beta-delayed fission of Ac-228

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

Search for beta-delayed fission of Ac-228

Radium was radiochemically separated from natural thorium. Thin Ra-228 ->beta Ac-228 sources were prepared and exposed to mica fission track detectors, and measured by an HPGe gamma-ray detector. The beta-delayed fission events of Ac-228 were observed and its beta-delayed fission probability was found to be (5 +/- 2)x10(-12).

从60MeV/u~(18)O离子辐照过的钍中分离Ra

对以212Pb, 133Ba和224Ra作示踪剂,(NH4)2H2EDTA为淋洗剂,用阳离子交换法从Pb、Ba中分离Ra的工艺条件做了研究。提出了一个从60 MeV/u 18O离子辐照过的ThO2靶中分离Ra的放射化学流程。实验结果表明,该流程对主要反应产物,特别是Ba的去污较好,Ra的产额可达70%以上。

Production cross-section of Ra-230 in the reaction of 60 MeV/u O-18 ions with U-238

A thick natural uranium target was bombarded with a 60 MeV/u O-18 beam. The neutron-rich isotope Ra-230 as the target residue was produced through the multinucleon transfer reaction (U-238-4p-4n). The barium and radium fraction as BaCl2 precipitate were radiochemically separated first from the mixture of uranium and reaction products. Then, the radium fraction was separated from BaCl2 precipitate by using cation exchange technique. The gamma-ray spectra of the Ra fraction were measured using an HPGe detector. The production cross sections of Ra-230 were obtained by a combination of the radiochemical separation technique and off-line gamma-ray spectroscopy. The cross section of Ra-230 has been determined to be 66 +/- 20 mu b.

He, Ne and Ar isotope compositions of fluid inclusions in hydrothermal sulfides from the TAG hydrothermal field, Mid-Atlantic Ridge

Helium, rieon and argon isotope compositions of fluid inclusions have been measured in hydrothermal sulfide samples from the TAG hydrothermal field at the Mid-Atlantic Ridge. Fluid-inclusion He-3/He-4 ratios are 2.2-13.3 times the air value (Ra), and with a mean of 7.2 Ra. Comparison with the local vent fluids (He-3/He-4=7.5-8.2 Ra) and mid-ocean ridge basalt values (He-3/He-4=6-11 Ra) shows that the variation range of He-3/He-4 ratios from sulfide-hosted fluid inclusions is significantly large. Values for Ne-20/Ne-22 are from 10.2 to 11.4, which are significantly higher than the atmospheric ratio (9.8). And fluid-inclusion Ar-40/Ar-36 ratios range from 287 to 359, which are close to the atmospheric values (295.5). These results indicate that the noble gases of fluid inclusions in hydrothermal sulfides are a mixture of mantle- and seawater-derived noble gases; the partial mantle-derived components of trapped hydrothermal fluids may be from the lower mantle; the helium of fluid inclusions is mainly from upper mantle; and the Ne and Ar components are mainly from seawater.

铅－210、钍－228、钚年代学在滇池、洞庭湖和昆明湖环境问题上的应用

笔者在大量的文献调研基础上，试图利用 ~(210)Pb、~(228)Th 等短半衰期的铀系子体确定某些湖泊沉积物的沉积速率及年代，结合 239，240 pu 在我国内陆湖泊的分布规律，以全球 pu 随时间的分布规律探索其测年的可能性，以多核素方法探讨测年结果的可靠性，建立沉积的时间尺度。同时，利用这些核素作示踪研究沉积物表层的生物扰动所造成的混合效应。通过对沉积物垂直方向上物质成份。矿物成份和元素分析，研究沉积环境的演化及近百年工业污染的历史。根据所选湖泊的纬度差别，研究湖泊沉积环境和沉积物类型对所研究的核素方法的影响。本论文是首次利用多核素方法研究我国一些内陆湖泊的环境问题，对在我国继续开展这方面研究具有重要意义。