(Table 1) Nd isotope ratios of ODP Leg 208 samples

We present new Nd isotope records from Walvis Ridge Ocean Drilling Program (ODP) sites 1262-1264 (southeastern Atlantic) spanning the past 24 Ma to investigate the Neogene evolution of Atlantic thermohaline circulation. The new data indicate that deepwater epsilon-Nd(t) values from ODP Site 1262 decrease from -11.0 at 10.6 Ma to -12.5 by 7.3 Ma. This decrease parallels the Nd isotope trends contained in Fe-Mn crust records from the northwestern Atlantic; however, the shift at ODP Site 1262 (4755 m water depth) occurred up to ~6 Ma earlier than the corresponding changes in crust records from the Atlantic and earlier than any Atlantic site shallower than 2700 m paleowater depth. Recent interpretations of the rapid decrease in Fe-Mn crust Nd epsilon-Nd(t)ss values invoke changes in weathering inputs to the Labrador Sea region rather than a fundamental change in deepwater convection in the Labrador Sea. However, the new evidence for significant depth stratification of the Nd isotope signal in the southeastern Atlantic between 10.6 and 7.3 Ma suggests that the onset of deepwater convection in the Labrador Sea may have played a role in the deepwater decrease in Nd isotopic composition. Climatic conditions during the middle to late Miocene likely favored an increase in the importance of glacially induced mechanical weathering, while at the same time promoting deep convection in the Labrador Sea.

Neodymium isotopes in benthic foraminifera from the South Atlantic

Records of the past neodymium (Nd) isotope composition of the deep ocean can resolve ambiguities in the interpretation of other tracers. We present the first Nd isotope data for sedimentary benthic foraminifera. Comparison of the epsilon-Nd of core-top foraminifera from a depth transect on the Cape Basin side of the Walvis Ridge to published seawater data, and to the modern dissolved SiO2- epsilon-Nd trend of the deep Atlantic, suggests that benthic foraminifera represent a reliable archive of the deep water Nd isotope composition. Neodymium isotope values of benthic foraminifera from ODP Site 1264A (Angola Basin side of the Walvis Ridge) from the last 8 Ma agree with Fe-Mn oxide coatings from the same samples and are also broadly consistent with existing fish teeth data for the deep South Atlantic, yielding confidence in the preservation of the marine Nd isotope signal in all these archives. The marine origin of the Nd in the coatings is confirmed by their marine Sr isotope values. These important results allow application of the technique to down-core samples. The new epsilon-Nd datasets, along with ancillary Cd/Ca and Nd/Ca ratios from the same foraminiferal samples, are interpreted in the context of debates on the Neogene history of North Atlantic Deep Water (NADW) export to the South Atlantic. In general, the epsilon-Nd and delta13C records are closely correlated over the past 4.5 Ma. The Nd isotope data suggest strong NADW export from 8 to 5 Ma, consistent with one interpretation of published delta13C gradients. Where the epsilon-Nd record differs from the nutrient-based records, changes in the pre-formed delta13C or Cd/Ca of southern-derived deep water might account for the difference. Maximum NADW-export for the entire record is suggested by all proxies at 3.5-4 Ma. Chemical conditions from 3 to 1 Ma are totally different, showing, on average, the lowest NADW export of the record. Modern-day values again imply NADW export that is about as strong as at any stage over the past 8 Ma.

Sapientia, 2000, Vol. LV, nº 208 (número completo)

Contenido: Estructuras mentales y principios racionales / Lorenzo Vicente Burgoa – Autonomía moral y deliberación en Santo Tomás de Aquino / Ciro E. Schmidt Andrade – Thomas Aquinas and the reality of time / Steven C. Snyder – Fe y razón en Ramón Llull / Marc Egea I Ger – Idealismo y personalismo en Husserl / Francisco Leocata – El discurso no consensuado de Jürgen Habermas / Marisa Villalba de Tablón – Hacia el tercer milenio : el clima posmoderno y la recuperación de la naturaleza humana del hombre (observaciones tomistas) / William R. Darós – Razón, voluntad y praxis / María Celestina Donadío Maggi de Gandolfi – Meditación sobre la felicidad / Alberto Caturelli – “Y llegarán a ser virtuosos” : ley jurídica positiva penal y educación / Héctor H. Hernández – Todos los hombres desean la felicidad / Ignacio E. M. Andereggen – Justicia y derecho en Ley Natural y Derechos Naturales de John Finnis / Carlos I. Massini Correas – El itinerario antiguo y medieval de la negación nominalista de la metafísica / Mario Enrique Sacchi – Notas y comentarios -- Bibliografía

