用于铀钍含量测定的α计数方法

本文介绍了用α计数测量U/Th含量的原理和方法,研制了一种具有时间符合功能的α计数器.对一些地质样品进行测试,通过α总计数率和符合对计数率计算出U/Th含量,并将其结果和NaI γ能谱仪的分析结果进行对比,两种方法测量结果大致相近.结果表明:α计数器可用于地质样品中钍和铀含量的分析,进而进行年剂量率的估算.     

通用视频输出控制器IP核的低功耗设计

随着芯片的集成度越来越高,芯片的功耗成为芯片设计中越来越重要的优化参数。设计了一种可应用于视频处理芯片、多媒体手持设备、嵌入式SoC等系统中的视频输出控制器。设计中通过多种工艺无关的低功耗设计技术优化控制器的动态功耗。首先分析各子模块的工作频率,降低低速子模块的工作时钟,然后通过添加门控时钟单元降低时钟的翻转次数。应用Design Compiler[1]进行工程的功耗分析,结果表明设计中使用的低功耗设计方法有效降低了模块的动态功耗。     

The Effect of the Size of Radiotherapy Photon Beams on the Absorbed Dose to an Al2O3 Dosimeter

The effect of the size of radiotherapy photon beams on the absorbed dose to an Al2O3 dosimeter was investigated using the Monte Carlo method. The EGSnrc/DOSRZnrc program code was used to simulate the absorbed dose to the Al2O3 dosimeter, as well as the absorbed dose to water at the corresponding position in the absence of the dosimeter. The incident beams were 60Co γ and 6 MV with a different beam radius ranging from 0.1 cm to 2 cm. Results revealed that the absorbed dose ratio factor depends on the size of the incident photon beam. When the radius of the incident beam is smaller than that of the dosimeter, the absorbed dose ratio factor decreases as the incident beam size increases. The absorbed dose ratio factor reaches its minimum when the radius of the incident beam is almost the same as that of the dosimeter. When the radius of the incident beam is larger than that of the dosimeter, the absorbed dose ratio factor increases as the incident beam size increases. The maximum difference among these absorbed dose ratio factors can be up to 14% in 60Co γ beams and 23% in 6 MV beams. However, when the size of the incident beam is much larger than that of the dosimeter, the effect of the incident beam size on the absorbed dose ratio factor becomes quite small. The maximum discrepancy between the absorbed dose ratio factors and the average value is not more than 1%.     

多尺度法与二阶光学非线性系统的稳定性

在经典力学框架内,把偶极子的运动方程化为带有阻尼项和受迫项的广义外尔斯特拉斯方程.在无扰动情况下,用外尔斯特拉斯函数分析了系统的相平面特征;在扰动情况下,用多尺度法讨论了系统的稳定性.结果表明,在相平面上,分支轨道是一条过不稳定点的同宿轨道,系统除了存在ω=ω0 的主共振和ω=2ω0 的倍频共振外,还存在ω=ω0/2的分频共振.对系统的稳定性分析表明,只需适当选择参数就可以保证系统是稳定的.