Alpha Decay, Shell Structure, and New Elements

We systematically analyze the experimental data of alpha decay in even-even heavy nuclei far from stability and find that the Geiger-Nuttall law brea^s for an isotopic chain when its neutron number is across a marc number or there is a deformed subshell. This break can be used to identify new magic numbers of superheavy nuclei. It is also discovered that there is a new linear relation between the logarithm of half-life and the reciprocal of the square root of decay energy for N = 126 and N = 152 isotones. It could be a new law of alpha decay for nuclei with magic neutron numbers but the physics behind it is to be explored. The significance of these researches for the search of new elements is discussed.

Shell Effect of Superheavy Nuclei in Self-consistent Mean-Field Models

We analyze in detail the numerical results of superheavy nuclei in deformed relativistic mean-field model and deformed Skyrme-Hartree-Fock model. The common points and differences of both models are systematically compared and discussed. Their consequences on the stability of superheavy nuclei are explored and explained. The theoretical results are compared with new data of superheavy nuclei from GSI and from Dubna and reasonable agreement is reached. Nuclear shell effect in superheavy region is analyzed and discussed. The spherical shell effect disappears in some cases due to the appearance of deformation or superdeformation in the ground states of nuclei, where valence nucleons occupy significantly the intruder levels of nuclei. It is shown for the first time that the significant occupation of valence nucleons on the intruder states plays an important role for the ground state properties of superheavy nuclei. Nuclei are stable in the deformed or superdeformed configurations. We further point out that one cannot obtain the octupole deformation of even-even nuclei in the present relativistic mean-field model with the σ, ω and ρ mesons because there is no parity violating interaction and the conservation of parity of even-even nuclei is a basic assumption of the present relativistic mean-field model.

紫外光通信中副载波强度调制的低密度奇偶校验码研究

在紫外光散射通信系统中,脉冲展宽和噪声会对信号产生严重影响。为降低系统误码率、提高通信距离,加入了低密度奇偶校验码(LDPC)进行码元纠错。对比了开关键控(OOK)和二进制相移键控(BPSK)副载波强度调制的性能,仿真分析了BPSK副载波强度调制下不同编码效率、不同译码方式的LDPC码对非直视(NLOS)紫外光通信系统误码率的影响。结果表明:BPSK副载波强度调制的性能优于OOK调制,编码效率越小的LDPC码的纠错能力越强,置信传播算法和对数似然比置信传播算法译码性能几乎一致,均优于最小和算法。在小角度、短距离时,非直视紫外光通信系统误码率更小,当误码率为6.5×10-6时,LDPC(672,168)码与未编码序列相比,通信距离提高约一倍。