SEARCH · Searcharxiv

Results for “nucl-ex”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40Linked to original sources

arXiv2014

Isospin properties of electric dipole excitations in 48Ca

Two different experimental approaches were combined to study the electric dipole strength in the doubly-magic nucleus 48Ca below the neutron threshold. Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and nearly mono-energetic linearly polarized photons with energies between 6.6 and 9.51 MeV provided strength distribution and parities, and an (α,α'γ) experiment at E_α=136 MeV gave cross sections for an isoscalar probe. The unexpected difference observed in the dipole response is compared to calculations using the first-order random-phase approximation and points to an energy-dependent isospin character. A strong isoscalar state at 7.6 MeV was identified for the first time supporting a recent theoretical prediction.

nucl-ex↗

arXiv2014

Probing the critical behavior in the evolution of GDR width at very low temperatures in A~100 mass region

The influence of giant dipole resonance (GDR) induced quadrupole moment on GDR width at low temperatures is investigated experimentally by measuring GDR width systematically in the unexplored temperature range $T$=0.8-1.5 MeV, for the first time, in $A$ $\sim$ 100 mass region. The measured GDR widths, using alpha induced fusion reaction, for $^{97}$Tc confirm that the GDR width remains constant at the ground state value up to a critical temperature and increases sharply thereafter with increase in $T$. The data have been compared with the adiabatic Thermal Shape Fluctuation Model (TSFM), phenomenological Critical Temperature Fluctuation Model (CTFM) and microscopic Phonon Damping Model (PDM). Interestingly, CTFM and PDM give similar results and agree with the data, whereas the TSFM differs significantly even after incorporating the shell effects.

nucl-ex↗

arXiv2014

11Be(beta-p), a quasi-free neutron decay?

We have observed beta-delayed proton emission from the neutron-rich nucleus 11Be by analysing a sample collected at the ISOLDE facility at CERN with accelerator mass spectrometry (AMS). With a branching ratio of (8.4 +- 0.6) 10^{-6} the strength of this decay mode, as measured by the B(GT)-value, is unexpectedly high. The result is discussed within a simple single-particle model and could be interpreted as a quasi-free decay of the 11Be halo neutron into a single-proton state.

nucl-ex↗

arXiv2014

Nuclear modification factor in intermediate-energy heavy-ion collisions

The transverse momentum dependent nuclear modification factors (NMF), namely $R_{CP}$, is investigated for protons produced in Au + Au at 1$A$ GeV within the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. It is found that the radial collective motion during the expansion stage affects the NMF at low transverse momentum a lot. By fitting the transverse mass spectra of protons with the distribution function from the Blast-Wave model, the magnitude of radial flow can be extracted. After removing the contribution from radial flow, the $R_{CP}$ can be regarded as a thermal one and is found to keep unitary at transverse momentum lower than 0.6 GeV/c and enhance at higher transverse momentum, which can be attributed to Cronin effect.

nucl-th↗

arXiv2014

Alpha induced reaction cross section measurements on 162Er for the astrophysical gamma process

The cross sections of the 162Er(a,g,)166Yb and 162Er(a,n)165Yb reactions have been measured for the first time. The radiative alpha capture reaction cross section was measured from Ec.m. = 16.09 down to Ec.m. = 11.21 MeV, close to the astrophysically relevant region (which lies between 7.8 and 11.48 MeV at 3 GK stellar temperature). The 162Er(a,n)165Yb reaction was studied above the reaction threshold between Ec.m. = 12.19 and 16.09 MeV. The fact that the 162Er(a,g)166Yb cross sections were measured below the (a,n) threshold at first time in this mass region opens the opportunity to study directly the a-widths required for the determination of astrophysical reaction rates. The data clearly show that compound nucleus formation in this reaction proceeds differently than previously predicted.

nucl-ex↗

arXiv2014

$K^+Λ$ and $K^+Σ^0$ photoproduction with fine center-of-mass energy resolution

Measurements of $γp \rightarrow K^{+} Λ$ and $γp \rightarrow K^{+} Σ^0$ cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel $K^+$ meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy ($W$) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quark-diquark dynamics in the nucleon.

nucl-ex↗

arXiv2014

Excitation of Giant Monopole Resonance in $^{208}$Pb and $^{116}$Sn Using Inelastic Deuteron Scattering

