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Background: The hexadecapole deformation β4 is usually difficult to determine experimentally, especially its sign. The rapidly accumulated knowledge of β2 inspires the desire of β4 for radioactive nuclei, but the current low-quality beam is a severe experimental challenge. Therefore, a simple but sensitive method to extract β4 in such a condition is urgently called for. Purpose: To study the feasibility of extracting β4 from the lower-energy backward quasi-elastic (QEL) scattering. Methods: The QEL scattering at sub-barrier energy region is sensitive to the coupled-channels (CC) effect and consequently may be used to extract β4. The QEL scattering excitation functions for 16O + 152Sm, 170Er, and 174Yb were measured at a backward angle with small energy intervals at energies near the Coulomb barrier. Experimental fusion barrier distributions were also derived. The lower-energy data were analyzed to extract β4 with the help of the CC calculations. Results: The obtained β4 agrees with the available results reasonably well. Conclusions: We have demonstrated that the QEL scattering at sub-barrier energies provides a feasible and sensitive method to extract the value of β4, which is essentially meaningful for the radioactive nucleus because of its low beam intensity. [ABSTRACT FROM AUTHOR]

The effect of the positive Q-value neutron transfer (PQNT) channels on the subbarrier fusion process is still far from a clear understanding and hence is worth further investigation. To this end, we have measured the fusion excitation function for 32S+94Zr at energies near and below the Coulomb barrier with rather good accuracy, and deduced the experimental fusion barrier distribution. The reaction system 32S+94Zr is a good candidate for the evaluation of PQNT effect because it has multineutron transfer channels with positive ground-state Qxn values as well as the relatively weak low-lying 3- vibrational state in 94Zr. Our results show that the fusion cross sections of 32S+94Zr are strongly enhanced at the lower-energy region. By means of a cross comparison of the 32S,40Ca+90,94,96Zr systems, further evidence is given that the positive Qxn-value neutron transfer channels, rather than the strong low-lying 3- vibrational state, bring about the additional subbarrier fusion enhancement. Relative to the coupled-channels results with couplings to the low-lying inelastic collective excitations, an unexpectedly large enhancement for the subbarrier fusion cross sections is observed in 32S+94Zr compared to 32S+96Zr. Some existing theoretical models have been discussed, but a good explanation cannot be achieved. Exact coupled-channels theory and more experiments on transfer reactions themselves are strongly desired to comprehensively understand the effect of transfer on fusion. [ABSTRACT FROM AUTHOR]

Angular distributions of the 208Pb(7Li,6He)209Bi reactions with one-proton transferred to the ground, first-excited, and second-excited states of 209Bi were measured at E1ab = 25.67, 28.55, 32.55, 37.55, and 42.55 MeV. The experimental data and the data available in the literature at E|ah = 52 MeV were analyzed within the theoretical framework of the distorted wave Born approximation and coupled reaction channels, respectively. The optical model potentials for the exotic system 6He + 209Bi, which is the exit channel of the reaction studied, have been extracted by means of fitting the angular distributions of transfer reactions. In the analyses, interaction potentials of the entrance channel 7Li + 208Pb were derived from the elastic scattering data. For the 6He + 209Bi system, the phenomenon of the so-called breakup threshold anomaly was observed. Furthermore, the angular distributions of elastic scattering and total reaction cross sections by direct measurement for the 6He + 209Bi system in the energy region near and above the Coulomb barrier can be satisfactorily reproduced by employing the potentials extracted through the transfer reactions. [ABSTRACT FROM AUTHOR]

The new neutron-deficient isotope 205Ac was synthesized in the complete-fusion reaction 169Tm(40Ca, 4n)205Ac. The evaporation residues were separated in-flight by the gas-filled recoil separator SHANS in Lanzhou and subsequently identified by the α-α position and time correlation method. The α-decay energy and half-life of 205Ac were determined to be 7.935(30) MeV and 20+97-9 ms, respectively. Previously reported decay properties of the ground state in 206Ac were confirmed. [ABSTRACT FROM AUTHOR]

