Sm Isotopes Research Articles

Complete resolution across the neodymium/samarium isotopic envelope with a liquid sampling-atmospheric pressure glow discharge - Orbitrap mass spectrometer.

Nd and Sm isotope ratios play an important role in geological dating and as nuclear forensic signatures; however, the overlap of the respective 144, 148, 150 Nd/Sm isobars requires prior separations to be performed before analysis on typical MS platforms. The work presented here overcomes these isobaric interferences using ultrahigh-mass resolution to alleviate interference without prior chemical separations. A liquid sampling-atmospheric pressure glow discharge ion source was coupled to a standard, QExactive Focus Orbitrap mass spectrometer, providing a mass resolution of ~80 k. A Spectroswiss FTMS booster X2 data acquisition package was used to collect extended transients, providing much higher mass resolution; ~230 k and ~600 k are employed here for Nd and Sm isotopes. While the standard Orbitrap resolution is far greater than typical "atomic" MS platforms, it was insufficient to alleviate all isobars. The use of a resolution of ~230 k resulted in baseline separation across the entire isotopic envelope for both Nd and Sm. Isotope ratios obtained from Nd:Sm mixtures using high-resolution were equivalent to those found for individual-element solutions, while isotope ratios obtained at a resolution of ~80 k (standard for the OEM data system) showed large deviations. Use of ultrahigh-resolution is an attractive alternative to extensive chemical separations to alleviate severe isobaric interferences. Sufficient mass resolution greatly reduces/eliminates the need for sample manipulations (separations) before analysis while reducing costs and total analysis times.

Optimization of separation and MC-ICP-MS methods for determining Eu isotopic ratios in Si- and Ba-rich fractionated igneous rocks and other natural materials

Eu isotope ratio can be precisely measured by MC-ICP-MS using a Sm isotope pair as spike for normalization. The standard chemical reagent NIST3117a exhibits almost no Eu isotope fractionation regardless of the kind of Sm isotope pairs used in normalization. However, Eu isotope fractionation can appear even in high purity Eu chemical reagents due to Gd and Ba impurities, interference with Sm isotope pair or use of different sample introduction methods. The Eu isotope fractionation in highly fractionated igneous rocks or feldspar minerals can arise from Gd and Ba impurities left by incomplete chemical separation. This study describes a modified, optimal method for accurately and precisely determining the degree of Eu isotope fractionation in highly fractionated Si-rich igneous rocks and Ba-rich feldspar. Ba oxide effects on Sm, Eu and Gd isotopes were monitored by MC-ICP-MS using different wet and dry plasma conditions for sample introduction. The Gd impurities exerts more influence than Ba impurities on Eu isotope ratios. The highly fractionated igneous rocks and feldspar materials showed consistent enrichment in the lighter Eu isotope (151Eu) which becomes a negative Eu isotopic value relative to NIST3117a. Results showed that highly purified Eu solutions from reagents containing no detectable Gd and Ba gave consistent Eu isotopic values regardless of Sm isotope pair (e.g., 147Sm149Sm, 147Sm152Sm, 147Sm154Sm, 149Sm154Sm, 150Sm154Sm) used in normalization. In order to obtain the best estimates of Eu isotope fractionation in different kinds of geological materials (including Si- and Ba-rich materials), Ba and Gd matrix must be completely removed and the Eu isotopic values calculated using four or more Sm spike isotope pairs.

Role of natural isotopic fractionation in isotope geo- and cosmo-chronology: A theoretical investigation

