De-excitation Of States Research Articles

Evidence for spherical-oblate shape coexistence in Tc87

Excited states in the neutron-deficient nucleus Tc87 have been studied via the fusion-evaporation reaction Fe54(Ar36,2n1p)Tc87 at 115 MeV beam energy. The AGATA γ-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of γ rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc87 were identified by comparing γ-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in Tc87 is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.1 MoreReceived 10 September 2021Revised 24 January 2022Accepted 23 March 2022DOI:https://doi.org/10.1103/PhysRevC.106.034304Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectromagnetic transitionsLow & intermediate energy heavy-ion reactionsNuclear structure & decaysNucleon distributionTransfer reactionsProperties59 ≤ A ≤ 89Nuclear Physics

The formation of atomic oxygen and hydrogen in atmospheric pressure plasmas containing humidity: picosecond two-photon absorption laser induced fluorescence and numerical simulations

Atmospheric pressure plasmas are effective sources for reactive species, making them applicable for industrial and biomedical applications. We quantify ground-state densities of key species, atomic oxygen (O) and hydrogen (H), produced from admixtures of water vapour (up to 0.5%) to the helium feed gas in a radio-frequency-driven plasma at atmospheric pressure. Absolute density measurements, using two-photon absorption laser induced fluorescence, require accurate effective excited state lifetimes. For atmospheric pressure plasmas, picosecond resolution is needed due to the rapid collisional de-excitation of excited states. These absolute O and H density measurements, at the nozzle of the plasma jet, are used to benchmark a plug-flow, 0D chemical kinetics model, for varying humidity content, to further investigate the main formation pathways of O and H. It is found that impurities can play a crucial role for the production of O at small molecular admixtures. Hence, for controllable reactive species production, purposely admixed molecules to the feed gas is recommended, as opposed to relying on ambient molecules. The controlled humidity content was also identified as an effective tailoring mechanism for the O/H ratio.

De-Excitation of Excited States in a Nitrogen Switch After Discharge

The de-excitation of nitrogen excited states after spark gap discharge was investigated with time-resolved optical emission spectroscopy method. Recombination of ionized particles was experimentally proved less than several tens microseconds. After the recombination process, it was shown that atomic nitrogen in ground state [N(4S)] and molecular nitrogen in first excited state [N2( $\text{A}^{3} {\Sigma }_{u}^{+}$ )] was long-lived particles (metastable state) after gas discharge. Characteristics of decay for N(4S) and [N2( $\text{A}^{3} {\Sigma }_{u}^{+}$ )] were studied, and their lifetime and decay of density were estimated in this paper. Peculiar unexponential decay of N2( $\text{A}^{3} {\Sigma }_{u}^{+}$ ) showed there was reproduction process of N2( $\text{A}^{3} {\Sigma }_{u}^{+}$ ) after gas discharge. N(4S) could be the source for reproduction process under their mechanism of three-body recombination. Low ionization energy and high ionization collision cross section of N2( $\text{A}^{3} {\Sigma }_{u}^{+}$ ) make it a possible factor limiting the switch recovery. The de-excitation of metastable states opens novel perspectives for understanding the recovery of gas switch.

Excitation-tailored dual-color emission of manganese(II)-doped perovskite nanocrystals

Manganese(II)-doped perovskite nanocrystals with superior dual-color light emission properties are promising for optoelectronic applications. Here, we report that the emission color of these nanocrystals can be tailored by continuous-wave excitation because of the saturation of dopant emission at a record low light density (∼10 mW/cm2). By detuning the repetition rates of excitation laser sources, we show that the bottleneck of exciton-manganese(II) energy transfer caused by the imbalanced excitation and deexcitation of 4T1 states is the primary mechanism underlying the emission saturation properties. Such a dual-color luminescence tunable by weak excitation is promising for uses in potential applications such as luminescent solar concentrators, light intensity sensors, anti-counterfeit printing, and photo-switchable image markers.