Angular distributions of 7Li + 11B elastic scattering were measured at Elab(7Li) = 9.85, 13.3, 18.3, 23.3, and 28.3 MeV within the angular range of θc.m. ≈ 15°-80°. Optical model potentials have been extracted from these angular distributions and the data available in the literature at Elab(7Li) = 34 MeV and Elab(11B) = 44 MeV to study the gross influences of intricate coupling effects varying with the reaction energy. With fixed geometrical shapes, the strengths of both real and imaginary potentials show a linear decrease with increasing energy, which is different from previous observations. [ABSTRACT FROM AUTHOR]

Fusion excitation functions with high precision have been measured for the 16O + 76Ge and 18O + 74Ge systems at energies near and below the Coulomb barrier. The barrier distributions have been extracted from the corresponding excitation functions. The coupling effect of the positive Q-value neutron transfer channel in the heavy-ion fusion reaction was examined by a comparison of the two systems. The fusion excitation functions are well reproduced by coupled-channels calculations including the 2+ and 3- vibrational states of the targets and the 2+ rotational state of 18O projectile. No obvious fusion enhancement due to the positive Q-value two-neutron transfer for the 18O + 74Ge system is observed as compared with the reference system of 16O + 76Ge. Analogous systems which are available in the literature are also discussed to realize the role of one- and/or two-neutron transfers with positive Q values in the fusion process. [ABSTRACT FROM AUTHOR]

A new, very short-lived neutron-deficient isotope 222Np was produced in the complete-fusion reaction 187Re (40Ar, 5n) 222Np, and observed at the gas-filled recoil separator SHANS. The new isotope 222Np was identified by employing a recoil- α correlation measurement, and six α -decay chains were established for it. The decay properties of 222Np with E α = 10 016 (33) keV and T1/2 = 38 0 + 260 - 110 ns were determined experimentally. The α -decay systematics of Np isotopes is improved by adding the new data for 222 Np, which validates the N = 126 shell effect in Np isotopes. The evolution of the N = 126 shell closure is discussed in the neutron-deficient nuclei up to Np within the framework of α -decay reduced width. [ABSTRACT FROM AUTHOR]

The heaviest N = 127 even-odd isotone 219U was produced in a fusion evaporation reaction employing 40Ar ions bombarding 183W target. Fusion evaporation residues were separated in flight by the gas-filled recoil separator Spectrometer for Heavy Atoms and Nuclear Structure and subsequently identified using a recoil-α correlation method. The α-decay properties of 219U were measured with improved precision, and two new α-decay lines were observed and assigned as the decays from the ground state of 219U to the (5/2-) and (3/2-) states of 215Th, respectively. The systematics for the α decay of the N = 127 even-odd isotones as well as the low-lying nuclear structure of their N = 125 daughter nuclei are discussed. [ABSTRACT FROM AUTHOR]

The multinucleon transfer (MNT) reaction has aroused wide interest in recent years largely due to its ability to produce neutron-rich heavy nuclei. The semiclassical model GRAZING can describe well the experimental MNT data for many medium-heavy systems, but only simply considers neutron evaporation in the deexcitation of primary fragments. In order to describe the final MNT products for heavy and even superheavy systems, we try to consider both the transfer and subsequent deexcitation processes by combining, for the first time, the GRAZING model and the statistical-decay model GEMINI as well as the improved version GEMINI++. Considering fission in the deexcitation of primary fragments by GEMINI++ model, the isotope distributions of final fragments are much wider than those only by GRAZING model, indicating an important role of fission in the deexcitation process for heavy and superheavy fragments. However, our results have large deviations from the GRAZING-F results, which may result from the different technique adopted in the deexcitation process. Moreover, it is shown that the GEMINI++ model is more reasonable than the GEMINI model, because the latter overpredicts the fission probability and the width of fission isotope distributions to a large extent. With GEMINI++ model, the predictions of cross sections for final isotopes can be improved by taking into account charged-particle evaporations, especially the a evaporation. [ABSTRACT FROM AUTHOR]