We introduce a new isotope chronological model in which the natural mass-dependent isotopic fractionation effects of the radioactive (“parent”) and radiogenic (“daughter”) elements are systematically and rigorously considered. Using this model, we show that internally-normalized radiogenic isotopic ratios, commonly determined for daughter elements such as Sr, Nd, Cr, Ni, Hf, W, and Os, are dependent on the extent of natural isotopic fractionation of the daughter and parent elements at the time of system closure. This dependence indicates that (1) in two samples derived from the same isotopically homogeneous source at the same time and with identical radiogenic ingrowth over time, the present-day internally-normalized radiogenic isotope ratios would be different if they were initially fractionated to different degrees, and (2) if different internally-normalized radiogenic isotopic ratios are observed for two co-genetic objects, the difference between them would include contributions from both radiogenic ingrowth and natural isotopic fractionation. Consequently, the isochron dating equations employed in traditional chronological studies will yield inaccurate results when significant natural isotopic fractionation is present among the studied samples. Modified isochron equations that can be used to retrieve correct chronological information from isotopically-fractionated samples are presented. These theoretical considerations are applied to the 87Rb–87Sr, 147Sm–143Nd, and 146Sm–142Nd isotope systems of calcium–aluminium-rich inclusions (CAIs), a set of samples that have undergone significant natural Sr, Nd, and Sm isotope fractionation during their formation. The large natural Sr isotope fractionation (up to ca. 5.3 ‰ for 88Sr/86Sr) in fine-grained CAIs can generate analytically well-resolvable biases (>120 ppm) in the internally-normalized 87Sr/86Sr ratios and lead to significant scatters of their 87Rb–87Sr isochron (in conjunction with scatters induced by open-system disturbances). The 87Rb–87Sr systems of coarse-grained CAIs, on the contrary, are essentially not affected by natural Sr isotopic fractionation due to their much subdued fractionation degrees, resulting in a more robust isochron. Similarly, the large natural Nd (up to ca. 4.0 ‰ for 146Nd/144Nd) and Sm (up to ca. 7.1 ‰ for 152Sm/148Sm) isotopic fractionation in fine-grained CAIs can induce significant scatters of the 147Sm–143Nd isochron if the natural fractionation followed the kinetic or power law, and 146Sm–142Nd isochron if the natural fractionation followed the equilibrium, Rayleigh, or power law. This implies that when studying radioactive isotope systems in objects whose daughter and parent elements can undergo significant isotope fractionation in nature, accompanying stable isotope analyses are necessary for accurate chronological interpretations.

Toward a new approach for the pygmy dipole resonance in even–even nuclei. Application to isotopes 144,148,150,152,154Sm

A many-body Hamiltonian consisting of a spherical shell model mean-field term, a pairing interaction for alike nucleons and a dipole–dipole interaction, with the dipole operator involving a cubic term in the radial coordinate, was studied within a quasiparticle random-phase approximation and applied numerically to five even–even isotopes of Sm. The resulting wavefunctions were further used to calculate the B(E1) values, which at their turn were employed to calculate the photoabsorption cross section, integrated moments of the cross section and energy weighted sum rule (EWSR). The calculated cross section and its integrated moments were compared with the available data, and a good agreement was observed. Two regions were distinguished: one corresponding to the pygmy dipole resonance (PDR) (1–10 MeV) and the other to the giant dipole resonance (GDR) (10–20 MeV), which were studied separately. The peaks belonging to each of the two ranges were analyzed in detail. The PDR states were located around the neutron separation energy and were mainly formed by the collective isoscalar and neutron collective states. The PDR states describe oscillations of the neutron excess against protons from the isospin-saturated core. The character of the states from the GDR region, isoscalar or isovector, is also pointed out. The PDR states carry only 0.8%–2.7% of the total EWSR and 0.4%–5.9% of the total E1 strength. The dependence of the dipole strength on nuclear deformation is evidenced. A comment on the cross section splitting into two branches for deformed isotopes is included. The r-cubic term and nuclear deformation have opposite effects on the dipole strength. In addition, it diminishes the effect of nonconservation of the center of mass momentum. The famous Thomas–Reiche–Kuhn sum rule formula is generalized to the case of the Schiff dipole momentum. The new sum rule is well satisfied. The projected spherical single-particle basis used in our formalism allows for a unified description of spherical transitional and deformed isotopes.

High-precision Sm isotope analysis by thermal ionisation mass spectrometry for large meteorite samples (> 1g)

This study presents a new procedure for high-precision Sm isotope analysis by thermal ionisation mass spectrometry (TIMS) for geological samples. A four-step chemical separation scheme results in sharp separation of...

