10C nuclei. A detailed analysis of the behavior of the structure functions is performed for these nuclei. The density distributions, form factors, and pair correlation functions are considered. The momentum distributions are obtained for the alpha particles and extra nucleons. The structure functions for the 10Be and 10C four-cluster nuclei are compared with those for the 6He three-cluster nucleus. The bound states of the nuclei are studied within a high-precision variational approach by using Gaussian bases.

Formation of six-nucleon systems and nuclei in 16Op collisions at a momentum of 3.25 GeV/c per nucleon

The results obtained by studying the production of six-nucleon systems and nuclei that is accompanied by the yield of charged pions in 16Op collisions at a momentum of 3.25 GeV/c per nucleon are presented. It is shown that the correlation of the yield of mirror 3H (3He) nuclei with the production of π+ (π−) mesons is due to the charge-exchange process involving an oxygen-nucleus proton (neutron) knocked out predominantly from an alpha-particle cluster.

Brink model with tetrahedral alpha-particle clusters for three-particle forces

Three-particle interaction is introduced in the Brink model modification that takes into account an arbitrary localization of nucleons within alpha-particle clusters. Simultaneously, the class of single-particle variational functions is substantially extended by replacing the traditionally employed Gaussian function by the sum of Gaussian functions. In the case of the Bonche-Koonin-Negele (BKN) interaction, three Gaussian functions provide a good upper bound on the results of solving the Hartree-Fock equation for the 4He nucleus. It is shown that the BKN three-particle interaction simulates to some extent the effect of short-range correlations in the multiparticle wave function.

Channel coupling and exchange of an alpha-particle cluster in deuteron scattering on 6Li nuclei

Existing experimental data on elastic and inelastic deuteron scattering on 6Li nuclei in the energy range from 8 to 50 MeV were analyzed within the approach of coupled reaction channels. The coupling of elastic scattering and inelastic scattering accompanied by the transition to the 3+ state at E x = 2.186 MeV and the mechanism involving the exchange of an alpha-particle cluster were taken into account in respective calculations. The phenomenological potentials obtained from the present analysis describe well experimental angular distributions at all energies and in full angular ranges. The depths of the real and imaginary parts of the potentials in question depend smoothly on energy at fixed values of the remaining parameters. The energy dependence of relevant volume integrals agrees well with similar data for the p + 6Li, α + 6Li, and 12C + 12C systems and with the predictions of a microscopic theory.

Breakup of an oxygen nucleus to light fragments of mass number in the range A ⩽ 4 in 16Op interactions at a momentum of 3.25 GeV/c per nucleon

New experimental data on the correlations of the yields of 4He and 2H nuclei in semi-inclusive reactions involving by the production of 3He and 3H mirror nuclei in 16Op collisions at a momentum of 3.25 GeV/c per nucleon are presented. The mean multiplicities of protons and neutrons appearing as fragments are found to be independent of the number of associated deuterons, this indicating that a considerable part of these fragments originate from the breakup of the alpha-particle clusters forming the oxygen nucleus.

Interaction of intermediate-energy protons with 20Ne and 24Mg nuclei within the multiple-scattering model

Observables of the elastic and inelastic scattering of 800- and 250-MeV protons on 20Ne and 24Mg nuclei were calculated on the basis of the theory of multiple diffractive scattering and the dispersive α-cluster model. The 20Ne and 24Mg nuclei were assumed to consist of a core (16O nucleus) and additional alpha-particle clusters, which could be situated with the highest probability both in the vicinity of the center of mass of the core and outside the core. The multiparticle densities of these nuclei and single-particle nucleon-distribution densities as obtained from the dispersive α-cluster model were used in the calculations. The differential cross sections and polarizations for elastic and inelastic p 20Ne and p 24Mg scattering at the energy of 800 MeV are in better agreement with experimental data than the analogous calculations at the energy of 250 MeV. The spin-rotation functions calculated in the singleparticle approximation for elastic p 20Ne and p 24Mg scattering at these two energy values differ qualitatively from their counterparts calculated on the basis of the dispersive α-cluster model.

Production of cumulative deuterons in collisions of oxygen nuclei with protons at a momentum of 3.25 GeV/c per nucleon

The production of cumulative nuclei of 2H in 16O p collisions at a momentum of 3.25 GeV/c per nucleon was studied for the first time under conditions of a 4π acceptance. The parameter T 0 characterizing the slope of the spectrum of invariant cross sections for cumulative-deuteron production in 16Op interactions was determined. The contribution to cumulative-deuteron production from the decay of the alpha-particle clusters in nuclei upon slow-pion absorption by these clusters was found on the basis of an analysis of the momentum distribution of these cumulative nuclei. The estimates obtained for the contribution of these processes from a comparison of the mean multiplicities of particles and fragments in cumulative and noncumulative events agree well with the respective result extracted from the momentum distribution of cumulative deuterons.

Structure of the 6He nucleus in the three-particle model

The properties of the 6He nucleus were investigated in a three-particle approximation (a alpha-particle cluster plus two neutrons) on the basis of the variational approach by using a Gaussian basis. For nn and nα interactions, potentials that make it possible to describe S-wave phase shifts for elastic scattering and, simultaneously, to reproduce faithfully the energy and the size of the 6He nucleus were proposed. Characteristic structural features of this nucleus that are manifested in the density distributions, elastic form factor, pair correlation functions, and momentum distributions of particles constituting the 6He nucleus in the three-particle model were revealed.

Experimental determination of the symmetry energy of a low density nuclear gas

Experimental analyses of moderate-temperature nuclear gases produced in the violent collisions of 35 MeV/nucleon Zn-64 projectiles with Mo-92 and Au-197 target nuclei reveal a large degree of alpha particle clustering at low densities. For these gases, temperature- and density-dependent symmetry energy coefficients have been derived from isoscaling analyses of the yields of nuclei with A <= 4. At densities of 0.01 to 0.05 times the ground-state density of symmetric nuclear matter, the temperature- and density-dependent symmetry energies range from 9.03 to 13.6 MeV. This is much larger than those obtained in mean-field calculations and reflects the clusterization of low-density nuclear matter. The results are in quite reasonable agreement with calculated values obtained with a recently proposed virial equation of state calculation.

Contribution of excited nuclei 12C* to the channel of three-alpha-particle production in 16Op collisions at a momentum of 3.25 GeV/c per nucleon

A phenomenological analysis of the channel involving the production of three alpha particles in collisions of relativistic oxygen nuclei with protons is performed for the first time. It is shown that one-third of it is saturated by the decay of an excited nucleus 12C*, while the remaining part is due to direct Fermi breakup or the quasielastic knockout of one alpha-particle cluster from a loosely bound residual nucleus consisting of three alpha particles. The results obtained by simulating the decay of the excited system involving three alpha particles for an isotropic phase space describe experimental data satisfactorily at moderate values of the excitation energy (ΔE*<15 MeV).

Elastic scattering of intermediate-energy protons on 9Be nuclei within the 2αn model

The α-cluster model involving dispersion is adapted to the case of the 9Be nucleus. Two configurations of the ground state of this nucleus are employed in calculations: (i) a core (8Be nucleus) and a complementary cluster (neutron), which oscillates with the highest probability about the center of mass of the core, and (ii) an isosceles triangle formed by two alpha-particle clusters and a neutron. Polarization observables of elastic proton scattering on 9Be nuclei are calculated on basis of this approach and the theory of multiple diffractive scattering. The results of these calculations are in good agreement with available experimental data.