In a recent transfer reaction measurement of 208Pb(7Li,6He)209Bi at energies around and below the Coulomb barrier, the optical model potentials of the halo nuclear system 6He+209Bi were extracted by fitting the experimental data with the theoretical frameworks of the distorted-wave Born approximation and coupled reaction channels, respectively. With the high-precision result, a complete picture of the behavior of the optical potential for this halo system is clearly derived for the first time. The real potential presents a bell-like shape around the barrier as a normal threshold anomaly. However, for the imaginary part, it first increases with the energy decreasing below the barrier and then falls quickly to 0, hence the threshold energy can be determined by fitting the variation trend. Moreover, the result also provides some evidence that the dispersion relation does not hold for this halo nuclear system, which calls for further investigation of the underlying physics. [ABSTRACT FROM AUTHOR]

The threshold anomaly of the phenomenological potential has been known for a long time in nuclear reactions at energies around the Coulomb barrier, where the connection between the real and imaginary potentials is well described by the dispersion relation. However, this connection is not clear yet for some weakly bound nuclear systems, especially for reactions induced by exotic radioactive nuclei. In this study, precise optical potentials of the halo nuclear system 6He+209Bi were extracted via 208Pb(7Li,6He) transfer reactions with energies measured downward to the extremely sub-barrier region. The real potential presents a bell-like shape around the barrier as a normal threshold anomaly in tightly bound nuclear systems. However, the imaginary potential shows an abnormal behavior: it increases first with energy decreasing below the barrier and then falls quickly down to 0. It is the first time the threshold of the imaginary potential has been determined in an exotic nuclear system. Moreover, experimental results show the dispersion relation is not applicable for this system, which may be a common phenomenon for exotic nuclear systems. We discuss possible explanations for such a peculiar behavior, but further study is still desired for the underlying physics. [ABSTRACT FROM AUTHOR]

Angular distributions of the transfer reaction 63Cu(7Li,6He)64Zn were measured at Elab(7Li)=12.67, 15.21, 16.33, 23.30, 27.30, and 30.96 MeV. With the interaction potentials of the entrance channel 7Li+63Cu obtained from elastic scattering data as input, the optical potentials of the halo nuclear system 6He+64Zn in the exit channel were extracted by fitting the experimental data with the distorted-wave Born approximation (DWBA) and coupled reaction channels (CRC) methods, respectively. The results show that the threshold anomaly presents in the weakly bound system of 7Li+63Cu and the dispersion relation can be adopted to describe the connection between the real and imaginary potentials, while both the real and imaginary potentials nearly keep constant within the researched energy region for the halo system of 6He+64Zn. Moreover, calculations by the potentials extracted from the CRC method can reproduce the experimental elastic scattering of the 6He+64Zn system rather well, but those by the potentials from the DWBA method cannot, where the couplings between 7Li and 6He are absent. This work verifies the validity of the transfer method in the medium-mass target region and lays a solid foundation for the further study of optical potentials for exotic nuclear systems. [ABSTRACT FROM AUTHOR]

The cluster structure of the neutron-rich isotope ^{10}Be has been probed via the (p,pα) reaction at 150  MeV/nucleon in inverse kinematics and in quasifree conditions. The populated states of ^{6}He residues were investigated through missing mass spectroscopy. The triple differential cross section for the ground-state transition was extracted for quasifree angle pairs (θ_{p},θ_{α}) and compared to distorted-wave impulse approximation reaction calculations performed in a microscopic framework using successively the Tohsaki-Horiuchi-Schuck-Röpke product wave function and the wave function deduced from antisymmetrized molecular dynamics calculations. The remarkable agreement between calculated and measured cross sections in both shape and magnitude validates the molecular structure description of the ^{10}Be ground-state, configured as an α-α core with two valence neutrons occupying π-type molecular orbitals.

β decay of proton-rich nuclei plays an important role in exploring isospin mixing. The β decay of ^{26}P at the proton drip line is studied using double-sided silicon strip detectors operating in conjunction with high-purity germanium detectors. The T=2 isobaric analog state (IAS) at 13 055 keV and two new high-lying states at 13 380 and 11 912 keV in ^{26}Si are unambiguously identified through β-delayed two-proton emission (β2p). Angular correlations of two protons emitted from ^{26}Si excited states populated by ^{26}P β decay are measured, which suggests that the two protons are emitted mainly sequentially. We report the first observation of a strongly isospin-mixed doublet that deexcites mainly via two-proton decay. The isospin mixing matrix element between the ^{26}Si IAS and the nearby 13 380-keV state is determined to be 130(21) keV, and this result represents the strongest mixing, highest excitation energy, and largest level spacing of a doublet ever observed in β-decay experiments.

