Nuclear Structure Effects Research Articles

Fusion dynamics of 12C with 92Zr and 194,198Pt targets at energies lying in the neighbourhood of Coulomb barrier

This work theoretically analyzed the role played by intrinsic degrees of freedom of the colliding partners and/or nucleon transfer channel in the fusion dynamics of [Formula: see text]C + [Formula: see text]Zr and [Formula: see text]C + [Formula: see text]Pt reactions. The theoretical calculations for the chosen reactions have been done by using symmetric–asymmetric Gaussian barrier distribution (SAGBD) model, coupled channel code CCFULL and one-dimensional Wong formula. The fusion excitation functions for these reactions are enhanced at energies lying in the sub-barrier regions with respect to calculations based on one-dimensional Wong formula. Such enhancement can be ascribed to the involvement of the low-lying inelastic surface excitations of the colliding systems and some other favored channels. The CCFULL calculations consider the couplings to low lying vibrational states of target isotopes and hence intimate the dominance of the collective excitations associated with the fusing partners. For all the studied reactions, the SAGBD model adequately addresses the sub-barrier fusion dynamics and thus the impacts of nuclear structure degrees of freedom associated with the collision partners are intrinsically incorporated via single Gaussian type of weight function. In the SAGBD approach, the nuclear structure effects are analyzed in terms of channel coupling parameter [Formula: see text] and percentage reduction of effective fusion barrier [Formula: see text] with reference to the Coulomb barrier. The larger values for [Formula: see text] and [Formula: see text] imply that the channel couplings due to internal structure of participants are significant at below barrier energies. The CCFULL calculations and SAGBD predictions consistently explain the fusion dynamics of chosen systems and hence reveal that both models have almost similar predictive power with respect to reported fusion data.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 237Np

Mass yield distribution in the epi-cadmium neutron-induced fission of 237Np has been carried out by measuring the cumulative yields of fission products within the mass ranges of 78 to 117 and 123 to 157. A radiochemical and off-line gamma-ray spectrometric technique was used for the measurement. From the cumulative yields of the fission products, mass chain yields were obtained by applying the charge distribution correction. Mass yield distribution parameters such as the full-width at tenth-maximum of light and heavy mass wings, the peak-to-valley (P/V) ratio, and the average light mass <AL> and heavy mass (<AH>) as well as the average number of neutrons <ν> were obtained. The mass yield data in the epi-cadmium neutron-induced fission of 237Np were compared with the similar data in thermal and 14.5- to 14.7-MeV neutrons to examine the role of excitation energy in nuclear structure effect and P/V ratio.

Post-neutron mass yield distribution in the thermal neutron induced fission of 238Pu

The cumulative and independent yields of various fission products within the mass range of 83–155 have been measured in the thermal neutron induced fission of 238Pu by using an off-line γ-ray spectrometric technique. From the cumulative yields, post-neutron mass chain yields were obtained by using the charge distribution correction. From the mass yields data, the full width at tenth maximum (FWTM) of light and heavy mass wing, the average light mass (<AL > ) and heavy mass (<AH > ) as well as the average number of neutrons (<ν > ) emitted were obtained. The mass yield data in the 238Pu(nth, f) reaction was compared with the similar data of 241Pu(nth, f) reaction to examine the nuclear structure effect.