The excitation of the isoscalar giant monopole resonance (ISGMR) in $^{116}$Sn and $^{208}$Pb has been investigated using small-angle (including $0^\circ$) inelastic scattering of 100 MeV/u deuteron and multipole-decomposition analysis (MDA). The extracted strength distributions agree well with those from inelastic scattering of 100 MeV/u $α$ particles. These measurements establish deuteron inelastic scattering at E$_d \sim$ 100 MeV/u as a suitable probe for extraction of the ISGMR strength with MDA, making feasible the investigation of this resonance in radioactive isotopes in inverse kinematics.

nucl-ex↗

arXiv2014

Final state effects on charge asymmetry of pion elliptic flow in high-energy heavy-ion collisions

Within a multi-phase transport (AMPT) model with the string melting mechanism and imported initial electric quadrupole moment, the difference between the elliptic flow of positive and negative pions is calculated. The slope parameter $r$ of the linear dependence of $Δv_{2}=v_{2}(π^{-})-v_{2}(π^{+})$ on $A_{ch}=(N^{+}-N^{-})/(N^{+}+N^{-})$ is yielded owing to the parton cascade, which converts the initial electric quadrupole distribution into the final charge-dependent elliptic flow. The slope parameter $r$ is found to be increased by the hadronization given by the coalescence, and decreased by the resonance decays. The slope parameter $r$ is very sensitive to both the initial electric quadrupole percentage and centrality bin and consequently a helpful constraint on the quadrupole moment of the chiral magnetic wave is obtained for Au+Au collisions at the top RHIC energy.

nucl-th↗

arXiv2014

Improved estimates of the nuclear structure corrections in $μ$D

We calculate the nuclear structure corrections to the Lamb shift in muonic deuterium by using state-of-the-art nucleon-nucleon potentials derived from chiral effective field theory. Our calculations complement previous theoretical work obtained from phenomenological potentials and the zero range approximation. The study of the chiral convergence order-by-order and the dependence on cutoff variations allows us to improve the estimates on the nuclear structure corrections and the theoretical uncertainty coming from nuclear potentials. This will enter the determination of the nuclear radius from ongoing muonic deuterium experiments at PSI.

nucl-th↗

arXiv2014

Basic features of the pion valence-quark distribution function

The impulse-approximation expression used hitherto to define the pion's valence-quark distribution function is flawed because it omits contributions from the gluons which bind quarks into the pion. A corrected leading-order expression produces the model-independent result that quarks dressed via the rainbow-ladder truncation, or any practical analogue, carry all the pion's light-front momentum at a characteristic hadronic scale. Corrections to the leading contribution may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea-quarks. Working with available empirical information, we use an algebraic model to express the principal impact of both classes of corrections. This enables a realistic comparison with experiment that allows us to highlight the basic features of the pion's measurable valence-quark distribution, $q^π(x)$; namely, at a characteristic hadronic scale, $q^π(x) \sim (1-x)^2$ for $x\gtrsim 0.85$; and the valence-quarks carry approximately two-thirds of the pion's light-front momentum.

nucl-th↗

arXiv2014

Isotopic 32S/33S ratio as a diagnostic of presolar grains from novae

Measurements of sulphur isotopes in presolar grains can help to identify the astrophysical sites in which these grains were formed. A more precise thermonuclear rate of the 33S(p,gamma)34Cl reaction is required, however, to assess the diagnostic ability of sulphur isotopic ratios. We have studied the 33S(3He,d)34Cl proton-transfer reaction at 25 MeV using a high-resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. Deuteron spectra were measured at ten scattering angles between 10 and 55 degrees. Twenty-four levels in 34Cl over Ex = 4.6 - 5.9 MeV were observed, including three levels for the first time. Proton spectroscopic factors were extracted for the first time for levels above the 33S+p threshold, spanning the energy range required for calculations of the thermonuclear 33S(p,gamma)34Cl rate in classical nova explosions. We have determined a new 33S(p,gamma)34Cl rate using a Monte Carlo method and have performed new hydrodynamic nova simulations to determine the impact on nova nucleosynthesis of remaining nuclear physics uncertainties in the reaction rate. We find that these uncertainties lead to a factor of less than 5 variation in the 33S(p,gamma)34Cl rate over typical nova peak temperatures, and variation in the ejected nova yields of S--Ca isotopes by less than 20%. In particular, the predicted 32S/33S ratio is 110 - 130 for the nova model considered, compared to 110 - 440 with previous rate uncertainties. As recent type II supernova models predict ratios of 130 - 200, the 32S/33S ratio may be used to distinguish between grains of nova and supernova origin.

