Li Zhankui

(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

Nonionizing energy loss (NIEL) has been applied to a number of studies concerning displacement damage effects in materials and devices. However, most studies consider only the contribution of displacement damage effects, neglecting the contribution from phonons. In this paper, a NIEL model, which considers the contribution of phonons, has been established using the Monte Carlo code SRIM. The maximum endurable fluence for silicon detectors has been estimated using the equivalent irradiation fluence compared with experimental data for the incident particles. NIEL is proportional to the equivalent irradiation fluence that the detector has received.

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+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.

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

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.

Phonon contribution to nonionizing energy loss in silicon detectors

The annealing process for boron implantation is a crucial step during large size nuclear radiation detector fabrication. It can reduce the lattice defects and the projection straggling. A two-step annealing process for boron implantation was developed instead of a one-step annealing process, and the reverse body resistance of a silicon micro-strip detector was significantly increased, which means that the performance of the detector was improved.