Relativistic Abrasion–Ablation De-excitation Fragmentation (RAADFRG) model

Astronauts are exposed to ionizing radiation that may pose significant health risks from missions to low Earth orbit (LEO) and beyond. The National Aeronautics and Space Administration (NASA) uses the deterministic radiation transport code, High charge (Z) and Energy TRaNsport (HZETRN), to estimate particle fluxes inside shielded vehicles to evaluate risk of radiation exposure to crew members. Highly efficient radiation transport algorithms and cross section models are needed to perform calculations in realistic vehicles with complex geometrical configurations. The HZETRN code uses the NUClear FRaGmentation (NUCFRG) model to evaluate fragmentation cross section products from nucleus–nucleus collisions. Although highly efficient, the NUCFRG model has some limitations that are based on its unique implementation of the abrasion–ablation formalism. NUCFRG performs well in predicting fragmentation cross sections on the average when compared to experimental data; however, even–odd nuclear structure effects observed in laboratory measurements are absent. The aim of the present work is to formulate a self-consistent theory that produces accurate nuclear fragmentation cross sections while maintaining numerical efficiency. To that end, the Relativistic Abrasion–Ablation FRaGmentation (RAADFRG) model has been developed. The theoretical framework for nuclear interaction is multiple scattering theory (MST), where relativistic kinematics may be included in the momentum–space representation of the Lippmann–Schwinger equation. The nuclear abrasion model employs the Eikonal (Eik) approximation and is used to predict prefragment cross sections. A novel approach is utilized for the excitation energy of prefragment, where in addition to differences of binding energies between two nuclei, energy is transferred to the prefragment from subsequent multiple scattering of abraded nucleons with the spectator nucleon constituents of the prefragment. Next, the excited prefragment liberates particles through the nuclear ablation process, and a nuclear coalescence model that forms aggregate particles for each prefragment channel is included in the yield. The ElectroMagnetic Dissociation FRaGmentation (EMDFRG) model is also included for peripheral interactions that stimulates particle emission via nuclear-photon field interactions. When compared to NUCFRG3, uncertainty quantification analysis shows that RAADFRG is better able to predict experimental nuclear fragmentation cross sections. RAADFRG is also shown to produce the even–odd nuclear structure effects, which is achieved by modification of isospin pairing correction in the prefragment excitation energy model.

Low-lying electron energy levels in three-particle electron-muon ions of Li, Be, and B

The electron Lamb shift $(2P-2S)$ and the energy interval $(2S-1S)$ in muon-electron ions of lithium, beryllium, and boron have been calculated within the framework of the perturbation theory method for the fine structure constant and the electron-muon mass ratio. The corrections of the first and second orders of the perturbation theory, which include the effects of vacuum polarization, nuclear structure and recoil, are taken into account. The obtained analytical results in perturbation theory are compared with the results of calculations within the variational approach. The obtained values for the Lamb shift $(2P-2S)$ and the interval $(2S-1S)$ can be used for comparison with future experimental data and verification of quantum electrodynamics.

Hyperfine structure of the 2P3 state in Be9 and the nuclear quadrupole moment

We have performed accurate calculations of the hyperfine structure of the $2\,^3\!P$ state in the $^9$Be atom with the help of highly optimized, explicitly correlated functions, accounting for the leading finite nuclear mass, radiative, nuclear structure and relativistic effects. By comparison with measurements, we have determined the $^9$Be nuclear quadrupole moment to be $Q_{\rm N} = 0.05350(14)$ barns, which is not only the most accurate result, but also disagrees with previous determinations.

Post-Neutron Mass Yield Distribution in the Spontaneous Fission of 252Cf

Cumulative and independent yields of various fission products within mass ranges of 86 to 119 and 127 to 162 were measured in the spontaneous fission of 252Cf by using an off-line gamma-ray spectrometric technique. From the cumulative yields of the fission products, their mass chain yields were obtained by using the charge distribution correction. Mass yield distribution parameters such as full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, and total average neutron multiplicity <ν>expt were obtained. Fission yield data in the 252Cf(SF) reaction were compared with similar data in neutron-induced fission and spontaneous fission of other actinides to examine the role of excitation energy and nuclear structure effect. The role of standard I and standard II asymmetric modes of fission is also discussed.

Extracting the number of short-range correlated nucleon pairs from inclusive electron scattering data

The extraction of the relative abundances of short-range correlated (SRC) nucleon pairs from inclusive electron scattering is studied using the generalized contact formalism (GCF) with several nuclear interaction models. GCF calculations can reproduce the observed scaling of the cross-section ratios for nuclei relative to deuterium at high-$x_B$ and large-$Q^2$, $a_2=(\sigma_A/A)/(\sigma_d/2)$. In the non-relativistic instant-form formulation, the calculation is very sensitive to the model parameters and only reproduces the data using parameters that are inconsistent with ab-initio many-body calculations. Using a light-cone GCF formulation significantly decreases this sensitivity and improves the agreement with ab-initio calculations. The ratio of similar mass isotopes, such as $^{40}$Ca and $^{48}$Ca, should be sensitive to the nuclear asymmetry dependence of SRCs, but is found to also be sensitive to low-energy nuclear structure. Thus the empirical association of SRC pair abundances with the measured $a_2$ values is only accurate to about $20\%$. Improving this will require cross-section calculations that reproduce the data while properly accounting for both nuclear structure and relativistic effects.

