Spin-parity of the 13.35 MeV state and high-lying states around 20 MeV in excitation energy in $^{12}$C nucleus
A. S. Demyanova, V. I. Starastsin, A. A. Ogloblin, A. N. Danilov, S. V. Dmitriev, W. H. Trzaska, P. Heikkinen, T. L. Belyaeva, S. A. Goncharov, V. A. Maslov, Yu… 展开作者
A. S. Demyanova, V. I. Starastsin, A. A. Ogloblin, A. N. Danilov, S. V. Dmitriev, W. H. Trzaska, P. Heikkinen, T. L. Belyaeva, S. A. Goncharov, V. A. Maslov, Yu. G. Sobolev, Yu. B. Gurov, N. Burtebaev, D. Janseitov
Study of the $^{11}$B($^{3}$He,d)$^{12}$C reaction at incident $^{3}$He energy E$_{lab}$ = 25 MeV has been performed at the K-130 cyclotron at the University of Jyväskylä, Finland. Differential cross sections have been measured for the 13.35 MeV state and for the states with excitation energy around 20 MeV. The data were analyzed with the DWBA method. A tentative assignment, 4$^{-}$, is given for the state at 13.35 MeV. For the state at 20.98 MeV, the spin-parity 3$^{-}$ and the isospin T = 0 are assigned for the first time. Our model description of the broad state at 21.6 MeV is consistent with the previous assignments of isospin T = 0 and spin-parity of 2$^{+}$ and 3$^{-}$. The excited state at 22.4 MeV may have possible spin-parities of either 6$^{+}$ or 5$^{-}$. The collected statistics was insufficient to solve this question.
The parity-violating asymmetry including QED corrections in high-energy electron-nucleus collisions
Departament de Física Quàntica i Astrofísica（量子物理与天体物理学系）；Università degli Studi di Milano（米兰大学）；INFN, Sezione di Milano（意大利国家核物理研究所米兰分部）；Institut de Ciències del Cosmos, Universitat de Barcelona（巴塞罗那大学宇宙科学研究所）；Mathematics Institute, University of Munich（慕尼黑大学数学研究所）
The effects of charge symmetry breaking in nucleon electromagnetic form factors on parity- violating elastic electron-12C scattering is studied, and found to be much smaller than other known effects. The analysis of a planned experiment is discussed.
Background: The ground state neutron density of a medium mass nucleus contains fundamental nuclear structure information and is at present relatively poorly known. Purpose: We explore if parity violating elastic electron scattering can provide a feasible and model independent way to determine not just the neutron radius but the full radial shape of the neutron density $ρ_n(r)$ and the weak charge density $ρ_W(r)$ of a nucleus. Methods: We expand the weak charge density of $^{48}$Ca in a model independent Fourier Bessel series and calculate the statistical errors in the individual coefficients …
Properties of particle-unstable nuclei lying beyond the proton drip line can be ascertained by considering those (usually known) properties of its mirror neutron-rich system. We have used a multi-channel algebraic scattering theory to map the known properties of the neutron-${}^{14}$C system to those of the proton-${}^{14}$O one from which we deduce that the particle-unstable ${}^{15}$F will have a spectrum of two low lying broad resonances of positive parity and, at higher excitation, three narrow negative parity ones. A key feature is to use coupling to Pauli-hindered states in the target.
Coulomb excitation of the exotic neutron-rich nucleus $^{26}$Ne on a $^{nat}$Pb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an $^{nat}$Al target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV $^{40}$Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the $^{25}$Ne+n channel, we observe a sizable amount of E1 strength betwe…
In order to clarify the nature of hypernuclear low-lying states, we carry out a comprehensive study for the structure of $^{144-154}_{~~~~~~~~Λ}$Sm-hypernuclei, which exhibit a transition from vibrational to rotational characters as the neutron number increases. To this end, we employ a microscopic particle-core coupling scheme based on a covariant density functional theory. We find that the positive-parity ground-state band in the hypernuclei shares a similar structure to that of the corresponding core nucleus. That is, regardless of whether the core nucleus is spherical or deformed, each hyp…
Radiative corrections to the parity-violating spin asymmetry
Mathematics Institute, University of Munich（慕尼黑大学数学研究所）；Departament de Física Quàntica i Astrofísica, Martí i Franqués, 1, 08028 Barcelona, Spain（巴塞罗那大学量子物理与天体物理学系）；Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano（米兰大学物理系）；INFN, Sezione di Milano（意大利国家核物理研究所米兰分部）；Institut de Ciències del Cosmos, Universitat de Barcelona（巴塞罗那大学宇宙科学研究所）
