Excited Nuclei Research Articles

High-field SABRE pulse sequence design for chemically non-equivalent spin systems.

Signal amplification by reversible exchange (SABRE) employs the non-equilibrium spin order of parahydrogen as a source of strong nuclear magnetic resonance (NMR) signal enhancement, with the objective of increasing NMR sensitivity. In SABRE, a parahydrogen molecule and a substrate form a transient polarization transfer complex. Performed within the high magnetic field of an NMR spectrometer, SABRE enables the hyperpolarization of nuclear spins without additional polarizers. Nevertheless, it requires thorough pulse sequence design. The high-field polarization transfer strategy strongly depends on the type of the spin system formed by the parahydrogen-nascent protons in the SABRE complex: chemically equivalent or non-equivalent. SABRE hyperpolarization in chemically equivalent spin systems has been the subject of considerable attention, even after being relevant only for a limited number of substrates. Efficient hyperpolarization in chemically non-equivalent complexes remained a key challenge, hindering the full potential of high-field SABRE and the ability to polarize a broader range of SABRE substrates. This work reports the multinuclear 1H-15N pulse sequence for efficient 15N hyperpolarization in chemically non-equivalent SABRE complexes. This approach relies on the simultaneous 1H and 15N radiofrequency excitation of the complex-bound nuclei with weak continuous wave magnetic fields. The proposed pulse sequence enabled the hyperpolarization of the 15N nuclei in a mixture of the antimicrobial drugs containing a 5-nitroimidazol moiety at their natural 15N isotopic abundance (0.76% of 15N polarization). Furthermore, it permitted the precise assignment of the SABRE complexes responsible for the polarization transfer.

The puzzle of suppression of nuclear level density in N ≈ Z Zn isotopes compared to N > Z

A systematic investigation of isospin dependence of nuclear level density (NLD) is performed for the Zn isotopes. Experimental level densities of 67Zn and 61Zn have been determined by analyzing the spectra of evaporated neutrons emitted from the excited 68Zn and 62Zn nuclei populated via 4He + 64Ni and 4He + 58Ni reactions, respectively. At the low excitation energies, the neutron spectra are predominantly contributed by the first-chance decay, leading to 67Zn and 61Zn as daughters for the two cases. A comparison of the present experimental data along with previously measured NLDs of 66Zn, 64Zn, and 60Zn is performed with state-of-the-art microscopic calculations. While the experimental NLDs of stable isotopes (i.e., 67Zn, 66Zn, and 64Zn) align excellently with theoretical predictions, a compelling contrast emerges for the unstable isotopes 61Zn and 60Zn, exhibiting NLDs an order of magnitude lower than predicted. The possible origins of the observed suppression of NLDs for the N ≈ Z isotopes are discussed. A significant reduction of level density for nuclei situated away from the stability line could have critical implications for the calculation of astrophysical reaction rates pertinent to heavy-element nucleosynthesis.

Giant quadrupole resonances within neutron-induced α-particle emission?

The particular conditions for the recent measurement of 91Zr(n,α)88Sr reaction cross sections at incident energies below 5.3 MeV [Phys. Rev. C 106, 064602 (2022)] as well as a previous detailed analysis of other reaction channels involving neutrons incident on 91Zr, using a consistent set of model parameters, have two main advantages. First, the close agreement between the calculated and experimentally obtained data for the incident energy associated mainly with the ground-state activation provides strong support for the α-particle optical potential involved in this analysis. Second, a further underestimation of the cross section is observed around the energy corresponding to the isoscalar giant quadrupole resonance (ISGQR), beyond any model parameter uncertainty. This underestimation is consistent with previous observations of ISGQR-like α-particle decay of excited nuclei for neutron-induced reactions in the mass range 54≤A≤98. To phenomenologically identify the ISGQR-like behavior, a comparison is made between their strengths and the ISGQR strengths measured through the (γ,α) reaction and inelastic scattering of 3He and α-particles. Additionally, an isotope effect, possibly related to the decrease in Q-value with the target-nuclei asymmetry parameter, supports the observation of a low energy-weighted sum rule (EWSR) fraction for the ISGQR-like strength function in the excited nucleus 92Zr.

Role of Brownian motion and Néel relaxations in Mössbauer spectra of magnetic liquids

The absorption cross-section of Mössbauer radiation in magnetic liquids is calculated, taking into consideration both translational and rotational Brownian motion of magnetic nanoparticles as well as stochastic reversals of their magnetization in the absence of an external magnetic field. The role of Brownian motion in ferrofluids is considered in the framework of the diffusion theory, while for the magnetorheological fluids with large nanoparticles, it is done with the aid of Langevin's approach. For stochastic rotation, we derived the equation analogous to Langevin's one and found the corresponding correlation function. In both cases, simple rotational correlation functions are obtained in the approximation of small rotations during the lifetime of the excited Mossbauer nuclei. Influence of the Néel's relaxations is considered in the framework of the Blume - Tjon model.

