Study of N = 16 for Ne isotopes

²⁷Ne has been investigated through the one neutron transfer reaction ²⁶Ne(d,p)²⁷Ne in inverse kinematics at 9.7 MeV/nucleon. The results support the existence of a low lying negative parity state in ²⁷Ne which is a signature of a reduced sd-fp shell gap in the N = 16 neutron rich region, at variance with stable nuclei.     

Evidence for a doubly magic O

The decay energy spectrum for neutron unbound states in ²⁴O (Z=8$Z=8$, N=16$N=16$) has been observed for the first time. The resonance energy of the lowest lying state, interpreted as the ²⁺$2^{+}$ level, has been observed at a decay energy above 600 keV. The resulting excitation energy of the ²⁺$2^{+}$ level above 4.7 MeV, supplies strong evidence that ²⁴O is a doubly magic nucleus. The data is also consistent with the presence of a second excited state around 5.33 MeV which can be interpreted as the ¹⁺$1^{+}$ level.     

In-beam γ spectroscopy using DIC with a radioactive Ne beam

A study of deep-inelastic and multi-nucleon transfer reactions to populate neutron-rich O, Ne and F nuclei is here presented. The reaction under analysis employed a beam of radioactive ²⁴Ne at 7.9 AMeV, provided by the SPIRAL facility at Ganil, impingin on a ²⁰⁸Pb target. The reaction products have been detected in the VAMOS spectrometer in coincidence with gamma rays measured by the EXOGAM array. Preliminary results here presented show a selectivity in the population of states of different nature.     

High-spin states in <Superscript>36</Superscript>Ar and their underlying shell model configurations

Eight high-spin states in ³⁶Ar below 10MeV excitation energy, among them a prospective J ^π = 8^- state at 9408keV and the J? 8 levels of the recently discovered superdeformed rotational band, have been observed by n-γ coincidence measurements with the ³³S(α, nγ) reaction at E _α = 14.4 and 13.4MeV. High-spin assignments of, respectively, J ^π = 6⁺ and 5^- were obtained for the E _p = 1209 and 1462keV (E _x = 9682 and 9927keV) resonances of the ³⁵Cl (p,γ) reaction by a measurement of γ-ray angular distributions. The spectrum of the high-spin and of the E _x? 7.4MeV levels is decomposed according to the underlying shell model configurations with n = 0, 1, 2, 4 particles excited from the N = 2 into the N = 3 major shell. The role of four-particle excitations, all connected with large prolate distortions, is elucidated for the entire A = 36-40 mass region. Received: 21 December 2001 / Accepted: 25 March 2002     

Theoretical Calculation for Half-Lives of Spherical Proton Emitters

Half-lives of the proton radioactivity for spherical proton emitters are investigated theoretically in the Wentzel- Kramers-Brillouin approximation. Microscopic proton-nucleus interaction potentials are obtained by folding the densities of the residual daughter nuclei with renormalized M3Y effective interactions. We also take the spectroscopic factor （Sp） into account in the calculation, which is evaluated in the relativistic mean field approach using the force NL3. The calculated results are found to be in good agreement with the experimental data.     

Quadrupole collectivity of neutron-rich neon isotopes

The Angular Momentum Projected Generator Coordinate Method, with the quadrupole moment as collective coordinate and the Gogny force (D1S) as the effective interaction, is used to describe the properties of the ground state and low-lying excited states of the even-even neon isotopes ^20-34Ne, that is, from the stability valley up to the drip line. It is found that the ground state of the N = 20 nucleus ³⁰Ne is deformed but to a lesser extent than the N = 20 isotope of the magnesium. In the calculations, the isotope ³²Ne is at the drip line in good agreement with other theoretical predictions. On the other hand, rather good agreement with experimental data for many observables is obtained. Received: 19 Novemeber 2002 / Accepted: 24 January 2003 / Published online: 8 April 2003     

Experimental Evidence of Two-Proton Emissions from 18Ne Excited State

Experiment ^18Ne＋^197 Au was performed in Heavy Ion Research Facility Radioactive Ion Beam Line at Lanzhou （RIBLL）. The nuclear energy levels of ^18Ne were built by complete kinematical reconstruction of the decay products and diproton decay were observed from ^18Ne excited states. At 6.15 MeV, the experimental relative momentum and angular correlations of the emitted protons are given. The obvious enhancement at ｜qrol｜= 23 MeV/c and θc.m. = 40° shows the experimental criterion of ^2He cluster decay from ^18Ne^q.     