Structure of Be13 studied in proton knockout from B14

The neutron-unbound isotope Be-13 has been studied in several experiments using different reactions, different projectile energies, and different experimental setups. There is, however, no real consensus in the interpretation of the data, in particular concerning the structure of the low-lying excited states. Gathering new experimental information, which may reveal the Be-13 structure, is a challenge, particularly in light of its bridging role between Be-12, where the N = 8 neutron shell breaks down, and the Borromean halo nucleus Be-14. The purpose of the present study is to investigate the role of bound excited states in the reaction product Be-12 after proton knockout from B-14, by measuring coincidences between Be-12, neutrons, and gamma rays originating from de-excitation of states fed by neutron decay of Be-13. The Be-13 isotopes were produced in proton knockout from a 400 MeV/nucleon B-14 beam impinging on a CH2 target. The Be-12-n relative-energy spectrum d sigma/dE(fn) was obtained from coincidences between Be-12(g.s.) and a neutron, and also as threefold coincidences by adding gamma rays, from the de-excitation of excited states in Be-12. Neutron decay from the first 5/2(+) state in Be-13 to the 2(+) state in Be-12 at 2.11 MeV is confirmed. An energy independence of the proton-knockout mechanism is found from a comparison with data taken with a 35 MeV/nucleon B-14 beam. A low-lying p-wave resonance in Be-13(1/2(-)) is confirmed by comparing proton- and neutron-knockout data from B-14 and Be-14.

Deexcitation spectroscopy of strongly interacting Rydberg gases

We present experimental results on the controlled de-excitation of Rydberg states in a cold gas of Rb atoms. The effect of the van der Waals interactions between the Rydberg atoms is clearly seen in the de-excitation spectrum and dynamics. Our observations are confirmed by numerical simulations. In particular, for off-resonant (facilitated) excitation we find that the de-excitation spectrum reflects the spatial arrangement of the atoms in the quasi one-dimensional geometry of our experiment. We discuss future applications of this technique and implications for detection and controlled dissipation schemes.

Spontaneous Emission inside a Hyperbolic Metamaterial Waveguide

The ability to control the rate of spontaneous emission via the design of nanostructured materials with appropriate electromagnetic properties is important in the development of novel fast sources of incoherent illumination, single photon emitters for quantum optical applications, laser physics and de-excitation of electronic states leading to photodegradation in organic materials. Here, for an emitter placed inside a hyperbolic metamaterial slab of finite thickness comprised of an array of gold nanorods, we experimentally demonstrate an enhancement of the fluorescence coupled to the waveguided plasmon-polariton modes of the metamaterial. We show that fluorescence properties in such finite-size metamaterial design behave differently from commonly studied infinite metamaterials or when the emitters are placed near the metamaterial interface. The emitters inside the metamaterial waveguide exhibit an almost 50-fold reduction of their lifetime, whereas a much smaller reduction (a factor of 2-3) is observed fo...

Neutron-capture rates for explosive nucleosynthesis: the case of 68Ni(n, γ)69Ni

Neutron-capture reactions play an important role in heavy element nucleosynthesis, since they are the driving force for the two processes that create the vast majority of the heavy elements. When a neutron capture occurs on a short-lived nucleus, it is extremely challenging to study the reaction directly and therefore the use of indirect techniques is essential. The present work reports on such an indirect measurement that provides strong constraints on the 68Ni(n, γ)69Ni reaction rate. This is done by populating the compound nucleus 69Ni via the β decay of 69Co and measuring the γ-ray deexcitation of excited states in 69Ni. The β-Oslo method was used to extract the γ-ray strength function and the nuclear level density. In addition the half-life of 69Co was extracted and found to be in agreement with previous literature values. Before the present results, the 68Ni(n, γ)69Ni reaction was unconstrained and the purely theoretical reaction rate was highly uncertain. The new uncertainty on the reaction rate based on the present experiment (variation between upper and lower limit) is approximately a factor of 3. The commonly used reaction libraries JINA-REACLIB and BRUSLIB are in relatively good agreement with the experimental rate. The impact of the new rate on weak r-process calculations is discussed.

Constraining the rp-process by measuring 23Al(d,n)24Si with GRETINA and LENDA at NSCL

The 23 Al(p, γ)24 Si stellar reaction rate has a significant impact on the light-curve emitted in X-ray bursts. Theoretical calculations show that the reaction rate is mainly determined by the properties of direct capture as well as low-lying 2+ states and a possible 4+ state in 24 Si. Currently, there is little experimental information on the properties of these states.In this proceeding we will present a new experimental study to investigate this reaction, using the surrogate reaction 23 Al(d,n) at 47 AMeV at the National Superconducting Cyclotron Laboratory (NSCL). We will discuss our new experimental setup which allows us to use full kinematics employing the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) to detect the γ-rays following the de-excitation of excited states of the reaction products and the Low Energy Neutron Detector Array (LENDA) to detect the recoiling neutrons. The S800 was used for identification of the 24 Si recoils. As a proof of principle to show the feasibility of this concept the Q-value spectrum of 22 Mg(d,n)23 Al is reconstructed.