Determination of Photon Mass with its Main Physical Parameters Energy, Wavelength and Velocity

The excitation, transition, vibration and rotation of nuclei, atoms and molecules leading to the emission of all photons from gamma rays to radio waves as a result of the physical mechanisms responsible for excited states. The photon energy with its corresponding frequency, wavelength and distance can be determined by the main physical parameters (mass, distance, time) of the mentioned particles (Sanad, 2024). The photon mass as a particle can be determined by its main physical parameters (energy, wavelength, velocity). The determined photon mass is 2.2X10-34 kg and it is the same value of all electromagnetic radiation from gamma rays to radio waves.

THSR wave function and non-localized clustering

The main ideas to construct the THSR wave function are given, and the relation to other approaches such as the Brink-type cluster wave function approach is shown. The effect of the Pauli-forbidden states on the inter-cluster potential is described by the orthogonality condition model. The duality of the cluster structure and shell-model structure for nuclei in the ground state and in excited states is discussed. Future work on nα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n \\alpha $$\\end{document} condensate states in more complex nuclei and the formation of cluster structures in excited nuclei is outlined.

Generation of neutron spectra and emission yields from proton-induced reactions on natC and natLi targets using CR-39 detectors

Fast neutron spectrometry and dosimetry at a specified location in a compact radiation environment is difficult due to large size of the conventional neutron spectrometers. In such situations, a small-size bare CR-39 detector can be used as a neutron detector to quantify the fast neutron fraction. In the present study, CR-39 detectors were placed very close to natural lithium and carbon targets during the proton irradiations to acquire the emission neutron spectra. The neutron spectra and the ambient dose equivalents in the forward and lateral directions with respect to the incident proton beam were estimated for both targets at incident proton energies between 8 and 20 MeV. The measured neutron spectra using CR-39 detectors could identify the quasi mono-energetic neutron features from the Li(p,n) and 13C(p,n) reactions effectively. An important observation of the present study is the identification of the fast neutron signature from the 13C(p,n) system from the discrete state de-excitations of excited 14N composite nuclei. The theoretical evaluation of the neutron spectral features and relative neutron energy distributions were performed using the FLUKA: FLUktuierende KAskade, a Monte Carlo simulation package, and the estimates agreed with the experimental results for both systems. The neutron ambient dose equivalents were also estimated from the measured spectra. These neutron fluence and dose estimates at close vicinity to the target can serve as an essential basis for shielding calculations and planning the pertinent radiation protection strategies.

Spin-flip-induced quadrupole resonance in odd- A exotic atoms

We examine the possible existence of quadrupole resonances in exotic atoms containing odd-A nuclei. We find that the spin flip of the deexciting exotic particle can induce a resonance, altering the orbital angular momentum of the nucleus by one quantum. This process results in an excited nucleus with a suppression in x-ray photon emissions during the exotic atom cascade. We provide specific cases of antiprotonic atoms of stable elements where this resonance effect is expected to occur. The study of this phenomena may provide insight into the strong interaction of deeply bound antiprotonic states in the proximity of the unpaired nucleon, and serve as a tool for probing short-lived excited nuclear states. Published by the American Physical Society 2024

Magnetic dipole excitations in magic nuclei with subtracted second random-phase approximation

Magnetic dipole excitations in magic nuclei with subtracted second random-phase approximation

Systematic investigation on semi-empirical thermodynamic quantities of excited nuclei using canonical ensemble