Reactions with fast radioactive beams of neutron-rich nuclei

The neutron dripline has presently been reached only for the lightest nuclei up to the element oxygen. In this region of light neutron-rich nuclei, scattering experiments are feasible even for dripline nuclei by utilizing high-energy secondary beams produced by fragmentation. In the present article, reactions of high-energy radioactive beams will be exemplified using recent experimental results mainly derived from measurements of breakup reactions performed at the LAND and FRS facilities at GSI and at the S800 spectrometer at the NSCL. Nuclear and electromagnetically induced reactions allow probing different aspects of nuclear structure at the limits of stability related to the neutron-proton asymmetry and the weak binding close to the dripline. Properties of the valence-neutron wave functions are studied in the one-neutron knockout reaction, revealing the changes of shell structure when going from the beta-stability line to more asymmetric loosely bound neutron-rich systems. The vanishing of the N = 8 shell gap for neutron-rich systems like ¹¹Li and ¹²Be, or the new closed N = 14, 16 shells for the oxygen isotopes are examples. The continuum of weakly bound nuclei and halo states can be studied by inelastic scattering. The dipole response, for instance, is found to change dramatically when going away from the valley of stability. A redistribution of the dipole strength towards lower excitation energies is observed for neutron-rich nuclei, which partly might be due to a new collective excitation mode related to the neutron-proton asymmetry. Halo nuclei, in particular, show strong dipole transitions to the continuum at the threshold, being directly related to the ground-state properties of the projectile. Finally, an outlook on future experimental prospects is given.     

The study of the reduced α-width and ANC of O states through its sequential breakup

In this work we theoretically study using continuum-discretized-coupled channel (CDCC) theory, the resonant breakup of ¹⁶O by comparison with a recent measurement. The ground state Asymptotic Normalization Coefficient (ANC) and the alpha spectroscopic factor of ¹⁶O are evaluated in this work. The peripheral aspect of resonance breakup through a ²⁺$2^{+}$ unbound state has been also studied.     

Measurement of the Proton Structure Function F 2 at Low Q 2 and Very Low x with the ZEUS Beam Pipe Calorimeter at HERA

Three different kinds of scaling are observed in a toy model of turbulence (“GOY”). The first has a multifractal spectrum of exponents. The second is a simple static selfsimilarity solution. The third phase is dynamic but has simple scaling. This last previously unreported equipartition behavior is discussed. It is drastically different from the other two in terms of its scaling exponent(s) and emerges when the energy flux on the boundaries vanishes (no dissipation and no forcing).     

Two-quasiparticle K-isomers and pairing strengths in the neutron-rich isotopes Er and Er

Isomeric two-quasiparticle states have been identified in the neutron-rich isotopes ¹⁷²Er and ¹⁷⁴Er using multi-nucleon transfer reactions with ¹³⁶Xe beams incident on various targets, and γ  -ray spectroscopy with Gammasphere. A candidate for the Kπ=⁶⁺$K^{\pi }=6^{+}$ two-quasineutron state in ¹⁷²Er is found at 1500 keV. In ¹⁷⁴Er, a nuclide whose level scheme was previously unknown, a long-lived isomer is identified at 1112 keV decaying via an inhibited E1 transition and revealing the yrast sequence of ¹⁷⁴Er. This isomer is proposed to be a Kπ=⁸⁻$K^{\pi }=8^{-}$ two-quasineutron state, defining a sequence in the N=106$N=106$ isotones extending from the well-deformed neutron-rich isotope ¹⁷⁴Er to the neutron-deficient isotope ¹⁸⁸Pb, where the presence of the isomer signifies a prolate minimum in an otherwise spherical well. Configuration-constrained potential-energy surface calculations are used to predict the excitation energies of the 6⁺ and 8⁻ intrinsic states and as a basis for extracting the pairing force strength, Gn$G_n$, in the N=104$N=104$ and N=106$N=106$ isotones.     