Extended Use of Coulomb’s Law in Relation to Established Laws within Electromagnetism

The competence of the basically electrostatic Coulomb's Law has historically been assumed to be restricted to pure electrostatics. As soon as electric charges were studied in motion, new sets of laws were introduced to explain the electromagnetic forces that are impelled by the motion. Among these new laws are Neumann's law of induction, Grassmann's force law, Lorentz' force law, and Ampere's force law. Furthermore, the difficulties in explaining the nature of light have given rise to the so-called wave-particle paradox. 1997 was the first year of the public circulation of research results that succeeded in showing that the basic force behind cases involving electricity or, more precisely, electromagnetism, can be derived from electrostatics. The aim of this article is to unify the results of existing theoretical research that discusses problems inherent within the prevailing standpoint on electromagnetism. In this paper, the conflict between the Lorentz Force Law and Ampere's Law is explored. Simultaneously, an alternative based strictly on electrostatics is closely examined. The very limited interest in this field of research, however, makes the amount of existing papers rather limited. The present study's new intervention is as follows: The so-called Ampe re forces between collinear currents, as in Ampere's bridge and in exploding wires, have been explained to be due to electrostatics, provided that the propagation delay dependant on the motion of charges is correctly taken into account. The Lorentz Force Law fails in this case. Additionally, electromagnetic induction can be explained by applying electrostatics, whereas the induction law fails. Light on the orbit electrons in the atoms involved in excitation and de-excitation of states can be explained using Coulomb's law (this has been widely disputed within science). The appearance of light at an atom hit by electromagnetic radiation can be shown to constitute a case of electromagnetic induction. The present study's conclusion is therefore that Coulomb's law is the only necessary force law within electromagnetism.

New model of the cascade gamma decay of neutron resonances for practitioners: Basic concepts and attainable precision

A model-free extraction of level densities and radiative strength functions for cascade dipole gamma transitions that has been performed to date revealed the need for developing a new model of the deexcitation of compound states of nuclei having arbitrary masses and belonging to any type over a broad range of their excitations. Such a model should provide a practical means for determining thresholds for the breaking of nucleon Cooper pairs below the neutron binding energy, the relationship between the level densities for excitations of the quasiparticle and phonon types, and the emission widths for nuclear-reaction products in excited nuclei. From an analysis of data on the intensities of two-step cascades initiated by radiative thermal-neutron capture, it can be seen that the highest precision in describing available experimental spectra is reached upon taking into account the breaking of three to four Cooper pairs of nucleons.

Influence of gas discharge parameters on emissions from a dielectric barrier discharge excited argon excimer lamp

A dielectric barrier discharge excited neutral argon (Ar I) excimer lamp has been developed and characterised. The aim of this study was to develop an excimer lamp operating at atmospheric pressure that can replace mercury lamps and vacuum equipment used in the sterilisation of medical equipment and in the food industry. The effects of discharge gas pressure, flow rate, excitation frequency and pulse width on the intensity of the Ar I vacuum ultraviolet (VUV) emission at 126 nm and near infrared (NIR) lines at 750.4 nm and 811.5 nm have been investigated. These three lines were chosen as they represent emissions resulting from de-excitation of excimer states that emit energetic photons with an energy of 9.8 eV. We observed that the intensity of the VUV Ar 2 * excimer emission at 126 nm increased with increasing gas pressure, but decreased with increasing excitation pulse frequency and pulse width. In contrast, the intensities of the NIR lines decreased with increasing gas pressure and increased with increasing pulse frequency and pulse width. We have demonstrated that energetic VUV photons of 9.8 eV can be efficiently generated in a dielectric barrier discharge in Ar.

Deexcitation of one-dimensional Rydberg atoms with a chirped train of half-cycle pulses

A protocol for deexcitation of one-dimensional high Rydberg states with the use of a chirped train of half-cycle pulses is given. It is found that the parameters of the efficiently deexciting train are directly related to the phenomenon of the dynamical stabilization of the initial state. Finally, numerical calculations are presented to demonstrate the efficiency of the protocol. The protocol allows to deexcite Rydberg atoms to states lying just above the ground one.

Searches for effects of fundamental-symmetry violation in isomeric nuclear states

The results of broad searches for schemes that are convenient for observing effects of time-inversion-invariance violation (T violation) simultaneously with parity violation (PT violation) in electromagnetic transitions in nuclei are presented. The main problems in observing such effects are discussed. A scheme that seems one of the most promising for this and which relies on measuring the linear polarization of gamma radiation accompanying the deexcitation of isomeric states of nuclei that were oriented by a magnetic field at ultralow temperatures is highlighted.

