Properties of the rotational bands in the transitional nucleus 189Pt

High-spin states in 189Pt have been studied experimentally using the 176Yb(18O,5n) reaction at beam energies of 88 and 95 MeV. The level scheme of189Pt has been revised significantly and extended to high-spin states.Rotational bands have been analyzed in the framework of triaxial particle-rotor model, and a γ ≈−30◦triaxial shape and a near-prolate shape have been proposed to the νi−113/2 and νf5/2(p3/2) bands, respectively. Two ΔI = 2 transition sequences with similar energies have been observed, and they have been proposed to be associated with the νi−213/2νf5/2(p3/2) configuration. The structure built on the νi−213/2νf5/2(p3/2) configuration could be interpreted theoretical calculations of the triaxial particle-rotor model if a near-oblate shape is assumed.

Prolate and oblate shape coexistence in Pt-188

A standard in-beam gamma-spectroscopy experiment for Pt-188 is performed via the Yb-176(O-18, 6n) reaction at beam energies of 88 and 95 MeV, and the level scheme for (188) Pt is established. Prolate and oblate shape coexistence has been demonstrated to occur in Pt-188 by applying the projected shell model. The rotation alignment of i(13/2) neutrons drives the yrast sequence changing suddenly from prolate to oblate shape at angular momentum 10th, indicating likely a new type of shape phase transition along the yrast line in Pt-188.

The beta decay of N-21

The beta-delayed neutron and gamma energy spectra taken from the decay of neutron-rich nucleus N-21 were measured by using the beta - gamma and beta - n coincidence detection method. Thirteen new neutron groups ranging from 0.28MeV to 4.98 MeV and with a total branching ratio of 88.7 +/- 4.2% were observed and presented. One gamma transition with an energy of 1222 keV emitted from the excited state of O-21, and four gamma transitions with energies of 1674, 2397, 2780, and 3175 keV emitted from the excited states of O-20 were identified in the 3 decay chain of N-21. The beta decay half-life for N-21 is determined to be 82.9 +/- 1.9 ms. The uncertainty of half-life is much smaller than the previous result.

Study on the localization of the electric dipole sources

The research of dipole source localization has great significance in both clinical research and applications. For example, the EEG recording from the scalp is widely used for the localization of sources of electrical activity in the brain. This paper presents a closed formula that describes the electric field of dipoles at arbitrary position, which is a linear transformer called the transfer matrix. The expression of transfer matrix and its many useful characteristics are given, which can be used for the analysis of the electrical fields of dipoles. This paper also presents the closed formula for determining the location and magnitude of single dipole or multi-dipoles according to its electrical field distribution. A calculation result for a single dipole shows that the dipole will be located at the midpoint of a line segment if there are equivalent fields at its two ends.

Probing the high density behavior of the symmetry energy by using the free neutron-proton ratio

Based on the isospin- and momentum-dependent transport model IBUU04, the transverse momentum distributions of the free neutron-proton ratio in the Sn-132+(124) Sn reaction system at mid-central collisions with beam energies of 400/A MeV, 600/A MeV and 800/A MeV are studied by using two different symmetry energies. It is found that the free neutron-proton ratio as a function of the transverse momentum at the mid-rapidity is very sensitive to the density dependency of the symmetry energy especially at incident energies around 400/AMeV.

Probing the high density behavior of the symmetry energy by using proton elliptic flow

Based on the isospin- and momentum-dependent transport model IBUU04, we calculated the reaction of the Sn-132+Sn-124 systems in semi-central collisions at beam energies of 400/A MeV, 600/A MeV and 800/A MeV by adopting two different density dependent symmetry energies. It was found that the proton differential elliptic flow as a function of transverse momentum is quite sensitive to the density dependence of symmetry energy, especially for the considered beam energy range. Therefore the proton differential elliptic flow may be considered as a robust probe for investigating the high density behavior of symmetry energy in intermediate energy heavy ion collisions.

Band properties of the transitional nucleus Pt-187

High-spin states in Pt-187 have been studied experimentally using the Yb-173(O-18, 4n) reaction at beam energies of 78 and 85 MeV. The previously known bands based on the nu i(13/2),nu 7/2(-)[503], and nu i(13/2)(2)nu j configurations have been extended to high-spin states, and new rotational bands associated with the nu 3/2(-)[512] and nu 1/2(-)[521] Nilsson orbits have been identified. The total Routhian surface calculations indicate that the transitional nucleus Pt-187 is very soft with respect to beta and gamma deformations. The band properties, such as level spacings, band crossing frequencies, alignment gains, and signature splittings, have been compared with the systematics observed in neighboring nuclei and have been interpreted within the framework of the cranked shell model. The rotational bands show different band crossing frequencies, which can be explained by the alignment either of i(13/2) neutrons or of h(9/2) protons. Importantly, evidence is presented for a pi h(9/2) alignment at very low frequency in the nu 7/2(-)[503] band. The proton nature of the band crossing is strongly suggested by comparing the measured B(M1;I -> I-1)/B(E2;I -> I-2) ratios with the theoretical values from the semiclassical Donau and Frauendof approach.