退火对He注入及随后~(208)Pb~(27+)辐照的Al_2O_3单晶PL谱的影响

利用高能离子研究了110keV的He+注入Al2O3单晶及随后230MeV的208Pb27+辐照并在不同温度条件下退火样品的光致发光的特性.从测试结果可以清楚地看到在375nm,390nm,413nm和450nm出现了强烈的发光峰.经过600K退火2h后测试结果显示,390nm发光峰增强剧烈,而别的发光峰显示不明显.在900K退火条件下,390nm的发光峰开始减弱相反在510nm出现了较强的发光峰,到1100K退火完毕后390nm的发光峰完全消失,而510nm的发光峰相对增强.从辐照样品的FTIR谱中看到,波数在460—510cm-1间的吸收是振动模式,经过离子辐照后,吸收带展宽,随着辐照量的增大,Al2O3振动吸收峰消失,说明Al2O3振动模式被完全破坏.1000—1300cm-1之间为Al-O-Al桥氧的伸缩振动模式,辐照后吸收带向高波数方向移动.退火后的FTIR谱变化不大.

高温注氦及随后230MeV的~(208)Pb~(27+)辐照Al_2O_3的光致发光谱的研究

主要研究了110keV的He~+高温注入Al_2O_3单晶及1.1MeV/u的~(208)Pb~(27+)辐照注氦Al_2O_3样品的光致发光的特性。从测试结果可以清楚地看到在375nm,413nm和450nm处出现了强烈的发光峰。并且在600K,5×10~(16) ions/cm~2剂量点,样品的发光峰是最强的。这表明He~+注入Al_2O_3后使带隙中深的辐射中心复合的效率大幅度提高,极大的增强了其发光强度,而且发光伴随着蓝移现象。而经过高能~(208)Pb~(27+)辐照后的样品,在390nm出现了新的发光峰,从FTIR谱中我们能够看到,可能是~(208)Pb~(27+)辐照相对沉积膜出现一定的晶化,其中含有许多纳米尺寸的Al_2O_3晶粒所致。

同位素~(208)Pb靶的制备

介绍了一种弧形靶框夹芯208Pb靶的制备工艺,包括核靶的制备装置和制备方法、核靶厚度和均匀性的控制和测量方法,并对结果进行了讨论。制备采用旋转蒸镀法,该法可以大大提高材料的利用率。所制靶的结构为30μg/cm2C+361μg/cm2208Pb+15μg/cm2C,同一次所制的靶平均厚度为361μg/cm2,不均匀性小于9.8%。其性能能够很好地满足超重核实验研究的要求。

~(208)Hgβ~-衰变γ纲图

以18 O重离子束轰击厚天然铅靶 ,通过多核子转移反应生成2 0 8Hg核 .辐照铅片放入离线熔化铅靶气相热色谱装置中处理 ,分离并收集汞元素产物 .完成了 4πΔEβγ γ ,γ X(γ)关联事件谱及γ射线时序单谱测量 .建议了 2 1条γ射线 ,以及能量为 1 3 65,1 72 7keV的两条2 0 8Tl新能级的2 0 8Hgβ- 衰变部分γ纲图 .

50MeV/u~(20)Na+~(208)Pb→p+~(19)Ne+~(208)Pb反应的探测效率模拟

用半经典模型考虑20Ｎａ＋２０８Ｐｂ→ｐ＋１９Ｎｅ＋２０８Ｐｂ的Ｃｏｕｌｏｍｂ解离过程。用ＭｏｎｔｅＣａｒｌｏ方法计算前角放置的望远镜阵列对Ｃｏｕｌｏｍｂ解离碎片的探测效率。讨论了天体环境下ｐ＋１９Ｎｅ→２０Ｎａ俘获反应道的低能级共振截面测量的可行性。

Sputtering induced by highly charged Pb-208(q+) bombardment on Al surface

Highly charged ions (HCls) carrying high Coulomb potential energy (E-p) could cause great changes in the physical and chemical properties of material surface when they bombard on the solid surface. In our work, the secondary ion yield dependence on highly charged Pbq+ (q = 4-36) bombardment on Al surface has been investigated. Aluminum films (99.99%) covered with a natural oxide film was chosen as our target and the kinetic energy (E-k) was varied between 80 keV and 400 keV. The yield with different incident angles could be described well by the equation developed by us. The equation consists of two parts due to the kinetic sputtering and potential sputtering. The physical interpretations of the coefficients in the said equation are discussed. Also the results on the kinetic sputtering produced by the nuclear energy loss on target Surface are presented.