Nuclear Structure Effects Research Articles

Systematic study of the isotopic dependence of heavy-ion fusion cross sections at below- and above-barrier energies

The present work provides a systematic study on the role of nuclear surface tension in the isotopic dependence of the fusion cross sections at below- and above-barrier energies over wide range of neutron content (0.5 < N/Z < 1.7). To realize our goal, we select three different versions of proximity-based potential, involving proximity potential 1977, 1988, and 2010, in order to calculate the nucleus-nucleus potential and ultimately the fusion barrier parameters. It is shown that the barrier positions, heights, and curvatures follow a (second-order) non-linear isotopic behavior with addition of neutrons which are dependent on the effect of variation in the nuclear surface tension. Our findings reveal that the sensitivity of isotopic dependence of the fusion barrier characteristics to the effect of surface energy coefficients γ increases by increasing the asymmetry of the colliding pair. In addition, we demonstrate the sensitivity toward the coefficient γ is seen more clearly from the more neutron-rich nuclei compared to the neutron-deficient ones. We discuss the isotopic dependence of the fusion cross sections at below- and above-barrier energies within the framework of the Wong model for a single potential barrier. For above-barrier energies, it is shown that the fusion cross sections follow an increasing (second-order) non-linear trend due to the addition of neutrons. While a decreasing (second-order) non-linear trend exists for the variation in the fusion cross sections at below-barrier energies. Simultaneous comparison the results obtained by the 3 versions of proximity potential for the isotopic dependence of fusion cross sections in the mentioned energy regions reveal the importance of the quantum tunneling and also nuclear structure effects.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 241Pu

The cumulative and independent yields of various fission products within the mass range of 83 to 117 and 123 to 157 have been measured in the epi-cadmium neutron–induced fission of 241Pu using an off-line γ-ray spectrometric technique. From the cumulative yields, post-neutron mass yields were obtained using the charge distribution correction. The full-width at tenth maximum of the light and heavy mass wings and the average light mass <AL> and heavy mass <AH>, as well as the average number of neutrons <ν>, were obtained. The mass yields in the epi-cadmium– and thermal neutron–induced fission of 241Pu were compared to examine the role of excitation energy on the nuclear structure effect.

Ramsey Spectroscopy of the 2S_{1/2} Hyperfine Interval in Atomic Hydrogen.

The 2S_{1/2} hyperfine interval in atomic hydrogen was measured using Ramsey spectroscopy with a thermal beam cooled to cryogenic temperatures. The measured value is 177 556 838.87(85)Hz, which represents the most precise determination of this interval to date. The 1S_{1/2} hyperfine interval f(1S_{1/2}) and the 2S_{1/2} hyperfine interval f(2S_{1/2}) can be combined to give the quantity D_{21}=8f(2S_{1/2})-f(1S_{1/2}), which mostly eliminates uncertainty due to nuclear structure effects and is well described by bound-state quantum electrodynamics. Using the value of f(2S_{1/2}) from this work gives a value of D_{21}^{expt}=48 959.2(6.8) Hz, which is in agreement with the theoretical value of D_{21}^{Theory}=48 954.1(2.3) Hz.

