Light Mass Nuclei Research Articles

Measurement of proton induced absolute production cross-section of 6.13, 6.92 and 7.12 MeV γ-rays from 16O(p,p ′γ )16O reaction

In this article, we report the absolute production cross-section of 6.13, 6.92 and 7.12 MeV γ-rays from the 16O(p,p ′γ )16O reaction for incident proton energy range of 8-16 MeV. Angular distributions of the three γ-rays have been measured for seven angles at 9 MeV proton energy. A detailed phenomenological optical model potential (OMP) was set up to analyse the cross-section data. The OMP parameters were optimised using elastic, polarization and total reaction data available in the literature for protons and neutrons. Low-lying states of 16O were coupled, the optical potential was deformed using deformation parameters, and several resonances were included in the calculations to account for the nuclear structure effects. The potentials so generated have been used to calculate the differential and total cross sections for both 16O(p,p ′ )16O and 16O(p,p ′γ )16O reactions. Our calculated cross-sections are in fairly good agreement with our measured data for 6.13, 6.92 and 7.12 MeV γ-rays. However, there still exist discrepancies in reproduction of the finer details of the cross sections. The comparisons of the calculations with the data bring forth the rather complex roles of channel couplings, resonances in the p+16O system and target deformation in the variation of the cross sections with projectile energy. The increased contribution of nuclear structure effects in light mass nuclei, leads to an apparent loss of predictive power of the theoretical calculation, as we approach the low-energy region of less than 10 MeV projectile energy.

Nuclear Structure Aspects of DCX Reactions and β β Decay Transitions

The theory of Double Charge Exchange (DCX) reactions between nuclei requires both the description of the reaction mechanism, which consists of the exchange of nucleons between the target and the projectile, as well as the structure of the matrix elements of the operators which mediate the transitions. From the point of view of the nuclear structure theory it requires the use of microscopic models for light and heavy mass nuclei. The reaction sector requires the use of momentum-dependent operators. It has been argued that these matrix elements could be associated to decay channels like the neutrinoless nuclear double beta decay (0νββ)(DBD). The motivation related to this claim is the need to determine, as accurately as possible, the values of the matrix elements of operators responsible for 0νββ. We shall focus the attention on the possible relationship between DBD and DCX nuclear matrix elements, by studying the dependence of the participant operators upon the momentum.

Latest results from the DAMPE space mission

The space-based DAMPE (DArk Matter Particle Explorer) particle detector has been taking data for more than 7 years since its successful launch in December 2015. Its main scientific goals include the indirect search for dark matter signatures in the cosmic lepton and gamma-ray spectra, the study of galactic cosmic rays up to energies of hundreds of TeV and studies on highenergy gamma ray astronomy. The measurement of galactic cosmic ray spectra are reported here, those being fundamental tools to investigate the mechanisms of acceleration at their sources and propagation through the interstellar medium. Results on proton and helium, which revealed new spectral features, are described. Ongoing analyses on the cosmic ray light, medium and heavy mass nuclei are outlined, together with studies of the so-called secondary cosmic rays. Latest results on gamma-ray astronomy and dark matter search will be also summarized.

A combined Glauber model plus relativistic Hartree–Bogoliubov theory analysis of nuclear reactions with light and medium mass nuclei

A combined Glauber model plus relativistic Hartree–Bogoliubov theory analysis of nuclear reactions with light and medium mass nuclei

Analysis of n-evaporation from light mass nuclei formed via p-induced reactions

This work deals with the decay analysis of three compound nuclei [Formula: see text], [Formula: see text] and [Formula: see text] formed in proton-induced reactions [Formula: see text], [Formula: see text] and [Formula: see text] at incident beam energies of 1–5 MeV using the Dynamical Cluster-decay Model (DCM). The motive is to explore the decay of compound systems formed via light charged particles as projectiles. The experimentally available data of n-evaporation for the aforementioned systems are addressed by optimizing the neck-length parameter [Formula: see text], using spherical fragmentation approach. The comparative analysis of the decay structure of the chosen systems is carried out at a common incident beam energy [Formula: see text] MeV. The effect of angular momentum [Formula: see text] and quadrupole [Formula: see text]-deformations is explored in reference to the decay structure/fragmentation of compound systems. In addition to this, the sensitivity of DCM-based cross-sections toward level density parameter (LDP) [Formula: see text] is also analyzed. The relative role of mass-dependent level density parameter [Formula: see text] is also investigated for compound systems belonging to light and heavy mass region. Lastly, a theoretical systematics is explored where the proton beam in the reaction [Formula: see text] is replaced by a neutron beam forming the compound system [Formula: see text], having the same [Formula: see text], but [Formula: see text] one less than that of the compound system formed in the reaction using proton beam, and its effect on the decay characteristics such as preformation probability, penetration probability and barrier height is analyzed.