Role of redox conditions and thermal metamorphism in the preservation of Cr isotopic anomalies in components of non-carbonaceous chondrites

Mass-independent isotopic anomalies in meteorites are probes to the dynamics and evolution of the protoplanetary disc and the reservoirs from which planetary bodies accreted. Variable Cr nucleosynthetic compositions between meteorite groups are observed but the cause is not well understood. Investigations on presolar carriers in unequilibrated chondrites are thus required to establish these relationships. For that purpose, we analysed the Cr isotope compositions of leachates (stepwise dissolution solutions) of one ordinary chondrite and two enstatite chondrites of EL and EH subgroups previously measured for Nd and Sm isotopes. The leachates of the ordinary chondrite display large variations of their Cr isotope compositions, whereas the leachates of the enstatite chondrites show very limited variations of their nucleosynthetic compositions, confirming other studies. The Cr isotope compositions of leachates of unequilibrated chondrites are significantly modified by thermal processing and aqueous alteration under various conditions. The leachates of the enstatite chondrites are relatively homogeneous for Cr isotope composition, suggesting that presolar carriers of Cr are not stable under very reduced conditions and are likely oxidised phases. After careful examination of the role of parent body processing, we conclude that there is one predominant presolar carrier enriched in 54Cr that produced most of the nucleosynthetic variations observed in leachates. This carrier is likely depleted in the carbonaceous reservoir relative to the non-carbonaceous reservoir. The drastically different isotope compositions of Cr and heavy refractory lithophile elements such as Nd of leachates of chondrites reflect relative preservation biases of their respective presolar carriers, namely a still poorly characterised presolar oxide and silicon carbide (SiC), respectively.

Investigating the strength of the scissors mode in 151Sm

Change in nuclei deformation leads to changes in statistical properties such as the nuclear level density (NLD) and γ-ray strength function (γSF). The NLD and γSF of 151Sm were extracted using the Oslo method. The strength of the scissors resonance (SR) and its centroid energy for 151Sm were found to be 2.13 ± 0.60 and 2.48 ± 0.25 MeV, respectively. These results were used to place the SR of 151Sm and its magnetic dipole strength B(M1)SR into the context of previously measured Sm isotopes.

A semiempirical evaluation of half-life of 146Sm isotope

A physical model that can quantitatively describe the spontaneous alpha-particle emission mechanism from atomic nuclei in the spherical nucleus approximation has been applied to the evaluation of the half-life of the [Formula: see text]Sm nuclide. The one-parameter, semi-empirical model used in this study has been developed in the frame of a quantum mechanical mechanism of alpha tunnelling through a potential barrier, taking into account centrifugal and overlapping effects. The calculation procedure yielded a value of [Formula: see text][Formula: see text]Myr for the half-life of the extinct [Formula: see text]Sm isotope. This value, even if in disagreement with the few old measurements performed on the artificially obtained [Formula: see text]Sm, is thought to represent the most reliable indication of the [Formula: see text]-decay rate for such challenging nuclide.

The impact of nuclear data uncertainty on identifying plutonium diversion in liquid-fueled Molten Salt Reactors

