Experimental Energy Spectra Research Articles

Octupole correlations in stable nucleus 153Eu within reflection-asymmetric particle rotor model

Abstract The observed low-lying K=5/2± positive- and negative-parity bands in the stable nucleus 153Eu are investigated by the reflection-asymmetric triaxial particle rotor model. The experimental energy spectra, the energy staggering parameters, as well as the intraband E2 and M1 transition probabilities are well reproduced. It is found that the calculated interband B(E1) values depend sensitively on the octupole deformation parameter β30, although the energy spectra and intraband E2 and M1 transitions can be reproduced without the octupole degree of freedom. The observed enhanced E1 transition probabilities can be reproduced with β30=0.05. The detailed analysis of the intrinsic wave functions shows these nearly degenerate positive- and negative-parity bands are built on two individual proton configurations, i.e., dominated by πg9/2[Ω=5/2] and πh11/2[Ω=5/2], respectively, which differs from the parity doublet bands built on a single parity-mixed configuration.

Shapes and structure for the lowest states of the 42,44Ca isotopes

The shape and the associated dynamics of the 42,44Ca isotopes are investigated within the Bohr-Mottelson Model and the Covariant Density Functional Theory for the presence of the shape coexistence and mixing phenomena. The corresponding experimental energy spectrum and most of the electromagnetic transitions are well reproduced only by taking into account such phenomena. New possible developments of the models are indicated where improvements in agreement with the experimental data are needed.

Indications of electron emission from the deuteron-deuteron threshold resonance

Electron emission in the deuteron-deuteron reaction supporting existence of the single-particle threshold resonance in He4 has been observed for the first time. The measured electron energy spectrum and the electron-proton branching ratio agree very well with the assumed electron-positron pair creation decay of the 0+ resonance state to the ground state and the detailed Monte Carlo simulations of the experimental energy spectrum. Published by the American Physical Society 2024

On the missing single collision peak in low energy heavy ion scattering

We present experimental and simulation data on the oblique angle scattering of heavy Sn ions at 14keV energy from a Mo surface. The simulations are performed with the binary collision approximation codes TRIM, TRIDYN, TRI3DYN, SDTrimSP, and IMSIL. Additional simulations were performed in the molecular dynamics framework with LAMMPS. Our key finding is the absence of an expected peak in the experimental energy spectrum of backscattered Sn ions associated with the pure single collision regime. In sharp contrast to this, however, all simulation codes we applied do show a prominent single collision signature both in the energy spectrum and in the angular scatter pattern. We discuss the possible origin of this important discrepancy and show in the process, that widely used binary collision approximation codes may contain hidden parameters important to know and to understand.

Comparative study on gamma-ray detectors for in-situ ocean radiation monitoring system

Large-sized crystals and state-of-the-art photosensors are desirable to cope with low environmental radioactivity (e.g., 1–2 Bq∙m−3137Cs in surface seawater) for homeland security purposes. We compared the performances of two different gamma-ray detector assemblies, GAGG crystal + silicon photomultiplier (SiPM) and NaI(Tl) crystal + photomultiplier tube, for our mobile in-situ ocean radiation monitoring system. We performed energy calibration, followed by water tank experiments with varying the depth of a137Cs point source. Experimental energy spectra were compared with MCNP-simulated spectra with identical setup and the consistency was validated. We finally assessed the detection efficiency and minimum detectable activity (MDA) of the detectors. Both GAGG and NaI detectors exhibited favorable energy resolutions (7.98 ± 0.13% and 7.01 ± 0.58% at 662 keV, respectively) and MDAs (33.1 ± 0.0645 and 13.5 ± 0.0327 Bq∙m−3 for 24-h 137Cs measurement, respectively). Matching the geometry of the GAGG crystal with that of the NaI crystal, the GAGG detector outperformed the NaI detector. The results demonstrated that the GAGG detector is potentially advantageous over the NaI detector in detection efficiency and compactness.

