Observation of a Strongly Isospin-Mixed Doublet in

ß decay of proton-rich nuclei plays an important role in exploring isospin mixing. The ß 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 ß-delayed two-proton emission (ß2p). Angular correlations of two protons emitted from ^{26}Si excited states populated by ^{26}P ß 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 ß-decay experiments.

Probing

The isomer depletion of ^{93m}Mo was recently reported [Chiara et al., Nature (London) 554, 216 (2018)NATUAS0028-083610.1038/nature25483] as the first direct observation of nuclear excitation by electron capture (NEEC). However, the measured excitation probability of 1.0(3)% is far beyond the theoretical expectation. In order to understand the inconsistency between theory and experiment, we produce the ^{93m}Mo nuclei using the ^{12}C(^{86}Kr,5n) reaction at a beam energy of 559 MeV and transport the reaction residues to a detection station far away from the target area employing a secondary beam line. The isomer depletion is expected to occur during the slowdown process of the ions in the stopping material. In such a low γ-ray background environment, the signature of isomer depletion is not observed, and an upper limit of 2×10^{-5} is estimated for the excitation probability. This is consistent with the theoretical expectation. Our findings shed doubt on the previously reported NEEC phenomenon and highlight the necessity and feasibility of further experimental investigations for reexamining the isomer depletion under low γ-ray background.

[A 10-year follow-up study of indications for artificial cervical disc replacement].

Objective: To investigate the influence of the preoperative factors on the segmental range of motion (ROM) during long-term follow-up after artificial cervical disc replacement (ACDR), so as to further improve the selection of surgical indications for ACDR. Methods: Retrospective analysis was performed on 71 patients with cervical degenerative diseases who underwent single-segment Bryan ACDR in Beijing Jishuitan Hosptial from December 2003 to December 2008, and a 10-year clinical follow-up was conducted. Among the patients, 44 were males and 27 were females, with a mean age of (45±8) years at operation. The mean follow-up time was (129±14) months. Preoperative and follow-up imaging evaluation including measurement of the segmental range of motion (ROM) by cervical X-ray, and preoperative height of intervertebral space was measured by cervical lateral X-ray. According to CT and coronal reconstruction, the grade of paravertebral ossification (PO) was assessed. Clinical symptoms assessment including the Japanese Orthopaedic Association scoring (JOA), the Neck Disability Index (NDI) evaluation was performed preoperatively. Multivariate logistic regression analysis was used to analyze the influencing factors of the range of motion of the surgical segment during follow-up. The best cut-off value was calculated by receiver operating characteristic (ROC) curve. Results: The preoperative and follow-up ROM at the operated segment was 9.7°±4.5° and 8.7°±5.4°, respectively (P>0.05). Univariate analysis revealed that the postoperative segmental ROM was not significantly correlated with the factors including the surgical level, gender, age, and preoperative clinical diagnosis (1: Radiculopathy; 2: Myelopathy; 3: Mixed type), preoperative segmental ROM, preoperative JOA score and preoperative NDI score (all P>0.05), and was significantly correlated with imaging diagnosis (1: cervical disc herniation; 2: degenerative cervical stenosis), preoperative PO grade (both P<0.05). The multi-factor analysis showed that preoperative segmental ROM (OR=1.228, 95%CI:1.012-1.489, P<0.05) and PO grade (OR=0.190, 95%CI: 0.085-0.424, P<0.05) had significance in the overall test, but imaging diagnosis had no significance in the overall test (P>0.05). The optimal cutoff value of preoperative segmental ROM and PO grade was 9.185° and grade 2.5 assessed by ROC curve, and the area under the ROC curve was 0.86 and 0.72, respectively. Conclusions: ACDR surgery can achieve satisfactory long-term effects for patients with nerve root type, spinal cord type and mixed type cervical degenerative diseases, and effectively retain the overall ROM of the cervical spine and the ROM of replacement segments. Patients with good preoperative segmental ROM and lower PO levels have a greater chance of obtaining good segmental ROM in the long-term postoperatively.