Molten salt-fueled reactors (MSRs) have gained popularity recently, but there are challenges in accounting for nuclear material due to the inability to count discrete items (e.g., fuel assemblies). The focus of this work is to calculate what changes would occur due to diversion of fissile material, and to evaluate the effect of nuclear data uncertainties on these quantities. The impact of other sources of uncertainty (e.g., measurement error) is out of the scope. A thermal-spectrum MSR was modeled using Serpent 2 and SCALE 6.3.b12 (beta), including plutonium diversion scenarios. The feed and removal capabilities were recently added into the depletion schemes of these codes. Protracted and abrupt diversion scenarios were developed for the removal of 1 and 10 significant quantities (SQs) of plutonium. The SCALE module Sampler was used to perform nuclear data uncertainty propagation along the depletion interval from neutron cross-sections, fission product yield and decay data. Results showed that along with plutonium species, other actinides and fission products presented significant changes between the reference scenario (i.e., no diversion) and the 10 SQ plutonium protracted diversion scenario. Considering their propagated nuclear data uncertainty from Sampler simulations, some actinides such Am and Cm showed changes higher than their nuclear data uncertainty, which goes from 2.23% for 241Am up to 4.88% for 242mAm. Some fission products also presented notable changes, Sr and Y isotopes are examples with positive changes, while Cd, Eu and Sm isotopes showed more prominent changes on the negative side, with uncertainties in the range of 1.89% for 149Sm to 3.31% for 113Cd. The analysis extended to nuclides regularly moved to other modeled inventories, showing that 105,106Ru can be good candidates given their low uncertainty that stands within the 1% range. Many other isotopes with considerable changes presented high uncertainty values and methods to improve their nuclear data uncertainty estimation will be sought in future work.

Enhanced Schiff and magnetic quadrupole moments in deformed nuclei and their connection to the search for axion dark matter

Deformed nuclei possess enhanced moments violating time reversal invariance ($T$) and parity ($P$). Collective magnetic quadrupole moments (MQM) appear in nuclei with a quadrupole deformation (which have ordinary $T$,$P$-conserving collective electric quadrupole moments). Nuclei with an octupole deformation have a collective electric octupole moment, electric dipole moment (EDM), Schiff moment and MQM in the intrinsic frame which rotates with the nucleus. In a state with definite angular momentum in the laboratory frame, these moments are forbidden by $T$ and $P$ conservation, meaning their expectation values vanish due to nuclear rotation. However, nuclei with an octupole deformation have doublets of close opposite parity rotational states with the same spin, which are mixed by $T$,$P$-violating nuclear forces. This mixing polarises the orientation of the nuclear axis along the nuclear spin, and all moments existing in the intrinsic frame appear in the laboratory frame (provided the nuclear spin $I$ is sufficiently large to allow such a moment). Such a mechanism produces enhanced $T$,$P$-violating nuclear moments. This enhancement also takes place in nuclei with a soft octupole vibration mode. In this paper we present updated estimates for the enhanced Schiff moment in isotopes of Eu, Sm, Gd, Dy, Er, Fr, Rn, Ac, Ra, Th, Pa, U, Np and Pu in terms of the CP-violating $\pi$-meson--nucleon interaction constants $\bar{g}_{0},\bar{g}_{1}$ and $\bar{g}_{2}$, the QCD parameter $\bar{\theta}$ and the quark chromo-EDMs. The implications of the enhanced $T$,$P$-violating moments to the search for axion dark matter in solid state experiments are also discussed, with potential alternative candidate compounds in which we may expect enhanced effects suggested.

High intermediate precision Sm isotope measurements in geological samples by MC-ICP-MS

A protocol for high intermediate precision Sm isotope measurements.

Study some of the nuclear characters of Samarium 148,150,152,154Sm isotopes in the IBM-1 framework

The interacting boson model IBM-1 has been applied to some 62Sm even-even isotopes .This study has included calculation of the positive-parity collectiv g-band and β,γ –degenerate bands of 148 62Sm, 150 62Sm, 152 62Sm and 154 62Sm isotopes and compared with experimental values of energy level. The used Hamiltonian parameters correspond to description close to the U(5)-SU(3). The potential energy surfaces E(β,γ) as function of geometrical parameter β and γ for these isotopes can be obtained where they were represented by contour lines and the minimum value of deformation factor βmin was fixed , which was in front of Emin, and so the γ factor. The transition from the spherical to the rotational shape can be observed in these isotopes. In the framework of IBM-1 , what we conclude from the energy spectra study and the geometrical picture of potential energy surface for these nuclei is that these nuclei are spherical shape (U(5)symmetry), prolate rotational shape (SU(3)symmetry) and deformed shape between these two symmetry limits in the U(5)-SU(3)transitional region .