Semi-empirical thermodynamic quantities (TQs) of 78 nuclei ranging from 43Sc to 243Pu have been systematically investigated in the temperature region below 1 MeV using the thermodynamic canonical ensemble. The latter is carried out by taking into account the experimental nuclear level density (NLD) data measured using the Oslo method for the low-excitation region below the neutron binding energy B n combining with the back-shifted Fermi gas NLD model for the excitation energy from B n to about 250 MeV. In particular, the uncertainty of the TQs propagating from the fluctuation of the experimental NLD data has been, for the first time, calculated. The results obtained indicate that the uncertainty of TQs due to the experimental NLD is incomparable with the changes caused by the nuclear structure effects. The free energy of even–even nuclei behaves differently from that of odd-A ones. The total energy in the low-temperature region below T E ≃ 0.4 − 0.6 MeV for medium-mass nuclei and T E ≃ 0.2 − 0.4 MeV for heavy-mass ones slowly varies. When temperature is from T E to 1 MeV, the total energy increases extremely faster than the increase of temperature, exhibiting the constant-temperature behavior. The entropy exhibits an abrupt change in their slope at T S ≃ 0.2 − 0.4 MeV in medium-mass nuclei and T S ≃ 0.5 − 0.6 MeV in heavy-mass ones. The existence of T E and T S has been interpreted due to the breaking of the first Cooper pair. Finally, the heat capacity shows a strongly pronounced S-shape in nuclei belonging to the rare-earth region. The temperatures defined at the center of the S − shaped heat capacities, which are known to closely relate to the critical temperature of the pairing phase transition T C, are quite close to those theoretically predicted, namely T C ≈ 0.5Δ − 0.6Δ with Δ = 12A −1/2 being the empirical pairing gap at zero temperature. The semi-empirical TQs obtained in the present work can be, therefore, a reliable data source to test and/or validate many nuclear thermodynamical models and to examine some nuclear structure properties such as pairing and deformation.

Some of the History Surrounding the Oliphant et al. Discovery of dd Fusion and an Inference of the d(d,p)t Cross Section from This 1934 Paper

A review of the flurry of papers involving deuteron beams in 1933 and 1934 reveals some aspects of historical significance. A team led by Lawrence saw several mega-electron-volt protons and neutrons from deuteron-plus-deuteron (dd) fusion in 1933 before the discovery of this process by Oliphant et al. in 1934. However, Lawrence et al. failed to notice deuteron contamination in their targets, and instead incorrectly concluded that the protons and neutrons were being emitted back to back from the breakup of the deuterons in the relevant center-of-mass frame. By observing disintegrations induced by deuteron beams incident on deuterated targets, Oliphant et al. correctly identified dd fusion proceeding through an intermediate excited 4He nucleus that broke up into either back-to-back protons and tritons or back-to-back neutrons and 3He nuclei. Here we use Oliphant et al.’s proton production rates to infer d(d,p) cross sections that are twice the known modern values. This discrepancy is likely due to our lack of knowledge of some key aspects of Oliphant et al.’s 1934 experimental setup. However, the deuterium beam energy dependence of Oliphant et al.’s d(d,p) proton production rate is clearly consistent with the quantum mechanical tunneling through the Coulomb barrier associated with the fusion of two hydrogen isotopes.

Subwavelength dielectric waveguide for efficient travelling-wave magnetic resonance imaging

Magnetic resonance imaging (MRI) has diverse applications in physics, biology, and medicine. Uniform excitation of nuclei spins through circular-polarized transverse magnetic component of electromagnetic field is vital for obtaining unbiased tissue contrasts. However, achieving this in the electrically large human body poses a significant challenge, especially at ultra-high fields (UHF) with increased working frequencies (≥297 MHz). Canonical volume resonators struggle to meet this challenge, while radiative excitation methods like travelling-wave (TW) show promise but often suffer from inadequate excitation efficiency. Here, we introduce a new technique using a subwavelength dielectric waveguide insert that enhances both efficiency and homogeneity at 7 T. Through TE11-to-TM11 mode conversion, power focusing, wave impedance matching, and phase velocity matching, we achieved a 114% improvement in TW efficiency and mitigated the center-brightening effect. This fundamental advancement in TW MRI through effective wave manipulation could promote the electromagnetic design of UHF MRI systems.

Quadrupole-octupole collective excitations in medium mass nuclei

A quadrupole-octupole axially symmetric collective model is used to describe the alternate parity bands observed in even–even medium mass nuclei. The nature of the octupole correlations in considered nuclei is ascertained from the phenomenology of the adopted model and the obtained parameters. It is found that the model parameters have a regular evolution as a function of neutron number, suggesting that the shape phase transition around N = 90 from low to well deformed shapes is also accompanied by the increase of the vibrational character for the octupole deformation. Model extrapolations are performed for various types of excited states and electromagnetic properties of measured energy levels.

Deep insights into the mechanism of isorhamnetin's anti-motion sickness effect based on photoshoproteomics.