Physics of the low-lying and high-lying hadrons in the light flavors sector is reviewed. While the low-lying hadrons are strongly affected by both $U(1)_A$ and spontaneous $SU(2)_L \times SU(2)_R$ breakings, in the high-lying hadrons these symmetries are restored. A manifestation is a persistence of the chiral multiplet structure in both baryon and meson spectra. A fundamental origin of this phenomenon is that effects of quantum fluctuations of both quark and gluon fields must vanish at large $n$ or $J$ and a semiclassical description becomes adequate. A relation between the chiral symmetry re…
A new measurement of proton resonance scattering on 7Be was performed up to the center-of-mass energy of 6.7 MeV using the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator) at the Center for Nuclear Study of the University of Tokyo. The excitation function of 7Be+p elastic scattering above 3.5 MeV was measured successfully for the first time, providing important information about the resonance structure of the 8B nucleus. The resonances are related to the reaction rate of 7Be(p, gamma)8B, which is the key reaction in solar 8B neutrino production. Evidence for the presence o…
High-spin states of 84Sr were populated through the reaction 70Zn(18O, 4n)84Sr at 75 MeV beam energy. Measurement of excitation function, gamma-gamma coincidences, directional correlation of oriented states (DCO) ratios and gamma-transition intensities were performed using eight anticompton HPGe detectors and one planar HPGe detector. Based on the measured results, a new level scheme of 84Sr was established in which 12 new states and nearly 30 new gamma-transitions were identified in the present work. The positive-parity states of the new level scheme were compared with results from calculatio…
The neutron-rich $^{28,29}$F isotopes have been recently studied via knockout and interaction cross-section measurements. The $2n$ halo in $^{29}$F has been linked to the occupancy of $pf$ intruder configurations. We investigate bound and continuum states in $^{29}$F, focusing on the $E1$ response of low-lying excitations and the effect of dipole couplings on nuclear reactions. $^{29}\text{F}$ ($^{27}\text{F}+n+n$) wave functions are built within the hyperspherical harmonics formalism, and reaction cross sections are calculated using the Glauber theory. Continuum states and $B(E1)$ transition …
A precise determination of the neutron skin thickness of a heavy nucleus sets a basic constraint on the nuclear symmetry energy (the neutron skin thickness is the difference of the neutron and proton rms radii of the nucleus). The parity radius experiment (PREX) may achieve it by electroweak parity-violating electron scattering (PVES) on 208Pb. We investigate PVES in nuclear mean field approach to allow the accurate extraction of the neutron skin thickness of 208Pb from the parity-violating asymmetry probed in the experiment. We demonstrate a high linear correlation between the parity-violatin…
The neturon rich nucleus 13B was studied via the proton transfer reaction 4He(12Be,13B γ) at 50AMeV. The known 4.83-MeV excited state was strongly populated and its spin and parity were assigned to 1/2+ by comparing the angular differential cross section data with DWBA calculations. This low-lying 1/2+ state is interpreted as a proton intruder state and indicates a deformation of the nucleus.
Parity violating elastic electron-nucleus scattering provides an accurate and model independent measurement of neutron densities, because the $Z^0$ couples primarily to neutrons. Coulomb distortion corrections to the parity violating asymmetry $A_l$ are calculated exactly using a relativistic optical model. Distortions significantly reduce $A_l$ in a heavy nucleus. However even with distortions, an experiment to measure the neutron radius is feasible. This will aid the interpretation of future atomic parity violation measurements and provide fundamental nuclear structure information. Coulomb d…
We study the low-lying energy spectrum of the rp-process waiting point nucleus 80Zr with state-of-the-art beyond mean field methods with the Gogny D1S interaction. Symmetry restoration and configuration mixing of axial and triaxial shapes are included in the calculations. Five 0+ states corresponding to different nuclear shapes are obtained below 2.25 MeV and several rotational and γ- bands built upon them are identified. Nevertheless, these states do not modify the β-decay half-life having a negligible effect in the rp-process. A good agreement with the available experimental data is obtained…