Measuring the β-decay Properties of Neutron-rich Exotic Pm, Sm, Eu, and Gd Isotopes to Constrain the Nucleosynthesis Yields in the Rare-earth Region

The β-delayed neutron-emission probabilities of 28 exotic neutron-rich isotopes of Pm, Sm, Eu, and Gd were measured for the first time at RIKEN Nishina Center using the Advanced Implantation Detector Array (AIDA) and the BRIKEN neutron detector array. The existing β-decay half-life (T 1/2) database was significantly increased toward more neutron-rich isotopes, and uncertainties for previously measured values were decreased. The new data not only constrain the theoretical predictions of half-lives and β-delayed neutron-emission probabilities, but also allow for probing the mechanisms of formation of the high-mass wing of the rare-earth peak located at A ≈ 160 in the r-process abundance distribution through astrophysical reaction network calculations. An uncertainty quantification of the calculated abundance patterns with the new data shows a reduction of the uncertainty in the rare-earth peak region. The newly introduced variance-based sensitivity analysis method offers valuable insight into the influence of important nuclear physics inputs on the calculated abundance patterns. The analysis has identified the half-lives of 168Sm and of several gadolinium isotopes as some of the key variables among the current experimental data to understand the remaining abundance uncertainty at A = 167–172.

Tunable diamond raman lasers for resonance photo-ionization and ion beam production

Lasers with wide tunability and tailored linewidth are key assets for spectroscopy research and applications. We show that diamond, when configured as a Raman laser, provides agile access to a broad range of wavelengths while being capable of efficient and selective photo-excitation of atomic species and suitable spectroscopic applications thanks to its narrow linewidth. We demonstrate the use of a compact diamond Raman laser capable of efficient ion beam production by resonance ionization of Sm isotopes in a hot metal cavity. The ionization efficiency was compared with a conventional Ti:sapphire laser operating at the same wavelength. Our results show that the overall ion current produced by the diamond Raman laser was comparable -or even superior in some cases-to that of the commonly used Ti:sapphire lasers. This demonstrates the photo-ionization capability of Raman lasers in the Doppler broadening-dominated regime, even with the considerable differences in their spectral properties. In order to theoretically corroborate the obtained data and with an eye on studying the most convenient spectral properties for photo-ionization experiments, we propose a simple excitation model that analyzes and compares the spectral overlap of the Raman and Ti:Sapphire lasers with the Doppler-broadened atomic spectral line. We demonstrate that Raman lasers are a suitable source for resonance photo-ionization applications in this regime.

Study of nuclear low-lying excitation spectra with the Bayesian neural network approach

Nuclear low-lying excitation spectra are studied with the Bayesian neural network (BNN) approach by taking 02+, 21+, and 41+ states as examples. The BNN approach can well describe the low-lying excitation energies in a large energy scale from about 0.1 MeV to about several MeV, by including an input related to nuclear collectivity besides proton and neutron numbers and employing the logarithm of excitation energy as the output. Comparing with the sophisticated microscopic collective Hamiltonian model, the BNN approach significantly improves the description of nuclear low-lying excitation energies, which can generally reproduce the experimental data within about 1.12 times including those of transitional nuclei and magic nuclei. Taking Mg, Ca, Kr, Sm, and Pb isotopes as examples, it is found that the BNN approach well describes the isotopic trend of low-lying excitation energies, including those abrupt increases at magic numbers due to the shell effect, very low excitation energies of 02+ states due to the shape coexistence, and complex nuclear shape evolution due to the shape phase transition.

