Systematic trends in the beta minus strength functions of neutron-rich rubidium isotopes

Experimental β^?-strength functions (S_β) are presented for the odd-mass Rb isotope sequence A=89to97. As expected from general nuclear structure considerations, but in contrast to present purely statistical concepts, these strength functions exhibit well separated “pygmy” resonances and a systematic behaviour as a function of mass number and β-decay energy.     

The EMC effect at low x in perturbative QCD

The EMC effect is studied in the perturbative QCD hard pomeron approach. In this framework the nuclear structure function can be expressed directly in terms of the proton one. In the limit x → 0 and for a nucleus with a constant density the effect is found to be a function of a single variable which combines its x-, Q- and A-dependence. The EMC ratio of the nuclear to nucleon structure functions goes to zero for x → 0 or/and A ? 1. At large Q ² the effect dies out as ln Q/Q. To describe the present data at 0. 005 < x < 0. 05 an attempt is made to take into account subasymptotic effects by introducing an anomalous dimension falling with x. This leads to a weaker x- and Q-dependence, which almost disappears as x grows and the anomalous dimension becomes small.     

Meson-exchange corrections to the nuclear weak axial charge density in the hard pion model and 0+ 3 0− transitions in A = 16 nuclei

Starting with the hard-pion model based on a minimal chiral invariant phenomenological lagrangian, the two-body part of the time component of the weak axial-vector current is constructed in the tree approximation. Pion, rho- and A₁-meson exchanges are considered. The mesonic exchange operator obtained is applied to describe the purely weak axial 0⁺?0^?, ΔT = 1 transition in the nuclear A = 16 system. In order to treat nuclear structure correlation effects, explicit use of shell-model wave functions with configuration mixing is made. We confirm the large enhancement of the nuclear weak axial charge density with respect to impulse approximation.     

A-dependence of shadowing and the small-x EMC data

We examine the gluon-interaction model for shadowing in the light of the new EMC data on nuclear structure functions. In the model, x_n and x_A characterise the points where shadowing begins abd becomes total. Good agreement with the data occurs when x_n varies with A but x_A does not - conversely to the original formulation of the model. The A-dependence of x_n can be described by the same dynamics that generates the A-dependence of the EMC effect at large x.     

The solution of the quantum mechanical many-body problem bound by harmonic forces as a translationally invariant basis for nuclear structure calculations

A very simple method to obtain the translationally invariant wave functions of anA-particle system of bosons or fermions bound by harmonic forces is derived and a formalism to apply these solutions as a basis for nuclear structure calculations is presented. The simplicity of this formalism is demonstrated for⁴He. The method is not restricted toA≦4.     

Structure functions of bound nucleons: From the EMC effect to nuclear shadowing

We describe the nuclear structure functions in the whole range of the Bjorken variablex, by combining various effects in a many-step procedure. First, we present a QCD motivated model of nucleons, treated, in the limit of vanishingQ ², as bound states of three relativistic constituent quarks. Gluons and sea quarks are generated radiatively from the input valence quarks. All parton distributions are described in terms of the confinement (or nucleon's) radius. The results for free nucleons are in agreement with the experimental determinations. The structure functions of bound nucleons are calculated by assuming that the main effect of nucleon binding is stretching of nucleons. The larger size of bound nucleons lowers the valence momentum and enhances the radiatively generated glue and sea densities. In the small-x region the competitive mechanism of nuclear shadowing takes place. It also depends on the size of the nucleons. By combining stretching, shadowing and Fermi motion effects (the latter confined to very largex), the structure function ratio is well reproduced. Results are also presented for theA-dependence of the momentum integral of charged partons, the nuclear gluon distribution and the hadron-nuclei cross sections.     

Mass and charge distributions in the very asymmetric thermal neutron induced fission of the odd-Z nucleus 242mAm

Yields of light fission products (A = 68, 70–84, 87, 88, 94, 96, 98, 102 and 106–108), their kinetic energies and nuclear charge distributions (A = 71–84, 87 and 88) in the thermal neutron induced fission of the odd-Z nucleus ^242mAm(Z = 95) were measured using the mass-separator Lohengrin at the Institute Laue-Langevin in Grenoble (France). The mass yield curve shows a fine structure at A = 70, probably due to shell and/or odd-even effects affecting also the nuclear charge distribution. The analysis of isotopic chain yields gives evidence for a very low excitation energy of the lightest fission fragments observed. A preferential formation of fragments with even Z is found for this odd-Z compound nucleus. Calculated values for the local odd-even effect are comparable with those for the neighbouring even-Z fissile nuclides and increase from 13% to 30% with increasing asymmetry of the mass split (A_L = 84 to 68 and Z_L = 35 to 28). The neutron odd-even effect shows a similar but less pronounced behaviour.     

Nuclear Corrections in ν A DIS and Their Compatibility with Global NPDF Analyses

We perform a global χ ²-analysis of nuclear parton distribution functions using data from charged current neutrino–nucleus (ν A) deep inelastic scattering (DIS), charged-lepton–nucleus (? ^± A) DIS, and the Drell–Yan (DY) process. We show that the nuclear corrections in ν A DIS are not compatible with the predictions derived from ? ^± A DIS and DY data. We quantify this result using a hypothesis-testing criterion based on the χ ² distribution which we apply to the total χ ² as well as to the χ ² of the individual data sets. We find that it is not possible to accommodate the data from ν A and ? ^± A DIS by an acceptable combined fit. This implies that either the twist-2 parton distribution functions in nuclei are not universal, or that higher-twist terms play a more important role in the nuclear environment and have to be taken into account.     

