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The experiments of two-alpha emission from Ne-17,Ne-18 excited levels were performed at the HIRFL-RIBLL facility of the Institute of Modern Physics, Lanzhou. The beams of Ne-17 at the energy of 49.9 MeV/u and Ne-18 at 51.8 MeV/u bombarded a Au-197 target to populate excited states of Ne-17,Ne-18 via Coulomb excitation. Complete kinematics measurements were achieved by the detectors of a silicon strip and CsI+PIN array. The experimental results combined with simple MC simulations show the characteristic of sequential two-alpha emission via O-14 excited states for Ne-18. The results of two-alpha emission from Ne-17 are preliminary and need further analyses.

Two-proton emissions from the excited states of 17,18Ne, 28P and 28,29S were investigated experimentally by the radioactive beams bombarding on the 197Au target via the Coulomb excitation. The complete-kinematics measurements were actualized by the stacks of silicon-strip detectors and CsI+PIN array detectors. The invariant mass of final systems as well as the relative momentum, opening angle, and relative energy of the two emitted protons was reconstructed under the framework of relativistic kinematics. Visible proton-proton correlations were observed in these systems. The mechanisms of two-proton emission were analyzed in a simple schematic model, in which the extreme decay modes like 2He cluster emission, three-body phase-space decay, and two-body sequential decay were taken into account. With the help of Monte-Carlo simulations, the two protons emitted from the 6.15 MeV excited state of 18Ne and the excited states in the energy region of 9.6–10.4 MeV of 29S, respectively, exhibited prominent features of 2He cluster decay while for the other cases, no obvious diproton emissions were observed.

A series of experiments have been performed by complete kinematics measurements to study two-proton (2 p) correlated emission from the excited states of 17,18Ne and 28,29S via the Coulomb excitation by bombarding on 197Au target. 2p and residua coincident events were picked out under strict conditions. Visible p − p correlations were observed. It is shown that 2p can be emitted from the high-lying excited states. 2p halo may lead to 2p emission with large spectroscopy factor for the states close to or beyond the threshold.

Excited states in 188Tl have been studied experimentally using the 157Gd (35Cl, 4n) reaction at a beam energy of 170MeV. A rotational band built on the πh 9/2 ⊗ νi 13/2 configuration with oblate deformation has been established for 188Tl. Based on the structure systematics of the oblate πh 9/2 ⊗ νi 13/2 bands in the heavier odd-odd Tl nuclei, we have tentatively proposed spin values for the new band in 188Tl. The πh 9/2 ⊗ νi 13/2 oblate band in 188Tl shows low-spin signature inversion, and it can be interpreted qualitatively by the two-quasiparticle plus rotor model including a J-dependent p-n residual interaction.

Excited states in 190 Tl have been studied experimentally using the 160 Gd( 35 Cl, 5n) reaction, and resulted in the identification of a strongly coupled band based on the πh 9/2 ⊗ vi 13/2 configuration with oblate deformation. Combining with the results from the previous α-decay of 194 Bi, spin values have been proposed for the πh 9/2 ⊗ vi 13/2 oblate band in 190 Tl. This oblate band shows low-spin signature inversion. It is the first experimental observation of low-spin signature inversion for a band associated with the oblate πh 9/2 ⊗ vi 13/2 configuration.

The high-spin states of {sup 198}Bi have been studied via the reaction {sup 187}Re({sup 16}O,5{ital n}){sup 198}Bi at {sup 16}O energies from 85 to 105 MeV. In-beam measurements of {gamma}-ray excitation functions, {gamma}-{gamma}-{ital t} coincidences, and {gamma}-ray angular distributions were carried out with 6 BGO(AC)HPGe detectors and one intrinsic Ge planar detector. A level scheme for {sup 198}Bi with 26 {gamma} rays was established for the first time, including a 15{sup +} isomer with a measured half-life of 8.0{plus_minus}3.6 ns. The level structure of {sup 198}Bi was qualitatively interpreted by using semiempirical methods. {copyright} {ital 1996 The American Physical Society.}

Two-{alpha} emission from high-lying excited states of {sup 18}Ne was studied by complete-kinematics measurements. The {sup 18}Ne beam at the energy of 51.8 MeV/u was bombarding a {sup 197}Au target to populate the excited states via Coulomb excitation. Products of two-{alpha} emission, {sup 10}C-{alpha}-{alpha}, were measured by an array of silicon strip detectors and a CsI + PIN telescope. With the help of Monte Carlo simulations, the experimental results show the characteristics of sequential two-{alpha} emission via {sup 14}O excited states. Sequential two-{alpha} and two-proton emissions from {sup 18}Ne via one-particle daughter states are compared and the distinction of the opening angles of these two modes originates from the difference of the mass ratio of emitted particles to daughter nuclei.