An iterative approach for the exact solution of the pairing Hamiltonian

A new iterative algorithm is established for the exact solution of the standard pairing problem, based on the Richardson-Gaudin method using the polynomial approach. It provides efficient and robust solutions for both spherical and deformed systems at a large scale. The key to its success is that the initial guess for the solutions of such a large set of the non-linear equations is provided in a physically meaningful and controllable manner. Moreover, one reduces the large-dimensional problem to a one-dimensional Monte Carlo sampling procedure, which improves the algorithm's efficiency and avoids the non-solutions and numerical instabilities that persist in most existing approaches. We calculated the ground state and low-lying excited states of equally spaced systems at different pairing strengths G. We then applied the model to study the quantum phase transitional Sm isotopes and the actinide nuclei Pu isotopes, where an excellent agreement with experimental data is obtained. Program summaryProgram Title: IterV1.mCPC Library link to program files:https://doi.org/10.17632/rjnbhgk2p6.1Licensing provisions: GPLv3Programming language: MathematicaNature of problem: The program calculates exact pairing energies based on a new iterative algorithm. The key is the procedure of determining the initial guesses for the large-set non-linear equations involved in a controllable and physically motivated manner. It provides an efficient and robust solver for both spherical and deformed systems in super large model spaces.Solution method: The new iterative algorithm approach starts with simple systems with k nucleon pairs and n=k levels, which can be solved iteratively by including one pair and one level at each step using the Newton-Raphson algorithm with a Monte Carlo sampling procedure. Then it takes the solutions of those systems as initial values and obtain the converged results for the full space by gradually adding the remaining levels. In this way, one reduces the k-dimensional Monte Carlo sampling procedure to a one-dimensional sampling, which improves the efficiency of the algorithm and avoids the non-solutions and numerical instabilities.

Machine learning the nuclear mass

The masses of $$\sim$$ 2500 nuclei have been measured experimentally; however, >7000 isotopes are predicted to exist in the nuclear landscape from H ( $$Z=1$$ ) to Og ( $$Z=118$$ ) based on various theoretical calculations. Exploring the mass of the remaining isotopes is a popular topic in nuclear physics. Machine learning has served as a powerful tool for learning complex representations of big data in many fields. We use Light Gradient Boosting Machine (LightGBM), which is a highly efficient machine learning algorithm, to predict the masses of unknown nuclei and to explore the nuclear landscape on the neutron-rich side from learning the measured nuclear masses. Several characteristic quantities (e.g., mass number and proton number) are fed into the LightGBM algorithm to mimic the patterns of the residual $$\delta (Z,A)$$ between the experimental binding energy and the theoretical one given by the liquid-drop model (LDM), Duflo–Zucker (DZ, also dubbed DZ28) mass model, finite-range droplet model (FRDM, also dubbed FRDM2012), as well as the Weizsäcker–Skyrme (WS4) model to refine these mass models. By using the experimental data of 80 $$\%$$ of known nuclei as the training dataset, the root mean square deviations (RMSDs) between the predicted and the experimental binding energy of the remaining 20% are approximately $$0.234\pm 0.022$$ , $$0.213\pm 0.018$$ , $$0.170\pm 0.011$$ , and $$0.222\pm 0.016$$ MeV for the LightGBM-refined LDM, DZ model, WS4 model, and FRDM, respectively. These values are approximately 90%, 65%, 40%, and 60% smaller than those of the corresponding origin mass models. The RMSD for 66 newly measured nuclei that appeared in AME2020 was also significantly improved. The one-neutron and two-neutron separation energies predicted by these refined models are consistent with several theoretical predictions based on various physical models. In addition, the two-neutron separation energies of several newly measured nuclei (e.g., some isotopes of Ca, Ti, Pm, and Sm) predicted with LightGBM-refined mass models are also in good agreement with the latest experimental data. LightGBM can be used to refine theoretical nuclear mass models and predict the binding energy of unknown nuclei. Moreover, the correlation between the input characteristic quantities and the output can be interpreted by SHapley additive exPlanations (a popular explainable artificial intelligence tool), which may provide new insights for developing theoretical nuclear mass models.

