缺中子稀土区滴线附近新的β缓发质子衰变

用重离子束³⁶Ar和³²S轰击缺中子同位素靶⁹²Mo,⁹⁶Ru和¹⁰⁶Cd产生了质子滴线附近的β缓发质子先驱核¹²⁵Nd,¹²¹Ce,¹²⁸Pm,¹²⁹Sm,¹³⁵Gd,¹³⁷Gd和¹³⁹Dy.配合氦喷嘴带传输系统用"p-γ"符合方法对它们进行了首次肯定的鉴别.它们的半衰期分别为:0.60(15)s,1.1(1)s,1.0(3)s,0.55(10)s,1.1(2)s,2.2(2)s和0.6(2)s.用统计模型理论计算对实验测定的¹²⁵Nd,¹²¹Ce,¹²⁹Sm,¹³⁵Gd,¹³⁷Gd和¹³⁹Dy的β缓发质子衰变的能谱和分支比进行了拟合.提取出¹²⁵Nd,¹²¹Ce,¹²⁹Sm,¹³⁵Gd,¹³⁷Gd和¹³⁹Dy的基态自旋-宇称分别为5/2^±,5/2^±,1/2⁺(或3/2⁺),5/2⁺,7/2^±和7/2⁺.实验初步指认的基态自旋(宇称值与Nilsson能级图的预言值相符间接表明这6个核素的基态具有大形变,形变参数β₂在0.3左右.     

稀土区近滴线的β缓发质子衰变

简要回顾了自20世纪70年代以来实验研究稀土区β缓发质子衰变的历史. 综合报道了在过去10年内中科院近物所实验研究稀土区近滴线核的β缓发质子衰变的进展, 主要包括首次观测沿奇Z质子滴线的9种新核素的β缓发质子衰变以及rp-过程中两种等待点核的衰变新数据, 并将这些结果与不同的核模型理论计算进行了比较和讨论. 最后对今后的工作进行了初步展望.     

对质子滴线核19Na的β延迟质子衰变的首次观察

由²⁰Ne(P,2n)¹⁹Na反应,对质子滴线核¹⁹Na进行了研究,实验在中国科学院高能物理研究所质子直线加速器上进行,首次观察到了¹⁹Na的β延迟质子衰变,测定其质子能量为1.10±0.08MeV,半衰期为47±20ms,它相应于¹⁹Na基态到¹⁹Ne的7.62MeV、T=3/2同位旋相似态的超允许β跃迁和由此态到¹⁸F基态的级联质子衰变.     

利用改进的Gamow-like模型研究原子核的α衰变和质子放射性

通过引入离心势和静电屏蔽效应对Gamow-like模型进行了改进,并将其用于α衰变和质子放射性研究,发现改进的Gamow-like模型能更好地符合实验数据。另外,还利用改进的Gamow-like模型预言了16个丰质子核的质子放射性的半衰期以及7个$Z=120$超重核素($^{296-308}120$)α衰变链上原子核的α衰变的半衰期,为将来在大科学装置上合成和鉴别这些新核素提供重要的理论参考。     

质子滴线附近的β缓发质子衰变

简要回顾了实验小组在过去8年中获得的实验结果, 即采用氦喷嘴快速带传输系统 +“p-γ”符合方法, 在稀土区质子滴线附近首次观测了9种新核素的β缓发质子衰变, 在A=90核区的N=Z线附近获得了5种核素的β缓发质子衰变的新数据. 并把这14种核素的半衰期, 自旋宇称, 形变以及生成反应截面的实验值与流行的核模型理论预言进行了系统地对比讨论. 从中看出:(1)⁸⁵Mo, ⁹²Rh以及“等待点”核⁸⁹Ru和⁹³Pd半衰期的实验值比近期Moller等人的宏观-微观理论预言值[At. Data Nucl Data Tables, 66, 131(1997)]长5—10倍, 因而明显地影响天体rp过程生成的核素丰度;(2)实验指认的质子滴线核¹⁴²Ho和¹²⁸Pm的自旋宇称与流行理论预言不符, 但用Woods-Saxon-Strutinsky方法可以计算得到相符的位能面;(3)实验估计的9种稀土核的生成截面比通用的Alice和HIVAP程序的计算值要小1—2个数量级.     