Accelerated recombination due to resonant deexcitation of metastable states

In a recombining plasma the metastable states are known to accumulate population thereby slowing down the recombination process. We show that an account of the doubly excited autoionizing states, formed due to collisional recombination of metastable ions, results in a significant acceleration of recombination. A fully time-dependent collisional-radiative (CR) modeling for stripped ions of carbon recombining in a cold dense plasma demonstrates an order of magnitude faster recombination of He-like ions. The CR model used in calculations is discussed in detail.

Rupture luminescence from natural fibers

Fibers of cotton and wool, and samples of paper, have been ruptured in tension in vacuum and in air, and give detectable luminescence in the visible range. All have a common emission peak at around 2.0 eV, which is ascribed to the deexcitation of states excited by the rupture of organic chain molecule bonds. Rubber bands give stronger emission in air, but no emission in vacuum, suggesting the material breaks only at weak interchain bonds. Mohair, cat, and horse hair also give emission in air. The phenomena reveal effects that would occur widely in nature.

Lasers as a bridge between atomic and nuclear physics

This paper reviews the application of visible and ultraviolet laser radiation to several topics in low-energy nuclear physics. We consider laser-induced nuclear anti-Stokes transitions, laser-assisted and laser-induced internal conversion, and the electron bridge and inverse electron bridge mechanisms as tools for deexcitation and excitation of low-lying nuclear isomeric states. A study of the anomalously low-lying nuclear isomeric states (in the case of the 229Th nucleus) is presented in detail.

Limits on Nuclear Gamma‐Ray Emission from Orion

The discovery of γ-ray line emission in the 3-7 MeV range from the Orion complex was recently reported. The observed Compton Telescope (COMPTEL) spectrum suggested that the emission results from the de-excitation of excited states of 12C and 16O. We report on a search for these lines using the Oriented Scintillation Spectroscopy Experiment (OSSE) on the Compton Gamma Ray Observatory (CGRO) during a 5 week observation in 1995 from April to June. The OSSE detectors were pointed midway between the Orion A and B radio sources in three different viewing configurations. We find no compelling evidence for line emission near 4.4 or 6.1 MeV. The sensitivity of the OSSE measurements is dependent on the widths of the reported C and O lines and on the source location and spatial extent. A point source at the flux level reported by COMPTEL and located on-axis would have been detected by OSSE at ~7 σ and ~5 σ levels of confidence for narrow and broad lines, respectively. A spatially distributed source of the same strength with a distribution following the intense CO emission localized around Orion A and Orion B would have been detected by OSSE at ~3.5 σ and ~2.5 σ, respectively. Thus, these OSSE observations require that any γ-ray line source must be even more extended to be consistent with the reported COMPTEL intensity.

Numerical Simulation for Metastable States' Deexcitation in Electron Beam Evaporation Process

A direct simulation Monte Carlo (DSMC) method was modified in order to analyze the evaporation process in atomic vapor laser isotope separation (AVLIS), whereby energy transfer between discrete energy levels of metastable states and continuous energy level of translation took place. The atomic excitation temperatures of gadolinium atom were calculated for the model in five low-lying states. Calculation results were compared with those of the experiments obtained by laser absorption spectroscopy. Two types of DSMC simulations which were different in inelastic collision procedures were carried out. It was concluded that the energy transfer was forbidden unless the total energy of the colliding atoms exceeded a threshold value. It was also found that the DSMC method is suitable for treating deexcitation of metastable states accompanied by rapid expansion in the AVLIS evaporation process.

Numerical Simulation for Metastable States' Deexcitation in Electron Beam Evaporation Process.

A direct simulation Monte Carlo (DSMC) method was modified in order to analyze the evaporation process in atomic vapor laser isotope separation (AVLIS), whereby energy transfer between discrete energy levels of metastable states and continuous energy level of translation took place. The atomic excitation temperatures of gadolinium atom were calculated for the model in five low-lying states. Calculation results were compared with those of the experiments obtained by laser absorption spectroscopy. Two types of DSMC simulations which were different in inelastic collision procedures were carried out. It was concluded that the energy transfer was forbidden unless the total energy of the colliding atoms exceeded a threshold value. It was also found that the DSMC method is suitable for treating deexcitation of metastable states accompanied by rapid expansion in the AVLIS evaporation process.