Large Isospin Asymmetry in

ß-delayed one-proton emissions of ^{22}Si, the lightest nucleus with an isospin projection T_{z}=-3, are studied with a silicon array surrounded by high-purity germanium detectors. Properties of ß-decay branches and the reduced transition probabilities for the transitions to the low-lying states of ^{22}Al are determined. Compared to the mirror ß 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_{1/2} orbit that introduces explicitly the isospin-symmetry breaking force and describes the loosely bound nature of the wave functions of the s_{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.

Positive-Parity Linear-Chain Molecular Band in

An inelastic excitation and cluster-decay experiment ^{2}H(^{16}C,^{4}He+^{12}Be or ^{6}He+^{10}Be)^{2}H was carried out to investigate the linear-chain clustering structure in neutron-rich ^{16}C. For the first time, decay paths from the ^{16}C resonances to various states of the final nuclei were determined, thanks to the well-resolved Q-value spectra obtained from the threefold coincident measurement. The close-threshold resonance at 16.5 MeV is assigned as the J^{π}=0^{+} band head of the predicted positive-parity linear-chain molecular band with (3/2_{π}^{-})^{2}(1/2_{σ}^{-})^{2} configuration, according to the associated angular correlation and decay analysis. Other members of this band were found at 17.3, 19.4, and 21.6 MeV based on their selective decay properties, being consistent with the theoretical predictions. Another intriguing high-lying state was observed at 27.2 MeV which decays almost exclusively to ^{6}He+^{10}Be(∼6 MeV) final channel, corresponding well to another predicted linear-chain structure with the pure σ-bond configuration.

[Institutional delivery rate in minority inhabited areas of China from 1996 to 2017].

Objective: To describe the secular trends of institutional delivery (ID) rate in minority inhabited areas of China from 1996 to 2017 according to national health policies. Methods: The number of live births and IDs for each county/district in 31 provinces of China were derived from the datasets collected by the Office for National Maternal & Child Health Statistics of China. Information on health policies and ethnical areas was derived from official governmental websites. The calendar years were divided into three periods: pre-program period (1996 to 1999), program implementation period (2000 to 2008) and post-program period (2009 to 2017). Minority autonomous regions, autonomous prefectures, and autonomous counties were defined as minority inhabited areas. The ethnic that a county was classified into was determined by a principle of close proximity to the name of the county or its next higher level administrative division. A total of 700 counties in minority inhabited areas were included in the analysis. Results: A total of 45 684 265 live births including 35 098 855 delivered in institutions were analyzed. The ID rate in minority inhabited areas was 37.5% (696 221/1 856 164) in 1996 and 99.2% (2 371 209/2 390 131) in 2017, with an annual growth rate of 4.7%. During the 22-years period, the ID rates in the eastern, central and western regions increased simultaneously, with the annual growth rates of 3.1%, 4.2% and 4.9% respectively. The difference between the eastern and western regions decreased steadily from 16% in 1996 to <1% in 2017 and the difference between the urban and rural areas decreased from 32.1% in 1996 to <1% in 2017. Besides, the ID rates in Tibetan and Yi inhabited areas with lower baseline levels increased 73 and 63 percentage points respectively. The number of counties with the ID rate of <96% were substantially reduced from 589 in 1996 to 72 in 2017; the 71 counties were all located in national deep poverty-stricken areas named Three Districts and Three States, predominantly involving Tibetan (58), Yi (6), Uygur (2) and Lisu (2) ethnics. Conclusion: During the past 22 years, the ID rate in minority inhabited areas in China has dramatically increased, achieving the goal of 2 020 ahead of schedule, but there remains a few western counties where ID rates are still<96%, indicating that minority inhabited western areas should be focused in developing national policies concerning institutional delivery.