Measurements and computational analysis of the natural decay of Lu176

Background: Mainly because of its long half-life and despite its scientific relevance, spectroscopic measurements of $^{176}\mathrm{Lu}$ forbidden $\ensuremath{\beta}$ decays are very limited and lack formulation of shape factors. A direct precise measurement of its Q value is also presently unreported. In addition, the description of forbidden decays provides interesting challenges for nuclear theory. The comparison of precise experimental results with theoretical calculations for these decays can help to test underlying models and can aid the interpretation of data from other experiments.Purpose: Perform the first precision measurements of $^{176}\mathrm{Lu}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay spectra and attempt the observation of its electron capture decays, as well as perform the first precision direct measurement of the $^{176}\mathrm{Lu}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay Q value. Compare the shape of the precisely determined experimental $\ensuremath{\beta}$ spectra to theoretical calculations, and compare the end point energy to that obtained from an independent Q value measurement.Method: The $^{176}\mathrm{Lu}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay spectra measurements and the search for electron capture decays were performed with an experimental setup that employed lutetium-containing scintillator crystals and a NaI(Tl) spectrometer for coincidence counting. The $\ensuremath{\beta}$ decay Q value was determined via high-precision Penning trap mass spectrometry (PTMS) with the LEBIT facility at the National Superconducting Cyclotron Laboratory. The $\ensuremath{\beta}$-spectrum calculations were performed within the Fermi theory formalism with nuclear structure effects calculated using a shell model approach.Results: Both $\ensuremath{\beta}$ transitions of $^{176}\mathrm{Lu}$ were experimentally observed and corresponding shape factors formulated in their entire energy ranges. The search for electron capture decay branches led to an experimental upper limit of $6.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ relative to its $\ensuremath{\beta}$ decays. The $^{176}\mathrm{Lu}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay and electron capture Q values were measured using PTMS to be 1193.0(6) and 108.9(8) keV, respectively. This enabled precise $\ensuremath{\beta}$ end point energies of 596.2(6) and 195.3(6) keV to be determined for the primary and secondary $\ensuremath{\beta}$ decays, respectively. The conserved vector current hypothesis was applied to calculate the relativistic vector matrix elements. The $\ensuremath{\beta}$-spectrum shape was shown to significantly depend on the Coulomb displacement energy and on the value of the axial vector coupling constant ${g}_{A}$, which was extracted according to different assumptions.Conclusion: The implemented self-scintillation method has provided unmatched observations of $^{176}\mathrm{Lu}$, independently validated by the first direct measurements of its $\ensuremath{\beta}$-decay Q value by Penning trap mass spectrometry. Theoretical study of the main $\ensuremath{\beta}$ transition led to the extraction of very different effective ${g}_{A}$ and ${log}_{10}\phantom{\rule{0.16em}{0ex}}f$ values, showing that a high-precision description of this transition would require a realistic nuclear structure with nucleus deformation.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 245Cm

The cumulative and independent yields of various fission products within the mass ranges of 83 to 117 and 123 to 161 have been measured in the epi-cadmium neutron-induced fission of 245Cm by using an off-line gamma-ray spectrometric technique. Charge distribution correction was applied on the cumulative yields to obtain the post-neutron mass yield distribution. From the mass yield distribution data, the full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, average neutron number <ν>, and peak-to-valley ratio were obtained for the first time. Comparison of mass yield distributions was made between the epi-cadmium and thermal neutron–induced fission of 245Cm to examine the role of excitation energy on the nuclear structure effect and P/V ratio.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 229Th

In the epi-cadmium neutron-induced fission of 229Th, cumulative yields of relatively long-lived fission products within the mass range of 77 to 151 were measured by using an off-line gamma-ray spectrometric technique. The mass yields were obtained from the cumulative fission product yields by using charge distribution correction. The peak-to-valley (P/V) ratio, full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, and average neutron number <ν> were obtained. The P/V ratio was obtained for the first time and was found to be about three times lower in the epi-cadmium neutron fission than in the thermal neutron fission of 229Th, which shows the role of excitation energy. The fine structure of the mass yield distribution in the 229Th(nf,f) reaction was explained from the viewpoint of nuclear structure effect and the Standard I and Standard II asymmetric modes of fission.

Systematic study of the effect of individual rotational energy levels on the fusion cross-section of 16 O-based reactions of range 480 ≤ Z P Z T ≤ 592

In heavy-ion fusion reactions, the enhancement in the sub-barrier fusion cross-section has been observed as compared to the 1-Dimensional barrier penetration model due to the coupling of many degrees of freedom to the relative motion. This enhancement can be explained theoretically by including nuclear structure effects like deformation and the coupling of relative motion among two colliding nuclei. The present work aims to investigate the effect of individual rotational energy levels on the fusion cross-sections for 16O-based reaction systems, namely, 16O + 182,184,186W, 16O + 176,180Hf, 16O + 174,176Yb, 16O + 166Er, 16O + 148,152,154Sm, 16O + 150Nd at energies below the fusion barrier. Using the CCFULL code, the effect of low-lying rotational energy levels on the fusion cross-section for 16O induced reactions has been investigated at energies below and around the Coulomb barrier. The calculations are performed by assuming the fixed value of diffuseness parameter a 0 = 0.65 fm in the Woods-Saxon nuclear potential and the other two parameters are optimised by fitting the experimental data at the above barrier. Here we have determined the V 0 and r 0 as a function of Z P Z T , where experimental cross-sections are available. From our calculations, it is observed that the hexadecapole deformation (β 4) with different magnitudes has a significant influence on the fusion cross sections. For the case of the +ve value of β 4, beyond 10+, the rotational levels cease to contribute significantly and also there is a significant difference between the contribution of sequential channels. On the other hand, in the case of -ve β 4, up to 6+ levels contribute significantly. Furthermore, we have established an algebraic systematic of fitting, which one can use to determine the parameters V 0, r 0 of Woods-Saxon nuclear potential within the range of Z P Z T lie in between 480 ≤ Z P Z T ≤ 592.

