Rotational Bands Research Articles

Machine learning method for 12C event classification and reconstruction in the active target time-projection chamber

Active target time projection chambers are important tools in low energy radioactive ion beams or gamma rays related researches. In this work, we present the application of machine learning methods to the analysis of data obtained from an active target time projection chamber. Specifically, we investigate the effectiveness of Visual Geometry Group (VGG) and the Residual neural Network (ResNet) models for event classification and reconstruction in decays from the excited 22+ state in 12C Hoyle rotation band. The results show that machine learning methods are effective in identifying 12C events from the background noise, with ResNet-34 achieving an impressive precision of 0.99 on simulation data, and the best performing event reconstruction model ResNet-18 providing an energy resolution of σE<77 keV and an angular reconstruction deviation of σθ<0.1 rad. The promising results suggest that the ResNet model trained on Monte Carlo samples could be used for future classifying and predicting experimental data in active target time projection chambers related experiments.

Peculiarities of Rotational Bands in Heavy and Superheavy Nuclei: Description of Yrast-Band States in 248Cm

A further development of the expanded microscopic version of the IBM is presented by considering two-quasiparticle phonons with multipolarity up to J = 14+J. The developed theoretical scheme is applied to describe the properties of the yrast-band states in 248Cm up to spin 34+. This heavy transactinide nucleus is the only nucleus in this mass region where the values of B(E2) up to spin I = 28+ are measured. That is why it is considered foremost, because this information allows testing the presented theoretical scheme based on a larger volume of experimental data. The region of transactinide nuclei differs from lighter ones by the absence of the effect of the back bending in the moment of inertia dependence on the square of the rotation frequency up to the spin I = 28+. This article is intended in particular to find out the reason for this effect. Peculiar properties of the rotational bands in heavy and superheavy nuclei are discussed.

Incipient reflection asymmetry in 127Xe

Excited states in 126,127,128Xe were populated via 122Sn(9Be, xnγ) fusion-evaporation reaction at a beam energy of 48 MeV. A positive parity rotational-like sequence of ΔI=2γ-transitions, which is found to decay into the negative parity band via E1 transitions, is observed above Iπ=19/2+ state at 2307 keV in 127Xe. Such enhanced E1 γ-transitions are also observed between the antimagnetic rotational (AMR) and longitudinal wobbling (LW) bands in this nucleus. These indicate the presence of simplex symmetry with s=±i excitation in 127Xe.

Wormhole model for Neon-20

A quantum mechanical model for the Neon-20 nucleus is developed that allows for the splitting of a bipyramidal structure of five alpha-particles into an alpha-particle and an Oxygen-16 nucleus. The geometry of the configuration space is assumed to be a 3-dimensional spatial wormhole, and on the wormhole background there is an attractive short-range potential. This leads to a radial Schrödinger equation of the Heun form, which simplifies for threshold bound states to an associated Legendre equation that has explicit solutions. The energies of the true bound states for all spin/parities are numerically calculated, and match those of the well-established Kπ=0+ and Kπ=0− rotational bands of Neon-20, and certain higher bands.

Energy estimates for 2+1, 4+1, 6+1 states in heavy and superheavy nuclei

Based on the available energy correlation deformation and the lowest excitation energy, estimates were obtained for the energy of the 2+1 – states. The considered systematics of the energy ratios in the rotational band also made it possible to obtain estimates for the 4+1 and 6+1 – states. A comparison with the results of other works was carried out.

Coexistence of single-particle and collective excitation in Ni61

The high spin states in 61 Ni have been studied using the fusion evaporation reaction, Ti( $^{14}$C,3n) $^{61}$Ni at an incident beam energy of 40 MeV. A Compton suppressed multi-HPGe detector setup, consisting of six Clover detectors and three single crystal HPGe detectors was used to detect the de-exciting $\gamma$ rays from the excited states. The level scheme has been extended up to an excitation energy of 12.8 MeV and a tentative J$_{\pi}$ = 35/2$^+$ . The low-lying negative parity levels are found to be generated by single particle excitation within the f p shell and also excitations to the g$_{9/2}$ orbitals as explained well with shell model calculations using the GXPF1Br+V M U (modified) interaction. Two rotational structure of regular E2 sequences with small to moderate axial deformation have been established at higher excitation energy. Most interestingly, two sequences of M1 transitions are reported for the first time and described as magnetic rotational bands. The shears mechanism for both the bands can be described satisfactorily by the geometrical model. The shell model calculation involving the cross shell excitation beyond the fp shell well reproduce the M1 and E2 sequences. The shell model predicted B(M1) values for the magnetic rotational band B1 show the decreasing trend with spin as expected with closing of the shears.