The role of Fermi motion and quark exchange as a nuclear medium effect in the nuclear structure function of 3He, 3H nuclei and their EMC effects

To extract the nuclear structure function of light nuclei like ³He and ³H, the convolution of proton and neutron structure functions in the conventional approach could not explain the modification of nuclear structure functions of these nuclei because of some nuclear medium effects. There are some models that have some success to explain the modification of nuclear structure functions in limited x range. So in this investigation the quark exchange model is considered to extract the nuclear medium effect of this phenomenon (quark exchange effect) for nuclear structure functions of ³He and ³H nuclei. The Fermi motion part of the nuclear structure functions for these nuclei is extracted by taking the GRV’s neutron and proton structure functions in the conventional approach. So the nuclear structure functions and the EMC ratios of ³He and ³H nuclei are calculated by considering both Fermi motion and the nuclear medium effect of quark exchange. Finally the extracted results are compared with available data.     

Structure functions of nuclei for all x and Q 2

We propose a modified version of the quark cluster model to describe the structure functions of nuclei over the complete kinematical region of the variables x = Q ²/2m _N ν and Q ². The model accounts for shadowing effects at very small x and anti-shadowing in the region 0.1 ≤ x ≤ 0.3. The experimental observation that the ratio of structure functions F ₂ ^A /F ₂ ^D is less than unity in the region x ? 0.5 is related to the influence of multiquark clusters. The model agrees with all available data on nuclear structure fuctions for a large variety of nuclei, and can be used to make predictions for kinematical regions not yet studied experimentally.     

Shell-model approach to the nucleon elastic scattering by nuclei

On the basis of the shell-model approach to nuclear reactions the averaged scattering matrix is parametrized. The method is applied to the calculation of s-neutron strength functions. It is shown that in contrast to the optical model predictions the isotopic dependence of the strength function in its minimum (A ≈ 100?140) is mainly determined by the 3s-state spectroscopic factor.     

Variation of even-odd proton effects with excitation energy in fission of 252Cf: Confirmation of fine structure in v(A)

The existence of even-odd proton effects (fine structure) in νv(A) of individual fragments from ²⁵²Cf(sf) has been confirmed by analysis of previously reported data. The fine structure is seen to increase in amplitude as the fragment excitation energy decreases, a behaviour similar to the well-known behaviour of the mass yield curve. The present mass yield data also show these effects, as expected. Conversely, our total kinetic energy data TKE(A), not previously reported, show very little even-odd proton effect. It is shown that energy balance considerations, also, support the existence of even-odd proton effects in neutron emission from ²⁵²Cf(sf).     

Asymptotic Normalization Coefficients (Nuclear Vertex Constants), Three-Body Asymptotic Normalization Functions (On-Shell Vertex Functions) and Nuclear Astrophysics

In the present review work, the main methods of the determination of asymptotic normalization coefficients (or respective nuclear vertex constants) for the A + x → B channel and of threebody asymptotic normalization functions (or respective on-shell vertex functions) for the A + b + c → B channel are briefly discussed. The main attention is paid both to the use of the specific asymptotic normalization coefficients and three-body asymptotic normalization functions as a source of getting the valuable information about the pair (nucleon–nucleon, nucleon–cluster and cluster–cluster) nuclear interactions and to their application for the specific direct nuclear-astrophysical radiative capture and peripheral transfer reactions at low energies.     

Charge radii and moments of strontium nuclei by laser spectroscopy

The isotope shifts and hyperfine splittings for 11 strontium isotopes (A=80–90) and two isomers for the optical transition λ=293.2 nm were measured. The magnetic dipole and electric quadrupole moments and the changes of the mean square charge radii are derived. The results are discussed with respect to the increasing nuclear deformation and the anomalous coupling scheme of light Sr nuclei.     

Change of confinement scale in nuclei and the EMC effect

We study a model in which the confinement scale of quarks in a nucleus of massA changes asA ^1/3. This explains theA dependence of structure functions (emc effect) as seen in muon, electron and antineutrino deep inelastic scattering from nuclear targets. We also investigate a prediction of this model—anA dependence of theqcd scale parameter A.     

The response of Mo to supernova neutrinos

Knowledge about nuclear responses to neutrinos is essential for both astrophysical applications and studies of neutrino properties. We perform in this paper calculations of the cross sections for neutral-current neutrino scattering off the odd A=95,97 Mo isotopes for energies appropriate for the detection of supernova neutrinos. Both the incoherent and coherent contributions to the cross sections are evaluated. The prominently contributing nuclear final states are identified and analysed. We employ the microscopic quasiparticle-phonon model (MQPM) to construct the wave functions of the initial and final nuclear states. The response of the aforementioned nuclei to supernova neutrinos are computed by folding the obtained cross sections with a two-parameter Fermi-Dirac distribution. The sensitivity of the calculated nuclear responses to the adopted supernova model is also discussed.     

Electroinduced two-nucleon knockout and correlations in nuclei

A model to calculate cross sections for electroinduced two-nucleon emission from finite nuclei is presented. Short-range correlations in the wave functions and meson-exchange contributions to the photoabsorption process are implemented. Effects of the short-range correlations are studied with the aid of a perturbation expansion method with various choices of the Jastrow correlation function. The model is used to investigate the relative importance of the different reaction mechanisms contributing to the A(e,e′pn) and A(e,e′pp) process. Representative examples for the target nuclei ¹²C and ¹⁶O and for kinematical conditions accessible with contemporary high-duty cycle electron accelerators are presented. A procedure is outlined to calculate the two-nucleon knockout contribution to the semi-exclusive (e,e′p) cross section. Using this technique we investigate to what extent far semi-exclusive (e,e′p) reactions can be used to detect high-momentum components in the nuclear spectral function.