A new α-emitting isotope ^{214}U, produced by the fusion-evaporation reaction ^{182}W(^{36}Ar,4n)^{214}U, was identified by employing the gas-filled recoil separator SHANS and the recoil-α correlation technique. More precise α-decay properties of even-even nuclei ^{216,218}U were also measured in the reactions of ^{40}Ar, ^{40}Ca beams with ^{180,182,184}W targets. By combining the experimental data, improved α-decay reduced widths δ^{2} for the even-even Po-Pu nuclei in the vicinity of the magic neutron number N=126 are deduced. Their systematic trends are discussed in terms of the N&#95;{p}N&#95;{n} scheme in order to study the influence of proton-neutron interaction on α decay in this region of nuclei. It is strikingly found that the reduced widths of ^{214,216}U are significantly enhanced by a factor of two as compared with the N&#95;{p}N&#95;{n} systematics for the 84≤Z≤90 and N<126 even-even nuclei. The abnormal enhancement is interpreted by the strong monopole interaction between the valence protons and neutrons occupying the π1f&#95;{7/2} and ν1f&#95;{5/2} spin-orbit partner orbits, which is supported by the large-scale shell model calculation.

β-delayed one-proton emissions of ^{22}Si, the lightest nucleus with an isospin projection T&#95;{z}=-3, are studied with a silicon array surrounded by high-purity germanium detectors. Properties of β-decay branches and the reduced transition probabilities for the transitions to the low-lying states of ^{22}Al are determined. Compared to the mirror β decay of ^{22}O, the largest value of mirror asymmetry in low-lying states by far, with δ=209(96), is found in the transition to the first 1^{+} excited state. Shell-model calculation with isospin-nonconserving forces, including the T=1, J=2, 3 interaction related to the s&#95;{1/2} orbit that introduces explicitly the isospin-symmetry breaking force and describes the loosely bound nature of the wave functions of the s&#95;{1/2} orbit, can reproduce the observed data well and consistently explain the observation that a large δ value occurs for the first but not for the second 1^{+} excited state of ^{22}Al. Our results, while supporting the proton-halo structure in ^{22}Al, might provide another means to identify halo nuclei.

A new, very short-lived neutron-deficient isotope ^{222}Np was produced in the complete-fusion reaction ^{187}Re(^{40}Ar,5n)^{222}Np, and observed at the gas-filled recoil separator SHANS. The new isotope ^{222}Np was identified by employing a recoil-α correlation measurement, and six α-decay chains were established for it. The decay properties of ^{222}Np with E&#95;{α}=10016(33)  keV and T&#95;{1/2}=380&#95;{-110}^{+260}  ns were determined experimentally. The α-decay systematics of Np isotopes is improved by adding the new data for ^{222}Np, which validates the N=126 shell effect in Np isotopes. The evolution of the N=126 shell closure is discussed in the neutron-deficient nuclei up to Np within the framework of α-decay reduced width.

The threshold anomaly of the phenomenological potential has been known for a long time in nuclear reactions at energies around the Coulomb barrier, where the connection between the real and imaginary potentials is well described by the dispersion relation. However, this connection is not clear yet for some weakly bound nuclear systems, especially for reactions induced by exotic radioactive nuclei. In this study, precise optical potentials of the halo nuclear system ^{6}He+^{209}Bi were extracted via ^{208}Pb(^{7}Li,^{6}He) transfer reactions with energies measured downward to the extremely sub-barrier region. The real potential presents a bell-like shape around the barrier as a normal threshold anomaly in tightly bound nuclear systems. However, the imaginary potential shows an abnormal behavior: it increases first with energy decreasing below the barrier and then falls quickly down to 0. It is the first time the threshold of the imaginary potential has been determined in an exotic nuclear system. Moreover, experimental results show the dispersion relation is not applicable for this system, which may be a common phenomenon for exotic nuclear systems. We discuss possible explanations for such a peculiar behavior, but further study is still desired for the underlying physics.