RESUMO
Developing highly superior precious-metal-free electrocatalysts for oxygen reduction reaction (ORR) are challenging and great significance. In this study, it is reported that an efficient ORR catalysts with N and S co-doped carbon nanotubes anchored to copper (Cu) nanoclusters by mechanical grinding and high temperature heat treatment. The obtained Cu-S1-N-C electrocatalysts exhibited a high ORR performance with an onset potential (Eonest) of 0.989 V and a half-wave potential (E1/2) of 0.905 V (vs. RHE) in alkaline electrolyte, which was superior to that of commercial Pt/C catalyst. In contrast to N doping alone, the defect structures and active species of the catalysts were optimized by precise modulation of S-atom doping, and moreover, the introduction of S-atoms provided more thiophene-sulfur active sites. This study provides an innovative idea for designing excellent ORR catalysts.
RESUMO
ABSTRACT: In order to provide safe operating conditions for radiation workers and the public at large, the radiation shielding for radiotherapy treatment rooms will have to be determined by an expert physicist according to the applicable radiation control regulations. A new radiosurgery system with integrated self-shielding, called the Zap-X, obviates the need for costly and complex radiation bunkers. Radiation levels in the vicinity of the ZAP-X radiosurgery system were acquired for a number of different operating conditions, and a 3D radiation dose distribution was measured for better visualization of hot spots and the general dose distribution. The radiation shielding requirements were evaluated according to the International and Chinese standards, respectively. While the integral self-shielding of the Zap-X was designed in accordance with international standards, it was found to be insufficient for Chinese standards. In order to meet the needs of the growing new generation of radiotherapy equipment, several suggestions for improvement of Chinese standards are proposed.