Nuclear polarization effects in atoms and ions

Nuclear structure effects lead to small corrections to electron energy-level shifts and isotope shifts in neutral atoms but have enhanced effects on heavy hydrogenlike ions. The authors analyze how nuclear structure effects scale with nuclear charge, mass number, and other parameters in various atoms and ions, with an emphasis on heavy hydrogenlike ions.

Post-neutron mass yield distribution in the epi-cadmium neutron induced fission of $${}^{{\mathbf {240}}}$$Pu

In the epi-cadmium neutron induced fission of $${}^{\text {240}}$$ Pu, cumulative yields of fission products within the mass range of 83–117 and 123–157 as well as independent yields of few fission products have been measured by using an off-line $$\gamma $$ -ray spectrometric technique. The post-neutron mass yields were obtained from the cumulative yields after applying the charge distribution correction. From the mass yields data, the mass distribution parameters like full width at tenth maximum (FWTM) of light and heavy mass wing, the peak-to-valley (P/V) ratio, the average light mass ( $$ $$ ) and heavy mass ( $$ $$ ) as well as the average neutrons number ( $$ $$ ) were obtained. Since, the even–odd effect in between the $${}^{\text {240}}$$ Pu(n, f) and $${}^{\text {241}}\hbox {Pu}(\hbox {n}_{\text {th}}$$ , f) reactions are comparable, the mass yield data in between the two fissioning systems were compared to examine the role of small difference in excitation energy on nuclear structure effect. The role of standard I and standard II asymmetric modes of fission was also examined.

Precision physics of muonic ions of lithium, beryllium and boron

The problem of determining the main parameters of light nuclei from precision atomic spectroscopy is considered. Within the framework of the quasipotential method in quantum electrodynamics, the energy interval [Formula: see text] in muonic ions of lithium, beryllium and boron is calculated. Corrections of orders [Formula: see text], which are determined by relativistic effects, effects of vacuum polarization, nuclear structure and recoil, as well as combined corrections, including the above, are taken into account. Nuclear structure effects are expressed in terms of the nuclear charge radius in the case of one-photon interaction and the electromagnetic form factors of nuclei in the case of two-photon interaction. The obtained numerical values for the [Formula: see text] interval can be used for comparison with future experimental data and for a more accurate determination of the nucleus charge radii.

Dispersive evaluation of the Lamb shift in muonic deuterium from chiral effective field theory

We merge the dispersive relation approach and the ab initio method to compute nuclear structure corrections to the Lamb shift in muonic deuterium. We calculate the deuteron response functions and corresponding uncertainties up to next-to-next-to-next-to-leading order in chiral effective field theory and compare our results to selected electromagnetic data to test the validity of the theory. We then feed response functions calculated over a wide range of kinematics to the dispersion-theory formalism and show that an improved accuracy is obtained compared to that with the use of available experimental data in the dispersive analysis. This opens up the possibility of applying this hybrid method to other light muonic atoms and supplementing experimental data with ab initio theory for kinematics where data are scarce or difficult to measure with the goal of reducing uncertainties in estimates of nuclear structure effects in atomic spectroscopy.

Energy interval 3S−1S in muonic hydrogen

The energy interval $ (3S-1S) $ in muonic hydrogen is calculated on the basis of quasipotential approach in quantum electrodynamics. We take into account different corrections of orders $\alpha^3\div \alpha^6 $, which are determined by relativistic effects, the effects of vacuum polarization, nuclear structure and recoil, as well as combined corrections including the above. Nuclear structure effects are expressed in terms of the charge radius of the proton in the case of one-photon interaction and the proton electromagnetic form factors in the case of two-photon exchange interaction. The value of the energy interval (3S-1S) can be used for a comparison with future experimental data and determining the proton charge radius with greater accuracy.

