12N、12B、11C 在Si靶上反应总截面研究

核反应总截面是描述原子核反应基本特征的一个重要的物理量，从中可以得到有关核反应、核结构和核内核子分布的信息。在由放射性束所产生的奇异核结构与各种反应机制的研究中，反应总截面更是具有特殊的重要性。具有奇异核结构的核的一个典型物理现象就是其反应总截面要比稳定核大得多，I.Tanihata等人最早就是通过对放射性束流的相互作用截面的测量发现了具有奇异结构的核－中子晕核。由于反应截面的测量对探测器的要求不高，而且数据分析过程相对较为简单，因此反应截面的测量已经成为放射性束物理研究的一个非常重要的实验手段。目前，奇异核研究的重点在丰中子一侧，理论预言的很多中子晕核如8He、11Li、11、14Be、15、17、19C、等已经从实验上得到证实，而理论预言的质子晕核目前只有8B得到实验证实，其他的核实验数据较少或相互矛盾，无法作出准确的结论。12N就是其中之一，理论学家认为其具有质子晕结构；而实验数据主要集中在的反应截面测量上，实验数据较少又相互矛盾或不肯定，不能得出确切结论。因此，进一步开展研究是十分必要和有意义的。考虑到以上因素，充分利用兰州放射性束流线现有的实验条件，我们采用束流透射法测量了中能区多个能量点12N、11C、12B与Si靶的反应总截面和12N去质子截面。同时用CLOVER探测器测量与碎片符合的γ能谱。利用透射法测量核的反应总截面对于模型没有依赖性，因而得到的结果更加可靠。利用Shen公式和采用各种密度分布形式的零力程Glauber模型计算了12N、11C、12B的激发函数并与实验结果比较，提取了12N、11C、12B的密度分布与核半径，对12N去质子截面作了简单分析。使用Shen公式拟合实验数据时发现，Shen公式在整个能区范围内基本上可以很好的拟合12B、11C的反应数据，但Shen计算得到的12N的反应总截面与实验测量值有明显的差异，计算结果偏小。在使用Glauber模型拟合实验数据之前，分别使用有限力程和零力程Glauber模型拟合了12C＋12C的实验数据。在计算时，两种Glauber模型输入的密度分布采用Gauss密度分布形式。结果显示，使用零力程Glauber模型可以更好的拟合实验数据。分别使用高斯密度分布、HO密度分布、双参数费米密度分布、SHF模型计算得到的密度分布、基于少体模型的Gauss＋尾巴密度分布形式代入零力程Glauber模型拟合实验数据。对于12B、11C、12C，这些密度分布形式代入零力程Glauber模型计算得到的激发函数曲线在整个能区范围内都可以很好的拟合实验数据。但是对于12N，只有基于少体模型的Gauss＋尾巴密度分布形式代入零力程Glauber模型计算得到的激发函数曲线可以拟合实验结果。其他的密度分布形式计算得到的激发函数曲线明显低于实验数据。提取的12B、11C、12N均方根半径显示，12N的核半径明显大于其镜像核12B及其周围的核素。对12B、11C、12N的分析结果表明：12N的密度分布形式和稳定核有明显的不同，最后一个质子的密度分布具有很大的弥散，其可能具有奇异结构。对12N去质子截面的简单分析也表明了这一点

Metals in the Exosphere of the Highly Irradiated Planet WASP-12b

We present near-UV transmission spectroscopy of the highly irradiated transiting exoplanet WASP-12b, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. The spectra cover three distinct wavelength ranges: NUVA (2539-2580 Å), NUVB (2655-2696 Å), and NUVC (2770-2811 Å). Three independent methods all reveal enhanced transit depths attributable to absorption by resonance lines of metals in the exosphere of WASP-12b. Light curves of total counts in the NUVA and NUVC wavelength ranges show a detection at a 2.5s level. We detect extra absorption in the Mg II ??2800 resonance line cores at the 2.8s level. The NUVA, NUVB, and NUVC light curves imply effective radii of 2.69 ± 0.24 R J , 2.18 ± 0.18 R J , and 2.66 ± 0.22 R J respectively, suggesting the planet is surrounded by an absorbing cloud which overfills the Roche lobe. We detect enhanced transit depths at the wavelengths of resonance lines of neutral sodium, tin, and manganese, and at singly ionized ytterbium, scandium, manganese, aluminum, vanadium, and magnesium. We also find the statistically expected number of anomalous transit depths at wavelengths not associated with any known resonance line. Our data are limited by photon noise, but taken as a whole the results are strong evidence for an extended absorbing exosphere surrounding the planet. The NUVA data exhibit an early ingress, contrary to model expectations; we speculate this could be due to the presence of a disk of previously stripped material.

A high C/O ratio and weak thermal inversion in the atmosphere of exoplanet WASP-12b

The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior, as opposed to the silicate-dominated composition found on Earth; the atmosphere can also differ from those in the Solar System. The solar C/O is 0.54 (ref. 3). Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b (ref. 6) that reveals C/O>=1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T>2,500K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.

Defocused transmission spectroscopy: a potential detection of sodium in the atmosphere of WASP-12b

We report on a pilot study of a novel observing technique, defocussed transmission spectroscopy, and its application to the study of exoplanet atmospheres using ground-based platforms. Similar to defocussed photometry, defocussed transmission spectroscopy has an added advantage over normal spectroscopy in that it reduces systematic errors due to flat-fielding, PSF variations, slit-jaw imperfections and other effects associated with ground-based observations. For one of the planetary systems studied, WASP-12b, we report a tentative detection of additional Na absorption of 0.12+/-0.03[+0.03]% during transit using a 2A wavelength mask. After consideration of a systematic that occurs mid-transit, it is likely that the true depth is actually closer to 0.15%. This is a similar level of absorption reported in the atmosphere of HD209458b (0.135+/-0.017%, Snellen et al. 2008). Finally, we outline methods that will improve the technique during future observations, based on our findings from this pilot study.

5a-Butyl-1,3,8,10-tetra-chloro-7,13-bis-(4-nitro-benzo-yl)-5a,6a,12a,12b-tetra-hydro-7H,13H-thieno[2,3-b:4,5-b']bis-(1,4-benzoxazine)

The title compound, C(34)H(24)Cl(4)N(4)O(8)S, is a linear penta-cyclic system formed of two substituted benzoxazinyl groups fused to 2-n-butyl-tetra-hydro-thio-phene. The oxazine ring, which is fused to the n-butyl-substituted side of the thio-phene ring, is in a boat conformation. The other fused oxazine ring and the tetra-hydro-thiene ring are each in an envelope conformation. The bridgehead C atom alpha to both the S and N atoms forms the flap of each envelope. This results in a twist of the penta-cyclic system such that the dihedral angle between the terminal dichloro-benzene rings is 82.92 (8)°. In the crystal, inversion-related mol-ecules form a weakly hydrogen-bonded dimer, with two C-H⋯O inter-actions between an H atom on the oxazine ring and an amide O atom. Additionally, C-H⋯O inter-actions occur between an H atom on a screw-related nitro-benzene ring and an O atom on the nitro-benzene ring of one mol-ecule. One of the Cl atoms and the butyl group are disordered over two sets of sites with occupancy ratios of 0.94 (2):0.06 (2) and 0.624 (4):0.376 (4), respectively.