Theory of rigidity and numerical analysis of density of states of two-dimensional amorphous solids with dispersed frictional grains in the linear response regime.

Using the Jacobian matrix, we obtain a theoretical expression of rigidity and the density of states of two-dimensional amorphous solids consisting of frictional grains in the linear response to an infinitesimal strain, in which we ignore the dynamical friction caused by the slip processes of contact points. The theoretical rigidity agrees with that obtained by molecular dynamics simulations. We confirm that the rigidity is smoothly connected to the value in the frictionless limit. We find that there are two modes in the density of states for sufficiently small k_{T}/k_{N}, which is the ratio of the tangential to normal stiffness. Rotational modes exist at low frequencies or small eigenvalues, whereas translational modes exist at high frequencies or large eigenvalues. The location of the rotational band shifts to the high-frequency region with an increase in k_{T}/k_{N} and becomes indistinguishable from the translational band for large k_{T}/k_{N}.

Nuclear Data Sheets for A=245

Available information pertaining to the nuclear structure of ground and excited states for all known nuclei with mass numbers A=245 have been compiled and evaluated. The adopted level and decay schemes, as well as the detailed nuclear properties and configuration assignments based on experimental data, are presented for these nuclides. When there are insufficient data, expected values from systematics of nuclear properties and/or theoretical calculations are utilized. Unexpected or discrepant experimental results are also noted. Since the last evaluation, new rotational bands in 245Pu have been observed to high spin from transfer reaction 244Pu(209Bi, 208Biγ) by 2014Ho16. While in 245Am, the 249Bk α decay measurements by 2013Ah03 added a new rotational band based on π3/2[521] configuration. The 245Pu β− decay scheme is basically what was proposed in the late 60's and 47 γ rays have still not been placed. In 245Cm, precise alpha energies and intensities were measured by 2015Ah03 in 249Cf α decay. Their reported alpha energies of the main α group were about 2 keV lower than in the previous evaluation. The spin and parity of the g.s. of 245Es is still ambiguous as more detailed information on the decay is needed. With the production of 249No via fusion evaporation reaction by groups in Dubna and GSI, it's alpha decay was studied and some properties of the daughter 245Fm were published and included in this evalaution. Information on the other nuclides is scarce and not much has been investigated since the last evaluation. A summary and compilation of the discovery of the various nuclides in this mass region is given in: 2013Fr02 (245Pu, 245Am, 245Cm, 245Bk, 245Cf), 2011Me01 (245Es), and 2013Th02 (245Md, 245Fm).

Invariant-mass spectroscopy of B10, C11, F14, F16 , and Na18

The invariant-mass method is used to study the structure of a number of light proton-rich isotopes utilizing fast beams. Reactions where the projectile picks up a proton have been used to study $d$-wave resonances in $^{14}\mathrm{F}, ^{16}\mathrm{F}$, and $^{18}\mathrm{Na}$. While the $^{16}\mathrm{F}$ and $^{18}\mathrm{Na}$ results are consistent with previous studies, the $^{14}\mathrm{F}$ results are not consistent with the only previous work. We have tentatively identified the ${4}^{+}$ member of a rotational band in $^{10}\mathrm{B}$, which is the analog of well-known states with strong $\ensuremath{\alpha}$-cluster structure in $^{10}\mathrm{Be}$ and $^{10}\mathrm{C}$. Finally, spin and parities of newly observed states in $^{11}\mathrm{C}$ which decay sequentially into three-body exit channels have been determined or restricted.

