Proton Emission Research Articles

Structure and decay of the extremely proton-rich nuclei O11,12

${\rm \bf Background:}$ The recent observation of the unbound nucleus $^{11}$O offers the unique possibility to study how the structure and dynamics of two-proton ($2p$) decay is affected by the removal of one neutron from $^{12}$O, and provides important information on the Thomas-Ehrman effect in the mirror pairs $^{11}_{~8}$O$_3$-$^{11}_{~3}$Li$_8$ and $^{12}_{~8}$O$_4$-$^{12}_{~4}$Be$_8$, which involve the $2p$ emitters $^{11}$O and $^{12}$O. ${\rm \bf Purpose:}$ We investigate how continuum effects impact the structure and decay properties of $^{11}$O and $^{12}$O, and their mirror partners. ${\rm \bf Methods:}$ We solve the three-body core-nucleon-nucleon problem using the Gamow coupled-channel (GCC) method. The GCC Hamiltonian employs a realistic finite-range valence nucleon-nucleon interaction and the deformed cores of $^{9,10}$C, $^{9}$Li, and $^{10}$Be. ${\rm \bf Results:}$ We calculate the energy spectra and decay widths of $^{11}$O and $^{12}$O as well as those of their mirror nuclei. In particular, we investigate the dynamics of the $2p$ decay in the ground state of $^{12}$O by analyzing the evolution of the $2p$ configuration of the emitted protons as well as their angular correlations in the coordinate space. We also show how the analytic structure of the resonant states of $^{10}$Li and $^{10}$N impacts the low-lying states of $^{11}$Li and $^{11}$O. ${\rm \bf Conclusions:}$ We demonstrate that, in both nuclei $^{11}$O and $^{12}$O, there is a competition between direct and "democratic" $2p$ ground-state emission. The broad structure observed in $^{11}$O is consistent with four broad resonances, with the predicted $3/2^-_1$ ground state strongly influenced by the broad threshold resonant state in $^{10}$N, which is an isobaric analog of the antibound (or virtual) state in $^{10}$Li.

TAMUTRAP facility: Penning trap facility for weak interaction studies

In the low-energy regime, precision measurements in nuclear β −decay continue to be a sensitive tool to search for new physics beyond the standard model (SM). The primary goal of the Texas A&M University Penning trap facility (TAMUTRAP) is to improve the limits on non-SM processes in the weak interaction. In particular, scalar currents, by measuring the β − ν angular correlation parameter (aβν), for T = 2, super-allowed β −delayed proton emitters. The precise measurement of energy Doppler shift of the proton following β+ −decay is sensitive to β − ν angular correlation coefficient, which is unity (aβν= 1) for pure Fermi transition in the absence of scalar currents. The experiments will be performed in a unique large bore cylindrical Penning trap with an inner radius of 90 mm, which is larger than any existing Penning trap across the world. The TAMUTRAP facility has been commissioned off-line and has demonstrated the ability to perform high precision mass measurements. We describe here the facility overview and summarize the current status towards the first measurement of β − ν angular correlation for T = 2, beta delayed proton emitters using a large bore cylindrical Penning trap with closed end caps.

Zero-energy proton dissociation of H2+ through stimulated Raman scattering

We show that (near-)zero energy proton emission from H$_2^+$ in strong two-color and broadband laser fields is dominated by a stimulated Raman scattering process taking place on the electronic ground state. It is furthermore shown that in the (near-)zero energy region the asymmetry in proton ejection induced by asymmetric laser fields is due to the interplay of several processes, rather than only pathway interferences, with vibrational trapping (or bond-hardening) taking a key role.

Systematic study of proton radioactivity of spherical proton emitters within various versions of proximity potential formalisms

In this work we present a systematic study of the proton radioactivity half-lives of spherical proton emitters within the Coulomb and proximity potential model. We investigate 28 different versions of the proximity potential formalisms developed for the description of proton radioactivity, $\mathcal{\alpha}$ decay and heavy particle radioactivity. It is found that 21 of them are not suitable to deal with the proton radioactivity, because the classical turning points $r_{\text{in}}$ cannot be obtained due to the fact that the depth of the total interaction potential between the emitted proton and the daughter nucleus is above the proton radioactivity energy. Among the other 7 versions of the proximity potential formalisms, it is Guo2013 which gives the lowest rms deviation in the description of the experimental half-lives of the known spherical proton emitters. We use this proximity potential formalism to predict the proton radioactivity half-lives of 13 spherical proton emitters, whose proton radioactivity is energetically allowed or observed but not yet quantified, within a factor of 3.71.

