Xu Shu-Wei

(EC+

Abstract: The (EC+β+) decay of 128Ce was reinvestigated in the 116Sn (16O, 4n) reaction by using a helium-jet tape transport system. The close half-lives of 128Ce and 129Ce made it difficult to separate the decay γ rays of both nuclei apart. Instead of the excitation-function measurements, both reactions of 16O+116Sn and 16O+117Sn were carried out, and from their comparisons, the decay γ rays of 128Ce were clearly told from those of 129Ce. Based on X-γ and γ-γ coincidence measurements, a detailed (EC +β+) decay scheme of 128Ce has been proposed, which revises the previous one.

\beta^{+}

Abstract: The (EC+β+) decay of 128Ce was reinvestigated in the 116Sn (16O, 4n) reaction by using a helium-jet tape transport system. The close half-lives of 128Ce and 129Ce made it difficult to separate the decay γ rays of both nuclei apart. Instead of the excitation-function measurements, both reactions of 16O+116Sn and 16O+117Sn were carried out, and from their comparisons, the decay γ rays of 128Ce were clearly told from those of 129Ce. Based on X-γ and γ-γ coincidence measurements, a detailed (EC +β+) decay scheme of 128Ce has been proposed, which revises the previous one.

) decay study of

The ?-delayed proton decay of 147Er is studied experimentally using the 68Ni+92 Mo reaction at a beam energy of 383 MeV. Based on a He-jet apparatus coupled with a tape transport system, the ?-delayed proton radioactivities both from the ?s1/2 ground state and the ?h11/2 isomer in 147Er are identified by proton-? coincidence measurements. By analyzing the time distribution of the 4+ ? 2+? transition in the grand-daughter nucleus 146Dy, a half-life of 1.6 ? 0.2 s is determined for the ?h11/2 isomer in 147Er. The half-life for the ground state of 147Er is estimated to be 3.2 ? 1.2 s.

^{128}

Previous experimental results of (EC+beta(+)) decay for the medium-heavy nuclei reported by our group since 1996, including Er-153, Yb-157, Fr-209, Ce-128, Ce-130, and Pr-128 have been briefly summarized. The observed low-lying states in their daughter nuclei have been reviewed in a systematic way and compared with different model calculations. Finally, some questions have been put forward for further study and discussion.

Ce

The β-delayed proton precursors125Nd128Pm129Sm,137Gd and139Dy near the proton drip line were produced by the irradiation of92Mo,96Ru and106Cd with an36Ar beam, and conclusively identified for the first time by using proton-gamma coincidence in combination with a He-jet tape transport system. Their half-lives were determined to be 0.60(15)s,1.0(3)s,O.55(10)s,2.2(2)s and 0.6 (2)s, respectively. The measured energy spectra of β-delayed protons and estimated proton branching ratios to the final states in “daughter” nuclei for the precursors125Nd,129Sm,137Gd and139Dy, as well as the previously reported ones for the precursors135Gd and121Ce, were fitted by a statistical model calculation. The ground-state spins and parities of121Ce,125Nd,129Sm,139Gd,137Gd and139Dy were then assigned as 5/2±,5/2±, 1/2± (or 3/2+), 5/2+,7/2+- and 7/2, respectively. The consistency between the experimental spin-parity assignment and the predicted Nilsson diagrams indirectly indicates that the ground states of121Ce,125Nd,129Sm,135Gd,137Gd and139Dy are highly deformed with β2, - 0.3.

(EC +β+) decay study of 128Ce

Abstract A new neutron-rich nuclide 208 Hg has been produced and identified for the first time in the 30 MeV/u 12 C+ nat Pb reaction at HIRFL. A new technique was employed for the identification. A half-life of 42± 12 23 min has been determined for 208 Hg and the average cross section in the energy region from 5 to 30 MeV/u deduced to be 1.1μb. In addition, 185 Hf has already been produced and identified and its half-life was determined to be 3.5±0.6 min. A new γ-ray(164.5KeV) has been assigned to come from 185 Hf β − decay. The identification and study of new heavy neutron-rich nuclides has been attractive due mainly to the anomalous half-lives calculated and the predicted new β-delayed neutron precursor island Z=82 and N=126. The mechanism and techniques for production and identification of the nuclides far off β stability in this mass region are also challenging which are taken as one of the main tasks at HIRFL in recent years.

Properties of the β-Delayed Proton Decay of 147Er

The proton-rich isotope 146Ho was produced via the fusion-evaporation reaction 92Mo (58Ni, 3p1n). The β-delayed proton decay of 146Ho was studied by proton-y coincidence measurements using a He-jet tape transport system. The γ-transitions in 145Tb following the proton emissions were observed, and the β-delayed proton branching ratios to the final states in the grand-daughter nucleus 145Tb were determined. According to the relative branching ratios, the ground-state spin of 146Ho has been proposed and the possible configuration discussed.

EC/β+ decay of six medium-heavy nuclei

The ?+/EC decay of doubly odd nucleus 176Ir has been studied via the 146Nd(35Cl, 5n?) heavy ion fusion evaporation reaction at 210?MeV bombarding energy. With the aid of a helium-jet recoil fast tape transport system, the reaction products were transported to a low-background location for measurement. Based on the data analysis, the previously known ? rays from the decay of 176Ir are proven. Moreover, three new excited levels and ten new ? rays are assigned to 176Os. The time spectra of typical ? rays clearly indicate a long-lived low-spin isomer in 176Ir.

New β-delayed proton decays in the rare-earth region near the proton drip line

The (EC+β+) decay of 128Ce was reinvestigated in the 116Sn (16O, 4n) reaction by using a helium-jet tape transport system. The decay γ rays of 128Ce were unambiguously described from those of 129Ce after taking the comparing experiments of 16O+116Sn and 16O+117Sn. Based on x-γ and γ-γ coincidence measurements, a detailed (EC+β+) decay scheme of 128Ce has been proposed which modifies the previous one, and takes accounts of 100 observed γ-lines.

Synthesis and identification of new heavy nuclides far off stability

The nuclide130Ce was produced by a (16O, 4n) reaction on an enriched118Sn target. Reaction products were transported to a shielded location by using a heliumjet tape transport system. A 22.9 min activity in chemically separated cerium sample was identified as130Ce. The (EC+β+) decay scheme of130Ce was proposed for the first time. This scheme includes 108γ-lines, 107γ-lines among them being new. More than 13 1+ low-lying states of130La are populated in the decay of130Ce. Two new isomers with half-life of 77±10 ns and 17±5 ns were observed by means of delayedγ-γ coincidence measurements.