Narrow Results

PIXE analysis has been performed at NMCC (Nishina Memorial Cyclotron Center) as a common utilization in Japan since 1993. In order to cope with a variety of samples, various sample-preparation methods have been developed at NMCC. In order to make uniform hair samples of large quantity, a method of powdering in liquid nitrogen was carried out. A powdered-internal-standard method was applied to the powdered hair sample thus prepared and the results were compared with those obtained by a standard- free method for untreated hairs and with those by an internal-standard method combined with the chemical ashing method. As a result, good agreement was obtained for the principal elements such as sulfur, calcium and zinc. Moreover, good reproducibility was achieved in the results obtained by repeated measurements, and it is found that uniformity of the powdered sample and the powdered- internal standard (palladium-carbon) was almost satisfactory.

The performances of proton irradiated silicon–germanium (SiGe) power heterojunction bipolar transistors (HBTs) at extreme temperatures (liquid nitrogen temperature and high stage-temperature of 120°C with junction temperature over 160°C) are reported in this work. SiGe power HBTs with total emitter area of ~ 1460 μm² are fabricated in a commercial BiCMOS process, and irradiated with proton at different fluences from 1 × 10¹² p/cm² to 5 × 10¹³ p/cm². Experimental characterizations are conducted for pre- and post-radiation devices at room temperature, cryogenic temperature and high temperature. The results demonstrate that the proton-irradiated SiGe power HBTs are naturally suitable for electronic operations at extreme temperatures. Specifically, investigation of proton radiation on SiGe power HBTs at liquid nitrogen temperature (77 K) indicates a significant potential for space applications. In addition, SiGe power HBTs show better tolerance of proton radiation at high temperature of 120°C (junction temperature over 160°C). SiGe power HBTs demonstrate great potential in power amplification for wireless communication systems under severe radiation and extreme temperature environment (cryogenic and high temperatures) even without any intentional radiation hardening.

To explore the influence of liquid nitrogen (LN${}_2)$ cooling on the structural damage and failure characteristics of coal, a series of structural experiments, uniaxial compression tests, and crack morphology characterization experiments were carried out in this study. Based on the fractal theory, the pore structure damage and failure characteristics of the coal before and after the LN₂ cooling treatment were compared. After the LN₂ treatment, the structural damage inside the coal increases. Compared to the untreated coal, the fractal dimensions of the total pores, seepage pores, and adsorption pores in the LN₂-treated coal decrease by 0.88%, 0.24%, and 5.16%, respectively. The results indicate that the LN₂ cooling treatment can increase the connectivity of pores, especially adsorption pores. The internal structure damage of the coal induced by the LN₂ treatment reduces its compressive strength and elastic modulus by 27.86% and 32.62%, respectively. Simultaneously, it can be found that the fragments fractal dimension of the coal decreases by 9.53%, and the fractal dimension of the induced fracture surface increases from 2.134 to 2.151 after the LN₂ treatment. By the LN₂ treatment, the distribution of fragments becomes more uniform, and the complexity of the generated fracture surface increases. Therefore, the LN₂ cooling treatment can increase the effective seepage path and the contact area between the crack and the coal matrix to promote the gas flow and enhance the gas desorption in the coal matrix. The experimental results also show that the damage of the single LN₂ treatment on the coal is limited. LN₂ cycling treatment is suggested to use to improve the efficiency of the coalbed methane extraction because that it can give full play to the multiple cracking effects of LN₂ on the coal.