Nuclear moments of neutron-rich aluminum isotopes

Ground-state magnetic-dipole moments (μ) of ^30-32Al and electric quadrupole moments (Q) of ^31,32Al have been measured with the β-NMR method using spin-polarized radioactive-isotope beams produced in projectile-fragmentation reactions. Beams of ^30-32Al were obtained by using RIKEN projectile-fragment separator RIPS after the fragmentation of ⁴⁰Ar projectiles at an energy of E = 95A MeV on a ⁹³Nb target. The obtained μ_exp[^30-32Al] and values agree well with shell-model calculations within the sd shell using the USD interaction. Also, Q_exp[³¹Al] was found to be small. Thus, we can conclude that these aluminum isotopes are located outside the island of inversion.     

Molecular-orbital structure in neutron-rich Be and C isotopes

The structure of Be and C isotopes are investigated based on the molecular-orbit (MO) model. The low-lying states are characterized by several configurations of valence neutrons, which are constructed as combinations of basic orbits. In ¹⁰Be, all of the observed positive-parity bands and the negative-parity bands are described within the model. The second 0⁺ state of ¹⁰Be has a large α-α cluster structure, and this is characterized by a (1/2⁺ _σ)² configuration. An enlargement of the α-α distance due to two-valence neutrons along the α-α axis makes their wave function smooth and reduces the kinetic energy drastically. Furthermore, the contribution of the spin-orbit interaction due to coupling between the S _z = 0 and the S _z = 1 configurations, is important. In the ground state of ¹²Be, the calculated energy exhibits similar characteristics, that the remarkable α clustering and the contribution of the spin-orbit interaction make the binding of the state with (3/2^- _π)²(1/2⁺ _σ)² configuration properly stronger in comparison with the closed p-shell (3/2^- _π)²(1/2^- _π)² configuration. This is related to the breaking of the N = 8 (closed p-shell) neutron magic number. Also, the molecule-like structure of the C isotopes is investigated using a microscopic α+α+α+n+n+ ^{. . .} model. The combination of the valence neutrons in the π- and the σ-orbit is promising to stabilize the linear-chain state against the breathing and bending modes, and it is found that the excited states of ¹⁶C are the most promising candidates for such structure. Received: 1 May 2001 / Accepted: 4 December 2001     

The β Decay of 21N

The β-delayed neutron and γ energy spectra taken from the decay of neutron-rich nucleus ²¹N were measured by using the β-γ and β-n coincidence detection method. Thirteen new neutron groups ranging from 0.28MeV to 4.98MeV and with a total branching ratio of 88.7±4.2% were observed andpresented. One γ transition with an energy of 1222keV emitted from the excited state of ²¹O, and four γ transitions with energies of 1674, 2397, 2780, and 3175keV emitted from the excited states of ²⁰O were identified in the β decay chain of ²¹N. The β decay half-life for ²¹N is determined to be 82.9±1.9ms. The uncertainty of half-life is much smaller than the previous result.     

Helium-cluster decay widths of molecular states in beryllium and carbon isotopes

⁴He (i.e., α particle) and ⁶He emissions from possible molecular states in beryllium and carbon isotopes have been investigated using a mean-field-type cluster potential. Calculations can reasonably describe the α-decay widths of studied states in beryllium and carbon isotopes, and also ²⁰Ne, compared with experiments. For the nucleus ¹⁰Be, we discussed α-decay widths with different shapes or different decay modes, in order to understand the very different decay widths of two excited states. The widths of ⁶He decays from ¹²Be and α decays from ^13,14C are predicted, which could be useful for future experiments.     

Test of Determination of (p,γ) Astrophysical S-Factors Using the Asymptotic Normalization Coefficients from Neutron Transfer Reactions

The asymptotic normalization coefficients （ANCs） for the virtual decay ^17 O→^16 O＋n are derived from the angular distributions of the 16 O（d, p）^17O reaction leading to the ground and first excited states of ^17O, respectively, using the distorted wave Born approximation and the adiabatic wave approximation. The ANCs of ^17F are then extracted according to charge symmetry of mirror nuclei and used to calculate the astrophysical S-factors of ^16 O（p, γ）^17 F leading to the first two states of ^17 F. The present results are in good agreement with those from the direct measurement. This provides a test of this indirect method to determine direct astrophysical S-factors of （P, γ） reaction. In addition, the S-factors at zero energy for the direct captures to the ground and first excited states of ^17 F are presented, without the uncertainty associated with the extrapolation from higher energies in direct measurement.