Relativistic proton emission from ultrahigh-energy-density nanosphere generated by microbubble implosion

Laser intensity scalings are investigated for accelerated proton energy and attainable electrostatic field using microbubble implosion (MBI). In MBI, the bubble wall protons are subject to volumetric acceleration toward the center due to the spherically symmetric electrostatic force generated by hot electrons filling the bubble. Such an implosion can generate an ultrahigh density proton core of nanometer size on the collapse, which results in an ultrahigh electrostatic field to emit energetic protons in the relativistic regime. Three-dimensional particle-in-cell and molecular dynamics simulations are conducted in a complementary manner. As a result, underlying physics of MBI are revealed such as bubble-pulsation and ultrahigh energy densities, which are higher by orders of magnitude than, for example, those expected in a fusion-igniting core of inertially confined plasma. MBI has potential as a plasma-optical device, which optimally amplifies an applied laser intensity by a factor of two orders of magnitude; thus, MBI is proposed to be a novel approach to the Schwinger limit.

New and comprehensive β - and βp -decay spectroscopy results in the vicinity of Sn100

A decay spectroscopy experiment on proton-rich nuclei in the vicinity of the doubly magic Sn100 was carried out at RIKEN Nishina Center. More than 20 nuclei with 43≤Z≤50 and N≤51, produced by fragmentation reactions were investigated via analyses of β-decay, βp-decay, and subsequent γ-ray data. Owing to higher statistics, the precision on the half-lives of many of the ground states and isomers was improved. β-decay endpoint energies of 11 states in 8 nuclei were measured for the first time, and the corresponding QEC and excitation energies were generally consistent with various mass models. Many β-delayed proton emission branching ratios were measured either for the first time or with higher precision compared to literature values, and some of them differed by more than 2σ. Many of the large discrepancies were associated with nuclei with long-lived isomeric states, highlighting large systematic uncertainties involved in these measurements. Twenty-five new γ rays were observed, and ten new states are proposed with unambiguous excitation energies, spins, and parities. Most of the energies of the excited states were consistent within 300 keV or 20%, whichever was greater, compared to shell model predictions in the proton/neutron (p1/2,g9/2) model space assuming a Sr76 core. A signature of a new (1/2-) isomer in Cd97 with T1/2=0.73(7) s was found, in good agreement with shell model predictions.

Proton emission from the drip-line nuclei I-Bi using the WKB approximation with relativistic mean-field densities * * Supported by the Department of Science and Technology, Govt. of India (EMR/2015/002517)

We study the properties of proton rich nuclei reported as proton emitters in the region from I to Bi with Z = 53 to 83 and N = 56 to 102 as a crucial application to the existence of exotic nuclei. The effective relativistic mean-field formalism (E-RMF), with NL3, FSUGarnet, G3 and IOPB-I interactions, is adopted for analysis of the ground state properties of proton emitters. Furthermore, in the E-RMF background, the Wentzel-Karmers-Brillouin (WKB) barrier penetration method is used for the calculation of proton emission half-lives. It is found that the calculated half-lives are in good agreement with the experimental results for all emitters considered in this study.

Nuclear decay studies of rare isotopes

This article overviews recent developments and achievements on decay spectroscopic studies at the Radioactive-Isotope Beam Factory (RIBF) in RIKEN Nishina Center, which has come online in 2007 as the first 3rd-generation in-flight separator facility. The research territory on the chart of nuclides has been dramatically expanded both towards the proton-rich and neutron-rich frontiers with the advent of RIBF. Taking advantage of the world’s currently strongest RI beams, in conjunction with new experimental techniques and state-of-the-art detector systems, more than 400 species of rare isotopes have been explored in experimental programs dedicated to radioactive-decay measurements performed in the last decade. Some selected topics are introduced in this review. Excited levels investigated by $\gamma$-ray measurements following $\beta$ decay have provided significant information on the evolution of shell structures and nuclear shapes, and thus serve as a stringent benchmark for testing microscopic and macroscopic nuclear model calculations. Systematic studies of $ \beta$-decay half-lives of very neutron-rich nuclei have an enormous impact on a better understanding of explosive nucleosynthesis in the rapid neutron-capture (r) process. On the proton-rich side of the $ \beta$-stability line, new proton emitters have been identified, allowing an exploration of atomic nuclei beyond the proton drip line. New results obtained in a series of decay experiments include various types of nuclear isomers, for example, seniority, spin-trap, shape, and K isomers. The identification and characterization of such exotic isomers have revealed the underlying single-particle orbits and nucleon-nucleon correlations, as well as the change of nuclear shape and spin orientation. These new results will offer further insight into exotic nuclei and contribute to the development of new theories of nuclear structure and nucleosynthesis. In this review article, some of the ongoing research projects and future prospects for decay studies at RIBF are also presented.

