EC/β+ decay of six medium-heavy nuclei

Previous experimental results of (EC+β⁺) decay for the medium-heavy nuclei reported by our group since 1996, including ¹⁵³Er, ¹⁵⁷Yb, ²⁰⁹Fr, ¹²⁸Ce, ¹³⁰Ce, and ¹²⁸Pr 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.     

Systematical law of β+-decay half-lives of nuclei far from β-stable line

Experimental data of nuclear β⁺-decay half-lives are systematically analyzed and investigated. We present an exponential law between the half-life of β⁺-decay with the same forbiddenness and the nucleon number (Z,N) of parent nucleus far from the β-stable line. A formula with four parameters is proposed to describe the β⁺-decay half-lives of nuclei far from stability. Experimental β⁺-decay half-lives of the first and second forbidden transitions are well reproduced by this simple formula. The physics of the exponential law is related to the statistical properties of β⁺-decay far from β-stable line.     

Calculation of prompt fission neutron spectrum for 233U（n,f）reaction by the semi-empirical method~

The prompt fission neutron spectra for the neutron-induced fission of ²³³U for low energy neutrons (below 6 MeV) are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the n_th+²³³U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.     

Structure of β-emitting nuclei 29P

The extoic structure of ²⁹P was investigated by measuring its magnetic moment in the ground state with β-NMR method. We got the experimental value of 1.2346 μ_N after diamagnetism correction. It is very close to the calculated value of 1.1009 μ_N computed with shell model. The shell model calculation also gave a proton density distribution of ²⁹P with a long tail. The present results show that 2s_1/2 proton in the ²⁹P may lead to the proton-skin structure.     

Study of a position-sensitive scintillator neutron detector

The investigation of a novel thermal neutron detector is developed to fulfill the requirements of the high intensity power diffractometer (HIPD) at the Chinese Spallation Neutron Source (CSNS). It consists of two layers of ⁶LiF/ZnS(Ag) scintillators, two layers of crossed WLSF arrays, several multi-anode photo multiplier tubes (MA-PMT), and the matching readout electronics. The neutron detection efficiency of the scintilltors, the light transportation ability of the WLSF, and the spatial linearity of the readout electronics are measured and discussed in this paper. It shows that the sandwich structure and the compact readout electronics could fulfill the needs of the HIPD. A prototype with a 10 cm×10 cm sensitive area has been constructed to further study the characteristics of the neutron scintillator detector.     

β-delayed fission of 228Ac

The basic process of an exotic decay mode namely β-delayed fission is simply introduced. The progress status of the study in the world is essentialized. The observation of β-delayed fission of ²²⁸Ac is reported. The radium was radiochemically separated from natural thorium. Thin Ra sources in which ²²⁸Ac was got through ²²⁸Ra →β^－228Ac were prepared for observing fission fragments from β-delayed fission of ²²⁸Ac. They exposed to the mica fission track detectors, and measured by an HPGe γ-ray detector. The β-delayed fission events of ²²⁸Ac were observed and its β-delayed fission probability was found to be (5±2)×10^－12.     

Theoretical investigation of the structure of 19N

We have employed the shell model and Skyrme-Hartree-Fock methods to investigate the structure of the neutron-rich nucleus ¹⁹N. The level scheme of ¹⁹N from the shell-model calculation with the WBT interaction is displayed. The potential-energy-surface calculation with the SGII interaction implies that ¹⁹N should be a deformed nucleus. The theoretical β-decay half life of ¹⁹N reproduces well the available experimental data.     

Search for exotic state 1－+ π1(1400) at BESⅢ

The J/ψ hadronic decays provide good laboratory to search for the hybrid states with exotic quantum numbers. A full Partial Wave Analysis (PWA) is performed to the generated Monte Carlo J/ψ→ρηπ data, based on the design of BESⅢ detector, to study the sensitivity of searching for a possible exotic state at BESⅢ.     

Design of magnet and control of the beam emittance for Penning H－ ion source

The design requirement and principle of the deflection magnet for Magnetron and Penning H^－ ion source are discussed. It is proved that there exists a maximum emittance for the beam that may be transformed by the magnet into a state with equal Twiss parameters of α_r=α_y and β_r=β_y, which is the requisite condition to get a minimum emittance at the entrance of RFQ after transporting by a LEBT with solenoids. For this maximum emittance, the corresponding magnetic field gradient index is 1.     

Measurement and analysis of the 238U(n, 2n) reactionrate in depleted uranium/polyethylene shells

In order to check the conceptual design of the subcritical blanket in a fusion-fission hybrid reactor, a depleted uranium/polyethylene simulation device with alternate shells has been established. The measurement of the ²³⁸U(n, 2n) reaction rate was carried out using an activation technique, by measuring the 208 keVγ rays emitted from ²³⁷U. The self-absorption of depleted uranium foils with different thicknesses was experimentally corrected. The distribution of the ²³⁸U(n, 2n) reaction rate at 90° to the incident D⁺ beam was obtained, with uncertainty between 5.3% and 6.0%. The experiment was analyzed using MCNP5 code with the ENDF/BVI library, and the calculated results are all about 5% higher than the measured results.