An experiment to study exotic two-proton emission from excited levels of the odd-$Z$ nucleus $^{28}\mathrm{P}$ was performed at the National Laboratory of Heavy Ion Research-Radioactive Ion Beam Line (HIRFL-RIBLL) facility. The projectile $^{28}\mathrm{P}$ at the energy of $46.5$ MeV/$u$ was bombarding a $^{197}\mathrm{Au}$ target to populate the excited states via Coulomb excitation. Complete-kinematics measurements were realized by the array of silicon strip detectors and the $\mathrm{CsI}+\mathrm{PIN}$ telescope. Two-proton events were selected and the relativistic-kinematics reconstruction was carried out. The spectrum of relative momentum and opening angle between two protons was deduced from Monte Carlo simulations. Experimental results show that two-proton emission from $^{28}\mathrm{P}$ excited states less than $17.0$ MeV is mainly two-body sequential emission or three-body simultaneous decay in phase space. The present simulations cannot distinguish these two decay modes. No obvious diproton emission was found.

An experiment of a $^{29}\mathrm{S}$ beam bombarding a $^{197}\mathrm{Au}$ target at an energy of 49.2 MeV/u has been performed to study the two-proton correlated emission from $^{29}\mathrm{S}$ excited states. Complete-kinematics measurements were carried out in the experiment. The relative momentum, opening angle, and relative energy of two protons, as well as the invariant mass of the final system, were deduced by relativistic-kinematics reconstruction. The $^{27}\mathrm{Si}$-$p\text{\ensuremath{-}}p$ coincident events were picked out under strict conditions and the phenomenon of $p\text{\ensuremath{-}}p$ correlations was observed among these events. The mechanisms of two-proton emission were analyzed in a simple schematic model, in which the extreme decay modes like $^{2}\mathrm{He}$ cluster emission, three-body phase-space decay, and two-body sequential emission were taken into account. Associated with the Monte Carlo simulations, the present results show that two protons emitted from the excited states between 9.6 MeV and 10.4 MeV exhibit the features of $^{2}\mathrm{He}$ cluster decay with a branching ratio of ${29}_{\ensuremath{-}11}^{+10}%$.

High-spin level structure in Au-184 has been reinvestigated using the multidetector array of GASP via the Tb-159 (Si-29, 4ngamma)Au-184 reaction at a beam energy of 140 MeV. The ground-state band and the excited pii(13/2) circle times vi(13/2) 2-qp band have been extended up to lower and higher spin states. An upbend has been observed in the excited band at homegasimilar to0.25 MeV and is interpreted as resulting from a pair of pih(9/2) alignment. This low-frequency (pih(9/2))(2) alignment is supported by the measured B(M1)/B(E2) ratios and alignment properties in neighboring odd-A nuclei. The linking transitions between the two bands and to the ground state have been established leading to a firm spin-and-parity assignment for the pii(13/2) circle times vi(13/2) band in Au-184. This result provides strong evidence for the low-spin signature inversion in the pii(13/2) circle times vi(13/2) bands of odd-odd nuclei in the A similar to 180 mass region.

High-spin states in141Nd have been studied using in-beam γ-ray spectroscopic techniques via the130Te(16O, 5nγ)141Nd reaction. The level scheme of141Nd has been extended up to an excitation energy of 7614.5 keV including 12 new γ rays deexciting 15 new levels. According to particle-vibrator coupling and semi-empirical shell model calculations, the level structure of141Nd can be well interpreted by coupling an h11/2 neutron-hole to the respective excited states in142Nd core.

A contrastive research on two-proton (2p) emissions from excited states of the even-Z nucleus 28S and its one-proton daughter, the odd-Z nucleus 27P was performed by complete-kinematics measurements. The opening angles as well as relative momenta between two emitted protons and invariant masses of decaying systems were reconstructed through the event-by-event analysis of heavy fragments coincident with two protons. With the help of Monte Carlo simulations, results show a diproton-type decay with the branching ratio of 20 − 7 + 6 % for 28S while mainly three-body simultaneous decay in the phase space and/or 2p sequential emission for 27P. Present results show that the diproton correlations may result from the proton configuration in the initial state like 2p skin/halo structure rather than the deformed orbit.