Combining MD-LAMMPS and MC-McChasy2 codes for dislocation simulations of Ni single crystal structure

The unique capability of the new version of the McChasy code (called McChasy2) is to provide the possibility to simulate experimental energy spectra delivered by Rutherford Backscattering Spectrometry in channeling direction (RBS/C) using large atomic structures (ca. 108 atoms).Ni-based alloys are nowadays one of the most studied and promising materials that can be used in the power generation sector and in general for high-temperature applications because of their radiation resistance and proof against harsh environmental conditions.In this work, we present recent results of investigations regarding simulations of extended structural defects (edge dislocations and loops) developed in the directions typically observed in the fcc systems that are formed inside nickel-based single-crystal alloys. The extended defect models are created using ATOMSK and the Molecular Dynamics (MD)-LAMMPS thermalization process. The models are then used to create virtual samples and fit experimental RBS/C spectra.

Reaction dynamics and in-medium nucleon-nucleon cross section with C12+H1 at 95 MeV/nucleon

Reaction dynamics and effective in-medium nucleon-nucleon $(NN)$ cross section are studied, using the antisymmetrized molecular dynamics (AMD) model with one of the simplest heavy ion collisions, $^{12}\mathrm{C}+^{1}\mathrm{H}$. The roles of different stochastic processes are studied, which are installed in the original AMD. One is the diffusion process as a part of the quantum fluctuation originated from the Fermi motion during the time evolution of the wave packets in the mean field (AMD/D). The second is a coalescence treatment for light clusters with $A\ensuremath{\le}8$ (AMD/D-COALS). The third is the collision process, installed in AMD with different form of the in-medium $NN$ cross sections. These different processes are examined, using the experimental angular distributions and energy spectra of light charged particles and intermediate mass fragments. The effective in-medium $NN$ cross sections are evaluated from the simulated AMD events and compared with the experimentally extracted values. A good agreement is obtained between the AMD values from the $^{12}\mathrm{C}$ $+$ $^{1}\mathrm{H}$ reaction at 95 MeV/nucleon and the experimental results for nuclear matter.

Emissions of Hydrogen Isotopes from the Nuclear Muon Capture Reaction in natSi

The energy spectra of protons, deuterons and tritons produced by the nuclear muon capture reaction in natSi were measured at the M1 beam line of Muon Science Innovative Channel (MuSIC) in Research Center for Nuclear Physics (RCNP) using a counter telescope consisting of a Si detector and a CsI(Tl) scintillation detector. The measured energy spectra were consistent with the previous ones. The experimental energy spectra were compared with theoretical model calculations using the Particle and Heavy Ion Transport code System (PHITS). In PHITS, both the dynamical and statistical processes in the nuclear muon capture reaction are described by the Quantum Molecular Dynamics (QMD) or the modified QMD and the Generalized Evaporation Model (GEM), respectively. The PHITS simulation reproduced generally well the measured proton spectrum at emission energies below 20 MeV, while underestimation was seen at emission energies above 20 MeV. The PHITS simulation underestimates remarkably the measured energy spectra of light complex particles (deuterons, tritons, and alpha particles) in the high energy region.

Pushing multiphoton resonant ionization of the argon atom to the low-intensity regime

Resonance-enhanced multiphoton ionization process of the argon atom by an 800-nm 30-fs linearly polarized laser field is investigated at intensities range from 1.1 to $4.55\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$. At $4.55\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ intensity the experimental photoelectron energy spectrum is in a good agreement with the time-dependent Schr\"odinger equation (TDSE) calculation where the double structure originating from dressed $4p\ensuremath{-}4d$ coupled transition is clearly identified. At lower intensity of $1.1\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$, the resonant ionization process via the $4f$ state is observed, however, the expected peak (jet) at ${90}^{\ensuremath{\circ}}$ in the photoelectron angular distribution from the zeroth order above threshold ionization, has vanished completely. Such behavior is attributed to the destructive interference phenomenon in the coherent contributions of different partial waves of the photoelectron, namely, $\ensuremath{\epsilon}d$ and $\ensuremath{\epsilon}g$ states, and has been confirmed in our TDSE calculations.