Interpretation of the anomaly in the diffuseness parameter of the Woods–Saxon potential for light fusion reactions using the effects of nuclear matter equation of state

The present study has been aimed at understanding the role of nuclear matter (NM) incompressibility effects on the description of the problem of the abnormally large diffuseness parameter of the Woods–Saxon (WS) potential for the fusion reactions induced by the light-mass nuclei. In order to assess this aim, we simulate theoretically the saturation properties of NM within the framework of the double-folding (DF) model for a total of 26 colliding systems with condition 64 ≤ Z1Z2≤ 204 for charge product of their participant nuclei. It is shown that the DF model supplemented with the effects of nuclear matter equation of state (EOS) provides an appropriate description for measured fusion cross sections of our selected systems at around and above barrier energies. We find that the diffuseness parameters of the equivalent WS potential fitted to the DF model in the fusion barrier region are ranging from 0.62 to 0.71 fm, whereas this range is increased to aWS=0.66−0.81 fm after modeling the incompressibility effects. Our results show that the extracted values of the diffuseness parameter based on the modified form of the DF model follow an increasing trend with the charge product Z1Z2. We also present for the first time a discussion on a decreasing linear dependence of the diffuseness parameter of the nucleus–nucleus potential on the nuclear incompressibility constant K.

Microscopically based energy density functionals for nuclei using the density matrix expansion

While ab initio many-body techniques have been able to successfully describe the properties of light and intermediate mass nuclei based on chiral effective field theory interactions, neutron-rich nuclei still remain out of reach for these methods. Conversely, energy density functional approaches can be used to calculate properties of heavy nuclei but rely mostly on phenomenological interactions. A usable form of the nuclear energy density functional that is rooted in the modern theory of nuclear forces was presented recently. The first component of this new set of functionals corresponds to the direct part (Hartree term) of the expectation value of local chiral potentials on a Slater determinant. The exchange term, which is a functional of the non-local density, is transformed into a local functional by applying the density matrix expansion. In order to reduce the computational cost due to the direct implementation of non-separable, local interactions in the Hartree term, we use an approximation to represent the regularized Yukawa functions in terms of a sum of (separable) Gaussian functions. These proceedings analyze the accuracy of such an approximation in terms of the number of Gaussian functions and look for an optimal value that gives an acceptable level of accuracy while maintaining the computational memory requirements in a many-body calculation as low as possible.

Systematic analysis on spectral statistics of odd-A nuclei

Level statistics for given spin and parity below 10MeV within A≤71, 71≤A≤151, and 151≤A≤221 mass regions are systematically analyzed. We have taken 5316 level spacings from 266 odd-A nuclei in the light mass region, 6897 level spacings from 478 ones in the medium mass region, and 2768 level spacings from 143 ones in the heavy mass region for the statistics. In the analysis, the chaoticity parameter in the Berry–Robnik distribution is determined based on the method of maximum likelihood estimation. The results show a mass number A-dependence in the level statistics. The larger the mass number, the relatively stronger in chaoticity. In addition, with the level statistics in using data sequences classified according to the order of magnitude of half-lives, it is shown that the level energies to be more chaotic for longer lived light and heavy mass odd-A nuclei, and intermediate between regular and chaotic in medium mass odd-A nuclei. The level statistical analysis in concerning E2 transition strengths of E2 or mixed E2+M1 transitions in odd-A nuclei is also made, which shows chaos in level energies likely occurring in those with weaker E2 transition strengths. Therefore, it can be concluded that odd-A nuclei are, more often than not, chaotic. Chaos is likely emergent in level energies of stable light mass nuclei with weaker E2 transition strengths, while it is definitely emergent in level energies of heavy mass nuclei, and even stronger in comparatively stable ones and those with weaker E2 transition strengths.

Study of giant dipole resonance in hot rotating light mass nucleus 31P

An exclusive systematic study of the giant dipole resonance (GDR) parameters has been performed in very light mass nucleus P31 in the temperature range of ∼0.8–2.1MeV and average angular momentum of ∼11–16ħ. The high-energy γ rays from the decay of the GDR, evaporated neutrons and γ-ray multiplicities have been measured. The angular distribution of high-energy γ rays has also been measured at Ebeam=42MeV. The GDR parameters, nuclear level density parameter and nuclear temperature were precisely determined by simultaneous statistical model analysis of high-energy γ ray and evaporated neutron spectra. It is observed that the measured width remains roughly constant up to a temperature of ∼1.6MeV. Moreover, the thermal pairing plays no role in describing the GDR width in this open-shell light nucleus at the above-mentioned temperatures and angular momenta. The present measurements provide an excellent platform to extend the applicability of the existing theoretical models down to the very light mass nuclei.