We present a detailed formalism of the microscopic particle-rotor model for hypernuclear low-lying states based on a covariant density functional theory. In this method, the hypernuclear states are constructed by coupling a hyperon to low-lying states of the core nucleus, which are described by the generator coordinate method (GCM) with the particle number and angular momentum projections. We apply this method to study in detail the low-lying spectrum of $^{13}_{~Λ}$C and $^{21}_{~Λ}$Ne hypernuclei. We also briefly discuss the structure of $^{155}_{~~Λ}$Sm as an example of heavy deformed hyper…
Shell model calculations using realistic interactions reveal that the ground and low-lying yrast states of the $N=Z$ nucleus $^{92}_{46}$Pd are mainly built upon isoscalar neutron-proton pairs each carrying the maximum angular momentum J=9 allowed by the shell $0g_{9/2}$ which is dominant in this nuclear region. This structure is different from the ones found in the ground and low-lying yrast states of all other even-even nuclei studied so far. The low-lying spectrum of excited states generated by such correlated neutron-proton pairs has two distinctive features: i) the levels are almost equid…
The ground state and low-lying continuum states of 6He are found within a shell model scheme, in a basis of two-particle states built out of continuum p-states of the unbound 5He nucleus, using a simple pairing contact-delta interaction. This accounts for the Borromean character of the bound ground state, revealing its composition. We investigate the quadrupole response of the system and we put our calculations into perspective with the latest experimental results. The calculated quadrupole strength distribution reproduces the narrow 2+ resonance, while a second wider peak is found at about 3.…
The nucleus is one of the most multi-faceted many-body systems in the universe. It exhibits a multitude of responses depending on the way one 'probes' it. With increasing technical advancements of beams at the various accelerators and of detection systems the nucleus has, over and over again, surprised us by expressing always new ways of 'organized' structures and layers of complexity. Nuclear magnetism is one of those fascinating faces of the atomic nucleus we discuss in the present review. We shall not just limit ourselves to presenting the by now very large data set that has been obtained i…
Partial cross sections for the (p,gamma) reaction on the Y-89 nucleus that were measured previously at proton energies between 2.17 and 5.00 MeV and which were averaged over resonances were used to determine the absolute values and the energy distribution of the strength of dipole transitions from compound-nucleus states to low-lying levels of the Zr-90 nucleus. The data obtained in this way were compared with the predictions of various models.
Variable Energy Cyclotron Centre（变能回旋加速器中心）；Homi Bhabha National Institute（霍米·巴哈国家研究所）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；Department of Physics, University of Kashmir（克什米尔大学物理系）；Department of Higher Education (GDC Shopian)（高等教育部（Shopian政府学院））；Department of Higher Education (GDC Kulgam)（高等教育部（Kulgam政府学院））；Department of Physics, ICFAI University Tripura（特里普拉ICFAI大学物理系）；Government General Degree College（政府综合学位学院）
Parity violation in the $(n,α)$ reactions on $^6$Li and $^{10}$B nuclei and in the $γ$-transition between two lowest levels of $^7$Li nucleus is discussed. It appears that the effects (neutral currents contribution in particular) are measurable due to the large values of the neutron cross sections. This holds promise for the theoretical extraction of the constants of the weak NN potential because of the relative simplicity of the investigated systems.
The odd-odd fp-shell nucleus 52Sc was investigated using in-beam gamma-ray spectroscopy following secondary fragmentation of a 55V and 57Cr cocktail beam. Aside from the known gamma-ray transition at 674(5)keV, a new decay at E_gamma=212(3) keV was observed. It is attributed to the depopulation of a low-lying excited level. This new state is discussed in the framework of shell-model calculations with the GXPF1, GXPF1A, and KB3G effective interactions. These calculations are found to be fairly robust for the low-lying level scheme of 52Sc irrespective of the choice of the effective interaction.…
The partial decay widths of lowest lying negative parity baryons belonging to the 70-plet of SU(6) are analyzed in the framework of the 1/Nc expansion The channels considered are those with single pseudo-scalar meson emission. The analysis is carried out to sub-leading order in 1/Nc and to first order in SU(3) symmetry breaking. Conclusions about the magnitude of SU(3) breaking effects along with predictions for some unknown or poorly determined partial decay widths of known resonances are obtained.