Experimental study of high-energy fission and quasi-fission dynamics with fusion-induced fission reactions at VAMOS++

During the last decade, the use of inverse kinematics in the experimental study of fission is bringing a wealth of new observables obtained in single measurements, allowing their analysis and their correlations. An ongoing application of this technique is the basis of a series of experiments performed with the variable-mode, large-acceptance VAMOS++ spectrometer at GANIL. A recent experiment has been focused on the survival of the nuclear structure effects at high excitation energy in fission and quasi-fission. The full isotopic identification of fragments, the fission dynamics and the ratio between the production of fragments with even and odd atomic numbers, the so-called proton even-odd effect, are shown. The latter shows a different mechanism for fission and quasi-fission that could be used to separate fission from quasi-fission.

Experimental study of high-energy fission and quasi-fission with fusion- induced fission reactions at VAMOS++

Over the past decade, inverse kinematics has been increasingly employed in experimental studies of fission. This approach has yielded a wealth of new observables that can be obtained in single measurements, enabling their analysis and correlations. One ongoing application of this technique involves a series of experiments performed at GANIL using the variable-mode, large-acceptance VAMOS++ spectrometer. A recent experiment focused on examining the survival of nuclear structure effects at high excitation energy in both fission and quasi-fission. The results of the study involved a full isotopic identification of fragments, as well as an analysis of the elemental yields their relation to fission dynamics. The results indicate that fission and quasi-fission involve different mechanisms, which could be exploited to distinguish between the two phenomena.

Nuclear structure effects on over-barrier fusion reactions investigated with a new phenomenological model

We investigate the occurrence of nuclear structure effects in the cross section of heavy-ion fusion reactions at energies above the Coulomb barrier. To this end, we initially develop a universal phenomenological model capable to reproduce, with an unprecedented accuracy, all previously published experimental fusion excitation functions with a few parameters. The new model, which foresees exclusively charge, mass, and energy of the colliding systems, shows a clear saturation of the critical angular momentum and avoids analytical non-regularities. The predictions of the newly developed model are then inspected to pin down residual discrepancies with the data, which could be ascribed to the structure of the colliding systems. In this framework, we obtain the following findings: (1) for the first time, we suggest an anomaly in the optimum value of the fusion cross section for systems having nearly-zero fusion Q-values; (2) we point out the occurrence of shell closure effects in the fusion of light systems; (3) we suggest that shell effects are washed-out at relative velocities vrel≳0.07c; (4) in the higher energy part of the fusion excitation function, the cross section for colliding systems involving fluorine or neon isotopes impinging on 2p3/2-1f5/2 nuclei is suppressed, possibly due to the occurrence of α-clustering effects enhancing α-transfer reactions.

Hydrodynamic simulations of directed flow for light hadrons in Au+Au and isobar collisions at 200 GeV* *Supported by the National Natural Science Foundation of China (NSFC) (11935007), Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008), the Natural Science Foundation of Hubei Province (2021CFB272), the Education Department of Hubei Province of China with Young Talents Project (Q20212703), the Open

Using a (3+1)-D hydrodynamic model, CLVisc, we study the directed flow () of light hadrons produced in Au+Au, Ru+Ru, and Zr+Zr collisions at 200 GeV. The evolution of tilted energy density, pressure gradient, and radial flow along the x-direction is systematically investigated. The counter-clockwise tilt of the initial fireball is shown to be a vital source of directed flow for final light hadrons. A good description of directed flow is provided for light hadrons in central and mid-central Au+Au and isobar collisions at the RHIC. Our numerical results show a clear system size dependence for light hadron across different collision systems. We further study the effect of nuclear structure on the directed flow and find that for light hadrons is insensitive to nuclei with quadrupole deformation.