Эмиссия вторичных протонов из реакции (p,xp) при энергии 30 МэВ на ядре 103 Rh

Эмиссия вторичных протонов из реакции (p,xp) при энергии 30 МэВ на ядре 103 Rh

Spectroscopy of natural parity states in 20Ne via the 19F(p,α0) and 19F(p,απ)reactions at low energies

The 19F(p,α0)16O and 19F(p,απ)16O reactions can be fruitfully exploited to probe natural parity states above the proton emission threshold in the compound 20Ne nucleus. However, despite the relatively large number of data sets published in the literature, it is still not possible to draw a fully unambiguous picture of the spectroscopy of 20Ne, especially close to the proton emission threshold. To contribute to clarify these aspects, we have collected and reviewed all existing data sets of the 19F(p,α0)16O and 19F(p,απ)16O reactions to perform, for the first time, a comprehensive R-matrix fit including both reactions in the bombarding energy range Ep = 0:2–10 MeV. Our analysis clarifies several ambiguities present in the literature and affecting the spectroscopy of 20Ne and clearly demonstrates the importance of the 19F(p,απ) reaction to better constraint the spectroscopy parameters of the fit.

Emission of high energy particles in heavy ion collisions and a non-equilibrium equation of state

A hydrodynamic approach with a non-equilibrium equation of state is used to describe the collisions of heavy ions at medium and intermediate energies. In the development of this approach, with the inclusion of nuclear viscosity effects and the introduction of an amendment to the microcanonical distribution, the double differential cross sections of proton emission in collisions of different nuclei are calculated, which are in agreement with the available experimental data on the emission of high-energy particles, including the cumulative spectral region.

Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains

The proton-unbound argon and chlorine isotopes have been studied by measuring trajectories of their decay-in-flight products by using a tracking technique with micro-strip detectors. The proton ($1p$) and two-proton ($2p$) emission processes have been detected in the measured angular correlations "heavy-fragment"+$p$ and "heavy-fragment"+$p$+$p$, respectively. The ground states of the previously unknown isotopes $^{30}$Cl and $^{28}$Cl have been observed for the first time, providing the $1p$-separation energies $S_p$ of $-0.48(2)$ and $-1.60(8)$ MeV, respectively. The relevant systematics of $1p$ and $2p$ separations energies have been studied theoretically in the core+$p$ and core+$p$+$p$ cluster models. The first-time observed excited states of $^{31}$Ar allow to infer the $2p$-separation energy $S_{2p}$ of 6(34) keV for its ground state. The first-time observed state in $^{29}$Ar with $S_{2p} = -5.50(18)$ MeV can be identified either as a ground or an excited state according to different systematics.

Breakthroughs in 4π panorama ionology in plasma focus devices for mechanisms understanding with special regards to hydrogen ions (protons)

This paper reports breakthroughs on 4π panorama ion emission mechanisms understanding in a plasma focus device (PFD) in particular hydrogen ion (proton) images detected for the first time in panorama mega-size polycarbonate ion image detectors (MS-PCIDs). The MS-PCIDs were processed in novel panorama single-cell mega-size electrochemical etching (MS-ECE) image detection systems by 50 Hz - HV method. A circular and a rectangular MS-PCIDs form a “mega-size cylindrical ion detector” capable to efficiently detect 4π proton emission with “Proton Cathode Shadow” or any other phenomena on ionographs or images, observable by the unaided eyes with potential for relative “dynamic proton spectrometry”. The effects of 6 circular MC-PCID distances from a flat-end cone anode top, anode top geometry, and type of gas on ion emissions in particular protons are presented and discussed. The potential of near 4π availability of PFD space highly enhances efficient PFD applications, what has been limited by narrow beam emission exercises within small solid angle on or around z-axis.

Intensified proton and carbon ion flux from femtosecond laser driven plasma source

Ion acceleration from aluminium foils irradiated with a 30 fs laser pulse of ∼1020 W/cm2 intensity at an incidence angle of 45° was investigated. Laser intensity contrast enhancement by a factor of 100 resulted in a nearly 7 and 30 times increase in proton and carbon ion flux, respectively, while their maximum energy remains almost unchanged. More than 1013 protons and 1014 carbon C4+ ions per MeV bandwidth per steradian solid angle were measured. Simulations, being in a good agreement with the experimental findings, have revealed that the difference in proton emission between the low and high contrast cases is a narrower angular distribution of protons at high laser pulse contrast. In the low contrast scenario, the plasma density gradient increases the hot electron divergence, leading to the reduction of particle flux in a fixed solid angle. The analytical model verifies the concept of the theoretical limit of particle flux. These results open up the possibility for further optimization of the laser driven bright source of energetic particles.