原子核双β衰变和轻子数不守恒

 原子核双β衰变实质上是二个单β衰变同时发生的过程,是一个二级弱相互作用过程.原子核单β衰变的一个典型过程是中子衰变为质子,并放出电子和反中微子,即n→p+e^-+（?）_e。自从1914年查德威克测量β衰变的连续谱以来,β衰变的研究一直是原子核物理和粒子物理的重要研究课题之一.我们知道,李政道和杨振宁提出的宇称不守恒定律,就是吴健雄通过原子核的β衰变研究而得到实验证实的.无独有偶的是原子核双β衰变的研究和自然界的另一重要守恒定律--轻子数守恒律是否破坏密切相关.     

进一步指认近质子滴线核129Pm的衰变

2004年曾报道过利用⁴⁰Ca＋⁹²Mo融合蒸发反应产生了近质子滴线新核素Pm,并首次观测到它(EC+b+)衰变产生的能量为99keV的γ射线. 为了进一步确认上述指认，以下提供了三方面的新证据：1)在164－190MeV能量范围内测量了99keV衰变γ射线的激发函数;2)进行了交叉反应 ³⁶Ar＋⁹⁶Ru的实验,观察到了相同的99keV衰变γ射线；3)用Woods-Saxon Strutinsky方法计算了¹²⁹Pm的核势能面，其基态自旋宇称被预言为5/2^－，所以¹²⁹Pm的(EC＋b＋)衰变有利于馈送到子核¹²⁹Nd的5/2_－的低位态，这也与前期报道相符.     

质子滴线核8B的实验研究进展

质子滴线核8B的最后一个质子的分离能只有0.137 5 MeV,被认为是最有可能具有质子晕结构的候选核之一,对其反应机制和奇特结构的研究吸引了人们的关注。针对8B的奇特结构和反应机制研究是一个非常有趣的课题,研究人员在包括反应截面、碎裂产物动量分布宽度、电四极矩、熔合截面及弹性散射等方面开展了大量的工作。但是8B的研究至今仍不够充分,需要从理论和实验上对其进行更深入的研究。     

190，192Pb原子核的超形变带的带外衰变（英文）

将基于组合方法的角动量投影的位能曲面群用于研究铅同位素原子核190,192Pb 的超形变转动带。位能曲面群计算中采用了Gogny D1S 以及Skyrme SkP SLy4 三种相互作用。如用Gogny D1S 相互作用,190Pb 原子核没有明显的超形变转动带,而192Pb 原子核有非常显著的超形变转动带。用W. K. B. 方法计算了192Pb 原子核的超形变带穿透宽度。该穿透宽度很大与用GW模型（Nucl. Phys. A 660 （1999）197）分析实验数据给出的结果相近。在Gogny D1S 相互作用情形下,就角动量投影对位能曲面群的影响作了讨论,发现角动量投影压低了分隔超形变转动带与正常形变转动带之间的位垒。还用Skyrme SkP 和SLy4 相互作用计算了角动量投影的位能曲面群,发现位垒明显高于Gogny D1S 相互作用给出的位垒。在Skyrme 相互作用情形下,192Pb 原子核的超形变带穿透宽度明显小于Gogny 相互作用给出的宽度,但是较SB方法（Phys. Rev. C,60 （1999） 051305） 分析实验数据得到的结果高出几个数量级。于是,对SB 方法提出了质疑,因为它给出了极其微小的传播宽度。The combined method is applied to calculate the angular momentum projected potential energy surfaces (AMPPES) of 190,192Pb. The Supper-deformed(SD) rotational bands of the two nuclei are studied with the AMPPES computed with the Gogny D1S and Skyrme SkP and SLy4 interactions. It is found that there is no pronounced SD band in 190Pb in the case of the Gogny interaction, which is consistent with the experimental observation. A well developed SD band with the Gogny interaction is found in 192Pb. The tunneling width of 192Pb is comparable to that given by the GW approach (Nucl. Phys. A 660 (1999)197) and orders of magnitude larger than that given by the SB approach (Phys. Rev. C 60 (1999) 051305). The influence of the angular momentum projection on the potential energy surfaces is examined in the case of the Gogny interaction for 190,192Pb. It is shown that the angular momentum projection suppresses the barrier separating the SD and ND rotational bands. Higher barriers of the AMPPESs for the two nuclei computed with the Skyrme SkP and SLy4 interactions are obtained compared with those given by the Gogny force. The tunneling width of 192Pb is also big for the Skyrme interactions. We put the SB approach into question which gives only an extremely small spreading width.     