Isorhamnetin has recently been found to exhibit a remarkable anti-motion sickness effect, yet the underlying mechanism is still unclear. Herein, network pharmacology was employed to conduct a preliminary analysis on the possible biological processes involved. Results showed that common targets were localized in membranes, mitochondria, and glutamatergic synapses. In particular, protein phosphorylation, protein serine/threonine/tyrosinase activity and signal transduction might play a role in isorhamnetin's anti-motion sickness effect. Thus, mice phosphoproteomics analysis was further performed to explore the phosphorylated protein changes in the motion sickness process. Results showed that differentially phosphorylated proteins have an effect on postsynaptic density, glutamatergic synapses and other sites and are involved in various neurodegenerative disease pathways, endocytic pathways, cAMP signaling pathways and MAPK signaling pathways. Two key differentially phosphorylated proteins in glutamatergic synapses, namely, DLGAP and EPS8, might play key roles in isorhamnetin's anti-motion sickness process. The final molecular experimental verification results from qRT-PCR and western blot analyses indicated that isorhamnetin firstly regulates glutamatergic synapses and then reduces the excitability of the vestibular nucleus through inhibiting the NMDAR1/CaMKII/CREB signaling pathway, ultimately alleviating a series of symptoms of motion sickness in mice. The findings of this study provide valuable insights and a useful theoretical basis for the application of isorhamnetin as a new anti-motion sickness food ingredient.

Influence of temperature-dependent shell corrections on the prediction of production cross sections for superheavy nuclei

In the framework of the dinuclear system model, we introduce a formula accounting for temperaturedependent shell corrections to assess their influence on the fission barrier calculations and, consequently, the survival probability of excited nuclei. Our approach considers the excitation energy’s effect on the fission barrier, a crucial aspect in determining the likelihood of a nucleus persisting. Leveraging experimental data with associated errors, we constrain the region of the shell correction damping factor. Employing this refined methodology, we predict the production cross sections for the novel superheavy element (SHE) with atomic number Z=119. Specifically, at the 54Cr(243Am,3n)294119 reaction, cross sections are anticipated to range between 3-27 femtobarns (fb), while for the 51V(248Cm,3n)296119 reaction, they are projected to span 21-180 fb. These predictions offer valuable insights into the formation dynamics of this exotic superheavy element.

Global comparison between experimentally measured isomeric yield ratios and nuclear model calculations

The level density steers transition probabilities between different states in the decay and de-excitation of excited nuclei. Reliable level density modelling is, therefore, key in describing, e.g., de-excitation of fission fragments, with implications on neutron and gamma-rays multiplicities, and also manifested in the population of isomeric states. We test six currently used level density models and the spin distribution in the level density by comparing calculations with measured isomeric yield ratios. The model calculations are performed with the TALYS code and experimental data for nuclear reactions populating spin isomers are retrieved from the EXFOR database. On average, calculations are in agreement with measured data. However, we find that the population of the high-spin state in an isomeric pair is clearly favoured in all of the six studied level density models. Further studies are then performed on the three used phenomenological level density models, to investigate the significance of their effect. We find that a significant reduction of the spin width distribution improves the agreement between calculated and experimentally observed isomeric yield ratios. This result is independent of the incident particle in the nuclear reaction. The needed reduction of the spin width distribution to comply with empirical data has, e.g., implications for studies in angular momentum generation in fission using isomeric yield rations, calculations of anti-neutrino spectra from nuclear reactors, as well as neutron and gamma-ray multiplicities in nuclear reactor calculations.

Kinematic Calculation of the 16O(γ,4α) Reaction

The event distribution over the excitation energy of a system of two α-particles (Ex) is measured for the reaction 16O(γ,4α). It is found that an intermediate excited 8Be nucleus is formed, and the channels of the 8Be nucleus ground state (GS) formation are extracted. After the separation of the GS 8Be nucleus, a broad maximum with a center at ∼ 3 MeV appears in the distribution of Ex, which may correspond to the first excited state of the 8Be nucleus. There are two possible channels for the formation of this state in the reaction - γ + 16O → α1 + 12C* → α1 + α2 + 8Be* →α1 + α2 + α3 + α4 and γ + 16O → 8Be* + 8Be* → (α1 + α2) + (α3 + α4). Each decay mode is reduced to several two-particle systems. For a comprehensive study of the channel for the formation of the first excited state of the 8Be nucleus in the 16O(γ,4α) reaction, a kinematic model for calculating the parameters of α-particles has been developed. The model is based on the assumption of a sequential two-particle decay with the formation of intermediate excited states of 8Be and 12C nuclei. For the kinematic model of the 16O(γ,4α) reaction, a graphical application was created in the Python programming language. The matplotlib library is used for data visualization. To generate random values, a set of functions from the standard random library of the Python programming language is used. Monte Carlo simulations of several distributions for one parameter with a given numerical function were performed. Several excited states of the 12C and 8Be nuclei can contribute to the reaction. The created scheme allows us to choose the relative contribution for each channel of decay, as well as the contribution of a separate level in each channel. To correctly comparison of the experimental data and the results of the kinematic calculation, the α-particles were sorted by energy in such a way that T1sort > T2sort > T3sort > T4sort. As a result of comparing the experimental and calculated data, it was determined that predominantly occurs the process γ + 16O → α1 + 12C* → α1 + α2 + 8Be* → 4α with the formation of the 12C nucleus in states with E0 = 13.3 MeV, E0 = 15.44 MeV, and the 1st excited state of the 8Be nucleus with E0 = 3.04 MeV. The conditions for the identification of α-particles in the experiment for each decay of the stage are determined.