Possible antimagnetic rotational band in In114

High-spin states of $^{114}\mathrm{In}$ were populated using the reaction $^{110}\mathrm{Pd}\phantom{\rule{4pt}{0ex}}(^{7}\mathrm{Li}, 3n)^{114}\mathrm{In}$ at a beam energy of 26 MeV. More than 30 new $\ensuremath{\gamma}$ transitions and 20 new levels are identified in $^{114}\mathrm{In}$. In total, three new bands and a short cascade are observed, among which a new negative-parity $\mathrm{\ensuremath{\Delta}}I=2$ band built on the $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{d}_{5/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ configuration before the backbend and the $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{d}_{5/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}^{3}$ configuration after the backbend is established. The properties of this band are discussed based on the classical particle-rotor model calculations. The predicted $B(E2)$ and ${\ensuremath{\mathfrak{I}}}^{(2)}/B(E2)$ ratios indicate that the $\mathrm{\ensuremath{\Delta}}I=2$ band after the backbend, has the characteristics of antimagnetic rotation. Meanwhile, the two-shears-like mechanism for the possible antimagnetic rotational band is examined by investigating the orientation of the angular momenta. A new positive-parity $\mathrm{\ensuremath{\Delta}}I=1$ band with the configuration of $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}({g}_{7/2}/{d}_{5/2}){h}_{11/2}^{2}$ is observed.

Stimulated Raman scattering metrology of molecular hydrogen

Frequency combs have revolutionized optical frequency metrology, allowing one to determine highly accurate transition frequencies of a wealth of molecular species. These progresses have only marginally benefited infrared-inactive transitions, due to their inherently weak cross-sections. Here we overcome this limitation by introducing stimulated-Raman-scattering metrology, where a frequency comb is exploited to calibrate the frequency detuning between the pump and Stokes excitation lasers. We apply this approach to the investigation of molecular hydrogen, which is a recognized benchmark for tests of quantum electrodynamics and of theories that describe physics beyond the standard model. Specifically, we measure the transition frequency of the Q(1) fundamental line of H2 around 4155 cm−1 with few parts-per-billion uncertainty, which is comparable to the theoretical benchmark of ab initio calculations and more than a decade better than the experimental state of the art. Our comb-calibrated stimulated Raman scattering spectrometer extends the toolkit of optical frequency metrology as it can be applied, with simple technical changes, to many other infrared-inactive transitions, over a 50-5000 cm−1 range that covers also purely rotational bands.

High-spin rotational bands in Nd137

We have employed the cranked Nilsson-Strutinsky and cranked Nilsson-Strutinsky-Bogoliubov methods to predict the structure of the observed high-spin rotational bands in $^{137}\mathrm{Nd}$. Our study is motivated in particular by a previous observation of a rotational band more than 4 MeV above yrast. We discuss both possible interpretations of this band and in this connection also the HD band and the terminating states expected around $I=45$.

A stimulated Raman loss spectrometer for metrological studies of quadrupole lines of hydrogen isotopologues

We discuss layout and performance of a high-resolution Stimulated Raman Loss spectrometer that has been newly developed for accurate studies of spectral lineshapes and line centre frequencies of hydrogen isotopologues and in general of Raman active transitions. Thanks to the frequency comb calibration of the detuning between pump and Stokes lasers and to an active alignment of the two beams, the frequency accuracy is at a level of 50 kHz. Over the vertical axis the spectrometer benefits from shot-noise limited detection, signal enhancement via multipass cell, active flattening of the spectral baseline and measurement times of few seconds over spectral spans larger than 10 GHz. Under these conditions an efficient averaging of Raman spectra is possible over long measurement times with minimal distortion of spectral lineshapes. By changing the pump laser, transitions can be covered in a very broad frequency span, from 50 to 5000 cm−1, including both vibrational and rotational bands. The spectrometer has been developed for studies of fundamental and collisional physics of hydrogen isotopologues and has been recently applied to the metrology of the Q(1) 1–0 line of H2.

Dimer Absorption in the Longwave Wing of the H2O Rotational Band

Dimer Absorption in the Longwave Wing of the H2O Rotational Band

Robustness of pair structures for nuclear yrast states* *Supported by the National Natural Science Foundation of China (11875134, 11875188, 12175071, 11975151, 11961141003), and the Shanghai Key Laboratory of Particle Physics and Cosmology (21DZ2271500-2)

In this study, we investigate the robustness of pair structures for nuclear yrast states, that is, whether the structures of relevant collective pairs as building blocks of different yrast states are the same. We focus on deformed and transitional nuclei and study the yrast states of Si, Cr, and Xe, whose experimental values are 2.60, 2.40, and 2.16, respectively, using the nucleon-pair approximation (NPA) and shell-model effective interactions. For each yrast state, we consider optimized pair structures to be those providing the energy minimum for this state. To find the minimum, many full NPA calculations are performed with varying pair structures, and the numerical optimization procedure of the conjugate gradient method is implemented. Our results suggest that optimized pair structures remain the same for all states within a rotational band of a deformed nucleus. Our results also suggest that after backbending, that is, changing of the intrinsic state, the structure of the S pair, which is essential to build the monopole pairing correlation, remains approximately unchanged, whereas the structures of the non-S pairs, which are essential to build the quadrupole correlation, change significantly.