Calculations of Double-Differential Neutron and Proton Emission Cross Sections on 19F at 14.2-MeV Incident Neutron Energy

In the present paper, the double-differential cross sections (d2σ/dΩde) of emission spectra for the 19F(n, xn) and 19F(n, xp) structural fusion materials (contained in FLiBe) were calculated by using the Hybrid Monte-Carlo Simulation at 14.2-MeV incident neutron energy in emission angles ranging from 30◦ to 150◦. Theoretical model calculations were carried out by using ALICE-2011, EMPIRE, and TALYS computer codes. Theoretically calculated results of the double-differential cross section for neutron and proton emission are presented and compared with the existing experimental data taken from the international nuclear reaction EXFOR database.

Double differential cross sections of light charged particle production for the n+238U reaction**Supported by National Natural Science Foundation of China-NSAF (U1630122), IAEA Coordinated Research Projects (CRPs) on Recommended Input Parameter Library (RIPL) for Fission Cross Section Calculations (20464) and Science Challenge Project (TZ2018005)

Production of light complex particles from the n+238U reaction is analyzed with the exciton model including the improved Iwamoto-Harada pickup mechanism for the preequilibrium process. It is allowed that some of the nucleons forming the complex ejectile come from levels below the Fermi energy, and the intrinsic structure of the emitted particle is taken into account. The equilibrium-state emissions are also considered by using Hauser-Feshbach theory with the width fluctuation correction and the evaporation model. Moreover, all cross sections, angular distributions, energy spectra and double differential cross sections of neutron, proton, deuteron, triton and alpha emissions for the n+238U reaction are consistently calculated and analyzed with nuclear theoretical models in the energy range En ⩽ 150 MeV. ENDF-formatted nuclear data including information about the production of light charged particles are obtained.

Angular Distributions of Protons for the Two-Proton Decay of Superfluid Nuclei and Diproton Correlations

The approach proposed by A.B. Migdal for describing the virtual singlet diproton state is used to show the effect diproton decay channel has on the width and the angular distribution of emitted protons in the two-proton decay of a parent 45Fe nucleus is negligible. A conclusion is reached on the leading role of the two-stage virtual mechanism of the two-proton decay of the abovementioned nucleus, which corresponds to the sequential emission of two uncorrelated protons and is described in terms of the multiparticle shell nuclear model with allowance for superfluid nucleon–nucleon correlations.

Two-Proton Virtual Decay of the 19Mg Nucleus in the Superfluid Model

The two-stage two-proton virtual nuclear decay theory and superfluid atomic nucleus model are used to investigate the total and partial widths, and the angular distributions of the emitted protons, for the two-proton diagonal virtual decay of the ground state of the $${}^{{19}}{\text{Mg}}$$ nucleus into the ground state of the 17Ne nucleus. It is shown there is a set of parameters of the proton shell potential and superfluid proton–proton interaction for which the calculated total width of the two-proton decay of the $${}^{{19}}{\text{Mg}}$$ nucleus agrees with its experimental value.

Experimental demonstration of an electromagnetic pulse mitigation concept for a laser driven proton source.

The targets that are used to produce high-energy protons with ultra-high intensity lasers generate a strong electromagnetic pulse (EMP). To mitigate that undesired side effect, we developed and tested a concept called the "birdhouse." It consists in confining the EMP field in a finite volume and in dissipating the trapped electromagnetic energy with an electric resistor. A prototype was tested at a 10 TW 50 fs laser facility. The recorded average EMP mitigation ratio is about 20 for frequencies from 100 MHz to 6 GHz. The EMP mitigation ratio attains the level of 50 in the frequency range of 1-2 GHz where microwave emission is maximal. We measured the intensity of proton emission in two directions: along the laser propagation direction and along the edge of the proton beam. We observed that the "birdhouse" induces a two-fold increase of the intensity in the center of the proton beam and a two-fold reduction of the intensity on its edge. We did not observe any modification of the proton beam normalized spectrum.

Empirical formulas for proton decay half-lives: Role of nuclear deformation and Q-value

Two empirical formulas for the proton decay half-lives including nuclear deformation are proposed. The formula with parameter set I gives the logarithm of the proton decay half-lives as an explicit function of the orbital angular momentum with eight adjustable parameters, whereas that with set II represents the logarithm of the reduced half-lives as an implicit function of the angular momentum with seven adjustable parameters. Experimental data for the half-lives of 44 proton emitters in the ground state or isomeric state were used to obtain the parameters. The experimental and calculated Q values were used. Different sets of parameters were obtained for the ground state transition, isomeric state transition, and all transitions for both deformed and spherical nuclei. The best agreement with experimental data was observed for set I for deformed proton emitters with experimental Q values.