Nuclear predictions for H spectroscopy without nuclear errors

Nuclear-structure effects often provide an irreducible theory error that prevents using precision atomic measurements to test fundamental theory. We apply newly developed effective field theory tools to Hydrogen atoms, and use them to show that (to the accuracy of present measurements) all nuclear finite-size effects (e.g. the charge radius, Friar moments, nuclear polarizabilities, recoil corrections, Zemach moments etc.) only enter into atomic energies through exactly two parameters, independent of any nuclear-modeling uncertainties. Since precise measurements are available for more than two atomic levels in Hydrogen, this observation allows the use of precision atomic measurements to eliminate the theory error associated with nuclear matrix elements. We apply this reasoning to the seven atomic measurements whose experimental accuracy is smaller than 10 kHz to provide predictions for nuclear-size effects whose theoretical accuracy is not subject to nuclear-modeling uncertainties and so are much smaller than 1 kHz. Furthermore, the accuracy of these predictions can improve as atomic measurements improve, allowing precision fundamental tests to become possible well below the ‘irreducible’ error floor of nuclear theory.

Improved calculations of β decay backgrounds to new physics in liquid xenon detectors

We present high-precision theoretical predictions for the electron energy spectra for the ground-state to ground-state $\beta$ decays of $^{214}$Pb, $^{212}$Pb, and $^{85}$Kr most relevant to the background of liquid xenon dark matter detectors. The effects of nuclear structure on the spectral shapes are taken into account using large-scale shell model calculations. Final spectra also include atomic screening and exchange effects. The impact of nuclear structure effects on the $^{214}$Pb and $^{212}$Pb spectra below $\approx100$ keV, pertinent for several searches for new physics, are found to be comparatively larger than those from the atomic effects alone. We find that the full calculation for $^{214}$Pb ($^{212}$Pb) predicts 15.0-23.2% (12.1-19.0%) less event rate in a 1-15 keV energy region of interest compared to the spectrum calculated as an allowed transition when using values of the weak axial vector coupling in the range $g_{\rm A}=0.7-1.0$. The discrepancy highlights the importance of both a proper theoretical treatment and the need for direct measurements of these spectra for a thorough understanding of $\beta$ decay backgrounds in future experiments.

Single pencil beam benchmark of a module for Monte Carlo simulation of proton transport in the PENELOPE code.

PENH is a recently coded module for simulation of proton transport in conjunction with the Monte Carlo code PENELOPE. PENELOPE applies class II simulation to all type of interactions, in particular, to elastic collisions. PENH uses calculated differential cross sections for proton elastic collisions that include electron screening effects as well as nuclear structure effects. Proton-induced nuclear reactions are simulated from information in the ENDF-6 database or from alternative nuclear databases in ENDF format. The purpose of this work is to benchmark this module by simulating absorbed dose distributions from a single finite spot size proton pencil beam in water. Monte Carlo simulations with PENH are compared with simulation results from TOPAS Monte Carlo (v3.1p2) and RayStation Monte Carlo (v6). Different beam models are examined in terms of mean energy and energy spread to match the measured profiles. The phase-space file is derived from experimental measurements. Simulated absorbed dose distributions are compared to experimental data obtained with the ionization chamber array MatriXX 2D detector (IBA Dosimetry) in a water tank. The experiments were conducted with a clinical IBA pencil beam scanning dedicated nozzle. In all simulations a Fermi-Eyges phase-space representation of a single finite spot size proton pencil beam is used. In general, there is a good agreement between simulated results and experimental data up to a distance of 3cm from the central axis. In the core region (region where the dose is more than 10% of the maximum dose) PENH shows, overall, the smallest deviations from experimental data, with the largest radial rms (root mean square) smaller than 0.2. The results achieved by TOPAS and RayStation in that region are very close to those of PENH. For the halo region, that is the area of the dose distribution outside the core region reaching down to 0.01% of the maximum intensity, the largest rms achieved by TOPAS is always smaller than 0.5, yielding better results than the rest of the codes. The physics modeling of the PENELOPE/PENH code yields results consistent with measurements in the dose range relevant for proton therapy. The discrepancies between PENH appearing at distances larger than 3cm from the central-beam axis are accountable to the lack of neutron simulation in this code. In contradistinction, TOPAS has a better agreement with experimental data at large distances from the central-beam axis because of the simulation of neutrons.