Suggested icosahedral states in 208Pb

The known 6+ yrast and 12+ yrare states are recognized as members of an icosa-hedral rotational band. The 18+ state at 8813 keV is newly identified as icosahedral rotor.

Three-$$\alpha $$ configurations of the second $$J^\pi =2^+$$ state in $$^{12}$$C

We investigate geometric configurations of $\alpha$ ($^4$He nucleus) clusters in the second $J^\pi=2^+$ state of $^{12}$C, which has been discussed as a rotational band member of the second $0^+$ state, the Hoyle state. The ground and excited $0^+$ and $2^+$ states are described by a three-$\alpha$ cluster model. The three-body Schr\"odinger equation with orthogonality conditions is accurately solved by the stochastic variational method with correlated Gaussian basis functions. To analyse the structure of these resonant states in a convenient form, we introduce a confining potential. The two-body density distributions together with the spectroscopic information clarify the structure of these states. We find that main configurations of both the second $0^+$ and $2^+$ states are acute-angled triangle shapes originating from the $^8$Be($0^+$)$+\alpha$ configuration. However, the $^8$Be$+\alpha$ components in the second $2^+$ state become approximately 2/3 because the 8Be subsystem is hard to excite, indicating that the state is not an ideal rigid rotational band member of the Hoyle state.

Reflection-asymmetric mode in the structure of heavy nuclei

The properties and description of the reflection-asymmetric mode in heavy nuclei are discussed. Two approaches based on the collective octupole degree of freedom and the mass asymmetry mode are presented. Angular momentum dependence of the parity splitting, phase transition in alternating parity rotational band, stabilization of the reflection-asymmetric deformation with angular momentum increase and the rigidity of the reflection-asymmetric deformation are considered.

Parity-doublet bands in the odd- A isotones U237 and Pu239 investigated by a particle-number-conserving method based on the cranked shell model

Based on the reflection-asymmetric Nilsson potential, the parity-doublet rotational bands in odd-$A$ isotones \element{237}U and \element{239}Pu have been investigated by using the particle-number-conserving (PNC) method in the framework of the cranked shell model (CSM). The experimental kinematic moments of inertia (MOIs) and angular momentum alignments are reproduced very well by the PNC-CSM calculations. The significant differences of rotational properties between \element{237}U and \element{239}Pu are explained with the contribution of nucleons occupying proton octupole-correlation pairs of $\pi ^{2} i_{13/2}f_{7/2}$. The upbendings of moments of inertia of the parity-doublet bands in \element{237}U are due to the interference terms of alignments of protons occupying $\pi f_{7/2}$ (${1/2}$) and the high-$j$ intruder $\pi i_{13/2}$ $(1/2, 3/2)$ orbitals. The splittings between the simplex partner bands of the parity-doublet bands in both \element{237}U and \element{239}Pu result from the contribution of alignment of neutron occupying the $\nu d_{5/2}$ ($1/2$) orbital.

On the multipole mixing ratio of the 1066 keV transition from the 0.52 μs isomer of 180Hf

The nucleus 180Hf is one of the most primary examples of an axially symmetric prolate rotor. Combined with the presence of high-K isomers, spectroscopic studies can provide important information on the nature of its single-particle levels. Precise measurements are essential for constraining nuclear models and interpreting the nature of such isomeric states. In this work, the nucleus 180Hf was populated using the proton pick-up reaction 181Ta(11B,12C)180Hf at beam energy of 47 MeV at Horia Hulubei National Institute of Nuclear Physics and Engineering (IFIN-HH). The spin of the 1374 keV state and the mixing ratio of the 1066 keV transition have been measured, the latter with an increased precision compared to the previous value from literature. The presently measured spin of the 1374 keV state, currently assigned a tentative value of (41−), favors one of the two different values that were previously reported. The particular state constitutes the band-head of a rotational band in 180Hf. The measured multipolarity mixing ratio of the inter-band transition 1374→309 keV can provide important information for the testing and constraining of theoretical nuclear models used for the study of the intrinsic properties of 180Hf, as well as its neighboring isotopes.