Study of multi-quasiparticle excited states in Ce-139

High-spin states in Ce-139 have been populated using the Te-130(C-12, 3n) reaction at beam energy of 50MeV. The level scheme of Ce-139 has been revised and extended greatly up to E=5765.0keV. The level structure of Ce-139 shows typical characteristics of spherical nucleus, and the high-spin states were formed by the excitations of valence nucleons. Energies of the yrast and near yrast high-spin states in Ce-139 have been calculated by the empirical shell model, and the multi-quasiparticle nature of high-spin excited states has been discussed.

Double neutron-proton differential transverse flow as a probe for the high density behavior of the nuclear symmetry energy

The double neutron-proton differential transverse flow taken from two reaction systems using different isotopes of the same element is studied at incident beam energies of 400 and 800 MeV/nucleon within the framework of an isospin- and momentum-dependent hadronic transport model IBUU04. The double differential flow is found to retain about the same sensitivity to the density dependence of the nuclear symmetry energy as the single differential flow in the more neutron-rich reaction. Because the double differential flow reduces significantly both the systematic errors and the influence of the Coulomb force, it is thus more effective probe for the high-density behavior of the nuclear symmetry energy.

Beam energy dependence of the pi(-)/pi(+) ratio

Using the isopin- and momentum-dependant hadronic transport model IBUU04, the effect of symmetry energy on the pi(-)/pi(+) ratio are studied. Our investigations are based on the calculations of the Sn-132+Sn-124 semi-central collisions at beam energies of 400/ A MwV, 600/ A MeV and 800MeV. It is found that both the transverse momentum and kinetic energy distributions of the pi(-)/pi(+) ratio are rather sensitive to the symmetry energy, especially around the Colomb peaks. The position of the coulomb peak is shown to be nearly indrpendant of beam energy. The sesitivity of the pi(-)/pi(+) ratio to the symmetry ebergy decreases as the beam energy increases from 600/ A MeV to 800/ A MeV.

Probing the high density behavior of the symmetry energy by using the neutron-proton differential flow

Based on the isospin- and momentum-dependent transport model IBUU04, we investigated the neutron-proton differential flow in the (132) Sn + (124) Sn mid-central collisions at beam energies of 400MeV/A, 600MeV/A and 800MeV/A by adopting two different symmetry energies. It was found that the neutron-proton differential flow as a function of rapidity is very sensitive to the density dependence of symmetry energy, especially at incident energies around 400MeV/A

Properties of alpha-decay to ground and excited states of heavy nuclei

Branching ratios and half-lives of alpha-decay to the ground-state rotational bands as well as the high-lying excited states of even-even nuclei have been calculated in the framework of the generalized liquid drop model (GLDM) and Royer's formula that we improved very recently. The calculation covers the isotopic chains from Ra to No in the mass regions 222 <= A <= 252 and 88 <= Z <= 102. The agreement between the calculated results and the experimental data indicates the reliability of investigating the properties of the unfavored alpha-decay with our method, especially the improved Royer's formula, which is very valuable for the analysis of experimental data. In addition, the dependence of half-lives on excitation energies of daughter nuclei has been investigated. It is shown that the influence on half-lives becomes stronger and stronger with the increase of the excitation energies.

Neutron-Proton Asymmetry Dependence of Spectroscopic Factors in Ar Isotopes

Spectroscopic factors have been extracted for proton-rich Ar-34 and neutron-rich Ar-46 using the (p, d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton-rich nucleus Ar-34 compared to that of Ar-46. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutronproton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements.

Phenomenological analysis of the double-pion production in nucleon-nucleon collisions up to 2.2 GeV

With an effective Lagrangian approach, we analyze several NN -> NN pi pi channels by including various resonances with mass up to 1.72 GeV. For the channels with the pion pair of isospin zero, we confirm the dominance of N*(1440) -> N sigma in the near-threshold region. At higher energies and for channels with the final pion pair of isospin one, we find large contributions from N*(1440) -> Delta pi, double-Delta, Delta(1600) -> N*(1440)pi, Delta(1600) -> Delta pi and Delta(1620) -> Delta pi. There are also sizable contributions from Delta -> Delta pi, Delta -> N pi, N -> Delta pi, and nucleon pole at energies close to the threshold. We give a good reproduction to the total cross sections up to beam energies of 2.2 GeV except for the pp -> pp pi(0)pi(0) channel at energies around 1.1 GeV and our results agree with the existing data of differential cross sections of pp -> pp pi(+)p pi(-), pp -> nn pi(+)pi(+), and pp -> pp pi(0)pi(0) which are measured at CELSIUS and COSY.