Exploiting electron parity violation: from Standard Model tests to dark matter detection predictions

There has been recent interest in low energy, high luminosity polarized electron beams for studies of parity-violating (PV) electron scattering, such as the MESA accelerator at Mainz or an upgraded FEL facility at Jefferson Lab. Accurate measurements of the PV asymmetry in elastic electron scattering from nuclei can be used to determine Standard Model couplings, such as the weak-mixing angle or higher-order radiative corrections, as well as to extract specific information on the nuclear and nucleon structure. To this end, low uncertainties are required from modelling some confounding nuclear and nuclear structure effects, including isospin mixing, nucleon strangeness content or Coulomb distortion of electron wave functions. We estimate the sizes and theoretical uncertainties of such effects for a carbon 12 target. An experimental precision in the PV asymmetry of a few tenths of a percent may be reachable under certain kinematic conditions, that are also discussed for the same nuclear target.This high precision PV asymmetry in elastic electron scattering can also be used to relate in a very simple manner the elastic electron-nucleus scattering cross section with the elastic neutrino-nucleus cross section. This novel relationship allows us to exploit experimentally well-determined quantities to predict unknown or recently measured observables, such as coherent neutrino-nucleus cross sections. This idea can be extended to link electron scattering to an even more uncertain magnitude: the direct detection rate of hypothetical weak-interacting dark matter particles through axial and/or vector elastic interactions with nuclei.

Energy interval 2S-1S in muonic ions of lithium, beryllium and boron

Within the framework of the quasipotential method in quantum electrodynamics, the energy interval (2S – 1S) in muonic ions of lithium, beryllium and boron is calculated. Corrections of order α 3 – α 6, which are determined by relativistic effects, effects of vacuum polarization, nuclear structure and recoil, as well as combined corrections, including the above, are taken into account. Nuclear structure effects are expressed in terms of the nuclear charge radius in the case of one-photon interaction and the electromagnetic form factors of nuclei in the case of two-photon interaction. The obtained numerical values for the (2S – 1S) energy interval can be used for comparison with future experimental data and for a more accurate determination of the nuclear charge radii.

Determination of the proton charge radius from the study of the hydrogen S-energy levels

On the basis of quasipotential method in quantum electrodynamics, the energy interval (3S – 1S) in muonic hydrogen is calculated. The corrections of orders α 3, α 4, α 5, α 6 are taken into account, which are determined by relativistic effects, the effects of vacuum polarization, nuclear structure and recoil, as well as combined corrections. In the leading order proton structure effects are expressed in terms of the charge radius of the proton. In the case of two-photon exchange interaction proton structure corrections are determined by the proton electromagnetic form factors. The value of the energy interval (3S – 1S) can be used for comparison with future experimental data and determining the proton charge radius with greater accuracy.

Effect of nuclear structure and fissility on quasifission

In order to investigate the interplay between nuclear structure (shell closure) and dynamics, fission fragment mass distributions have been measured for reactions $^{35,37}\mathrm{Cl}+^{206,208}\mathrm{Pb}$. These reactions have similar entrance channel parameters except for the number of closed shell configuration in the entrance channel. Fission fragment mass distributions have been measured for these reactions in the energy region close to the Coulomb barrier. No mass-angle correlation was observed in any of the four reactions, indicating the absence of fast quasifission (QF), but mass distributions were wider than that of compound nucleus (CN) fission, which indicates the presence of slow QF. With comparable fissility and deformation values, extra stability against QF was observed for reactions which have more closed shell configurations in the entrance channel. Mass-angle distributions of these reactions do not follow the systematics with respect to mean fissility. A new systematics has been obtained by considering quadrupole deformation of the heavy reaction partner along with the fissility, which explains the absence of mass-angle correlation in the presently measured reactions.