Characterisation of a 1[formula omitted] LaBr2.85Cl0.15:Ce crystal for [formula omitted]-rays up to 4.4 MeV

This communication reports about complete characterisation of a small volume 1′′×1′′ cylindrical LaBr2.85 Cl0.15:Ce crystal supplied by Scionix Inc. for γ-rays up to 4.4 MeV. The various properties of the crystal studied, are, linearity of response for γ-rays, energy resolution up to 4.4 MeV, timing resolutions, quantification of internal activity, and full energy detection efficiencies for γ-rays from 276 to 4439 keV. Monte Carlo simulation toolkit GEANT4 was used to carry out realistic simulations of the detector’s response for γ-rays. Experimental γ-ray energy spectrum was reproduced in the simulations to estimate the full energy detection efficiency for γ-rays and compared with the measured value. We have obtained energy resolution of ∼3.8% at 662 keV using 2′′ ET-9266B PMT biased at −800 V with the energy signal drawn from the 8th dynode. Timing resolutions of 422 and 364 ps were obtained using 2′′ ET-9807B PMT for 22Na and 60Co, respectively. To the best of our knowledge, this is the first report on the performance of the newly manufactured and marketed LBC crystal. We do not find any significant difference in the performance of LBC from that of a standard Lanthanum Bromide (Ce activated) crystal of similar volume.

The effect of neutrons on the background of HPGe detectors operating deep underground

The background of a High Purity Germanium (HPGe) detector measured in a deep underground laboratory was investigated analytically and by Monte Carlo simulations using the GEANT4 toolkit. Contributions of different background sources to the experimental γ-ray background were determined. Namely, contribution of radionuclides in materials of the detector and around the detector, neutrons produced by (α, n) reactions due to presence of radionuclides in rock and concrete and by spontaneous fission of mainly 238U, and finally, cosmic rays with neutron generation. The simulation, including radionuclides in the material, was in a good agreement with the experiment. At the same time, neutron and muon induced spectra were simulated. The radiation coming from the presence of members of the 238U, and 232Th decay series, and 40K in the detector parts and the laboratory walls contribute to the continuum of the experimental spectrum at the level of around 94%. According to simulations, the contribution of muon events to the experimental energy spectrum was below 1% and it was confirmed that muon induced spectra are about three orders of magnitude lower than the experimental one. The comparison of integral count rates of the experimental spectrum with the simulated spectrum induced by neutrons showed that about 6% of the measured background continuum originated from neutron reactions. Fast neutrons contributed more to the background (at around 65%) than thermal neutrons. Despite only a 6% share of neutron contributions in the total γ-ray background, they contributed mainly to the lower continuum of the spectrum up to 250 keV, which is a region of interest for potential low mass weakly interacting massive particle (WIMP) dark matter interactions. In addition, they interact with the detector and the shield by inelastic scattering and induce unwanted γ-rays. Neutron capture, elastic and inelastic scattering were simulated separately as well. It was found that inelastic scattering is the major contributor to the spectrum induced by neutrons. The effect of neutrons on the background of the HPGe detector operating underground, such as Obelix, is manifested mainly by their contribution to the continuum up to 1 MeV, especially in the lower part up to 500 keV. Thus, neutrons are an important background component in deep underground laboratories, too. Possible detector optimization is also discussed.

Evolution of the chiral rotation mode in rhodium isotopes

Self-consistent solutions for the chiral rotation in the rhodium isotopes $^{102--107}\mathrm{Rh}$ are obtained within the three-dimensional tilted axis cranking covariant density functional theory. The orientation of angular momenta is determined self-consistently by minimizing the total Routhian surface calculations with respect to the azimuth angle $\ensuremath{\varphi}$ and polar angle $\ensuremath{\theta}$ for a given rotational frequency. It is found that when neutrons are added the critical rotational frequency ${\ensuremath{\omega}}_{\text{crit}}$ of the appearance of chiral aplanar rotation decreases, which can be attributed to the neutrons in $(gd)$ shells having smaller and larger angular momentum components along the short and medium axes, respectively. The theoretical results agree well with the experimental energy spectra, electromagnetic transition probabilities, as well as the kinetic and dynamic moments of inertia.