An Analytical Formula for 1s 2s2p 3s3p3d Energy Shifts of Finite-Size Nuclei due to Fluctuating Vacuum Fields

In quantum electrodynamics, the vacuum is not empty but has fluctuating fields which cause an orbiting lepton (electron or muon) to deviate from its quantum orbit and as a result, weaken its coupling with the nucleus, thus causing small changes in lepton energy states. Therefore, in this study, the quantum electrodynamics theory is then applied to determine qualitatively the mean square positions of an oscillating lepton by taking into account the vacuum fields and nuclear size effects. The first-order time-independent perturbation theory as an approximation method is applied to solve for the small changes in the nuclear lepton interaction caused by the two effects. The general expression that can be applied to calculate the changes in lepton energy states is deduced and then applied to calculate numerically these effects on the energy states of single-electron and single muonic atoms. The results showed the dependence of these effects on the principal quantum number n, the orbital quantum number l, the azimuthal quantum number m and the proton number Z. A more significant effect on s (l = 0) states of the large atomic nucleus and muonic atoms is observed. The obtained energy level corrections can be considered as additional energy level corrections that have to be investigated for reanalyzing the existing measured nuclear structure effects and for comparison with future spectroscopic investigations. Moreover, the new proposed formula would be suitable for calculating the energy level corrections in both muonic and electronic atoms caused by the fluctuating vacuum fields.

Search for the chiral magnetic effect in collisions between two isobars with deformed and neutron-rich nuclear structures

Isobar collisions, which were thought to have the same background and different magnetic fields, provide an opportunity to verify the chiral magnetic effect (CME) in relativistic heavy-ion collisions. However, the first result from the RHIC-STAR isobar experiment did not observe the CME signal, but discovered that the backgrounds are different between $_{44}^{96}\mathrm{Ru}+_{44}^{96}\mathrm{Ru}$ and $_{40}^{96}\mathrm{Zr}+_{40}^{96}\mathrm{Zr}$ collisions. We test eighteen cases of Woods-Saxon parameter settings resulting from different nuclear deformation or nuclear structure effects using a mutiphase transport model. We find out that seven cases can reasonably reproduce three reference ratios measured by the STAR experiment. Considering both the halo-type neutron skin structure and CME-like charge separation, we demonstrate that it is difficult for the CME observables ($\mathrm{\ensuremath{\Delta}}\ensuremath{\delta}, \mathrm{\ensuremath{\Delta}}\ensuremath{\delta}$ ratio, $\mathrm{\ensuremath{\Delta}}\ensuremath{\gamma}$, and $\mathrm{\ensuremath{\Delta}}\ensuremath{\gamma}$ ratio) to distinguish the presence or absence of the CME, if the CME strength is weak in isobar collisions. It is because the final state interactions significantly weaken the initial CME signal, resulting in nonlinear sensitivities of the CME observables to the CME strength. Therefore, more sensitive observables are required to search for the possible small CME signal in isobar collisions.

Post-Neutron Fission Product Yield Distribution in the Spontaneous Fission of 244Cm

The cumulative yield of fission products within the mass range of 85 to 115 and 127 to 156, as well as the independent yield of some of the fission products, have been measured in the spontaneous fission of 244Cm by using an off-line γ-ray spectrometric technique. From the cumulative yield of the fission products, their mass chain yields were obtained by applying the charge distribution correction. Mass yield distribution parameters like full width at tenth maximum of light and heavy mass wing and the average light mass <AL> and heavy mass <AH>, as well as the total average neutron multiplicity <ν>expt were obtained. The fission yield data in the 244Cm(SF) reaction were compared with similar data in the neutron-induced fission and spontaneous fission of other actinides to examine the role of excitation energy. The effect of nuclear structure on the excitation energy deficit spontaneous systems has been clearly observed.

Nuclear recoil correction to the hyperfine splitting in atomic systems

We consider leading $O(m/M)$ nuclear recoil corrections to the hyperfine splitting in light atomic systems. Due to the singularity of hyperfine interactions, the electromagnetic form factors of the nucleus have to be introduced as a function of the four-momentum square, which goes beyond the Hamiltonian description of the system. We present a compact formula for $O(Z\phantom{\rule{0.16em}{0ex}}\ensuremath{\alpha})$ recoil corrections and indicate the importance, especially for light atoms, of a more realistic description of the nuclear structure effects.