Isospin degree of freedom in even-even 68-76Ge and 62-70Zn isotopes

The introduction of isotopic spin is significant in light nuclei as Ge and Zn isotopes in order to take into account isospin effects on energy spectra. Dynamical symmetries in spherical, $\gamma$ -soft limits and transition in the interacting boson model IBM-3 are analyzed. Analytic expressions and exact eigenenergies, electromagnetic transitions probabilities are obtained for the transition between spherical and $\gamma$ -soft shapes by using the Bethe ansatz within an infinite-dimensional Lie algebra in light mass nuclei. The corresponding algebraic structure and reduction chain are studied in IBM-3. For examples, the nuclear structure of the 68-76Ge and 62-70Zn isotopes is calculated in IBM-3 and compared with experimental results.

Two-proton radioactivity with 2p halo in light mass nuclei A = 18–34

Two-proton radioactivity with 2p halo is reported theoretically in light mass nuclei A=18–34. We predict 19Mg, 22Si, 26S, 30Ar and 34Ca as promising candidates of ground state 2p-radioactivity with S2p<0 and Sp>0. Observation of extended tail of spatial charge density distribution, larger charge radius and study of proton single particle states, Fermi energy and the wave functions indicate 2p halo like structure which supports direct 2p emission. The Coulomb and centrifugal barriers in experimentally identified 2p unbound 22Si show a quasi-bound state that ensures enough life time for such experimental probes. Our predictions are in good accord with experimental and other theoretical data available so far.

Analysis of intermediate and light mass fragments from composite systems 26–29Al⁎ formed in [formula omitted] reactions

A comparative analysis of intermediate mass fragments (IMFs) and light particles (LPs) [equivalently, evaporation residues (ERs)] in the decay of 26,27,28,29Al⁎ has been carried out for reactions O16+10,11B and O18+10,11B at the energy range 1 MeV≤E/A≤4 MeV, within dynamical cluster decay model (DCM) of collective clusterisation approach. We find that, for IMFs having Z=3,4,5 and 6, the range of mass minima are ∑i=58Ai, ∑i=89Ai, ∑i=913Ai and ∑i=1115Ai, respectively. With increase in the mass of compound nuclei, Z=6 becomes more prominent as compared to its neighboring fragments which is also observed in the experimental data. The LPs cross sections (σLPs) in the decay of 26–29Al⁎ are also estimated. We find that the value of ∑P0 of LPs for 26,27Al⁎ is less as compared to that for 28,29Al⁎, contrary to the value of ∑P. Eventually, the cross sections for LPs are having higher contribution in the decay of 28,29Al⁎ in agreement with the experimental data. As expected for light mass nuclei, the σLPs for 26,27Al⁎ find better comparison with experimental data for spherical considerations rather than β2 deformations. We also conform Bohr's hypothesis via the entrance channel independence for compound nucleus 28Al⁎ formed through O18+10B and F19+9Be channels at an excitation energy ECN⁎∼44 MeV, by having a unique choice of neck length parameter ΔR for both the reactions.

Effective two-body model for spectra of clusters of H2,H3,He3 , and He4 with He4 , and H2−He4 scattering

Four light-mass nuclei are considered by an effective two-body clusterisation method; $^6$Li as $^2$H$+^4$He, $^7$Li as $^3$H$+^4$He, $^7$Be as $^3$He$+^4$He, and $^8$Be as $^4$He$+^4$He. The low-energy spectrum of each is determined from single-channel Lippmann-Schwinger equations, as are low-energy elastic scattering cross sections for the $^2$H$+^4$He system. These are presented at many angles and energies for which there are data. While some of these systems may be more fully described by many-body theories, this work establishes that a large amount of data may be explained by these two-body clusterisations.

Structural effects of Na34 in the Na33(n,γ)Na34 radiative capture reaction

The path towards the production of \textit{r}-process seed nuclei follows a course where the neutron-rich light and medium mass nuclei play a crucial role. The neutron capture rates for these exotic nuclei could dominate over their $\alpha$-capture rates, thereby enhancing their abundances at or near the drip line. We calculate the radiative neutron capture cross-section for the $^{33}$Na(n,$\gamma)^{34}$Na reaction via the Coulomb dissociation of $^{34}$Na as it undergoes elastic breakup on $^{208}$Pb when directed at a beam energy of 100 MeV/u using the entirely quantum mechanical theory of finite range distorted wave Born approximation upgraded to incorporate deformation effects. The non-resonant one neutron radiative capture cross-section for $^{33}$Na(n,$\gamma)^{34}$Na is calculated and is found to increase with increasing deformation of $^{34}$Na. An analytic scrutiny of the capture cross-section with neutron separation energy as a parameter is also done at different energy ranges. The calculated reaction rate is compared with the rate of the $^{33}$Na($\alpha$,n)$^{36}$Al reaction (deduced from the Hauser-Feshbach theory), and is found to be significantly higher below a temperature of $T_9 = 2$. Further, at the equilibrium temperature of $T_9 = 0.62$, the rate for the neutron capture had a small but non-negligible dependence on the structural parameters of $^{34}$Na. In addition, this neutron capture rate exceeded that of the $\alpha$-capture reaction by orders of magnitude, indicating that the $\alpha$-process should not break the (n,$\gamma$) \textit{r-}process path at the $^{33}$Na isotope, thus, effectively pushing the abundance of sodium isotopes towards the neutron drip line.