astro-ph.SR↗

arXiv2014

Half-lives of $α$ decay from natural nuclides and from superheavy elements

Recently, experimental researches on the $α$ decay with long lifetime are one of hot topics in the contemporary nuclear physics [e.g. N. Kinoshita {\sl et al.} (2012) and J. W. Beeman {\sl et al.} (2012) ]. In this study, we have systematically investigated the extremely long-lived $α$-decaying nuclei within a generalized density-dependent cluster model involving the experimental nuclear charge radii. In detail, the important density distribution of daughter nuclei is deduced from the corresponding experimental charge radii, leading to an improved $α$-core potential in the quantum tunneling calculation of $α$-decay width. Besides the excellent agreement between theory and experiment, predictions on half-lives of possible candidates for natural $α$ emitters are made for future experimental detections. In addition, the recently confirmed $α$-decay chain from $^{294}$117 is well described, including the attractive long-lived $α$-decaying $^{270}$Db, i.e., a positive step towards the "island of stability" in the superheavy mass region.

nucl-th↗

arXiv2014

Normal or abnormal isospin-fractionation as a qualitative probe of nuclear symmetry energy at supradensities

Within two different frameworks of isospin-dependent transport model, effect of nuclear symmetry energy at supradensities on the isospin-fractionation (IsoF) was investigated. With positive/negative symmetry potential at supradensities (i.e., values of symmetry energy increase/decrease with density above saturation density), for energetic nucleons, the value of neutron to proton ratio of free nucleons is larger/smaller than that of bound nucleon fragments. Compared with extensively studied quantitative observables of nuclear symmetry energy, the normal or abnormal isospin-fractionation of energetic nucleons can be a qualitative probe of nuclear symmetry energy at supradensities.

nucl-th↗

arXiv2014

First determination of the one-proton induced Non-Mesonic Weak Decay width of p-shell Λ-Hypernuclei

Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Lambda-Hypernuclei (A = 5-16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced decay widths, Gamma_2N/Gamma_p, are obtained from single proton spectra, Gamma_2N/Gamma_p = 0.50 +/- 0.24, and from neutron and proton coincidence spectra, Gamma_2N/Gamma_p = 0.36 +/- 0.14stat +0.05sys -0.04sys , in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Lambda decay width, Gamma_p/Gamma_Lambda, without resorting to Intra Nuclear Cascade models but by exploiting only experimental data, under the assumption of a linear dependence on A of the Final State Interaction contribution. This is the first systematic determination ever done and it agrees within the errors with recent theoretical calculations.

nucl-ex↗

arXiv2014

Charge Symmetry Breaking in dd->4Heπ0 with WASA-at-COSY

Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd->4Heπ0 have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +- 13(sys) +- 8(ext)) pb and first data on the differential cross section are consistent with s-wave pion production.

nucl-ex↗

arXiv2014

Neutron occupancy of the 0d5/2 orbital and the N=16 shell closure in 24O

One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at Edecay=50$\pm$3 keV, corresponding to an excited state in 23O at 2.78$\pm$0.11 MeV, as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d -wave neutron knockout, providing support for a Jπ assignment of 5/2+. The associated spectroscopic factor was deduced to be C2S(0d5/2)=4.1$\pm$0.4 by comparing the measured cross section (View the MathML source) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0d5/2 orbital is in line with the N=16 shell closure in 24O.

nucl-ex↗

arXiv2014

A measurement of the neutron to 199Hg magnetic moment ratio

The neutron gyromagnetic ratio has been measured relative to that of the 199Hg atom with an uncertainty of 0.8 ppm. We employed an apparatus where ultracold neutrons and mercury atoms are stored in the same volume and report the result $γ_{\rm n}/γ_{\rm Hg} = 3.8424574(30)$.

nucl-ex↗

arXiv2017

Two-Proton Radioactivity with 2p halo in light mass nuclei A$=$18$-$34

Two-proton radioactivity with 2p halo is reported theoretically in light mass nuclei A $=$ 18-34. We predict $^{19}$Mg, $^{22}$Si, $^{26}$S, $^{30}$Ar and $^{34}$Ca as promising candidates of ground state 2p-radioactivity with S$_{2p}$ $<$ 0 and S$_{p}$ $>$ 0. Observation of extended tail of spatial charge density distribution, larger charge radius and study of proton single particle states, Fermi energy and the wave functions indicate 2p halo like structure which supports direct 2p emission. The Coulomb and centrifugal barriers in experimentally identified 2p unbound $^{22}$Si show a quasi-bound state that ensures enough life time for such experimental probes. Our predictions are in good accord with experimental and other theoretical data available so far.

nucl-th↗