Ground-state hyperfine structure of light muon-electron ions

The ground state hyperfine splitting of light muon-electron ions of lithium, beryllium, boron and helium is calculated on the basis of analytical perturbation theory in terms of small parameters of the fine structure constant and electron-muon mass ratio. The corrections of vacuum polarization, nuclear structure and recoil effects and electron vertex corrections are taken into account. The dependence of the corrections on the nucleus charge Z is studied. The obtained total values of hyperfine splitting intervals can be used for comparison with future experimental data.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 241Am

Mass yield distribution has been carried out in the epi-cadmium neutron-induced fission of 241Am by measuring the cumulative yields of fission products within the mass ranges of 80 to 119 and 123 to 161. An 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. From the mass yield distribution, the full-width at tenth-maximum of the light and heavy mass wings, the peak-to-valley (P/V) ratio, the average light mass <AL> and heavy mass <AH>, and the average number of neutrons <ν> were obtained. The mass yield data in the epi-cadmium neutron fission of 241Am were compared with similar data of thermal and 14.8-MeV neutron-induced fission to examine the role of excitation energy on the nuclear structure effect and P/V ratio.

Post-neutron mass yield distribution in the epi-cadmium neutron induced fission of 243Am

The cumulative yields of fission products within the mass range of 83 to 119 and 123 to 158 have been measured in the epi-cadmium neutron-induced fission of 243Am by using an off-line gamma-ray spectrometric technique. Mass chain yields were obtained from the cumulative yields of the fission products by applying the charge distribution correction. From the mass yield data, the full-width at tenth-maximum of the light and heavy mass wing, the peak-to-valley (P/V) ratio, the average light mass <AL> and heavy mass <AH>, and the average number of neutrons <ν> were obtained. The mass yield data in the 243Am(n,f) reaction were compared with similar data in the 243Am(nth,f) and 243Am(n16.5 MeV,f) reactions to examine the role of excitation energy on the nuclear structure effect and P/V ratio.

Fusion of spherical-octupole pairs of colliding nuclei for compact and elongated configurations * *The financial support from Council of Scientific & Industrial Research (CSIR), in the form of a Senior Research Fellowship, DAE, Government of India, sanction no. 58/14/12/2019-BRNS and UGC-DAE consortium for Scientific Research, File No. UGC-DAE-CSR-KC/CRS/19/NP09/0920 are gratefully acknowledged

The deformation and associated optimum/uniquely fixed orientations play an important role in the synthesis of compound nuclei via cold and hot fusion reactions, respectively, at the lowest and highest barrier energies. The choice of optimum orientation ( ) for the ‘cold or elongated’ and ‘hot or compact’ fusion configurations of quadrupole ( ) deformed nuclei depends only on the +/- signs of -deformation [J. Phys. G: Nucl. Part. Phys. 31, 631-644 (2005)]. In our recent study [Phys. Rev. C 101, 051601(R) 2020], we proposed a new set of (different from the values reported for quadrupole deformed nuclei) after the inclusion of octupole deformation (up to ) effects. Using the respective of -deformed nuclei for cold and hot optimum orientations, we analyzed the impact of the soft- and rigid-pear shapes of octupole deformed nuclei on the fusion barrier characteristics (barrier height and barrier position ). This analysis is applied to approximately 200 spherical-plus- deformed nuclear partners, that is, 16O, 48Ca+octupole deformed nuclei. Compared with the compact configuration, the elongated fusion configuration has a relatively larger impact on the fusion barrier and cross-sections owing to the inclusion of deformations up to . Its agreement with available experimental data for the 16O+150Sm reaction ( =0.205, =-0.055) also improves when the optimum orientation degree of freedom is fixed in view of octupole deformations. This reinforces the fact that nuclear structure effects play an important role in the nuclear fusion process. Thus, octupole deformed nuclei can be used for the synthesis of heavy and superheavy nuclei.

Commissioning and performance of TITAN’s Multiple-Reflection Time-of-Flight Mass-Spectrometer and isobar separator

TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) has specialized in fast Penning Trap mass spectrometry of very short-lived radioactive isotopes. The facility has been upgraded with a Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS) to continue its quest towards more exotic nuclides, which are critical for our understanding of nuclear structure effects far from the valley of beta stability and for the nucleosynthesis of heavy elements in explosive astrophysical environments. In this publication, we discuss the implementation, operation and performance of TITAN’s MR-TOF-MS as a stand-alone high-precision mass spectrometer and as an isobar separator. By using the novel mass-selective re-trapping technique for the isobar separation, the MR-TOF-MS can consecutively perform separation and mass measurement of the same ion population, acting as its own isobar separator. The device boosts the dynamic range and reach of the TITAN facility by several orders of magnitude. The MR-TOF-MS reaches a high mass resolving power (m/Δm∼400000), high precision and mass accuracy (δm/m<10−7), is fast (common cycle time 20ms), shows high sensitivity and very large dynamic range (ion of interest to contaminant ratios of up to 1 to 106).