The reaction $K^-p\rightarrowΛη$ at low energies is studied with a chiral quark model approach. Good descriptions of the existing experimental data are obtained. It is found that $Λ(1670)$ dominates the reaction around threshold. Furthermore, $u$- and $t$-channel backgrounds play crucial roles in this reaction as well. The contributions from the $D$-wave state $Λ(1690)$ are negligibly small for its tiny coupling to $ηΛ$. To understand the strong coupling properties of the low-lying negative parity $Λ$ resonances extracted from the $\bar{K}N$ scattering, we further study their strong decays. It…
Parity violation effects (PV) in nuclear reaction were discovered in the 60 years of the last century in the capture of thermal transversal polarized neutrons by 113Cd nucleus. In this reaction experimentally was measured a non zero asymmetry of emitted gamma quanta and the results was interpreted by the existence of weak non leptonic interaction between nucleons in the compound nucleus. This first experimental result gave a serious impulse of theoretical and experimental developments of parity violation question in nuclear reactions. The weak interaction acts in the background of strong inter…
From the comparison of absolute intensities of the two-step gamma-cascades and known intensities of their primary and secondary transitions, the cascade and total population of about ~100 levels of 181Hf and 184,185,187W excited in thermal neutron capture was determined. These experimental results and intensities of two-step cascades to the low-lying levels of mentioned nuclei were reproduced in calculation using level densities with clearly expressed step-like structure. Radiative strength functions of the primary transitions following gamma-decay of these compound nuclei to the levels in the…
High-resolution gamma-ray spectroscopy of 18N is performed with the Advanced GAmma Tracking Array AGATA, following deep-inelastic processes induced by an 18O beam on a 181Ta target. Six states are newly identified, which together with the three known excitations exhaust all negative-parity excited states expected in 18N below the neutron threshold. Spin and parities are proposed for all located states on the basis of decay branchings and comparison with large-scale shell-model calculations performed in the p-sd space, with the YSOX interaction. Of particular interest is the location of the 0^-…
The neutron radius of a heavy nucleus is a fundamental nuclear-structure observable that remains elusive. Progress in this arena has been limited by the exclusive use of hadronic probes that are hindered by large and controversial uncertainties in the reaction mechanism. The Parity Radius Experiment at the Jefferson Laboratory offers an attractive electro-weak alternative to the hadronic program and promises to measure the neutron radius of 208Pb accurately and model independently via parity-violating electron scattering. In this contribution we examine the far-reaching implications that such …
Independent Validation of Octupole Collectivity in radium-224 through lifetime measurements of low-lying negative-parity states
University of the West of Scotland（西苏格兰大学）；TRIUMF（特利昂姆夫国家粒子加速器中心）；University of British Columbia（不列颠哥伦比亚大学）；Simon Fraser University（西蒙菲莎大学）；University of North Carolina, Chapel Hill（北卡罗来纳大学教堂山分校）；Triangle Universities Nuclear Laboratory（三角大学核实验室）；Duke University（杜克大学）
We report the first beyond-mean-field study of low-lying parity-doublet states in 224Ra by extending the multireference relativistic energy density functional method to include dynamical correlations related to symmetry restoration and quadrupole-octupole shape fluctuation with a generator coordinate method combined with parity, particle-number, and angular-momentum projections. We clarify full microscopically that the origin of spin-dependent parity splitting in low-spin states is related to the octupole shape stabilization of positive-parity states, the dominated shapes of which drift gradua…
We examine the importance of conserving the vector current in calculating low-energy neutrino-nucleus interactions by implicitly invoking Siegert's Theorem in describing the vector transverse electric current. We find that at low neutrino energies (E? <50 MeV), Siegert's Theorem can change neutrino cross sections for normal-parity non-spin-flip excitations by about a factor of two.The same is true of muon capture rates. At higher neutrino energies the effect of Siegert's Theorem diminishes, and by about 100 MeV the effect is very small.
A continuum approach to the three valence-quark bound-state problem in quantum field theory is used to perform a comparative study of the four lightest $(I=1/2,J^P = 1/2^\pm)$ baryon isospin-doublets in order to elucidate their structural similarities and differences. Such analyses predict the presence of nonpointlike, electromagnetically-active quark-quark (diquark) correlations within all baryons; and in these doublets, isoscalar-scalar, isovector-pseudovector, isoscalar-pseudoscalar, and vector diquarks can all play a role. In the two lightest $(1/2,1/2^+)$ doublets, however, scalar and pse…
Excitation functions of elastic and inelastic 7Be+p scattering were measured in the energy range between 1.6 and 2.8 MeV in the c.m. An R-matrix analysis of the excitation functions provides strong evidence for new positive parity states in 8B. A new 2+ state at an excitation energy of 2.55 MeV was observed and a new 0+ state at 1.9 MeV is tentatively suggested. The R-matrix and Time Dependent Continuum Shell Model were used in the analysis of the excitation functions. The new results are compared to the calculations of contemporary theoretical models.
The results of experimental studies of the low-energy isomeric state in the $^{229}$Th nucleus are presented. The work is consisted of several stages. During the first stage $^{229}$Th nuclei were excited with the inverse internal conversion to the low-lying isomeric level in plasma that was formed by laser pulse at the $^{229}$Th-containing target surface. Then thorium ions having excited nuclei were extracted from the plasma by an external electrical field and implanted into thin SiO$_2$ film grown on a silicon substrate (that is a dielectric material with about 9 eV band-gap). Gamma decay o…
Lifetimes of the positive-parity yrast band in 189Pt were measured using the recoil distance Doppler-shift method. A HPGe detector array consisting of 13 detectors was used in conjunction with the plunger device in CIAE. Excited states of 189Pt were populated by the 176Yb (18O, 5n) 189Pt fusion-evaporation reaction at a beam energy 87 MeV. The lifetimes of two levels belonging to the yrast band are measured. The results show that the 17/2+ state in the yrast band has large Qt value, but it deceases quickly with spin increasing. It may be contributed from the shape driving effect of the quasi-n…