Recent progress in configuration–interaction shell model

Since Mayer and Jensen employed the single-particle shell model to interpret the magic numbers, various microscopic nuclear models have been developed to study the nuclear force and structure. The configuration–interaction shell model (CISM), performed in truncated model space with the inclusion of the residual interaction, is one widely-used nuclear structure model. In the last decade, CISM has progressed in investigating the cross-shell excitation in exotic light nuclei, the similarity and difference in mirror nuclei, and the isomerism and seniority conservation in medium and heavy nuclei. Additionally, researchers have attempted to construct effective Hamiltonians for nuclei near [Formula: see text]Sn and [Formula: see text]Pb through a unified way in the CISM framework. In parallel, related models, including the nucleon-pair approximation (NPA) approach, the Monte Carlo shell model (MCSM), the projected shell model (PSM), the Gamow shell model (GSM), etc., have also been extensively developed and validated in the last decade. This paper reviews the recent progress in CISM and some related models.

On the Importance of Inelastic Interactions in Direct Dark Matter Searches

The approach proposed earlier for describing the scattering of weakly interacting nonrelativistic massive neutral particles off nuclei is used as the basis to derive explicit expressions for the event countingrate expected in experiments aimed at directly detecting dark matter (DM) particles. These expressions make it possible to estimate the rates in question with allowance for both elastic (coherent) and inelastic (incoherent) channels of DM particle interaction with a target nucleus. Within this approach, the effect of a nonzero excitation energy of the nucleus involved is taken into account for the first time in calculating the contribution of inelastic processes. A correlation between the excitation energy and admissible values of the kinetic recoil energy of the excited nucleus constrains substantially the possibility of detection of the inelastic channel with some nuclei. In addition to the standard model of the DM distribution in theMilkyWay Galaxy, the effect of some other models that allow significantly higher velocities of DMparticles is considered. A smooth transition from from the dominance of the elastic channel of the DM particle–nucleus interaction to the dominance of its inelastic channel occurs as the nuclear recoil energy TA grows. If the DM detector used is tuned to detecting elastic-scattering events exclusively, then it cannot detect anything in the casewhere the nuclear recoil energy turns out to be belowthe the detection threshold. As TA grows, such a detector loses the ability to see anything, since elastic processes quickly become nonexistent. Radiation associated with the deexcitation of the nucleus becomes the only possible signature of the interaction that occurred. In the case of a spin-independent interaction, the inelastic contribution becomes dominant rather quickly as TA grows, while the differential event counting rate decreases insignificantly. If a DMparticle interacts with nucleons via a spin-dependent coupling exclusively, detectors traditionally setup to detect an elastic spin-dependent DMsignal will be unable to to see anything since the signal entirely goes through the inelastic channel. It looks like the sought interactions ofDM particles may have a sizable intensity, but the instrument is unable to detect them.Therefore, experiments aimed at directly detecting DM particles should be planned in such a way that it would be possible to detect simultaneously two signals—that of the recoil energy of the nucleus involved and that of gamma rays having a specific energy and carrying away its excitation. A experiment in this implementation will furnish complete information about the DM interaction that occurred.

Signatures of elongated and compact configurations in the fusion barrier distribution of deformed nuclei

The fusion barrier distributions (BD) of 11 fusion reactions are investigated to understand the role of orientation as a degree of freedom in the fusion mechanism involving deformed nuclei, and seeking signatures of cold and hot fusion. We compared the experimentally extracted BD with those calculated using the coupled-channel method, starting from orientation-dependent folding potentials based on M3Y-Reid nucleon–nucleon interaction, with coupling to the anticipated vibrational and rotational excitations in projectile and target nuclei. We found that the signature of the hot fusion process within the compact configuration of the participating deformed nuclei is always evident in the extracted fusion barrier distribution. The different peaks appearing in the extracted BD can be individually assigned to the elongated-cold or compact-hot fusion process. The imprint of the compact-hot fusion may also manifest itself as a little increase in the value of the BD at certain related energy, compared with the preceding and succeeding values.