Decay of Hoyle state

The prediction of Hoyle state was necessitated to explain the abundance of carbon, which is crucial for the existence of life on Earth and is the stepping stone for understanding the abundance of other heavier elements. After the experimental confirmation of its existence, soon it was realized that the Hoyle state was ‘different’ from other excited states of carbon, led to intense theoretical and experimental activities over the past few decades to understand its structure. In recent times, precision, high statistics experiments on the decay of Hoyle state have been performed at the Variable Energy Cyclotron Centre, to determine the quantitative contributions of various direct 3 α decay mechanisms of the Hoyle state. The present results have been critically compared with those obtained in other recent experiments and their implications have been discussed.     

131Pm衰变的首次观测

利用³²S轰击¹⁰⁶Cd靶,通过3p4n反应产生了¹³¹Pm,反应产物经过毛细管及带收集传输系统传输到低本底区,测量了反应产物的X,γ单谱,并进行了X-γ,γ-γ符合测量,得到了¹³¹Pm的半衰期及衰变γ线,并建立了简单的衰变纲图.     

Transfer of Entangled States for Two Atoms Via Cavity Decay

In this paper, the entangled states of two atoms trapped in two corresponding cavities are teleported to another two single atoms trapped in another two corresponding cavities by detecting the photons which leak out from the cavities. The most distinctive advantage of our scheme is that a direct carrier of quantum information between distant atoms is not required.     

对北京谱仪上新观测态的一个理论解释

最近, 北京谱仪在J/ψ的辐射衰变中发现, 在正反质子的阈附近有反常增强, 即可能存在共振态X(1860)和X(1835). 针对这一发现, 提出了新粒子的三胶子胶球态解释方案, 并且应用QCD求和规则计算了此胶球态的质量. 考虑到理论上的不确定因素, 计算结果表明该胶球态的质量峰位于1.9GeV到2.7GeV之间. 事实上, 北京谱仪发现的新共振态的确表现出了一些三胶子态的行为. 结论是, 此新粒子很有可能是重子偶素和胶球态的混合态.     

Ground state properties of titaniumdiboride

Abstract

The electronics structure, the charge distribution and the total energy of hexagonal titaniumdiboride are calculated using non-local pseudopotentials in both the local density approximation (LDA) and the generalized gradient expansion approximation (GGA). In the LDA we obtain a = 3.023 Å, c = 3.166 Å and B_o = 271. GPa. For these quantities the GGA values are slightly lower and both compare well with experiment. We also determined selected elastic constants by fitting the total energies to a quadratic surface in the lattice parameters. Using strains that do not break the hexagonal symmetry we obtain C₁₁ + C₁₂ = 777.GPa, C₁₃ = 83. GPa and C₃₃ = 568. GPa. Again slightly lower values are obtained using the GGA. These values agree well with a recent experiment.     

Ground state theory of delta-Pu

Correlation effects are important for making predictions in the delta phase of Pu. Using a realistic treatment of the intra-atomic Coulomb correlations we address the long-standing problem of computing ground state properties. The equilibrium volume is obtained in good agreement with experiment when taking into account Hubbard U of the order 4 eV. For this U, the calculation predicts a 5f(5) atomiclike configuration with L = 5, S = 5/2, and J = 5/2 and shows a nearly complete compensation between spin and orbital magnetic moments.     

Ground state spectrum of methylcyanide

The rotational spectrum of methylcyanide (acetonitrile) in the ground vibrational state was measured in the spectral region from 91 to 810 GHz using the Cologne and Tsukuba spectrometers operated in the Doppler-limited and sub-Doppler saturation layouts. The resolution of the saturation Lamb-dip measurements is estimated to be about 1 kHz at the best of circumstances and the measuring accuracy of 10-60 kHz depending very sensitively on the quality of the spectrum. In the cases of rotational transitions with the low quantum number J (J<18) and with a low difference of the rotational quantum numbers J−K, the resolved or partly resolved hyperfine structures of the rotational transitions were observed. Together with the most accurate data from the literature, the newly measured experimental data were analyzed using the traditional polynomial energy formula as well as the Padè approximant for the effective rotational Hamiltonian. The resulting rotational, centrifugal distortion, and hyperfine structure spectroscopic constants were obtained with a significantly higher accuracy than the ones listed in the literature. In addition, an anomalous accidental resonance was detected between the K=14 ground state levels and the K=12, +l levels in the excited v₈=1 vibrational state.