Interpretation of enhanced electric dipole transitions in Br73 by the reflection-asymmetric triaxial particle rotor model

The recently observed positive and negative parity bands in $^{73}\mathrm{Br}$ are investigated by the reflection-asymmetric triaxial particle rotor model. The experimental energy spectra as well as the electric transition probabilities $B(E1), B(E2)$, and the ratio $B(E1)/B(E2)$ are well reproduced by the theoretical calculations. It is found that the enhanced interband $E1$ transitions between the opposite-parity bands, a crucial evidence for octupole correlations, are mainly contributed by the intrinsic single-particle electric dipole matrix elements.

A new radionuclide identification method for low-count energy spectra with multiple radionuclides

Radionuclide identification is to recognize the radionuclides in the environment by analyzing the energy spectrum. Rapid and accurate identification is important for nuclear security. Current radionuclide identification methods based on traditional peak search require background subtraction. As a result, they have difficulties to deal with complex situations in practical applications such as low-count energy spectrum and mixed nuclides. In this paper, we propose a new radionuclide identification method with a feature enhancer and a one-dimensional neural network. The training dataset in this method is from simulated data generated by Geant4. By preprocessing the input energy spectrum data through the feature enhancer and extracting the nonlinear information through the neural network, this approach performs well on experimental energy spectra even at low count. The method also shows a high recognition accuracy and little misjudgments when dealing with mixed radionuclides spectra. Due to its good performance in identifying mixed nuclides and low-count spectra, the method has been deployed in portable instrument for radionuclide identification in real-time measurement.

Possible existence of multiple wobbling modes in A≈60 nuclei

The nuclear multiple wobbling modes in $A\ensuremath{\approx}60$ mass region are explored by the adiabatic and configuration-fixed constrained covariant density functional theory for nickel isotopes for the first time. The potential-energy curves and deformation parameters $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ of the ground and excited states of $^{57\text{--}62}\mathrm{Ni}$ are obtained to search for the possible wobbling candidates. It is shown that there are suitable triaxial deformations and high-$j$ particle(s) or hole(s) configurations in $^{57\text{--}62}\mathrm{Ni}$, which are beneficial to the appearance of wobbling motion, including the simple, longitudinal and transverse modes. Moreover, possible multiple wobbling motions based on different high-$j$ configurations might coexist in one single nucleus, which provides a promising basis for future experiments to find wobbling bands in the $A\ensuremath{\approx}60$ mass region. Finally, taking the nucleus $^{62}\mathrm{Ni}$ as an example, the experimental energy spectra, the angular momentum components, and the azimuthal plots are investigated by the combination of the covariant density functional theory and quantum particle rotor model. The transverse wobbling mode is suggested in this nucleus.

Influence of Model Assumptions on Radial Flow Investigations in Heavy-Ion Collisions

An effective way for the investigation of nuclear matter under the extreme conditions of high density and temperature is the study of nuclear fragmentation, realized in intermediate-energy heavy-ion collisions. The potential energy accumulated in the compression zone of the collision is converted into collective flow of matter in the later stages of the reaction. During the expansion of the system, fragments are formed in a clusterization process. In the final stage of the reaction, the fragments are moving along Coulomb trajectories and may deexcite by particle emission or secondary break-up.In order to verify the influence of the collective energy on the experimental energy spectra and extract quantitative information on the thermal and collective components, a model simulation was developed. In this procedure, the evolution of the disintegrating system in a multifragmentation process was described after the freeze-out stage with a Monte-Carlo approach. A reconstruction procedure for the fragment kinetic energies has shown the possibility to obtain the thermal and collective components from measured fragment spectra. In the present work, we scrutinize the model simulation for the evolution of the disintegrating system by testing the sensitivity of the collective expansion energy extraction on the model assumptions concerning the freeze-out characteristics, such as the size and shape of the freeze-out volume. Furthermore, thermal aspects of the early stage of the expansion are tested with an examination of the relationship between the assumption of the degree of thermalization of the emitting source and the extracted value of the collective energy.

