Precise Radiometry: Some Recent Aspects of Fruitful Interaction with Atomic Physics

Modern radiometric analytics demands a complex consideration of nuclear and electron shell processes, if more pretentious aims are envisaged. As an example the small variation of decay rates of radionuclides presents possibilities for information on chemical situations of decaying atoms. In principle this phenomenon is well known since many years, but now the situation is such that, e.g. in ^99mTc internal conversion, a full agreement of the difficult experiments and the respective theory was established. The secondary emission of X-rays as a consequence of high excitation of electron shells in combination with nuclear transitions supplies another example for a methodical progress of radiometry. Investigations on ⁵¹Cr as an electron capture nuclide have shown that chemically induced variations of the K_α to K_β X-ray intensity ratio is at least qualitatively understood.     

推广的液滴模型对超重核288115及其α衰变链性质的研究

运用推广的液滴模型来确定新核素²⁸⁸115及其α衰变链上核的衰变位垒, 采用量子力学中处理α衰变的WKB方法, 对该链上各原子核的α衰变半寿命进行了研究．计算结果表明推广的液滴模型结合WKB方法可以很好地在超重区符合α衰变半寿命的实验值. 同时把推广的液滴模型的计算结果和采用密度相关的M3Y微观核力的结果做了详细的比较, 宏观模型(推广的液滴模型)和微观模型(密度相关的M3Y微观核力)计算的α衰变半寿命以及实验值三者之间的符合是对新核素²⁸⁸115及其α衰变链上核半寿命很好的检验.     

Numerical Investigation of Brownian,Gradient, and Turbulent Coagulation Under Moving Vehicle Conditions in an Underground Garage

Particle coagulation behavior can affect particle formation and dispersion in vehicle plumes. An Eulerian particle transport model combining a Realizable k–? model, Brownian, gradient, and turbulent coagulation has been developed to analyze particle coagulation behavior in an underground garage under moving-vehicle conditions. The results show that prominent coagulation of nanoparticles occurs within a limited region, which is at a distance of less than 0.2 m in the vertical direction and no more than 0.4 m in the exhaust direction from a given vehicle. The coagulation of small particles with diameters of less than 130 nm is dominated by Brownian motion, while gradient and turbulent coagulation significantly affect the coagulation of particles with median diameters of 420 nm and larger diameters of 600–950 nm, respectively. The influence of turbulent coagulation increases as vehicle speed and particle size increase. The half-time due to coagulation is approximately two times and 10–20 times larger than the corresponding value due to dilution in the regions less than 0.2 and 1.5 m along the tailpipe centerline, respectively. It is demonstrated that coagulation has considerable influence on particle dispersion in the region less than 0.2 m from the tailpipe, compared with dilution.