Lahroud, a Paleo-Tethys Remnant in Northwestern Iran: Implications for Geochemistry, Radioisotope Geochronology, and Tectonic Setting

Abstract —The Lahroud Ophiolite in northwestern Iran contains extensive zones of Paleozoic ophiolite as remnants of the Paleo-Tethys oceanic crust. The principal rock units are gabbro overlain by pillow basalt, which is intruded by granites and interbedded with pelagic sedimentary units including radiolarian cherts. Geochemistry and radioisotope studies, supported by Nd, Sm, Sr, and Pb isotope data, indicate that the Lahroud Ophiolite originates from a within-plate basaltic mantle source. The isotope studies show that the basalts are derived from Indian-type oceanic mantle sources. The radiogenic data indicate the involvement of subduction-related terrigenous materials in the source magma. All the rocks are geochemically cogenetic and were generated by fractionation of a melt with a composition of average E-MORB with a calc-alkaline signature. Two 40Ar/39Ar ages, 343 ± 3 Ma for muscovite minerals and 187.7 ± 7.7 Ma for glasses, suggest that metamorphic and basaltic rocks formed during the Late Paleozoic to Early Jurassic, respectively. Microfossil studies show the presence of Paleozoic biostratigraphy. The crystallization process and rifting into the oceanic crust in the Lahroud Ophiolite probably began in the Carboniferous, with volcanic activity continuing during the Late Triassic.

Quasi-SU(3) coupling of ( 1h11/2,2f7/2 ) across the N=82 shell gap: Enhanced E2 collectivity and shape evolution in Nd isotopes

The essence of the quasi-SU(3) coupling scheme suggested by Zuker et al. is that the high-$j$ intruder orbit alone is insufficient to induce required large collectivity, and it is necessary for the high-$j$ orbit to correlate through the quadrupole interaction with another higher-lying orbit with $\mathrm{\ensuremath{\Delta}}j=2$. To extend this idea to the medium-heavy mass region, we investigate the systematics of energy levels and $B(E2)$ values for Sn, Te, Xe, Ba, Ce, Nd, and Sm isotopes by applying the recently proposed realistic PMMU shell model. The calculations are performed by using the projected Hartree-Fock-Bogolyubov plus generator coordinate method in the model space of ($1{g}_{9/2},1{g}_{7/2},2{d}_{5/2},2{d}_{3/2},3{s}_{1/2},1{h}_{11/2}$). The calculations describe well the experimental data over a wide range of nuclei. However, it is found that, in some nuclei close to the neutron midshell, $^{124,126}\mathrm{Ce}$, $^{130,132}\mathrm{Nd}$, and $^{134}\mathrm{Sm}$, the calculated $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ values underestimate the data considerably. This problem can be resolved by inclusion of the $2{f}_{7/2}$ orbit into the model space, which, with $1{h}_{11/2}$, forms a quasi-SU(3) coupling scheme. It is shown that the $QQ$ interaction between the SU(3)-partner $1{h}_{11/2}\text{\ensuremath{-}}2{f}_{7/2}$ is a driving force for enhanced $E2$ collectivity in the above nuclei and is responsible for the shape evolution in Nd isotopes. In addition, the participation of the $2{f}_{7/2}$ orbit in the model space favors prolate shape in the ground state of $N\ensuremath{\le}76$ isotopes, thus subverting the oblate result from the same calculation but without $2{f}_{7/2}$.

Statistical properties of the well deformed Sm153,155 nuclei and the scissors resonance

The Nuclear Level Densities (NLDs) and the $\gamma$-ray Strength Functions ($\gamma$SFs) of $^{153,155}$Sm have been extracted from (d,p$\gamma$) coincidences using the Oslo method. The experimental NLD of $^{153}$Sm is higher than the NLD of $^{155}$Sm, in accordance with microscopic calculations. The $\gamma$SFs of $^{153,155}$Sm are in fair agreement with QRPA calculations based on the D1M Gogny interaction. An enhancement is observed in the $\gamma$SF for both $^{153,155}$Sm nuclei around 3 MeV in excitation energy and is attributed to the M1 Scissors Resonance (SR). Their integrated strengths were found to be in the range 1.3 - 2.1 and 4.4 - 6.4 $\mu^{2}_{N}$ for $^{153}$Sm and $^{155}$Sm, respectively. The strength of the SR for $^{155}$Sm is comparable to those for deformed even-even Sm isotopes from nuclear resonance fluorescence measurements, while that of $^{153}$Sm is lower than expected.