Large-scale nuclear shell-model calculations of isotopes in the southwest region of 208Pb

Abstract Large-scale nuclear shell-model calculations are performed in the neutron- and proton-deficient Pt, Au, Hg, and Tl isotopes ($Z < 82$ and $N \le 126$) near $^{208}$Pb. All the single-particle levels in the one-major shells, six neutron ($2p_{1/2}$, $1f_{5/2}$, $2p_{3/2}$, $0i_{13/2}$, $1f_{7/2}$, and $0h_{9/2}$) orbitals and five proton ($2s_{1/2}$, $1d_{3/2}$, $0h_{11/2}$, $1d_{5/2}$, and $0g_{7/2}$) orbitals are considered. For an effective two-body interaction, one set of the multipole pairing, quadrupole–quadrupole interactions is employed for all the nuclei considered. These phenomenological interactions are determined to reproduce the experimental energy spectra. Some of the isomeric states are analyzed in terms of the shell-model configurations. Octupole correlated states are discussed in terms of a collective octupole excitation on top of each shell model state.

Towards isolated attosecond electron bunches using ultrashort-pulse laser-solid interactions

We investigate MeV-level attosecond electron bunches from ultrashort-pulse laser-solid interactions through similarities between experimental and simulated electron energy spectra. We show measurements of the bunch duration and temporal structure from particle-in-cell simulations. The experimental observation of such bunches favors specular reflection direction when focusing the laser pulse onto a subwavelength boundary of thick overdense plasmas at grazing incidence. Particle-in-cell simulation further reveals that the attosecond duration is a result of ultra-thin (sim tenth of a micron) gaps of zero electromagnetic energy density in the modulated reflected radiation, while the bunching (locally peaked electron concentration) comes from the highly-directional electron angular distribution acquired by the electrons in a grazing incidence setup. To isolate a single electron bunch, we perform simulations using 1-cycle laser pulses and analyze the effect of carrier-envelop phase with particle tracking. The duration of the electron bunch can be further decreased by increasing the laser intensity and the focal spot size, while its direction can be changed by tuning the preplasma density gradient.

Description of the superdeformed rotational band in Ca40 with a shell-model-like approach

The superdeformed rotational band in $^{40}\mathrm{Ca}$ is investigated in the framework of a shell-model-like approach based on cranking covariant density functional theory, in which the pairing correlations are treated with conserved particle number. A superdeformed state is obtained at the deformation $(\ensuremath{\beta},\phantom{\rule{0.16em}{0ex}}\ensuremath{\gamma})=(0.70,\phantom{\rule{0.16em}{0ex}}{9}^{\ensuremath{\circ}})$ even though the depth of the superdeformation minimum is only about 0.2 MeV. With increasing rotational frequency, the potential around the superdeformed minimum becomes deeper. This indicates that the superdeformed state becomes more stable with increasing rotational frequency. Besides, the experimental data are well reproduced by the theoretical calculations with pairing correlations. Pairing correlations are important for the states with $I\ensuremath{\le}10\ensuremath{\hbar}$ in the superdeformed rotational band of $^{40}\mathrm{Ca}$ in reproducing the experimental energy spectrum and transition quadrupole moments.

Transition from Geostrophic Flows to Inertia–Gravity Waves in the Spectrum of a Differentially Heated Rotating Annulus Experiment

Abstract Inertia–gravity waves (IGWs) play an essential role in the terrestrial atmospheric dynamics as they can lead to energy and momentum flux when propagating upward. An open question is to what extent IGWs contribute to the total energy and to the flattening of the energy spectrum observed at the mesoscale. In this work, we present an experimental investigation of the energy distribution between the large-scale balanced flow and the small-scale imbalanced flow. Weakly nonlinear IGWs emitted from baroclinic jets are observed in the differentially heated rotating annulus experiment. Similar to the atmospheric spectra, the experimental kinetic energy spectra reveal the typical subdivision into two distinct regimes with slopes k−3 for the large scales and k−5/3 for the small scales. By separating the spectra into the vortex and wave components, it emerges that at the large-scale end of the mesoscale the gravity waves observed in the experiment cause a flattening of the spectra and provide most of the energy. At smaller scales, our data analysis suggests a transition toward a turbulent regime with a forward energy cascade up to where dissipation by diffusive processes occurs.