Quantifying statistical uncertainties in ab initio nuclear physics using Lagrange multipliers

Theoretical predictions need quantified uncertainties for a meaningful comparison to experimental results. This is an idea which presently permeates the field of theoretical nuclear physics. In light of the recent progress in estimating theoretical uncertainties in ab initio nuclear physics, we here present and compare methods for evaluating the statistical part of the uncertainties. A special focus is put on the (for the field) novel method of Lagrange multipliers (LM). Uncertainties from the fit of the nuclear interaction to experimental data are propagated to a few observables in light-mass nuclei to highlight any differences between the presented methods. The main conclusion is that the LM method is more robust, while covariance based methods are less demanding in their evaluation.

Status of the R-matrix Code AMUR toward a consistent cross-section evaluation and covariance analysis for the light nuclei

We report the status of the R-matrix code AMUR toward consistent cross-section evaluation and covariance analysis for the light-mass nuclei. The applicable limit of the code is extended by including computational capability for the charged-particle elastic scattering cross-sections and the neutron capture cross-sections as example results are shown in the main texts. A simultaneous analysis is performed on the 17 O compound system including the 16 O( n , tot ) and 13 C(α, n ) 16 O reactions together with the 16 O( n , n ) and 13 C(α,α) scattering cross-sections. It is found that a large theoretical background is required for each reaction process to obtain a simultaneous fit with all the experimental cross-sections we analyzed. Also, the hard-sphere radii should be assumed to be different from the channel radii. Although these are technical approaches, we could learn roles and sources of the theoretical background in the standard R-matrix.

Importance of resonance widths in low-energy scattering of weakly bound light-mass nuclei

What effect do particle-emitting resonances have on the scattering cross section? What physical considerations are necessary when modelling these resonances? These questions are important when theoretically describing scattering experiments with radioactive ion beams which investigate the frontiers of the table of nuclides, far from stability. Herein, a novel method is developed that describes resonant nuclear scattering from which centroids and widths in the compound nucleus are obtained when one of the interacting bodies has particle unstable resonances. The method gives cross sections without unphysical behavior that is found if simple Lorentzian forms are used to describe resonant target states. The resultant cross sections differ significantly from those obtained when the states in the coupled channel calculations are taken to have zero width, and compound-system resonances are better matched to observed values.

Application of an extended random-phase approximation to giant resonances in light-, medium-, and heavy-mass nuclei

We present results of the time blocking approximation (TBA) on giant resonances in light, medium and heavy mass nuclei. The TBA is an extension of the widely used random-phase approximation (RPA) adding complex configurations by coupling to phonon excitations. A new method for handling the single-particle continuum is developed and applied in the present calculations. We investigate in detail the dependence of the numerical results on the size of the single particle space and the number of phonons as well as on nuclear matter properties. Our approach is self-consistent, based on an energy-density functional of Skyrme type where we used seven different parameter sets. The numerical results are compared with experimental data.

Moments of inertia and B(E2;01+→21+)s in the NpNn scheme

We examine the collective nuclear structure of light and medium mass (Z = 50–82, N = 82–126) even–even nuclei using valence nucleon pair product (NpNn). We discuss the role of proton–neutron interaction in light mass nuclei and illustrate the variation of observables of collectivity and deformation (i.e., ground band moment of inertia) and B(E2) values with N and NpNn). The plot of these observables against NpNn vividly displays the formation of isotonic multiplets in quadrant I, strong dependence on NpNn in quadrant II and weak constancy with Z in quadrant III is illustrated.

Nuclear structure study of some bubble nuclei in the light mass region using mean field formalism

We study the structural properties of some light mass nuclei using two different formalisms (i) a recently developed simple effective interaction in the frame work of microscopic non-relativistic Hartree-Fock method and (ii) the well-known relativistic mean field approach with NL3 parameter set. The bulk properties like binding energy, root mean square radii and quadrupole deformation parameter are estimated and compared with the available experimental data. The predicted results of both the formalisms are well comparable with the experimental observations. The analysis of density profiles of these light mass nuclei suggest that 22O, 23F, 34Si and 46Ar have bubble like structure.